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API 570 Piping Inspection CodePart 3: Pipe Fabrication

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Objectives

Determine the Minimum Design Metal TempFamiliar with welding restrictionsFamiliar with basic fabrication requirementsDetermine Preheat & PWHT temperaturesKnow the NDE requirements for new pipeEvaluate weld discontinuities

This part will cover Chapter III, V & Vi in B31.3

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Materials

Listed Materials: Material “listed” in B31.3 in either Table A-1 or Table 326.1

Unlisted Materials: Materials not “listed” in B31.3 Use only if they meet the material property requirement of the Code

Unknown Materials Cannot be used for pressure containing components

Selection of material to resist corrosion is not within the Scope of the Code (323.5)

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Low Temperature Limits

Brittleness of a material is a major design issue for all types of pressure equipment. A brittle material can fail catastrophically!!

Some of the factors that affect brittleness of a material include: Material Temperature Stress Level Thickness

The opposite of brittleness is “Toughness”. Brittle materials have low toughness.

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Low Temperature Limits

Minimum Temperature per Code Most Material – Listed Table A-1 Most CS – Lists Curve Letter

Below this temperature Material cannot be used or The material must be impact tested at desired temperature

Carbon Steel Low Temp Process1. Find Curve Letter – Table A-12. Find Initial Min Temp

Use Table 323.2.2A (tnominal) Check Notes – Fig 323.2.2A

3. If Stress Ratio Fig 323.2.2B Reduction Temp

Enter at Left (Stress Ratio) At Curve go vertical to Reduction Temp

Subtract Reduction from Step 2

Impact Test Acceptance Criteria4. Each set has 3 bars5. Average ≥ Table 323.3.56. Minimum ≥ Table 323.3.57. Only 1 specimen ≤ Table Ave

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Exercise 1

1. What is the minimum design temperature for A-335-P5 (5% Cr)

2. What is the minimum design temperature for A-358 Type 304L?

3. What is the minimum design temperature for a 0.750” pipe that is made from A-106-B?

4. What is the minimum design temperature for a 0.500” pipe that is made from A-516-60 plate and is normalized?

5. What is the minimum design temperature for a 0.625” pipe that is made from A-106-C and has a Stress Ratio of 0.90?

6. If the designer wants to use a pipe material below the minimum temperature allowed by B31.3, then the material must be ________

7. Impact testing is performed on an pipe made from A-106-C (a fully deoxidized steel). Determine the following:

a. The impact procedure must follow what specs?b. The set consists of how many bars?c. The minimum average for the set is?d. The minimum value for a single bar is?e. How many bar(s) can be below the required average?

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Answers 1

1. What is the minimum design temperature for A-335-P5 (5% Cr) -20oF

2. What is the minimum design temperature for A-358 Type 304L? -425oF

3. What is the minimum design temperature for a 0.750” pipe that is made from A-106-B? Curve B, 15oF

4. What is the minimum design temperature for a 0.500” pipe that is made from A-516-60 plate and is normalized? Curve D, -55oF

5. What is the minimum design temperature for a 0.625” pipe that is made from A-106-C and has a Stress Ratio of 0.90? Curve B, -7oF

6. If the designer wants to use a pipe material below the minimum temperature allowed by B31.3, then the material must be impact tested

7. Impact testing is performed on an pipe made from A-106-C (a fully deoxidized steel). Determine the following:

a. The impact procedure must follow what specs? ASTM A370 & A333b. The set consists of how many bars? 3c. The minimum average for the set is? 20 Joulesd. The minimum value for a single bar is? 16 Joulese. How many bar(s) can be below the required average? 1

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Fabrication - Welding

Qualified Weld Procedure ASME B&PV Section IX Can accept some Procedures qualified by others

Welder Qualification ASME B&PV Section IX Can accept Qualifications by others

Welding Records Employer maintain procedures and performance records

Welder Identification Unique ID or Symbol Stamp each weld or Use weld maps

Tacks weld Fused with the root pass Made by a qualified welder

Bad weather – don’t weld

Fillet weld sizing Figure 328.5.2 Min weld size 1/8”

