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Pressure Vessel Inspections

The Pressure Vessel Inspections article provides you information about inspection of pressure vessel and pressure vessel test inmanufacturing shop.

This article provides you lots of invaluable information about following items:

Inspection and Testing During Manufacturing Phase

Inspection and Testing During operation Phase

Pressure Vessel Codes and Regulations

Maintenance and Repairs

Pressure vessel inspections article alongside other linked articles are useful for Manufactures Quality Control personnel, Second andThird Party Inspectors, Purchasers, Sellers, Plant Inspectors, HSE Engineers, Integrity Engineers, Operation and MaintenanceEngineers and any Other Interested Individuals.

Pressure Vessel Definition

The Pressure Vessel Definition article provides you the definition and boundaries of pressure vessel based API code and ASMECode.

Based the ASME Code Section VIII pressure vessels are containers for the containment of pressure, either internal or external.

This pressure may be obtained from an external source, or by the application of heat from a direct or indirect source, or anycombination thereof.

The ASME Code is construction code for pressure vessel and contains mandatory Requirements, specific prohibitions;

and nonmandatory guidance for pressure vessel materials, design, fabrication, examination, inspection, testing, and certification.

Pressure Vessel Definition - Scope

These scopes are based ASME Code Sec VIII Div 1

The vessel with maximum allowable working pressure(MAWP) higher than 15 psi

Inside diameter to be higher than 152 mm

No piping or piping component

No rotating or reciprocating Equipment

Not Water Vessel up to 300psi or 210°F

Not within the scope of other Sections

Also for gas fired double shell heat exchangers < 50 psi



Not Steam Boilers with direct firing

Not for Human Occupancy (PVHO)

Pressure Vessel Definition - Boundaries

The welding end of the first circumferential joint for welded connections

The first threaded joint for screwed connections

The face of the first flange for bolted, flanged connections

The first sealing surface for proprietary connections or fittings

Non pressure parts welded directly to a pressure retaining surface

Pressure retaining covers

Pressure relief devices

What is API Code Definition from Pressure Vessel ?

Contrary of ASME Code Sec VIII which developed for construction, the API STD 510 covers the in-service inspection, repair,alteration, and rerating activities for pressure vessels.

This inspection code applies to all refining and chemical process vessels that have been placed in service.

What is the API STD 510 coverage?

vessels constructed in accordance with an applicable construction code

Vessels constructed without a construction code (non-code)— A vessel not fabricated to a recognized construction code andmeeting no known recognized standard

Vessels constructed and approved as jurisdictional special based upon jurisdiction acceptance of particular design,fabrication, inspection, testing, and installation

Non-standard vessels—A vessel fabricated to a recognized construction code but has lost it‘s nameplate or stamping.



ASME Code Section 8; ASME Code Section 8 is construction code for Pressure Vessel.

This Code section addresses mandatory requirements, specific prohibitions, and nonmandatory guidance for Pressure VesselMaterials, design, fabrication, examination, inspection, testing, certification, and pressure relief.

You may know ASME Code Section 8 has three divisions. The Division 1 covers pressure up to 3000 psi, the Division 2 hasalternative rule and covers up to 10,000 psi and Division 3 can be used for pressure higher than 10,000 psi.

This section is divided into three Subsections, Mandatory Appendices, and Nonmandatory Appendices.

Subsection A consists of Part UG, covering the general requirements applicable to all pressure vessels.

Subsection B covers specific requirements that are applicable to the various methods used in the fabrication of pressure vessels. Itconsists of Parts UW, UF, and UB dealing with welded, forged, and brazed methods, respectively.

Subsection C covers specific requirements applicable to the several classes of materials used in pressure vessel construction.

It consists of Parts UCS, UNF, UHA, UCI, UCL, UCD, UHT, ULW, and ULT dealing with carbon and low alloy steels, nonferrousmetals, high alloy steels, cast iron, clad and lined material, cast ductile iron, ferritic steels with properties enhanced by heat treatment,layered construction, and low temperature materials, respectively.

Click on the above link for detail information about ASME code section 8 which specifically focused on pressure vessel inspections.

ASME Code Section 8

The ASME Code Section 8 is construction code for pressure vessel and covers design, manufacturing and pressure vessel inspectionand testing in manufacturing shop.

This Code section addresses mandatory requirements, specific prohibitions, and nonmandatory guidance for Press. Vessel Materials,design, fabrication, examination, inspection, testing, certification, and pressure relief.

This article describe you different subsections and provides guidelines to you for using and application of this code.

For ASME Code Section 8 scope and boundaries review Pressure Vessel Definition article.


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Hierarchy of Standard

1. Law and Regulation at Location of Installation

Mandatory application of ASME pressure vessel code is determined by rule and regulation at location of installation.

For example if you are living in the state of Minnesota the application of ASME Code for construction and stamping is mandatory inyour location but if you are living in the state of South Carolina it is not mandatory.

2. ASME Boiler and Pressure Vessel Code

The next item in this hierarchy is ASME Code itself, the ASME Code generally is divided in three groups as following

Group 1: Construction Codes

Some of them are; Section VIII for pressure vessel, Section I for Power Boiler, section III for Nuclear Power Plant and Section IV forheating Boiler

Group 2: Reference Codes

These are the codes which are referenced from construction codes as explained in group 1.

The ASME Section IX for welding and Section V for Non Destructive Testing are in this Group.

For example ASME Code section VIII for welding requirement such as WPS (Welding Procedure Specification), PQR (ProcedureQualification Record), Welder Performance Qualification and etc. refer you to ASME Section IX.

Group 3: In-Service Codes

These are the codes for in-service Inspection after placing the equipment into service.

The ASME Section VI for heating boiler and Section VII are from this group.

3. National Board Inspection Code(NBIC):

We have assigned a separate article for NBIC, but as require for this article, NBIC making certification for ASME AuthorizedInspectors also certifying R stamp for Repair services for stamped pressure vessels.

ASME Code Section 8 Content:

See following Fig, it shows ASME Code Section 8 Content:





Subsection B covers specific requirements that are applicable to the various methods used in the fabrication of pressure vessels.

It consists of Parts UW, UF, and UB dealing with welded, forged, and brazed methods, respectively.


It consists of Parts UCS, UNF, UHA, UCI, UCL, UCD, UHT, ULW, and ULT dealing with carbon and low alloy steels, nonferrousmetals, high alloy steels, cast iron, clad and lined material, cast ductile iron, ferritic steels with properties enhanced by heat treatment,

layered construction, and low temperature materials, respectively.

For example if you need to manufacture a pressure vessel with SA 516 Gr.70 material (Carbon Steel), then you need to meet themarked items in above Fig.

Please note ASME Code Section 8, does not provide you fabrication tolerances except of misalignment and weld reinforcement.

For example for nozzles orientation, projection, elevation and other required tolerances there are no values in the code and you mayrefer to pressure vessel handbooks for such information.

Review the Pressure Vessel Dimension Inspection article for such tolerances.

If you review ASME Forward statement it clearly says ―The Code does not address all aspects of construction activities and thoseaspects which are not specifically addressed should not be considered prohibited.‖

In continue says ―The Code is not a handbook and cannot replace Education, Experience, and the use of engineering judgments.‖

For example ASME Code Section 8 Div 1 in UG-28 mandating all loading to be considered in pressure vessel design, but the methodfor calculation of all of them have not been addressed.

For example the formula for wind, or earthquakes not provided in the ASME Code Section 8 and these items and other similar loadingneed to be designed by information provided in pressure vessel handbooks.

For ASME pressure vessel manufacture certification as well as Authorized Inspection Agency certification Review the PressureVessel Certification article.

What is the Summary of Important Points in ASME Code Section 8 ?

1. ASME Code Section 8 edition is issued once in 3 years and addenda, once a year – both on 1 July. Edition and addenda becomeeffective on 1st January of next year (i.e., 6 months after issue).

2. Thickness of cylindrical shell t = PR/(SE-0.6P) + C

3. Longitudinal weld is more critical because it is subjected to double the stress than Circ. Weld.

4. ―Weld joint categories‖ A, B, C, D – are based on joint locations in the vessel and stress levels encountered. ―Weld Types‖ (type 1,2, 3, etc.) describe the weld itself.

5. Depths of 2:1 Ellip. and hemisph. heads are D/4 and D/2 respectively. (D= Head diameter.)

6. Weld Joint categories:

Category A:

- All longitudinal welds in shell and nozzles.

- All welds in heads, Hemisph-head to shell weld joint

Category B:

- All circumferential welds in shell and nozzles

- Head to shell joint (other than Hemisph.)

Category C and D are flange welds and nozzle attachment welds respectively.

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7. Weld Types:

Type 1: Full penetration welds (Typically Double welded)

Type 2: Welds with backing strip

Type 3: Single welded partial penetration welds

Type 4, 5 and 6: Various Lap welds (rarely used)

8. For full penetration welds (type 1):

Joint efficiency, E = 100%, 85%, 70%

(For the radiography = Full, Spot, Nil respectively)

9. Radiography marking on name plates (typically for Type-1 welds)

RT-1: (E=1) All butt welds – full length radiography

RT-2: (E=1.0) All Cat. A Butt welds Full length, Cat B, spot

RT-3: (E=0.85) Spot radiography of both Cat A and B welds

RT-4: (E=0.7) Partial/No radiography

10. For Welded Heads for E=1, all welds within the head require full length radiography (since they are all Cat. A welds)

11. For seamless heads, E=1, If a) head to shell weld is fully radiographed (if Cat. A), and at least spot radiographed (if Cat. B)

12. Compared to Cylindrical shell, thickness of 2:1 Ellipsoidal head is approx. same as shell, Hemisph. head approx. half and Torisphhead is 77% higher.

13. MAWP is calculated for: Working condition (Hot & Corroded). Vessel MAWP is always taken at the Top of the Vessel and islowest of all part MAWPs adjusted for static pressure.

14. Hydro-Test is Standard Pressure test on Completed Vessels.

Hyd. Test Pr. = 1.3 x MAWP x stress ratio

Insp. Pressure (hydro) = test pr. / 1.3

Min. Test temp. = MDMT + 30°F

Max. Inspection temp. = 120°F

15. Pneumatic test is performed if hydro is not possible due to design or process reasons. Prior to the test, NDT as per UW-50 ismandatory.

Pneumatic test pressure = 1.1 x MAWP x stress ratio, Pressure should be increased in steps (Total 6).

1st step – 50% of test pressure

2nd to 6 step – 10% of test pressure

Insp. Pr. (pneumatic) = test pressure /1.1

16. Pressure gauge range should be about twice the test pressure. However, in any case it shall not be lower than 1.5 times and nothigher than 4 times the test pressure.

16. Vessel MAWP represents the maximum safe pressure holding capacity of the vessel. Vessel MAWP is measured at top-mostpoint. And is lowest of vessel part MAWPs, adjusted for hydrostatic head.

18. For vertical vessels, hydrostatic pressure caused due to liquid with specific gravity = 1, 1ft of height = 0.43 psig. Or 1 mtr of height= 0.1 Bar



19. Total pressure at any point of Vertical vessel is given by:

Total Pr. = Vessel MAWP + h x 0.433.

(h = height from top in ft.)

20. If part MAWP and elevations are known, Vessel MAWP can be calculated by the deducting hydrostatic head from part MAWP.

21. Ext. Pressure is worked out on basis of Geometric factor A (which depends on L/Do and Do/t ratios) and factor B (depends on A, )

Allowable Ext. Pressure, Pa = 4B/(3(Do/t))

22. For values of A falling to left of material line in the material chart:

Pa = 2AE/(3(Do/t))

23. Name plate shows The Code stamping, MAWP, design temp., MDMT, and Extent of Radiography.

24. ASME materials (SA) shall be used for code stamped vessel fabrication instead of ASTM (A) materials.

25. Reinforcement pad is not required, if the size of finished opening is (UG 36)

Not exceeding 2-3/8‖ for all thicknesses of vessel

Not exceeding 3-½‖, if vessel thickness is ≤ 3/8‘‘

26. Reinforcement pad with OD = 2d and thk = vessel thk is always safe (d = diameter of finished opening)

27. Reinforcement limit along vessel wall = 2d

28. Reinforcement limit normal to vessel wall = smaller of 2.5 t or 2.5 tn

29. In reinforcement pad calculations, credit can be taken for area available in shell and nozzle.

30. Fillet weld throat dimension = 0.707 x leg of weld

31. Adequacy of weld sizes shall be checked as required by UW-16. The nozzles construction shall be one of the Code acceptable

types.

32. The maximum permitted ovality tolerance (D max – D min) shall not exceed 1% of nominal diameter of vessel. If there is opening,then the tolerance can be increased by 2% x d (d = diameter of opening) if measurement is taken within a distance of ‗d‘ from axis ofopening.

33. The mismatch tolerances and the maximum allowable weld reinforcement is more strict on longitudinal welds compared tocircumferential welds (UW-35).

34. Principle of reinforcement:

Area removed = Area compensated.

Compensation area shall be within reinforcement limits.

35. For use as pressure parts, the plates shall be fully identified. Maximum permitted under tolerance on plates is 0.01‖ (0. 3 mm) or6% of ordered thickness, whichever is less.

36. All welding (including tack, seal, etc.) shall be done using qualified procedures and welders.

37. Mandatory full radiography in ASME Code Section 8 is required for all welding with thickness exceeding Table UCS-57, and alsofor lethal service vessels and unfired boilers with Design Pr. More than 50 psig.

38. PWHT is ASME Code Section 8 requirement if thickness exceeds those given in tables UCS-56 (given in notes under the tables).These tables also give min. PWHT temperature and min. holding time (soaking period) based on P-Nos. and thickness respectively.

39. For Furnace PWHT in ASME Code Section 8 , Loading Temperature shall not exceed 800°F, heating rate 400 deg F/hr/inch ofthickness, cooling rate 500°F /hr/inch of thickness. Still air cooling permitted below 800°F. During soaking period, temp difference

between hottest and coldest part shall not exceed 150°F.



40. Minimum overlap for PWHT in multiple heats = 5 ft.

41. For the ASME Code Section 8 impact test requirement, UCS 66 curve. If MDMT-thickness combination falls on or above thecurve, impact testing is exempted. Additional exemptions are given as per UG-20(f) and UCS=68 (c).

Pressure Vessel Plate Material;

You need to take care about your Pressure Vessel Plate Materials, there are lots of requirements and specific prohibitions in the

ASME code.

Some of these requirements are ASME and Non ASME plate material, plate specification, inspection requirement and material testreport.

Click on the above link for detail information about pressure vessel plate material which specifically focused on pressure vesselinspections.

Pressure Vessel Plate

The Pressure Vessel Plate article provides you information about the ASME Code requirement regarding plate material and relatedpoints in the pressure vessel inspection.

You need to take care about your Pressure Vessel Plate Materials, there are lots of requirements and specific prohibitions in the ASME code.

Some of these requirements are ASME and Non ASME plate materials, plates specification, inspection requirements and material testreports. This article describe you these requirements.

What is ASME Material?

ASME Code Sec VIII DIV 1 require the materials which are used for pressure containing parts to be one of material specified in ASMEsection II but with some restrictions which stated in ASME Code Sec VIII Div 1 in subsection C e.g. UCS, UHF, UNF.

For example SA 283 plate material is listed in ASME Sec II but when you refer to subsection C in Sec VIII Div 1, you see it is notallowed to be used for lethal substance services as well as for unfired steam boilers also you cannot use this material when you needyour thickness to be greater than 5/8 inch.

What is Difference Between ASTM Material and ASME Material?

When you refer to ASME Section II Part A, you see all material with SA prefix identification and in one side there is ASTM logo and inthe other side is ASME logo.

But ASTM prefix is single A.

The material specification in ASME Section II Part A originally developed by ASTM and then reviewed and adopted by ASME Code.That is the reason you see both societies Logo‘s.

For example if you open SA 516 material specification in ASME Section II material Part A edition 2004, you will see this statement

below the page title;

―Identical with ASTM specification A 516/ A516M-90‖;

This means you can use A 516 Edition 1990 instead SA 516 2004.

But if your ASTM material is A 516 and not manufactured based ASTM Edition 1990, you cannot use this material;

Unless you do assessment based clause UG-10 in ASME Section VIII Div 1 and your assessment result will determine either it ispermissible or you need to do more tests to recertify this material.

For some materials the specifications are not identical or may identical with some exception, so again we cannot use these ASTMmaterial unless make assessment based above mentioned clause (UG-10)

Is it possible to use Non ASME material instead ASME Section II material?

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The answer is ―Yes‖, but with some conditions, these conditions addressed in UG-10(a) as following items:

Melting method, melting practice, deoxidation, quality and heat treatment to be same between suggested non ASMEmaterial and equivalent permitted ASME section II material.

Material certificate prove there is no conflict in chemical analysis between suggested non ASME material and equivalentpermitted ASME material.

Material certificate prove the suggested non ASME material produced and tested in accordance to equivalent permitted

ASME material.

The material certificate to be recertified by equivalent permitted ASME material with notation of ― Certified per UG-10‖

Example:

A manufacture received an order for manufacturing a pressure vessel with SA 516 Gr.60 pressure vessel plate normalized materialbut apparently this material is not available in the market;

So material supplier recommend to pressure vessel manufacture to purchase available P265GH material instead, Manufacturerequest a copy of material certificate for P265GH to verify for recertification per UG-10

Pressure Vessel Manufacture Assessment:

Step 1: Checking of melting method, melting practices, deoxidation, and heat treatment

P265GH is produced based European EN-10028 Standard, manufacture controls plate material certificate and confirm;

Melting method, practice, deoxidation and heat treatment are consistent with SA 516 Gr.60 specification, the current availableP265GH material produced by basic oxygen process and secondary vacuum process refinement and both normalized.

Step 2: Plate material certificate prove there is no conflict in chemical analysis between suggested non ASME material and equivalentpermitted ASME material

Manufacture control chemical analysis in pressure vessel plate material certificate of P265GH with SA 516 Gr.60 specification andconfirm everything is in specific minimum or ranged limits

Step 3: Plate material certificate prove the suggested non ASME material produced and tested in accordance to equivalent permitted

ASME material

Manufacture first control the required number of test specimens for each mechanical tests as well as the size of specimens andconfirm both standard are same;

Then check the plate material mechanical test result for yield stress, tensile strength and elongation and confirm all are in specificrange of SA 516 Gr.60;

Manufacturer control for plate material impact test requirement and notice impact test carried out by ISO V method and in - 53 degreeF;

But SA 516 Gr.60 require to be impact tested in -60 degree F with Charpy V-notch test method based SA 370 Specification so thereare two conflicts here first the test method and secondly in the test temperature.

So pressure vessel manufacture requests from plate material supplier to provide test plate and send the test piece to laboratory forimpact testing based the SA 516 Gr.60 specification.

Lab test report confirms the P265GH plate material covers the SA 516 Gr.60 impact testing requirement.

Step 4: The material certificate to be recertified by equivalent permitted ASME material with notation of ―Certified per UG-10‖

Manufacture purchase the P265GH plate material and change marking on the plate and also recetify material test report with SA 516Gr.60 material, in fact this material identification will be SA 516 Gr.60

In above example vessel manufacturer with doing extra tests recertified non ASME pressure vessel plate material.

In some other cases might not be possible even by extra test for example if tensile strength to be less than ASME permitted material;



or sometimes might be recertified even without any extra test when everything fall in the limitation range of the ASME permittedmaterial.

What is the Other Requirement for Pressure Vessel Plate?

UG-93 in ASME Code Sec VIII Div 1 specify requirement for plate material inspection.

Based this clause only plate material require to have material test certificate(MTR).

It means this requirement only can be applied for plate material, for other material such as pipe, flange MTR's are not required and

marking on the materials would be acceptable.

You need to inspect the plate material per specification of ASME Sec II Part A, for example for SA 516 Gr.60 refer to this specificationand check the chemical composition, mechanical property with your MTR.

You need to check the Heat Number stated in MTR is the same stenciled on plate material marking and make sure this MTR belongto this material.

You need to check your pressure vessel plate dimensions such as thickness, width, length, weight as per tolerances stated inspecification SA 20, visual inspection for surface defect also need to be done based SA 20 specification.

ASME Pressure Vessel Joint Efficiencies;

The ASME Pressure Vessel Joint Efficiencies article provides you information about pressure vessel joint efficiency requirement andits connection with radiography testing.

You may know Pressure Vessel Joint Efficiencies are linked to the radiography testing grades and there is concession for fullradiography testing as per UW-11(a) (5) (b) clause which it is a little bit confusing.

This article provides you the ASME pressure vessel joint efficiencies requirements and also guidelines for above clause.

Based ASME Code requirement manufactures have to mark the type of RT i.e. RT1, RT2, RT3 and RT4 in the pressure vessel nameplate and state the same in Pressure Vessel Data Report.

We have seen many professions from inspectors and quality control engineers are confused between RT1 and RT2 specifically whenthey see ASME Pressure Vessel Joint Efficiencies for both of RT1 and RT2 is same and equal to 1(E=1);

They say both RT1 and RT2 are categorized in ―Full Radiography‖ part in UW-11 clause,

So why some joints in RT2 are radiographed in spot?

we are making spot radiography but it is categorized in full radiography!!!

So in this "ASME Pressure Vessel Joint Efficiencies" article we want to answer to this question in very simple way, but before this, weneed review joint categories and summarize them as below:

Category A:

All longitudinal welds in shell and nozzles

All welds in heads, Hemisph-head to shell weld joint

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Category B:

All circumferential welds in shell and nozzles

Head to shell joint (other than Hemisph.)

Category C and D are flange welds and nozzle attachment welds respectively

Longitudinal welds (Category A) are more critical than Circumferential welds (Category B) because they are under double stress.

This the reason in different part of ASME code we have stringent rules in category A joint comparing to category B joint.

See the following Fig. for joint categories:

Now let back to the ASME Pressure Vessel Joint Efficiencies subject, to remove above confusion about RT1 and RT2.

We need to know;

When and where there is code requirement for full radiography?

Item 1: All but welds in vessels used to contain lethal substance (UW-11(a)).Lethal substance has specific definition in ASME Code inUW-2 and it is the responsibility of end user to determine if they ordered vessel which contain lethal substances.

Item 2: All but welds in vessels in which the nominal thickness exceeds specified values (UW-11(a), you can find this values in

subsection C, in UCS-57, UNF-57 and etc for example this value for P-No.1 in UCS-57 is 1 ¼ inch

Item 3: All but welds in unfired steam boiler with design pressure > 50 psi (UW-11(a)).

Item 4: All category A and D butt welds in vessel when ―Full Radiography‖ optionally selected from table UW -12(column (a) in thistable is selected); and categories B and C which intersect Category A shall meet spot radiography requirement (UW-11(a) (5) (b)).

The point is here items 1, 2 and 3 are similar but item 4 is completely different, in items 1, 2 and 3 it is mandated by code;

To do full radiography in all butt welds in vessel so it means it is mandatory for designer to select column (a) in UW-12 table.

But in item 4 there is no mandating rule, manufacturer with his own decision has chosen to use column (a) in table UW-12 for fullradiography;

So here there is concession or bonus to manufacture for categories B and C.

What is concept behind of this concession or bonus in pressure vessel RT test?

If you review item 1, 2 and 3 one more time, you see pressure vessel RT test how related to type of welds and services;

you can see the pressure vessels in these items are critical from safety point of view, one contain lethal substance;

Other one high thickness which implicate to high pressure and the last one is unfired steam boiler, but item 4 has no criticality asmuch as the other items have.

But you should note all 4 items have been categorized in full radiography clause( U-11(a)), so to differentiate item 1, 2 and 3 fromItem 4, the RT symbols are used in Code (UG-116).

RT 1: Items 1, 2 and 3, (E=1), All butt welds-full length radiography



RT 2: Item 4 (E=1), Category A and D butt welds full length radiography and category B and C butt welds spot Radiography

RT 3: (E=0.85), Spot radiography butt welds

RT 4: (E=0.7), Partial / No radiography

You need to consider hemispherical head joint to shell as category A, but ellipsoidal and torispherical head joint to shell as categoryB;

Do you know why? Why ASME considered stringent rule for pressure vessel RT test in hemispherical head joint?

It is because this joint is more critical, because the thickness obtained from formula for hemispherical head approximately would behalf of the shell thickness;

It means if shell thickness is 1 inch, the hemispherical head thickness would be 0.5 inch.

for more detail you may review Pressure Vessel Heads article.

ASME Pressure Vessel Joint Efficiencies for welded Heads

For Welded Heads, joint efficiency of vessel will be 1(E=1), if all welds within the head full length radiographed (since they are all Cat. A welds), see above figure

ASME Pressure Vessel Joint Efficiencies for Seamless Heads

For seamless heads, joint efficiency of vessel will be 1(E=1) if head to shell weld is fully radiographed for hemispherical Head (Cat A);

See following Figure for RT types:

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and spot radiographed for ellipsoidal and torispherical heads (Cat. B)

Weld Types:

Here is some clarification about different type of welds which have specific definition in ASME Code SEC VIII DIV 1 and related to the

pressure vessel RT test.

The concept is to define different types and then introduce some restriction for using them.

For example Type 1 weld is defined as full penetration welds typically double welded and Type 2 is welds with backing strips;

So when you go to service restriction for vessel containing lethal substance, you see there is restriction there which s ays all category A joints shall be weld Type 1 and Category B and C shall be type 1 or type 2;

You should take this point in account which may same joint category with different weld types have different joint efficiencies.

Summary of weld types:

Type 1: Full penetration welds (Typically Double welded)

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Type 2: Welds with backing strip

Type 3: Single welded partial penetration welds

Type 4, 5 and 6: Various Lap welds (rarely used)

ASME Impact Test Requirement; You need to take care about ASME Impact Test Requirement. Suggest you have pressure vesselunder design process and construction has not started yet.