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Info

Other Miscellaneous Requirements

1. If excessive misalignment, taper with a maximum angle of 30 degrees

2. Peening is prohibited on the root & final pass

3. Seal welds allowed but must cover all exposed threads

4. Flange allignmenta. Parallel within 1/16” per foot (diameter)b. Bolt holes aligned within 1/8”

5. Bolt length: Bolts should extend completely through the nut. If not, has to be within one thread of complete engagement

6. Gaskets: Only 1 per flange assembly

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Welding & Distortion

The Principles Thermal Growth – As metals heat up they expand. When cooled, they shrink. A metal’s strength decreases with increasing temperatures

How Distortion Occurs The arc is initiated Hot surface expands & distorts the plate

Not much since the hot side is much weaker than the cool side Completed weld, as heat moves away from weld. Weld contracts Completed weld is distorted & has residual stresses

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Info

Stresses from Welding

1. When we apply heat in a non-uniform method (welding) the result is a dimensional change causing the part to be distorted or warped

2. The Principle – As the metals cool they shrink. A CS weld that is ¾” wide will shrink about 10 mils. The base metal is “anchored”. As the weld shrinks, the base pulls the cooling weld.

(Tensile Stress) At higher temperature, the weld metal is weak and ductile. It can be pulled and

reshaped to account for shrinkage At low temperature, the weld metal is stronger and less ductile. It is not easily

“reshaped” Remaining pull on the weld once cool – “Residual Stresses” If Residual Stresses exceed strength of weld – Crack

3. Residual stresses can be reduced or eliminated by:• Preheat• Thermal heat treatment• Peening – pneumatic hammer used to pound on welds eg jitterbug type of equipment

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Preheat & PWHT

Preheating (330) Used to minimize detrimental effects caused from welding Preheat temperatures; Use Table 330.1.1 Preheat zone shall extend at least 1” from toe of weld

Post Weld Heat Treating (331) Used to relieve detrimental effects caused from welding PWHT temperatures: Use Table 331.1.1 PWHT zone shall extend at least 1” from toe of weld Partial HT: Minimum overlap of 1’ Local HT: Full circumference Hardness Testing – if required 10% of Furnace welds, 100% of field welds

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Exercise 2

1. Determine the minimum preheat temperatures for the following situations. Determine whether the pre-heat is required (Req’d) or recommended (Rec)

a. 0.750” thick, P-1 material, SMTS = 65 ksib. 0.250” thick, P-8 materialc. 0.500” thick, P-1 material, SMTS = 75 ksid. 0.325” thick, P-5C materiale. 1.250” thick, P-1 material, SMTS = 70 ksi

2. At what base metal temperature, do all the recommend preheat temps become required temperatures?

3. Determine the PWHT temperature for the following situations.a. 0.750” thick, P-1 material, SMTS = 65 ksib. 0.250” thick, P-8 materialc. 0.800” thick, P-1 material, SMTS = 70 ksid. 0.325” thick, 5% Cr material

4. What is the minimum holding time a PWHT conducted on a CS pipe that is 1.500” thick?

5. What is the minimum holding time a PWHT conducted on a CS pipe that is 0.875” thick?

6. What is the minimum holding time a PWHT conducted on a 9% Cr pipe that is 0.750” thick?

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Answers 2

1. Determine the minimum preheat temperatures for the following situations. Determine whether the pre-heat is required (Req’d) or recommended (Rec)

a. 0.750” thick, P-1 material, SMTS = 65 ksi 50oF, Recb. 0.250” thick, P-8 material 50oF, Recc. 0.500” thick, P-1 material, SMTS = 75 ksi 175oF, Recd. 0.325” thick, P-5C material 350oF, Req’de. 1.250” thick, P-1 material, SMTS = 70 ksi 175oF, Rec

2. At what base metal temperature, do all the recommend preheat temps become required temperatures? < 0oC (32oF)

3. Determine the PWHT temperature for the following situations.a. 0.750” thick, P-1 material, SMTS = 65 ksi Noneb. 0.250” thick, P-8 material Nonec. 0.800” thick, P-1 material, SMTS = 70 ksi 1100 - 1200oF (593 - 649oC)d. 0.325” thick, 5% Cr material 1300 - 1400oF (704 - 760oC)