Based ASME impact test requirement you need to make assessment to see either your pressure vessel is exempted from impacttesting or you need to carry out the test.

There are 4 steps for impact test exemption assessment, you need to precede these steps, and you might be exempted in first,second or third steps and might not be exempted even in step 4;

So if you are in step 4 and you have not exempted then you need to carry out the test. This article explains you this assessmentprocess.

First you have to keep your pressure vessel design data available and then refer to UG-20 (f), if you are exempted from this clause

you do not need precede anymore.

But if you are not exempted by UG-20 (f), you have to proceed to UCS-66(a), again if you are exempted no need for moreassessment.

But if not, you have to proceed to UCS-66(b), if you are exempted now, no need for more assessment otherwise you have to proceedto UCS-68(c) again if you are still not exempted; you have to carry out impact testing.

It means for some cases we might be exempted from ASME impact test requirement in first stage in UG-20 (f), in others in UCS-66(a)or UCS-66(b) or UCS-68(c) or might not be exempted and prepare yourself for doing this costly test.

This test would be more costly out of US because of Laboratory Accreditation requirement. Accredited Laboratory based USaccreditation system is not too much in Europe, Middle East and other locations.

Click on the above link for detail information about ASME Impact Test Requirement which specifically focused on pressurevessel inspections.

ASME Impact Test Requirement

The ASME Impact Test Requirement article provides you information about impact test requirement in pressure vessel design andconstruction.

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Suggest you have pressure vessel under design process and construction has not started yet.

Based ASME impact test requirement you need to make assessment to see either your pressure vessel is exempted from impact

testing or you need to carry out the test.



Basic Concept:

You may know carbon steels and low alloy steels exhibit a drastic change in their room temperature ductility, at sub-zero servicetemperatures. Different types of materials exhibit different types of transition behavior.

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We can see there is a sudden, phenomenal drop in their notch-toughness properties below the "transition" range of temperature,which should be a matter of concern for us.

Body centered cubic or Ferritic alloys exhibit a significant transition in behavior when impact tested over a range of temperatures. Above transition temperature range, impact specimens fracture in a "ductile" manner, absorbing relatively large amounts of energy.

At lower temperatures, i.e. below the transition temperature range, the impact test specimens are found to fracture in a brittle(cleavage) manner, absorbing less energy.

And within the transition temperature range, the fracture is a mixture of ductile and brittle nature.

A material would be invulnerable to a sudden drop in notch-toughness at the lowest specified service (or design) temperature, if onlybe proved by conducting Charpy V-notch Impact tests on representative test samples, at reference (the lowest service) temperature.

Grain refined carbon steel forgings and wrought materials (thoroughly worked and normalized) generally exhibit good notchtoughness.

ASME Code Section VIII Div 1 exemption rules for ASME Impact Test Requirement:

There are specific rules in ASME Code for exemption from ASME Impact Test Requirement; this test is very expensive so pressurevessel manufactures are trying to be exempted for this costly test.

You need to follow following clauses to make exemption assessment for ASME impact test requirement:

UG-20(f) →→→UCS-66(a) →→→ UCS-66(b) →→→UCS-68(c)

First you have to keep your pressure vessel design data available and then refer to UG-20 (f), if you are exempted from this clauseyou do not need precede anymore.


But if not, you have to proceed to UCS-66(b), if you are exempted now, no need for more assessment otherwise you have to proceedto UCS-68(c) again if you are still not exempted, you have to carry out impact testing.



UG-20(f)

We start with UG-20(f) for ASME impact test requirement, if your MOC (Material of Construction) is categorized in P-No. 1 or 2 (Referto ASME Code Section IX for P-No Definition) and your MOC thickness has limited value defined in this clause, then you might beexempted from impact testing.

But you need to refer to Fig UCS-66 in ASME Code Section VIII Div 1 and see your MOC is listed in which A, B, C or D curves, all ASME carbon steel and low alloy steel material distributed in these 4 groups (Curves) of materials.

You need to know the materials listed in curve D has the best toughness property and better than materials listed in curve C, in similarway materials listed in curve C has better toughness property to materials listed in curve B and materials listed in Curve B has betterthan materials listed in Curve A .



See Following Fig UCS-66(a):


When you determined your MOC curve, then you has to review UG-20(f) and see for possibility for exemption from ASME impact testrequirement, there are some other condition in this clause which you should consider for exemption;

For instance the vessel should be hydrostatically tested after completion and also thermal and mechanical loading not be designcontrolling factor.

For example if your MOC is normalized SA 516 Gr.70 with 0.75 inch thickness you will be exempted from ASME impact testrequirement;

Your MOC is listed in curve D and up to 1 inch, impact testing is not required, of course you should assure you will be carry outhydrostatic test as well as mentioned loadings are not design controlling factor in your considered pressure vessel.

UCS-66(a)

So assume in above example your MOC thickness is 1.125 inch instead 1 inch, you will not be exempted by UG-20(f) and you have torefer to UCS-66(a);

But for assessment, based this clause, you need to know your pressure vessel MDMT (Minimum Design Metal Temperature), assumeit is -20 degree F, so you should now go to Fig. UCS-66 and locate 1.125 inch in horizontal axis and draw a vertical line;

In similar way locate -20 degree F in vertical axes and draw a horizontal line, these two lines will cross each other;

see above Figure, the lines identified in red

If the cross point fall above the curve D (because your MOC is listed in curve D) you are exempted otherwise not, so for currentexample you are above the curve D so you are exempted from impact testing .

To simplify your assessment for ASME impact test requirement the Fig-66 has been converted to the table(table UCS-66), so for anyMOC with specific thickness you can go to this table and see what is the minimum permissible temperature without impact testing.

See following UCS-66(a) Table:







In above example (normalized SA 516 Gr.70, Curve D, 1.125 inch thickness), minimum permissible Temperature without impact testis -26 degree F, it means if in above example your MDMT changes from -20 degree F to -27 degree F, then you cannot be exemptedfrom ASME impact test requirement by UCS-66(a) and you have to proceed to UCS-66(b)

UCS-66(b)

Let us explain this clause with above example your MDMT from above is -27 degree F, nominal thickness is 1.125 inch, normalizedSA 516 Gr.70 listed in curve D and you are not exempted by UCS-66(a)

So you are here to continue your assessment to find a chance for exemption, you have to refer to Fig UCS-66.1 and calculatefollowing formula;

Ratio= tr E / (tn –c)

tr is required design thickness for all applicable loading we assume for above example it is 0.95 inch, E is your joint efficiency and weassume for this vessel it is 1, it means your vessel is RT2, tn is your nominal thinness which in this example from above it is 1.125inches, and C is corrosion allowance and we assume it is 0.125 inches, so let calculate:

Ratio = 0.95x1/(1.125 – 0.125) Ratio= 0.95

See following Fig UCS-66(b):



Then go to the Figure UCS-66(b) and in vertical axes locate Ratio and draw a horizontal line then locate the cross point with graphand draw a vertical line to cross horizontal axis;

You will be reach to value of 8 in the horizontal axes, this 8, is your 8 degree F bonus from table UCS-66 which you can reduce 8degree F minimum permissible temperature in table without impact testing.

In above example your MDMT is -27 degree F and in UCS 66 table the minimum permissible temperature without impact testingdesignated -26 degree F so with this clause you can reduce it to -36 degree F(-26 -8 = -34), your MDMT is -27 degree F so you areexempted from impact testing with this clause.

UCS-68(c)

Let we change one variable in above example; we assume you need to have -45 degree F for your MDMT, other variable are thesame it means normalized SA 516 Gr.70 listed in curve D, thickness 1.125, so you can see you are not exempted by UCS-66(b);

Because minimum permissible temperature is -36 degree F but your MDMT is -45 degree F, so UCS-68(c) might be helpful;

It says if post weld heat treatment is not code requirement and your P-No is 1 and you carry out post weld heat treatment a 30 degreeF bonus will be granted to you to reduce minimum permissible temperature in table UCS-66.

So when post weld heat treatment is code requirement?

It is code requirement when your service is lethal and when your thickness for P-No. 1 is greater than 1.5 inch;

So for our example our service is not lethal and our P-No. is 1 and thickness is 1.125 and it is less than 1.5 inch therefore post weldheat treatment is not code requirement.

It means if you carry out post heat treatment a 30 degree F bonus will be granted by this clause, it means for this example ourminimum permissible temperature would be -36-30=-66 degree F and your MDMT is -45 degree F so you are exempted from impacttesting.

Now the worst case; in above you assume you need to have -70 degree F for your MDMT; you can see with this new condition youcannot be exempted even by UCS-68(c) and you have to carry out impact testing.

Pressure Vessel Dimension Inspection; Do you know what is Pressure Vessel Dimension Inspection requirement? You may know

some fabrication tolerances have not been addressed in ASME Code Section VIII.






So you need to refer to other sources for inspection. Most dimensional control of Pressure Vessel either addressed or not addressedin the ASME Code consists of following items:

Pressure Vessel Inspections - Dimension

Mill Undertolerance of Plates and Pipes

Tolerances for Formed Heads

Out of Roundness of shell

Nozzles and attachments Orientation

Nozzles and attachments Projection

Nozzles and attachments elevation

Nozzles and attachments levelness

Weld mismatch

Weld reinforcement

Click on the above link for detail information about Pressure Vessel Dimension Inspection which specifically focused onpressure vessel inspections.Pressure Vessel Dimension Inspection

The Pressure Vessel Dimension Inspection article provides you information about dimensional requirement in pressure vesselconstruction and pressure vessel inspection.

You may know some fabrication tolerances have not been addressed in ASME Code Section VIII.

So you need to refer to other sources for inspection. This article provides you most important dimensional inspection requirements.

Dimensional Check of Pressure Vessel consists of following items:










Weld mismatch

Weld reinforcement


Pressure Vessel Dimension Inspection - Plate:

Your pressure vessel plates with 0.01 inch or 6% undertoleance whichever is smaller may be used for full design pressure, instead ofat the given design thickness specified.

However if material specification allows greater undertolerance, then ordered thickness for the material should be sufficiently greater.

For example if you have SA 516 Gr.70 plate with 0.625 inch nominal thickness and actual thickness is 0.615, it is acceptable and youmay use this plate without any specific design consideration;

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But if the same plate has actual thickness of 0.595 inch, you need consider mill undertolarence in your design calculation;

This plate thickness is acceptable based material specification (see table in SA 20 for thickness tolerances), we cannot reject thisplate because it is in the permissible tolerance of plate specification but based ASME Code SEC VIII Div 1;

You need to consider this 0.03 inch in design calculation e.g. Thickness = Min Thickness + Corrosion Allowance + Mill Undertolrance

Pressure Vessel Dimension Inspection - Pipe:

Contrary to the plate material, your Pipe and Tube mill undertolrances need to be taken into account for design consideration.

Pipe and tube undertolrances is almost -12.5 % of nominal wall thickness but sometimes there are different for different materials sofor any specific material shall be referred to suggested pipe or tube material specification and obtain exact amount of millundertolrances.

For example if there is Pressure vessel with nominal shell thickness of 0.5 inch and it is needed an 6‖ SA 106 Gr.B nozzles to beattached to shell plate.

Assume external loading is not design controlling factor (is not governor), so as minimum our nozzle thickness shall be as the same ofshell thickness.

So with consideration of -12.5% the calculation will be: 0.5 / 0.875 = 0.571 inch so we refer to ASME B36.10 and select our Pipeschedule, it shall be SA 106 Gr.B Schedule 160

Pressure Vessel Dimension Inspection - Tolerances for Formed Head:

You may know there is specific rule for dimensional checking of formed heads, based UG-81 inner surface shall not deviate outside ofthe specified shape more than 11⁄4% of D and inside shape more than5⁄8%.

You can use sweep boards which are made from cutting of thin steel sheet or wood for checking of your Crown and Knuckle radius.

For your skirt; difference between the maximum and minimum inside diameter, shall not more than 1%, and you may use tapemeasure or leaser measure for dimensional control of Skirt.

So to fully understand let check together following head;







Head ID = 3364 mm

Head Type: Torispherical

Limit for Outside of specified Shape = 3364 x 1 ¼% = 42.05 mm

Limit for Inside of specified Shape = 3364 x 5/8 % = 21.025 mm

So we check the depth, the drawing is 656.3 mm and actual is 672 mm, so it is outside of shape, we need to check if it is in the rangeof tolerance the maximum outside of the shape will be 42.05 + 656.3 = 698.35 so our actual value is 672 mm so 672<698.35 then it isok.

We cut a sweep board equal to the head drawing crown radius (3400 mm) and other one for knuckle radius equal to 204 mm, so wetry to fit sweep boards in heads for above example sweep boards edge distance to head surface shall not deviate from above limitedvalues.

Skirt max and min ID shall not more than 1% of ID which is 33.64 mm, so in above example Skirt is also is ok. Our nominal thicknessis 20 mm so up to 19.746 is acceptable then for above example thikness dimension also is ok.

So the above head dimensions are ok

Pressure Vessel Dimension Inspection - Out of Roundness of Shell:

UG-80 deal with out of roundness of shell, the maximum permitted ovality tolerance (D max – D min) shall not exceed 1% of nominaldiameter of vessel.

If you have opening, then the tolerance can be increased by 2% x d (d = diameter of opening) if measurement is taken within adistance of‗d‘ from axis of opening.

The out of roundness generally is measured in two directions with normal measure tape or leaser measure, so one direction would beD max and other one would be D min.

Following picture shows out of roundness measurement;








Pressure Vessel Dimension Inspection - Nozzles and Attachments Orientation:

ASME Code SEC VIII Div 1 has not specified orientation tolerances for nozzles and attachment so you need refer to pressure vesselhandbook,

It is almost +/- 1 degree. The orientation check can be done by a simple calculation and using measure tape in actual measurementwork on the vessel.

For example we want to check N3 orientation in following drawing.

N3 is located in 120 degree in drawing, the manufacture has located in the vessel with marker, we want to check location and if it wasok, then allow the manufacture for cutting.

So we run this simple calculation:

Vessel OD = 97.875‖

Shell outside Circumference length = π x OD = 3.14 x 97.875 = 307.3275‖

307.3275 distributed to 360 degree so each degree represent

307.3275/ 360 =0.8536‖

N3 is located in 120 degree position so if we use measure tape and keep 0 at zero reference point in vessel and pull the tape, andthen nozzle center should be located in 120 x 0.8536 = 102.4425 inch,

This 102.4425 is perfect case so our tolerances is ±1 degree so if tape shows in following range it will be ok.

102.4425 – 0.8536 =101.5889‖



102.4425 + 0.8536 =103.2961‖

Pressure Vessel Dimension Inspection - Nozzles and Attachments Projection:

Nozzles and attachment projection is length of nozzles or attachment face to the vessel shell centerline.

Projection dimensions are addressed in general assembly drawings. The projection tolerances are not addressed in ASME Code SECVIII Div 1 but if you refer to pressure vessel hand book almost ± 0.25 inch is permissible.

In following figure we need to check BD nozzle projection, it should be 660 mm; it means it is distance from shell centerline to flange

face.

In practical measurement, you may use a measure tape to measure distance between shell outside circumference to nozzle face,then the measured value is summed with shell thickness and inside radius, so for above example following range is acceptable:



For levelness checking a level gage is used, if the bubble is in the middle of designated lines, the nozzle is level.

But if the bubble intersects the designated limit lines, you need to run a simple calculation and see if your deflection is in tolerancelimit.

You need to move one end of level gage up to bubble to be placed in middle, then measure distance between level gage end andflange face, the measured value is the X in figure.

Then obtain α, if α is less than 0.5˚, the deflection fall in tolerances and it is ok otherwise it is require be cutting out and re-welding.

Pressure Vessel Dimension Inspection - Weld Mismatch:

ASME Code SEC VIII Div. 1 specified tolerances for weld mismatch in UW-33, it is important to know the limit for weld mismatch isstringent in category A weld (Longitudinal joint and circumferential shell to hemispherical head).

The concept behind of this is that the longitudinal joint bear double amount of stress and inspectors should precisely check these joints.

For example you have pressure vessel with nominal thickness of 1 inch, you do visual and measure mismatch by welding gauge. Assume you found 0.143 inch mismatch in one longitudinal and one circumferential joint.

So you look to UW-33 table;



Permissible weld mismatch in longitudinal joint for your case is 0.125 inch and for circumferential joint is 0.1875 inch.

Your weld mismatches for both longitudinal and circumferential joints are 0.143 so your circumferential joint is ok but longitudinal jointshall be repaired.

Pressure Vessel Dimension Inspection - Weld Reinforcement:

The same concept for weld mismatch exist for weld reinforcement tolerances, longitudinal joint weld reinforcement limit is stringentthan circumferential joints.

It is because longitudinal joint bear double stress and it is required stress concentration to be minimized.

In same example assume there are 0.150 inch welds reinforcement for both category A and B welds; we want to review our weldacceptance?

Category A allowances = 0.093 inch

Category B allowances = 0.1875

So our circumferential joint is ok but longitudinal is not ok and shall be repaired be removing excess weld reinforcement.

Pressure Vessel RT Test; Do you know what is your Pressure Vessel RT tests Requirements? Is full radiography mandatory for yourvessel? When the full radiography is mandatory? What are the acceptance criteria? What are the RT symbols?

When one of following condition is existing, you need to do full radiography:

1. All but welds in vessels used to contain lethal substance2. All but welds in vessels in which the nominal thickness exceeds specified values3. All but welds in unfired steam boiler with design pressure > 50 psi

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4. All category A and D butt welds in vessel when ―Full Radiography‖ optionally selected

As you see the item numbers 1, 2, 3 are really mandatory for full RT test;

But pressure vessel manufacture makes optional decision for full radiography in item number 4

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Why pressure vessel manufactures want to spent more money for full radiography in item Number 4?

Because joint efficiency in full radiography condition is 1, so the higher joint efficiency in pressure vessel wall thickness formulacauses less wall thickness, so manufacture might save lots of money with lower thickness plate material.

But code has given some bonus to manufacture in item 4, because it is not mandated to do really full radiography in all but weld,manufacture can do spot radiography in B and C joints with the same joint efficiency of 1.

Click on the above link for detail information about Pressure Vessel RT Test which specifically focused on pressure vesselinspections.

Pressure Vessel RT Test

The Pressure Vessel RT Test article provides you information about Radiography testing in pressure vessel manufacturing processabd related items in pressure vessel inspection.

Do you know what is your Pressure Vessel RT test Requirements? Is full radiography mandatory for your vessel? When the fullradiography is mandatory? What are the acceptance criteria? What are the RT symbols?

So if you need this information, this article answers all of these questions.

We recommend you to review this article in conjunction with the ASME Pressure Vessel Joint Efficiencies article.

We need to know about Joint Categories before going into RT Test, these categories are based ASME Code Section VIII :

Category A:

All longitudinal welds in shell and nozzles.

All welds in heads, Hemisph-head to shell weld joint

Category B:

All circumferential welds in shell and nozzles

Head to shell joint (other than Hemisph.)

Category C and D are flange welds and nozzle attachment welds respectively

Longitudinal weld (Category A) is more critical because it is subjected to double the stress than Circ. Weld (Category B) and this thereason in different part of ASME code we have stringent rules in category A joint comparing to category B joint.

Pressure Vessel RT Test -When we need to do full radiography test?

When on of following condition is existing, you need to do full radiography:










1. All but welds in vessels used to contain lethal substance2. All but welds in vessels in which the nominal thickness exceeds specified values3. All but welds in unfired steam boiler with design pressure > 50 psi4. All category A and D butt welds in vessel when ―Full Radiography‖ optionally selected

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Pressure Vessel RT Test -Why pressure vessel manufactures want to spent more money for full radiography in item Number 4?



Item number 2 describing thickness limitations, any pressure vessel material designated to the specific P. Number by ASME sectionIX, so there are several table in ASME Code Section VIII Div. 1 Subsection C, which determining this limitation.

For example SA 516 material is P Number 1 and need to be fully radiographed if its thickness is greater than 1.25 inch in the sametime SA 204 material P Number is 3 and need to be full radiographed if thickness is greater than 0.75 inch.

Pressure Vessel RT Test - Acceptance Criteria in Full Radiography is Stringent or in Spot Radiography?

Acceptance criteria for welding defects in full radiography is stringent, these criteria stated in UW-51 and UW-52 in ASME CodeSection VIII Div. 1

It means a defect if interpreted based full radiography criteria in UW-51might be rejected but if interpreted by Spot radiography criteriain UW-52 might be accepted.


Pressure Vessel RT Test - What is Important Spot Radiography Requirement?

One spot shall be examined on each vessel for each 50 ft increment

For each increment of weld to be examined, a sufficient number of spot radiographs shall be taken to examine the welding ofeach welder or welding operator

Each spot examination shall be made as soon as practicable after completion of the increment of weld to be examined

The location of the spot shall be chosen by the Inspector after completion of the increment of welding to be examined

Pressure Vessel RT Test - Radiographic Personnel Qualification:

The radiographic personnel need to be certified by pressure vessel manufacture according to their written practice.

Holding the ASNT Radiographic certificate in not enough

In fact SNT-TC-1A can be used as a guideline for manufactures to establish their written practice for qualification and certification oftheir personnel.

Radiographic Examination Procedure and method

ASME Code Section VIII Div 1 mandating all test shall be done based ASME Code Section V article number 2.











Vessel Pressure Testing; You need to do hydro-static test after completion of construction process but before internal parts assemblyand also before painting process.

Please note replacing pneumatic test instead Pressure Vessel Hydro-Static Testing is not allowed and it can be replaced only when itis not possible due to design and process.

Vessel Pressure Testing requirements have been addressed in UG-99 and UG-100 in ASME Code Section VIII Div. 1.

The activities are done in 3 stages, the activities before start of the test, the activities during test and the activities after the test.

The Vessel Pressure Testing article provides you information about pressure vessel hydro-static testing requirements and relateditem in pressure vessel inspection.

The requirement have been described based ASME Code Section VIII. You need to do this test after completion of constructionprocess but before internal parts assembly and also before painting process.

This content covers all major requirements and provides you guidelines for test performance.

.


These are important points which you need to take care about them in vessel pressure testing:

Activities before Pressure Vessel Hydro-Static Testing which need to be checked by Manufacture Quality Control Team andThird Party Inspector:

1. Checking all welding already finished and fully accepted by NDT examination as per project Inspection and test plan.

2. Making sure inner part of the vessel is clean and free of remaining slag or other elements.

Controlling the external surface is dry for correct execution of visual inspection during the vessel pressure testing.

3. Checking pressure gauges calibration tag and certificate and the range of lower limit and upper limit of the gauges, it needs to bebetween 1.5 and 4 of Pressure Test Value.

4. Controlling testing equipment such as test pump and housing for soundness and tightness.

5. Making sure the test temperature will not violate following values:

Min. Test temperature= MDMT + 30°F

Max. Test temperature = 120°F

MDMT is pressure vessel minimum design metal temperature and it is stated in pressure vessel design document.

This is because of reducing the risk of brittle fracture during the test.

6. Making sure which reinforcement pads already soap tested.

7. Controlling the testing water quality and using corrosion inhibitor if it is necessary or when vessel metal is sensitive material

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8. Checking of vents, it is required to be placed at high points of the vessel in the position to be possible to purge air pockets while thevessel is filling.

Activities during the Pressure Vessel Hydro-Static Testing which need to be checked by Manufacture Quality Control Teamand Third Party Inspector:

1. Making sure the filling and pressurizing are done from the lowest point and venting from the highest point.

2. Witnessing water overflow through the venting in order to assure that no air bubbles remain in the vessel.

3. Controlling and witnessing which pressurizing is done in three stages as following:

First Stage: Raising the pressure to the 40% of the final pressure and stop pressurizing and keeping for 5 minutes and make a fastvisual inspection on external surface.

Second Stage: Restart pressurizing up to 70% of final pressure and stop the operation and keep for 5 minutes and make a fast visualinspection on external surface.

Third Stage: Restart pressurizing up to 100% of final pressure and stop the operation and keep for 45 minutes.


4. When 45 minutes elapsed, making sure the de-pressurizing is started and pressure dropped to the ―Inspection Pressure‖

This inspection pressure can be calculated as following:

Inspection Pressure = Hydrostatic Test Pressure / 1.3

And make sure a detail and comprehensive inspection is carried out in whole body of the vessel and in the welding joints andattachments.

5. Making sure the Pressure Vessel Hydro-Static Testing Pressure calculated correctly as following:

Hydrostatic Test Pressure = 1.3 x MAWP X Stress ratio

Stress Ratio = (Allowable Stress at Test Tempratuer)/(Allawable Stress at Design Tempratuer)

6. Making sure the vessel immediately and carefully drained after the test and dried by air.

Activities after the Pressure Vessel Hydro-Static Testing which need to be checked by Manufacture Quality Control Teamand Third Party Inspector:

1. The Pressure Vessel Hydro-Static Testing Report need to be prepared by manufacture quality control team and signed by ThirdParty or Authorized Inspector.

2. If the test failed by leaking from weld joints or any other kind of defect, it is necessary the vessel to be drained and dried andrepaired based of approved repair procedure. Pressure Vessel Hydrostatic testing need to be repeated.







Pressure Vessel Certification;

Do you what is pressure vessel certification process? How Pressure Vessel Manufactures can be ASME Stamp Holder? How ThirdParty inspection companies can be certified by ASME and to be Authorized Inspection Agencies? What is ―U‖ Stamped PressureVessel?

You may know pressure vessel manufacture certification is the same Authorization for ASME Stamp.

The pressure vessel manufactures can implement ASME Quality Control System and then apply for ASME Stamp.

It means if a manufacture accredited by ASME organization for pressure vessel per ASME Code Section VIII Div. 1 can stamp ―U‖ letter in the pressure vessel nameplate. These are the process for ASME Stamp Accreditation:

Obtain Application Forms from ASME

Sign a Service Agreement with Authorized Inspection Agency (AIA),Authorized inspection Agencies are Third PartyInspection Companies which have accredited by ASME organization and their inspectors certified by National BoardInspection Code(NBIC).These Inspectors are named Authorized Inspectors and hold Commission Cards issued by NBICorganization.Summary: AIAs are accredited by ASME but his inspectors are certified by NBIC.