4. What is the minimum holding time a PWHT conducted on a CS pipe that is 1.500” thick?

1.5 hr

5. What is the minimum holding time a PWHT conducted on a CS pipe that is 0.875” thick?1 hr

6. What is the minimum holding time a PWHT conducted on a 9% Cr pipe that is 0.750” thick?2 hr

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Examination

Category D Some visual

Normal Service Some visual: materials, fabrication & assembly Visual: 5% of all welds RT: 5% of circ welds

Severe Cyclic Visual: 100% of fabrication & assembly RT: 100% of circ welds MT/PT: All socket-welds

RT Criteria – Table 341.3.2 Tw = wall thickness “and” means “lesser of values”

Progressive Sampling Random Exam Reject Take 2 more RT: 5% of circ welds

Progressive Sampling Random Exam Reject Take 2 more

If these OK, repair & stop If any defects, then

Take 2 more for each reject If these OK, repair & stop If any defects, then

Exam all or Repair all Only those represented by

this Random Exam

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Exercise 3

1. A new Normal Service pipe is fabricated. The wall thickness is 0.500”. Determine the maximum allowed dimension for the following discontinuities:

a. Crackb. Lack of fusionc. Length of a slag inclusiond. Width of a slag inclusione. Cumulative Length of slag inclusionsf. Depth of Undercutg. Length of Undercuth. Maximum Cap Height

2. All NDE methods shall be performed in accordance with __________

3. All NDE personnel should be qualified in accordance with ____________

Info - NDE Definitions:100% Examination :“All of All”Random Examination : “All of Some”Spot Examination : “Some of All”Random Spot Examination : “Some of Some”

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Answers 3

1. A new Normal Service pipe is fabricated. The wall thickness is 0.500”. Determine the maximum allowed dimension for the following discontinuities:

a. Crack 0b. Lack of fusion 0c. Length of a slag inclusion ≤ 2Tw = ≤ 2 x 0.5 = 1”d. Width of a slag inclusion 1/8”e. Cumulative Length of slag inclusions 2” in any 6” lengthf. Depth of Undercut ≤ 1/32”g. Length of Undercut Unlimitedh. Maximum Cap Height 1/8”

2. All NDE methods shall be performed in accordance with ASME Section V

3. All NDE personnel should be qualified in accordance with SNT-TC-1A

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Pressure Testing

Purpose of testing Find leaks in joints Create higher stress than the operation stress Minimize the risk of brittle fracture while in-service

All new pipe is tested Cat D – Service Test

Minimum Hold Time 10 minutes

Joints - Uninsulated

Hydrotest Pneumatic Test

SPxS

P TT

5.1

PPPP

PP

T

Tinitial

T

inspect

TRV

P(lesser) psig 50Por 1.1P

(lesser) psig 25or 5.01.1

ST: Allowable Stress at Test Temperature (Usually @ 100oF)

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Info

Why ST/S?

Note that ST/S will always be ≥ 1.0. If greater than 1.0, then the pipe will be tested at a pressure higher than 1.5 x PT. A pipe will always be tested at or near ambient temperature. But at ambient temperature, a material is stronger than at some elevated temperature. So, for pipe that is designed for elevated temperatures, ST/S adjusts the test pressure upward, recognizing that the material is stronger at test temperature.

Actually P x ST/S is basically the pressure this pipe is “good for” if it was rerated to a design temperature of 100oF

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Exercise 4

1. Determine the required hydrotest pressure for a 8 NPS pipe. The design pressure is 500 psig at 600oF. The pipe is made of A-106 Gr A material.

2. A pneumatic pressure test is going to be performed on a 16 NPS piping system. The design pressure is 100 psig at 300oF. The pipe is made of A-106 Gr C material. Determine the following pressures.

a. Test Pressureb. Initial System Pressurec. Maximum Relief Valve Pressured. Inspection Pressure

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Answers 4

1. Determine the required hydrotest pressure for a 8 NPS pipe. The design pressure is 500 psig at 600oF. The pipe is made of A-106 Gr A material. PT = 811 psig

2. A pneumatic pressure test is going to be performed on a 16 NPS piping system. The design pressure is 100 psig at 300oF. The pipe is made of A-106 Gr C material. Determine the following pressures.

a. Test Pressure PT = 110 psigb. Initial System Pressure PInitial = 25 psigc. Maximum Relief Valve Pressure PRV = 121 psigd. Inspection Pressure PInspect = 100 psig