Submit Application Forms to ASME and transfer Fees

Purchase ASME Code Books

Describe a QC-System according ASME Code Quality Control manual and procedures need to be prepared by manufacture.

Prepare a Demonstration Item, A Representative Demo pressure vessel need to be constructed and all Drawing,Calculation, Part List, Purchase Orders, Material Test Reports, Fabrication, Inspection, Test and Reporting shall be based

ASME Code Section VIII Requirement.

Qualify Procedures and Personnel, Quality Control Procedures and Personnel also need to be approved by manufacture.

Pre-Joint Review by the Supervisor of AIA, Almost it takes 4 months to fulfill the above requirement. Then an audit need tobe conducted by supervisor Authorized inspector which designated by Authorized inspection agency which is under contractwith manufacture.This auditor would report non-conformities found in audit process, and then manufacture would have sometime to correct them.

Joint Review (Audit) with ASME Designee, Inspector and Supervisor,Finally the Audit would be conducted by ASMEdesignated Person, Supervisor Authorized Inspector and Authorized Inspector.That is the reason this audit is named jointreview.

Issuance of Certificate and Stamp by ASME

If the result of Audit was satisfactory, the certificate would be issued by ASME and then manufacture would be authorized to stampname plate with ―U‖ Stamp.

The Pressure Vessel Certification article provides you information about ASME stamp holder process for manufactures and third partyinspection companies.

Do you what is pressure vessel certification process? How Pressure Vessel Manufactures can be ASME Stamp Holder?

How Third Party inspection companies can be certified by ASME and to be Authorized Inspection Agencies? What is ―U‖ StampedPress. Vessel?

This article describes you all your required information regarding Press. Vessel certification and regulation.

Pressure Vessel Manufacture Certification:



It means if a manufacture accredited by ASME organization for pressure vessel per ASME Code Section VIII Div. 1 can stamp ―U‖ letter in the pressure vessel nameplate.






See following Fig. for Pressure Vessel Certification (The Stamp Item)

These are the process for ASME Stamp Accreditation:

1. Obtain Application Forms from ASME

2. Sign a Service Agreement with Authorized Inspection Agency (AIA)

Authorized inspection Agencies are Third Party Inspection Companies which have accredited by ASME organization and theirinspectors certified by National Board Inspection Code(NBIC).

These Inspectors are named Authorized Inspectors and hold Commission Cards issued by NBIC organization.

Summary: AIAs are accredited by ASME but his inspectors are certified by NBIC.

3. Submit Application Forms to ASME and transfer Fees

4. Purchase ASME Code Books

5. Describe a QC-System according ASME Code Quality Control manual and procedures need to be prepared by manufacture.

6. Prepare a Demonstration Item

A Representative Demo pressure vessel need to be constructed and all Drawing, Calculation, Part List, Purchase Orders, MaterialTest Reports, Fabrication, Inspection, Test and Reporting shall be based ASME Code Section VIII Requirement.

7. Qualify Procedures and Personnel

Quality Control Procedures and Personnel also need to be approved by manufacture.

8. Pre-Joint Review by the Supervisor of AIA

Almost it takes 4 months to fulfill the above requirement. Then an audit need to be conducted by supervisor Authorized inspector

which designated by Authorized inspection agency which is under contract with manufacture.

This auditor would report non-conformities found in audit process, and then manufacture would have some time to correct them.

9. Joint Review (Audit) with ASME Designee, Inspector and Supervisor

Finally the Audit would be conducted by ASME designated Person, Supervisor Authorized Inspector and Authorized Inspector.

That is the reason this audit is named joint review.

10. Issuance of Certificate and Stamp by ASME




What are the Different Pressure Vessel Stamps?

Manufacturing of Pressure Vessels (Shop and /or Field): U

Alternative Rules Section VIII, Division 2(Shop and /or Field):U2

Manufacturing of High Pressure Vessels (Shop and /or Field):U3

What is Quality Control System which needs to be implemented in pressure vessel certification?

For U Stamp the quality control system need to be based ASME Section VIII Div. 1 Appendix 10.

What is the Benefit for Pressure Vessel Purchaser to Order Stamped Pressure Vessel?

When a purchaser order stamped pressure vessel to stamp holder manufacture, it is not necessary to hire Third Party Inspector;

because his pressure vessel automatically would be inspected by AI(Authorized Inspector) and its data report would be signed byhim.

Another benefit can be purchaser assurance from quality of the pressure vessel because of manufacture responsibility to ASMEOrganization.

In same time ordering a stamped pressure vessel would be expensive than non stamped pressure vessel.

Pressure Vessel Heads;

Pressure Vessel Heads

The Pressure Vessel Heads article provides you information about different type of ASME heads and related points in pressure vesselinspection.

How many standard Pressure Vessel Heads are in the ASME Code? What are their characteristics?

This article introduce you different type of Heads, applications and dimensional features.

Ellipsoidal Head, Hemispherical Head and Torispherical Head are three types of ASME Pressure Vessel Dished Heads.

See following Fig. for these heads sketches:


Ellipsoidal Head Dimensional Characteristics:

In the same design condition such as design pressure, design temperature and material your calculated wall thickness under in ternalpressure for ellipsoidal head will be approximately equal to shell thickness, for torispherical head equal to 1.77 times to shell thicknessand for hemispherical head equal to half shell thickness.

For example if you have calculated your shell thickness under internal pressure and obtained 12 mm, your thickness for ellipsoidalhead will be approximately 12 mm, torispherical head 20.4 mm and for hemispherical head 6 mm.

Inside depth of your ellipsoidal head (h in above fig.) will be one-fourth of head inside diameter (h = D/4).

Your ellipsoidal head knuckle radius is 0.17D and a spherical radius is 0.9D.










Torispherical Head Dimensional Characteristics:

In the same design condition such as design pressure, design temperature and material your calculated wall thickness under internalpressure will be approximately equal to 1.77 times of shell thickness.

For example if you have calculated your shell thickness under internal pressure and obtained 12 mm, your torispherical headthickness will be approximately 21.24mm.

Your torispherical head knuckle radius is 6% of the inside crown radius and your crown radius is equal to outside diameter of the headskirt.

Hemispherical Head Dimensional Characteristics:

In the same design condition such as design pressure, design temperature and material your calculated wall thickness under in ternalpressure will be approximately the half of shell thickness.

For example if you have calculated your shell thickness under internal pressure and obtained 12 mm, your hemispherical headthickness also will be approximately 6 mm.

Inside depth of your hemispherical head will be one-half of head inside diameter (h = D/2).

Dimensional Inspection of Pressure Vessel Dished Heads

You need to make dimensional inspection on pressure vessel heads for any effort for fit-up process. The dimensional inspection isdone on knuckle radius, crown radius, skirt length, depth and thickness.

Review the Pressure Vessel Dimensional Inspection Article for detail description for heads inspection.

Pressure Vessel Dished Head Joint efficiencies:

If your dished head is welded and joint efficiency is 1, then all of your head welds need full length radiography

If your dished head is seamless and joint efficiency is 1, your head to shell need full radiography for your hemispherical head and spotradiography for your ellipsoidal or torispherical heads.

For more detail description; please review ASME Pressure Vessel Joint Efficiencies article.

Third Party Inspection for Pressure Vessel;

What is the third party inspection requirement for pressure vessel inspection in manufacturing shop?

This article provides information about pressure vessel inspection from material inspection to final inspection and dispatch to site.

Third Party Inspection for Pressure Vessel

The Third Party Inspection for Pressure Vessel article provides you information about pressure vessel inspection and pressure vesseltest in manufacturing shop.

This content guides you about all necessary stages in the production of the pressure vessels from the examination of raw material to

the final inspection, preservation and packing to despatch to site.







http://www.inspection-for-industry.com/third-party-inspection-for-pressure-vessel.html







You need to take this point in account this article is written for a typical pressure vessel and might not be complete for special cases.

This content may be useful for second party inspectors, pressure vessel manufacture quality control personnel, engineeringcompanies and purchasers as well.

You may also note if pressure vessel ordered with U Stamp, then any Third Party Inspection Agency can not do the inspectionand authorized third party ASME inspection need to be covered this also named third party inspection for U stamp.

This third party inspection agencies must be insurance company andaccreditation by ASME.

All pressure vessel inspections and tests are carried out against the approved drawings, purchase order specifications, purchasers orcompany standards, and within the practices and rules of the country, state or province and any government decrees, laws, ordinanceor regulation as may apply.

The applicable codes and specifications for the pressure vessel which is under construction process are:

Design code

Purchase order specification

Purchaser's standards

Approved drawings

and the applicable codes and standards are:

ASME VIII Division 1 or 2 ASME V

ASME IX

The applicable codes and standard may be based other international standards such as BS 5500 and etc. This content is general andcan be useful if even the design code is different from ASME Code.

Third Party Inspection for Pressure Vessel - Required Documents for Third Party Inspector Review:

The list of documents normally is agreed in the Pre Inspection meeting which is hold several weeks before actual commencement ofinspection work.

The parties which are participated in this meeting are manufacture, purchaser and third party inspection agency representatives.

This already explained in the Inspection and Test Plan for Pressure Vesselarticle.

These are the list of documents which are normally agreed to be presented to the inspector:

Pressure Vessel Manufacture Quality Control Plan

Pressure Vessel Inspection and test plan

Pressure Vessel Data Sheet

Pressure Vessel Approved Drawings

Pressure Vessel Strength calculation sheets

Pressure Vessel Material Test Reports

Pressure Vessel Welding Specification Procedures (WPS) and Procedure Qualification Records(PQR)

Pressure Vessel Welding Map

Pressure Vessel Welders Qualifications Reports Pressure Vessel NDE procedures

Pressure Vessel NDE Personnel qualifications Reports

Pressure Vessel Heat treatment procedure

Pressure Vessel Calibration Certificates for Test Equipment

Pressure Vessel Hydrostatic Testing Procedure and Water Quality Document

Pressure Vessel Preparation and Painting Procedure

Pressure Vessel Preservation, Packing and Shipping Procedure

Pressure Vessel Packing List

Third Party Inspection for Pressure Vessel - Material Inspection

The first actual inspection work in the pressure vessel is raw materials inspection. Based the ASME Code providing material test

reports for pressure vessel plates is mandatory, for other components only the marking inspection will be enough.

http://www.inspection-for-industry.com/inspection-and-test-plan-for-pressure-vessel.html





But if purchase order has mandated the MTR to be provided for all components such as nozzle pipes, fittings and etc. then themanufacture need provide them as well.

For more detail you may review the Pressure Vessel Plate article.

As mentioned in above, the original or authenticated copies of mill certificates for plates normally are available at manufacturer'spremises.

The third party inspector examines these certificates for compliance with specifications and where appropriate, drawings.

The review includes checks on:

Certificate No.

Heat or cast No.

Chemical composition.

Mechanical properties.

Heat treated condition.

NDE applied and results.

Then the inspector witnesses the plate material identification on the certificates against plate marking. It is also necessary to checkwith pressure vessel drawing datasheet, material list and other specification as appropriate.

The transfer identification to cut off plates also is checked.

Visual inspection for surface finish and probable defects are done and dimensional compliance with specification need also to becontrolled.

For more detail in pressure vessel raw material inspection you may reviewPressure Vessel Dimension Inspection article.

When the third party inspector carried out the material inspection, then provides inspection visit report, the report contains followingitems:

Confirmation of satisfactory document review

Record of the endorsement of certification reviewed/witnessed

Record of all non-conformities

Record of any tests witnessed and the result

Third Party Inspection for Pressure Vessel - Fabrication

When the pressure vessel material inspection carried out and result was satisfactory or non-conformities closed by remedial action,then pressure vessel manufacture will be authorised to start fabrication.

The third party Inspector checks following points on pressure vessel based on the inspection and test plan (ITP) which is alreadyagreed between purchaser and pressure vessel manufacture.

The inspection scope is determined in ITP, some clients prefer to have stringent control and put the TPI inspector in more ―h oldpoints‖ in fabrication activities and some others may take lesser ―hold points‖ and put TPI much more in the review document.

This depend to the inspection budget which client assign for inspection, much more inspection will have much more costs and lessrisks and conversely less more inspection will have less costs but more risks.

For more detail review Inspection and Test Plan for Pressure Vessel article. There is draft ITP in this article which I believe it is thebest practice for Pressure Vessel inspection.

Third Party Inspection for Pressure Vessel - Preparation for Welding

The third party inspector carries out visual and dimensional check to ensure compliance with WPS and other specifications. Wherespecified, weld bevels are examined by required code method after grinding/machining.

It is necessary edges and weld bevels to be clean, dry and free from surface defects, laminations, cracks, voids, notches, etc.

They are causes for rejection unless suitable/satisfactory remedial action can be taken.

Weld repairs are carried out in accordance with the code requirements and approved by the client before welding proceeds and

serious or excessive defects normally are reported.













If the third party inspector is not in the hold or witness point in the ITP for these stages, then will review the pressure vesselmanufacture quality control report in his/her coming visit or final inspection day.

Third Party Inspection for Pressure Vessel - Fit-Up Inspection

Shapes and dimensions are checked in accordance with the approved WPS and drawing.

Tack welds are produced using the applicable WPS conditions and it is necessary to be visual free from defects.

Magnetic Testing (MT) or Penetration Testing (PT) may be performed in accordance with the code requirement.

If third party inspector is not in the hold or witness point for this inspection stage then will review the manufacture quality control reportin his/her coming visit or in final inspection day.

Third Party Inspection for Pressure Vessel - Monitoring of Weld Conditions

The third party inspector controls preheat heat temperature and method, Interpass temperatures, weld material control, welder andprocess qualifications for conformity to the code requirements.


Third Party Inspection for Pressure Vessel - Back Gouging Inspection

The third party inspector controls the shape and dimensions of the back gouged groove for conformity to the WPS requirement.

It is necessary the visual appearance to be clean and free from defects. NDE examination is done in accordance with the coderequirement.


Third Party Inspection for Pressure Vessel - Post Weld Inspection

After completion of all welding and grinding operations a visual examination confirms there are no harmful defects such as cracks,lack of fusion, surface porosity or exposed slag inclusions, incomplete penetration, incorrect profile of the weld, lack of leg length andoverlap.

Temporary attachments are removed, ground smooth, and the areas checked for defects by MP or PT for defects.


Third Party Inspection for Pressure Vessel - Non Destructive Examination

NDE is performed by qualified personnel to the approved techniques. The techniques available are dependent on vessel classificationand the materials used.

The third party inspector checks that the correct method has been used and verifies the approved status of both the technique andthe personnel.

Third Party Inspection for Pressure Vessel Weld Repair

The pressure vessel weld repairs are completed using an approved WPS method and retested accordingly.

It is necessary all repairs to be approved before any post weld heat treatment is carried out.

Third Party Inspection for Pressure Vessel Post Weld Heat Treatment

The third party inspector reviews the post weld heat treatment record of temperature and time in accordance with the approvedcode/procedure.

Similarly the results of hardness tests are reviewed in accordance with the code requirements.

Third Party Inspection for Pressure Vessel Dimensional Measurement and Visual Inspection



The third party inspector checks all major dimensions and the position/orientation of attachments are in accordance with the coderequirements.

For more detail review Pressure vessel Dimension Inspection article.

In addition a full visual examination of both inside (where practicable) and outside surfaces of the vessel is completed by the thirdparty inspector.

Particular attention is paid to the cleanliness of the interior of the vessel, the condition/appearance of welds and associated areas, thecondition of sealing faces.


Third Party Inspection for Pressure Vessel Pneumatic Test

The third party inspector witnesses low pressure pneumatic test for nozzle reinforcing pads, support saddles or other attachmentswhen specified by approved low pressure pneumatic test procedure using soapy water as the indicating medium.

A minimum of 1 gauge with correct working ranges as described by the code is used.


Third Party Inspection for Pressure Vessel Hydrostatic Testing

The third party inspector controls following items for Hydrostatic Testing:

Calibration status and correct working ranges of gauges. A minimum of 2 pressure gauges are attached to item under test.

Adequate provision for venting of high points and draining is provided.

Test pressure is applied as directed by procedure or code until test limiting pressure is reached. During hold period, amethodical check for leaks is conducted.

Test pressures, metal and water temperatures are recorded.

Water quality is as specified.

Special requirements of the purchaser's specification for deflection or strain gauges or pressure/time/temperature recordings areexamined by the inspector and records verified.

For more detail in hydrostatic testing review Vessel Pressure Testing article.

Third Party Inspection for Pressure Vessel - Final Inspection

After hydrostatic testing, the vessel is thoroughly drained and dried out by approved methods. All internal fittings, attachments,coatings or other requirements need to be completed.

Specified post hydrostatic test NDE need to be completed and the vessel closed.

All pressure vessels are checked for cleanliness and dryness by an approved method.

The third party inspector rechecks nozzle, saddle and bracket locations and orientations against assembly drawings.

Third Party Inspection for Pressure Vessel - Name Plate

The content of the marking is checked in accordance with approved drawing and specifications by third party inspector.

Third Party Inspection for Pressure Vessel-Painting and Coating Inspection

Surface preparation for painting is checked for the following points, according to specification by third party inspector:

Cleaning method (Blast or scraping and wire brushing)

Preparation grades

Freedom from weld spatter, blow-holes and other defects

Dry film thickness is checked according to specification










Surface condition need to be free from pin-holes, runs damage and other discontinuity

Third Party Inspection for Pressure Vessel-Spares and Accessories

The third party inspector controls spares, tools and accessories and makes visual and dimensional inspection for materials,workmanship and quantity according to purchase order specification and packing list.

Marking and/or Tag is checked for identification.

Third Party Inspection for Pressure Vessel-Pressure Vessel Reporting

Third party inspector provides Inspection Visit Report (IVR) after each visit as well as a final report summarising the activities carriedout during the vessel production in accordance with the contract requirements and circulated within the time limits specified in thecontract.

The report is in the format required by the client and clearly indicates final acceptance or rejection of the pressure vessel.

Third Party Inspection for Pressure Vessel-Pressure Vessel Release Note

When required by the contract or purchase order a release note is issued by third party agency and given to the manufacturer whenthe pressure vessel have been finally accepted.

Third Party Inspection for Pressure Vessel-Packing, Marking and Shipping

The following points are checked by the third party inspector:

Cleanliness and dryness of pressure vessels

Rust prevention for all machined surfaces

Protection for cover for all opening and protruding parts

Packing style and suitably for overseas transportation

Shipping marks and other markings and notification of welding prohibited, etc.

Where nitrogen purge is specified the gas pressure is checked and the presence of warning notices checked.

Third Party Inspection for Pressure Vessel - Pressure Vessel Final Book (Dossier)

The following final documents are reviewed and signed off by third party inspector:

As built, drawings if required, Manufacturer's data reports, Material certificate or certified mill test reports for all pressureparts, Material list or map, Welder record for each seam or map, Heat treatment records (Temperature-time record chart duringPWHT), Dimensional record, NDE records, Production test record/mock test record, Alloy verification records, (if required), hydrostatictest record, Pneumatic test record, Hardness test record, Post weld heat treatment NDE, if specified, Name plate or othermarks, Packing list, Spare parts and tool list

Inspection and Test Plan for Pressure Vessel;

The Inspection and testing requirement distributed in different part of construction code.

The inspection and test plan have tabulated format and collects all these requirement in simple table and determine responsibly ofeach party i.e manufacture, third party inspector and purchaser.

Inspection and Test Plan for Pressure Vessel

The inspection and test plan for pressure vessel article provides you information about pressure vessel inspection and pressurevessel test in manufacturing shop. The draft Inspection and test plan for pressure vessel provided as well.

Click here if you like immediately review the Inspection & Test Plan for Pressure Vessel draft sheet.

You may need to review this article in conjunction of following articles:





http://www.inspection-for-industry.com/support-files/Inspection-and-Test-Plan-for-Pressure-Vessel.pdf



http://www.inspection-for-industry.com/pressure-vessel-inspections.html







The Pressure Vessel Inspections article provides you information about inspection of pressure vessel and pressure vessel test inmanufacturing shop.

This article provides you lots of invaluable information about following items:

Inspection and Testing During Manufacturing Phase

Inspection and Testing During operation Phase

Pressure Vessel Codes and Regulations

Maintenance and Repairs

Pressure vessel inspections article alongside other linked articles are useful for Manufactures Quality Control personnel, Second andThird Party Inspectors, Purchasers, Sellers, Plant Inspectors, HSE Engineers, Integrity Engineers, Operation and MaintenanceEngineers and any Other Interested Individuals.

Pressure Vessel Definition; Based the ASME Code Section VIII pressure vessels are containers for the containment of pressure,either internal or external.

This pressure may be obtained from an external source, or by the application of heat from a direct or indirect source, or anycombination thereof.

ASME Code Section 8; ASME Code Section 8 is construction code for Pressure Vessel.

This Code section addresses mandatory requirements, specific prohibitions, and nonmandatory guidance for Pressure VesselMaterials, design, fabrication, examination, inspection, testing, certification, and pressure relief.




Subsection B covers specific requirements that are applicable to the various methods used in the fabrication of pressure vessels. Itconsists of Parts UW, UF, and UB dealing with welded, forged, and brazed methods, respectively.


It consists of Parts UCS, UNF, UHA, UCI, UCL, UCD, UHT, ULW, and ULT dealing with carbon and low alloy steels, nonferrousmetals, high alloy steels, cast iron, clad and lined material, cast ductile iron, ferritic steels with properties enhanced by heat treatment,layered construction, and low temperature materials, respectively.

Click on the above link for detail information about ASME code section 8 which specifically focused on pressure vessel inspections.

Pressure Vessel Plate Material; You need to take care about your Pressure Vessel Plate Materials, there are lots of requirements andspecific prohibitions in the ASME code.

Some of these requirements are ASME and Non ASME plate material, plate specification, inspection requirement and material testreport.












ASME Code Sec VIII DIV 1 require the materials which are used for pressure containing parts to be one of material specified in ASMEsection II but with some restrictions which stated in ASME Code Sec VIII Div 1 in subsection C e.g. UCS, UHF, UNF.

For example SA 283 plate material is listed in ASME Sec II but when you refer to subsection C in Sec VIII Div 1, you see it is notallowed to be used for lethal substance services as well as for unfired steam boilers also you cannot use this material when you needyour thickness to be greater than 5/8 inch.

Click on the above link for detail information about pressure vessel plate material which specifically focused on pressure vesselinspections.

ASME Pressure Vessel Joint Efficiencies;

You may know ASME Pressure Vessel Joint Efficiencies are linked to the radiography testing grades and there is concession for fullradiography testing as per UW-11(a) (5) (b) clause which it is a little bit confusing.

Based ASME Code requirement manufactures have to mark the type of RT e.g. RT1, RT2, RT3 and RT4 in the pressure vessel nameplate and state the same in Pressure Vessel Data Report.

We have seen many professions from inspectors and quality control engineers are confused between RT1 and RT2 specifically whenthey see ASME Pressure Vessel Joint Efficiencies for both of RT1 and RT2 is same and equal to 1(E=1);

They say both RT1 and RT2 are categorized in ―Full Radiography‖ part in UW-11 clause, So why some joints in RT2 are radiographedin spot? We are making spot radiography but it is categorized in full radiography!!!

ASME Impact Test Requirement;

You need to take care about ASME Impact Test Requirement. Suggest you have pressure vessel under design process andconstruction has not started yet.

Based ASME impact test requirement you need to make assessment to see either your pressure vessel is exempted from impacttesting or you need to carry out the test.



First you have to keep your pressure vessel design data available and then refer to UG-20 (f), if you are exempted from this clauseyou do not need precede anymore.


But if not, you have to proceed to UCS-66(b), if you are exempted now, no need for more assessment otherwise you have to proceedto UCS-68(c) again if you are still not exempted; you have to carry out impact testing.



Pressure Vessel Dimension Inspection;

Do you know what is Pressure Vessel Dimension Inspection requirement? You may know some fabrication tolerances have not beenaddressed in ASME Code Section VIII.

So you need to refer to other sources for inspection. Most dimensional control of Pressure Vessel either addressed or not addressedin the ASME Code consists of following items:

Pressure Vessel Inspections - Dimension



















Weld mismatch

Weld reinforcement

Pressure Vessel RT Test;

Do you know what is your Pressure Vessel RT tests Requirements? Is full radiography mandatory for your vessel? When the fullradiography is mandatory? What are the acceptance criteria? What are the RT symbols?

When one of following condition is existing, you need to do full radiography:

1. All but welds in vessels used to contain lethal substance2. All but welds in vessels in which the nominal thickness exceeds specified values3. All but welds in unfired steam boiler with design pressure > 50 psi4. All category A and D butt welds in vessel when ―Full Radiography‖ optionally selected



Why pressure vessel manufactures want to spent more money for full radiography in item Number 4?



Click on the above link for detail information about Pressure Vessel RT Test which specifically focused on pressure vesselinspections.

Vessel Pressure Testing;

You need to do hydro-static test after completion of construction process but before internal parts assembly and also before paintingprocess.

Please note replacing pneumatic test instead Pressure Vessel Hydro-Static Testing is not allowed and it can be replaced only when itis not possible due to design and process.


The activities are done in 3 stages, the activities before start of the test, the activities during test and the activities after the test.

Click on the above link for detail information about Pressure Vessel Hydro-Static Testing which specifically focused on pressurevessel inspections.

Pressure Vessel Certification;

Do you what is pressure vessel certification process? How Pressure Vessel Manufactures can be ASME Stamp Holder? How ThirdParty inspection companies can be certified by ASME and to be Authorized Inspection Agencies? What is ―U‖ Stamped Pressure

Vessel?














It means if a manufacture accredited by ASME organization for pressure vessel per ASME Code Section VIII Div . 1 can stamp ―U‖letter in the pressure vessel nameplate. These are the process for ASME Stamp Accreditation:

Obtain Application Forms from ASME

Sign a Service Agreement with Authorized Inspection Agency (AIA),Authorized inspection Agencies are Third PartyInspection Companies which have accredited by ASME organization and their inspectors certified by National BoardInspection Code(NBIC).These Inspectors are named Authorized Inspectors and hold Commission Cards issued by NBICorganization.Summary: AIAs are accredited by ASME but his inspectors are certified by NBIC.

Submit Application Forms to ASME and transfer Fees

Purchase ASME Code Books

Describe a QC-System according ASME Code Quality Control manual and procedures need to be prepared by manufacture.

Prepare a Demonstration Item, A Representative Demo pressure vessel need to be constructed and all Drawing,Calculation, Part List, Purchase Orders, Material Test Reports, Fabrication, Inspection, Test and Reporting shall be based

ASME Code Section VIII Requirement.

Qualify Procedures and Personnel, Quality Control Procedures and Personnel also need to be approved by manufacture.

Pre-Joint Review by the Supervisor of AIA, Almost it takes 4 months to fulfill the above requirement. Then an audit need tobe conducted by supervisor Authorized inspector which designated by Authorized inspection agency which is under contractwith manufacture.This auditor would report non-conformities found in audit process, and then manufacture would have sometime to correct them.

Joint Review (Audit) with ASME Designee, Inspector and Supervisor,Finally the Audit would be conducted by ASMEdesignated Person, Supervisor Authorized Inspector and Authorized Inspector.That is the reason this audit is named jointreview.

Issuance of Certificate and Stamp by ASME


Pressure Vessel Heads;

How many standard Pressure Vessel Heads are in the ASME Code? What are their characteristics?

Ellipsoidal Head, Hemispherical Head and Torispherical Head are three types of ASME Pressure Vessel Dished Heads.

In the same design condition such as design pressure, design temperature and material your calculated wall thickness under in ternalpressure for ellipsoidal head will be approximately equal to shell thickness, for torispherical head equal to 1.77 times to shell thicknessand for hemispherical head equal to half shell thickness.

For example if you have calculated your shell thickness under internal pressure and obtained 12 mm, your thickness for ellipsoidalhead will be approximately 12 mm, torispherical head 20.4 mm and for hemispherical head 6 mm.

Third Party Inspection for Pressure Vessel; What is the third party inspection requirement for pressure vessel inspection inmanufacturing shop?

This article provides information about pressure vessel inspection from material inspection to final inspection and dispatch to site.


The Third Party Inspection for Pressure Vessel article provides you information about pressure vessel inspection and pressure vesseltest in manufacturing shop.









This content guides you about all necessary stages in the production of the pressure vessels from the examination of raw material tothe final inspection, preservation and packing to despatch to site.

You need to take this point in account this article is written for a typical pressure vessel and might not be complete for special cases.

This content may be useful for second party inspectors, pressure vessel manufacture quality control personnel, engineeringcompanies and purchasers as well.

You may also note if pressure vessel ordered with U Stamp, then any Third Party Inspection Agency can not do the inspection

and authorized third party ASME inspection need to be covered this also named third party inspection for U stamp.

This third party inspection agencies must be insurance company andaccreditation by ASME.

All pressure vessel inspections and tests are carried out against the approved drawings, purchase order specifications, purchasers orcompany standards, and within the practices and rules of the country, state or province and any government decrees, laws, ordinanceor regulation as may apply.

The applicable codes and specifications for the pressure vessel which is under construction process are:

Design code

Purchase order specification

Purchaser's standards

Approved drawings

and the applicable codes and standards are:

ASME VIII Division 1 or 2

ASME V

ASME IX

The applicable codes and standard may be based other international standards such as BS 5500 and etc. This content is general andcan be useful if even the design code is different from ASME Code.

Third Party Inspection for Pressure Vessel - Required Documents for Third Party Inspector Review:

The list of documents normally is agreed in the Pre Inspection meeting which is hold several weeks before actual commencement ofinspection work.

The parties which are participated in this meeting are manufacture, purchaser and third party inspection agency representatives.

This already explained in the Inspection and Test Plan for Pressure Vessel article.

These are the list of documents which are normally agreed to be presented to the inspector:

Pressure Vessel Manufacture Quality Control Plan

Pressure Vessel Inspection and test plan

Pressure Vessel Data Sheet

Pressure Vessel Approved Drawings

Pressure Vessel Strength calculation sheets

Pressure Vessel Material Test Reports

Pressure Vessel Welding Specification Procedures (WPS) and Procedure Qualification Records(PQR)

Pressure Vessel Welding Map

Pressure Vessel Welders Qualifications Reports

Pressure Vessel NDE procedures

Pressure Vessel NDE Personnel qualifications Reports

Pressure Vessel Heat treatment procedure

Pressure Vessel Calibration Certificates for Test Equipment

Pressure Vessel Hydrostatic Testing Procedure and Water Quality Document

Pressure Vessel Preparation and Painting Procedure

Pressure Vessel Preservation, Packing and Shipping Procedure

Pressure Vessel Packing List







Third Party Inspection for Pressure Vessel - Material Inspection

The first actual inspection work in the pressure vessel is raw materials inspection. Based the ASME Code providing material testreports for pressure vessel plates is mandatory, for other components only the marking inspection will be enough.

But if purchase order has mandated the MTR to be provided for all components such as nozzle pipes, fittings and etc. then themanufacture need provide them as well.

For more detail you may review the Pressure Vessel Plate article.

As mentioned in above, the original or authenticated copies of mill certificates for plates normally are available at manufacturer'spremises.

The third party inspector examines these certificates for compliance with specifications and where appropriate, drawings.

The review includes checks on:

Certificate No.

Heat or cast No.

Chemical composition.

Mechanical properties.

Heat treated condition.

NDE applied and results.

Then the inspector witnesses the plate material identification on the certificates against plate marking. It is also necessary to checkwith pressure vessel drawing datasheet, material list and other specification as appropriate.

The transfer identification to cut off plates also is checked.

Visual inspection for surface finish and probable defects are done and dimensional compliance with specification need also to becontrolled.

For more detail in pressure vessel raw material inspection you may reviewPressure Vessel Dimension Inspection article.

When the third party inspector carried out the material inspection, then provides inspection visit report, the report contains followingitems:

Confirmation of satisfactory document review

Record of the endorsement of certification reviewed/witnessed

Record of all non-conformities

Record of any tests witnessed and the result

Third Party Inspection for Pressure Vessel - Fabrication

When the pressure vessel material inspection carried out and result was satisfactory or non-conformities closed by remedial action,then pressure vessel manufacture will be authorised to start fabrication.

The third party Inspector checks following points on pressure vessel based on the inspection and test plan (ITP) which is alreadyagreed between purchaser and pressure vessel manufacture.

The inspection scope is determined in ITP, some clients prefer to have stringent control and put the TPI inspector in more ―holdpoints‖ in fabrication activities and some others may take lesser ―hold points‖ and put TPI much more in the review document.

This depend to the inspection budget which client assign for inspection, much more inspection will have much more costs and lessrisks and conversely less more inspection will have less costs but more risks.

For more detail review Inspection and Test Plan for Pressure Vessel article. There is draft ITP in this article which I believe it is thebest practice for Pressure Vessel inspection.

Third Party Inspection for Pressure Vessel - Preparation for Welding

The third party inspector carries out visual and dimensional check to ensure compliance with WPS and other specifications. Wherespecified, weld bevels are examined by required code method after grinding/machining.

It is necessary edges and weld bevels to be clean, dry and free from surface defects, laminations, cracks, voids, notches, etc.













They are causes for rejection unless suitable/satisfactory remedial action can be taken.

Weld repairs are carried out in accordance with the code requirements and approved by the client before welding proceeds andserious or excessive defects normally are reported.

If the third party inspector is not in the hold or witness point in the ITP for these stages, then will review the pressure vesselmanufacture quality control report in his/her coming visit or final inspection day.

Third Party Inspection for Pressure Vessel - Fit-Up Inspection

Shapes and dimensions are checked in accordance with the approved WPS and drawing.

Tack welds are produced using the applicable WPS conditions and it is necessary to be visual free from defects.

Magnetic Testing (MT) or Penetration Testing (PT) may be performed in accordance with the code requirement.


Third Party Inspection for Pressure Vessel - Monitoring of Weld Conditions

The third party inspector controls preheat heat temperature and method, Interpass temperatures, weld material control, welder andprocess qualifications for conformity to the code requirements.


Third Party Inspection for Pressure Vessel - Back Gouging Inspection

The third party inspector controls the shape and dimensions of the back gouged groove for conformity to the WPS requirement.

It is necessary the visual appearance to be clean and free from defects. NDE examination is done in accordance with the coderequirement.


Third Party Inspection for Pressure Vessel - Post Weld Inspection

After completion of all welding and grinding operations a visual examination confirms there are no harmful defects such as cracks,lack of fusion, surface porosity or exposed slag inclusions, incomplete penetration, incorrect profile of the weld, lack of leg length andoverlap.

Temporary attachments are removed, ground smooth, and the areas checked for defects by MP or PT for defects.


Third Party Inspection for Pressure Vessel - Non Destructive Examination

NDE is performed by qualified personnel to the approved techniques. The techniques available are dependent on vessel classificationand the materials used.

The third party inspector checks that the correct method has been used and verifies the approved status of both the technique andthe personnel.

Third Party Inspection for Pressure Vessel Weld Repair

The pressure vessel weld repairs are completed using an approved WPS method and retested accordingly.

It is necessary all repairs to be approved before any post weld heat treatment is carried out.

Third Party Inspection for Pressure Vessel Post Weld Heat Treatment



The third party inspector reviews the post weld heat treatment record of temperature and time in accordance with the approvedcode/procedure.

Similarly the results of hardness tests are reviewed in accordance with the code requirements.

Third Party Inspection for Pressure Vessel Dimensional Measurement and Visual Inspection

The third party inspector checks all major dimensions and the position/orientation of attachments are in accordance with the coderequirements.

For more detail review Pressure vessel Dimension Inspection article.

In addition a full visual examination of both inside (where practicable) and outside surfaces of the vessel is completed by the thirdparty inspector.

Particular attention is paid to the cleanliness of the interior of the vessel, the condition/appearance of welds and associated areas, thecondition of sealing faces.


Third Party Inspection for Pressure Vessel Pneumatic Test

The third party inspector witnesses low pressure pneumatic test for nozzle reinforcing pads, support saddles or other attachments

when specified by approved low pressure pneumatic test procedure using soapy water as the indicating medium.

A minimum of 1 gauge with correct working ranges as described by the code is used.


Third Party Inspection for Pressure Vessel Hydrostatic Testing

The third party inspector controls following items for Hydrostatic Testing:

Calibration status and correct working ranges of gauges. A minimum of 2 pressure gauges are attached to item under test.

Adequate provision for venting of high points and draining is provided.

Test pressure is applied as directed by procedure or code until test limiting pressure is reached. During hold period, amethodical check for leaks is conducted.

Test pressures, metal and water temperatures are recorded.

Water quality is as specified.

Special requirements of the purchaser's specification for deflection or strain gauges or pressure/time/temperature recordings areexamined by the inspector and records verified.

For more detail in hydrostatic testing review Vessel Pressure Testing article.

Third Party Inspection for Pressure Vessel - Final Inspection

After hydrostatic testing, the vessel is thoroughly drained and dried out by approved methods. All internal fittings, attachments,coatings or other requirements need to be completed.

Specified post hydrostatic test NDE need to be completed and the vessel closed.

All pressure vessels are checked for cleanliness and dryness by an approved method.

The third party inspector rechecks nozzle, saddle and bracket locations and orientations against assembly drawings.

Third Party Inspection for Pressure Vessel - Name Plate

The content of the marking is checked in accordance with approved drawing and specifications by third party inspector.

Third Party Inspection for Pressure Vessel-Painting and Coating Inspection

Surface preparation for painting is checked for the following points, according to specification by third party inspector:










Cleaning method (Blast or scraping and wire brushing)

Preparation grades

Freedom from weld spatter, blow-holes and other defects

Dry film thickness is checked according to specification

Surface condition need to be free from pin-holes, runs damage and other discontinuity

Third Party Inspection for Pressure Vessel-Spares and Accessories

The third party inspector controls spares, tools and accessories and makes visual and dimensional inspection for materials,workmanship and quantity according to purchase order specification and packing list.

Marking and/or Tag is checked for identification.

Third Party Inspection for Pressure Vessel-Pressure Vessel Reporting

Third party inspector provides Inspection Visit Report (IVR) after each visit as well as a final report summarising the activities carriedout during the vessel production in accordance with the contract requirements and circulated within the time limits specified in thecontract.

The report is in the format required by the client and clearly indicates final acceptance or rejection of the pressure vessel.

Third Party Inspection for Pressure Vessel-Pressure Vessel Release Note

When required by the contract or purchase order a release note is issued by third party agency and given to the manufacturer whenthe pressure vessel have been finally accepted.

Third Party Inspection for Pressure Vessel-Packing, Marking and Shipping

The following points are checked by the third party inspector:

Cleanliness and dryness of pressure vessels

Rust prevention for all machined surfaces

Protection for cover for all opening and protruding parts

Packing style and suitably for overseas transportation

Shipping marks and other markings and notification of welding prohibited, etc.

Where nitrogen purge is specified the gas pressure is checked and the presence of warning notices checked.

Third Party Inspection for Pressure Vessel - Pressure Vessel Final Book (Dossier)

The following final documents are reviewed and signed off by third party inspector:

As built, drawings if required, Manufacturer's data reports, Material certificate or certified mill test reports for all pressureparts, Material list or map, Welder record for each seam or map, Heat treatment records (Temperature-time record chart duringPWHT), Dimensional record, NDE records, Production test record/mock test record, Alloy verification records, (if required), hydrostatictest record, Pneumatic test record, Hardness test record, Post weld heat treatment NDE, if specified, Name plate or othermarks, Packing list, Spare parts and tool list

Inspection and Test Plan for Pressure Vessel;

The Inspection and testing requirement distributed in different part of construction code.

The inspection and test plan have tabulated format and collects all these requirement in simple table and determine responsibly ofeach party i.e manufacture, third party inspector and purchaser.

Pressure Vessel Handbook;

When there is ASME Code Section VIII, why we need Pressure Vessel Handbook? What are the applications? All design formulasand calculations methods have not been addressed in ASME Code and also there are no fabrication tolerances in ASME Code.

So Pressure Vessel handbook assists us to cover all these requirements.



http://www.inspection-for-industry.com/pressure-vessel-handbook.html






The Pressure Vessel handbook supports pressure vessel inspections engineers, designers, pressure vessel manufacturer qualitycontrol technicians and engineers and any other dealing persons with pressure vessels.

Spherical Pressure Vessel;

What is construction Code for Spherical Pressure Vessel? What is In-Service Code for Spherical Pressure Vessel? What are theSpherical Vessel applications? What are advantages?

Click on above link to see the answer of above questions which specifically focused on pressure vessel inspections.


The ASME Code Section VIII Div. 1 or 2 requirements normally are applied for inspection and test plan in pressure vesselmanufacturing shop.

The witness of some inspection and test by third party inspector or authorized inspector is mandatory and cannot be waived.

Some others can only monitored and fully witnessing are not necessary, for these items, the inspection man-days etc. depends to thepurchaser decision, some prefer stringent monitoring and even assign resident inspector in pressure vessel manufacturing shop andsome others relay to quality control system of the pressure vessel manufacture and assign only few days for monitoring points.

These are some of inspection points which need to be witnessed, checked monitored and reviewed by third party or ASME authorizedinspector.

Inspection and Test Plan for Pressure Vessel - Important Points

All plates need to be identified against mill test certificates at the Vendonr`s works before commencement of fabrication.

Ensuring that welding procedure and welders are qualified and welding electrodes are approved before commencement offabrication.

Selection of location for spot radiography

Reviewing of radiographs

Witnessing of hydrostatic test

Dimensionally checking and carrying out final internal and external inspection for quality of workmanship.

Checking that all material test certificates and, where applicable, heat treatment charts are in order

If specified witnessing any crack detection, hardness checks, ultrasonic tests etc.

Checking fit-up and chipping-back of welded seams.

Monitoring welding process based WPS

Monitoring all NDE activities

Ensuring that Vendor is familiar with the requirements regarding data books and ensure that the documentation is submittedwithout any delay.

Checking internal lining of reactors and vessels (if applicable) to specifications.

Checking trays of each diameter and type, mock assembled in the shop. (for process towers)

Checking for interchangeability of parts, where applicable for process towers

http://www.inspection-for-industry.com/spherical-pressure-vessel.html








Ensuring that any uncommon down comers are fully assembled and offered along with their respective trays. (for processtowers)

Pressure Vessel Handbook; When there is ASME Code Section VIII, why we need Pressure Vessel Handbook? What are theapplications? All design formulas and calculations methods have not been addressed in ASME Code and also there are no fabrica tion

tolerances in ASME Code.

So Pressure Vessel handbook assists us to cover all these requirements.

The Pressure Vessel handbook supports pressure vessel inspections engineers, designers, pressure vessel manufacturer qualitycontrol technicians and engineers and any other dealing persons with pressure vessels.

Click on above link for detail information about Pressure Vessel Handbook which specifically focused on pressure vesselinspection.

Pressure Vessel Handbook

The Pressure Vessel Handbook article provides you information about handbook application in pressure vessel design and pressurevessel inspection.

When there is ASME Code Section VIII, why we need Handbook? What are the applications?

All design formulas and calculations methods have not been addressed in ASME Code and also there are no fabrication tolerances in ASME Code.

So handbook assists us to cover all these requirements.

The Pressure Vessel handbook supports pressure vessel designers, pressure vessel manufacturer quality control technicians andengineers, third party inspectors and any other dealing persons with pressure vessels.

What is the Application of Pressure Vessel Handbook?

1. Non-Covered ASME Code Section VIII Design Formula and Methods

You may review ASME Code Section VIII Div. 1 in U2 (g) clauses, you will see following statement:

―This Division of Section VIII does not contain rules to cover all d etails of design and construction. Where complete details are notgiven, it is intended that the Manufacturer, subject to the acceptance of the Inspector, shall provide details of design and constructionwhich will be as safe as those provided by the rules of this Division.‖






So the manufacture is responsible for non-covered item in design process, but what reference manufactures need to use for thesekinds of cases.

Here is the place manufactures use handbook for design formulas and calculations.

The lists of non-covered design details have been addressed in UG-22 clauses; the code says the manufacturer need to considerfollowing loading in his design:

Weight of the vessel

Superimposed static reactions from weight of attached equipment

Cyclic and dynamic reactions

Wind, snow, and seismic reactions

etc.

Above items are examples, for design calculation manufactures need to use Press. Vessel Handbook.

2. Non-Covered Construction Tolerances

You may review ASME Code Forward, you will see following statement:

―The Code does not fully address tolerances. When dimensions, sizes, or other parameters are not specified with tolerances, thevalues of these parameters are considered nominal and allowable tolerances or local variances may be considered acceptable whenbased on engineering judgment and standard practices as determined by the designer.‖

So what is the reference book for these tolerances, here is another application of pressure vessel handbook.

Some of these construction tolerances are :

Nozzles and attachment deflection tolerances

Nozzles and attachment orientation tolerances

Nozzles and attachment elevation tolerances

Nozzles and attachment projection tolerances

Overall length, measured between the tangents lines tolerances

etc.

3. Facilitate Design Calculation

You may review following statements in ASME Code Forward:

―It is not intended that this Section be used as a design handbook‖

And in other place says:

―The Code is not a handbook and cannot replace education, experience, and the use of engineering judgment.‖

So the code book is like law book, we need take care about specific prohibitions and mandatory requirement but for design we needhandbook to facilitate our design process.

The aim of your handbook is to be easily handled and consulted. Some tables and charts eliminate the necessity for calculations.



Spherical Pressure Vessel; What is construction Code for Spherical Pressure Vessel? What is In -Service Code for Spherical PressureVessel? What are the Spherical Vessel applications? What are advantages?

Click on above link to see the answer of above questions which specifically focused on pressure vessel inspections.

Spherical Pressure Vessel

The Spherical Pressure Vessel article provides you information about this vessels characteristics and related points in pressurevessel inspection.

What is construction Code for Spherical Pressure Vessel? What is In-Service Code for Spherical Press. Vessel? What are theapplications? What are advantages?

This article either provides you the answers of your questions or refers you to the specific sources.

What is the Difference Between Design Formula of Cylindrical Shell and Spherical Shell?

In the same design condition such as design pressure, design temperature and material the thickness you obtain from internalpressure formula for spherical pressure vessel will be half of cylindrical pressure vessel.

The design formula for cylindrical shell is t = PR/ (SE-0.6P) And for spherical shell is t = PR/ (2SE-0.2P)

When the ―t‖ is represent Thickness, ―R‖ the Inside Radius,‖ S ―the Allowable Stress, ―P‖ the Design Pressure and ―E‖ the Joi ntEfficiency;

For example if your design pressure is 250 psi, inside radius 20 inch. , allowable stress 20,000 psi and joint efficiency 1;

Your thickness for cylindrical shell will be 0.24 inch. or 6.10 mm and for spherical shell will be 0.125 inch. or 3.175 mm.

What is the Application and Advantage of Spherical Pressure Vessel?

When you need to make storage for great amount of pressurized liquid or gas, so you need a big volume, then you need a bigpressure vessel, so spherical shell pressure vessel would be more economical.

As you see in above the thickness is half for similar design condition, also placing a long cylindrical pressure vessel might not be

suitable regarding plant layout.

What is the Disadvantage of Spherical Pressure Vessel?

Spherical shell pressure vessels are more expensive than cylindrical pressure vessels to fabricate and this higher price only justifiablefor large vessels.

What is Difference in Fabrication Method Between Cylindrical and Spherical Shell Pressure Vessel?

Cylindrical shell pressure vessel generally are built in the shop and then transferred to the plant field except long process towerswhich might build in two pieces and completed in the field by one circumferential weld.

This is only because of facilitating shipping process.

But spherical shell pressure vessels are assembled in field. The plates generally are formed in the rolling shop and then carefullytransferred to the field for assembly.

What is Difference in Post Weld Heat Treatment (PWHT) Process?

If PWHT is code or process requirement, the PWHT for cylindrical shell pressure vessel generally are done in the furnace, and if thevessel is too long, it is done in two heating process with 5 ft. overlap.

But PWHT for spherical shell pressure vessel are done by one or more high velocity burners are fired into the vessel using the top orbottom manways (or both) as burner entry and exhaust positions.

Because using of PWHT furnace is not possible.

What Kinds of Materials are Stored in Spherical Pressure Vessel?






Most of the LNG (Liquid Natural Gas) and LPG (Liquid Petroleum Gas) tanks are Spherical Vessels.

Butane, Propane, Ammonia, oxygen, hydrogen and nitrogen also are stored in spherical vessels.

What is In-Service Inspection Requirements for Spherical shell Pressure Vessel?

In-service inspection requirement is similar to cylindrical pressure vessel and is based the requirement of API STD 510 Standard.

Some important points about in-service inspection are:

The inspection plan need to be developed for the vessel and generally internal inspection is mandatory requirement.

You need to do internal inspection in interval not exceeding one half the remaining life or 10 years whichever is less.

You can calculate the remaining life with following simple formula:

RL = (Tc-Tmin)/CR ;

When Tc is Actual Thickness, Tmin is Minimum Required Thickness, it is can be obtained by deduction of nominal thickness fromcorrosion allowance;

And CR is corrosion rate;

Example: you have spherical shell storage vessel with actual thickness of 1.121 in. and min required thickness is 1.0 and the

corrosion rate is 0.005 in./year so the reaming life will be:

(1.121-1.0)/0.005 = 24.2 years;

So internal inspection interval will be:

Half-life = 24.2/2 = 12.1 so 10<12.1 then internal inspection interval will be 10 years;

But in most plants evacuation of storage vessels are very difficult and costly so integrity engineers try to find a new technique toreplace internal inspection.

API STD 510 admits the On-Stream inspection to be replaced to the internal inspection with some conditions.

This is the definition of On-Stream Inspection per API 510 Standard:

―An inspection performed from the outside of a pressure vessel while it is on-stream using NDE procedures to establish the suitabilityof the pressure boundary for continued operation.‖

But only you may replace this technique if all of following conditions are met to your vessel:

The general corrosion rate is less than 0.005 inch. per year, remaining life is greater than 10 years, there is no corrosive character inthe contents, No questionable condition is observed in the External inspection and vessel is not subject to SCC cracking.

What is the Best Technique to Use as On-Stream Inspection?

The best technique which is widely used is acoustic emission testing. In this technique the spherical vessel completely filled bycontent fluid to maximize stresses.

Meantime highly-sensitive proprietary acoustic sensors are attached to the vessel wall to detect the fracture of corrosion products,during the monitoring period.

The suspect areas are identified and located. If the suspect shows a high risk issue, then the vessel would be evacuated for internalinspection and necessary repairs.

What are the Repair Methods in Spherical Shell Pressure Vessel?

There are three sources for repair of spherical pressure vessel; API STD 510 has provided some repair requirement and instruction.

Based the API 510 only repair organizations are allowed to do repair, and the definition and condition for being repair organizationhas been provided in the API 510.

The other source is ASME-PCC-2, which provides you detail instructions and requirements.



The other source is NBIC Part 3 Code book, which similarly provides requirements and instructions.

Please note if your spherical pressure vessel is ―U‖ or ―U2‖ stamped pressure vessel, only repair organizations which are ‖ R‖ stampholder from NBIC allowed to do repair on your vessel.

For more detail on the stamped pressure vessel review the Pressure Vessel Certification article.





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