1.0 INTRODUCTION

There are numerous welding process variables that should be described in a welding

procedure. It is always desirable and often essential that the variables associated with the

welding be described in a welding procedure with sufficient detail to permit reproduction of

the weld and to afford a clear understanding of the parameters for performing the production

weld. These variables are stipulated in two different documents:

1. Welding procedure specification (WPS)

2. Procedure qualification record (PQR)

1.1 Welding procedure specification (WPS)

Welding procedure specification is a document that describes how welding is to be

carried out in production.  They are recommended for all welding operations and many

application codes and standards make them mandatory. The WPS document providing the

required welding variables for a specific application to assure repeatability by properly

trained welders and welding operators. Generally, proposed welding procedures should be

proven adequate by either procedure qualification tests or by sufficient prior use and service

experience to assure dependability. The purpose of a welding procedure specification is to

define those details that are to be carried out in welding specific materials or parts. To fulfill

this purpose effectively, a welding procedure specification should be as concise and clear as

possible or in other words it is a recipe of the welding.

1.2 Procedure qualification record (PQR)

Every welding to be carried out needs a report which detailed welding method, type

of material and welding material is in compliance according to standards and which its

welding is performed in compliance with ASME or other organization codes according to

project standards. The PQR should have several mechanical tests such as non-destructive test

and destructive test which provide the result of the testing. All the test also required the

endorsement from third party inspection bodies. The mechanical tests are conducted and its

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results are in compliance. Therefore, every WPS must require a supporting welding

procedure qualification record (PQR).

The PQR can support several WPS under validity areas. The PQR preparation and

tests must be conducted and approved under supervision of Third Party Inspection Bodies

such as Lloyd consultation and PQR must be in compliance with standard of the job carried

out. For jobs apart from ASME Code, related standard must be taken as a basis. The welding

terminology that will be used must be appropriate to manufacturing standard.

1.3 Welder Qualification Record

In the welded manufactures, welding must be performed by a welder who has

absolutely this qualification.  For certification of this, welders will be tested according to

ASME SEC. IX or other standard codes in compliance with project standard and will have a

certificate and badge that covers the welding specifications. Tests of welders must be

conducted under supervision of Independent Inspection Bodies, and then certificates must be

given by these bodies. Welders who do not have such a certificate or whose certificate is

expired, then before the project, they must be re-taken to test in supervision of authorized

inspection company. Badges that is submitted by Independent Inspection Body such LLoyd

and have also photograph on it must be present on the welder during work and quality

controller will check that welder is authorized to this welding and not by looking at this

badge.

1.4 WPS in industry

Industry today uses two common types of welding procedure specifications. One is a

broad, general type that applies to all welding processes of a given kind on a specific

material. The other is a narrower, more definitive type that spells out in detail the welding of

a single size and type of joint in a specific material or part. The narrower, more definitive

type is most frequently used by manufacturers for their own control of repetitive in-plant

welding operations or by purchasers desiring certain specific metallurgical, chemical, or

mechanical properties. However, either type may be required by a customer or agency,

depending upon the nature of the welding involved in charge.

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Welding procedure specifications (WPS) are sometimes required by the purchaser to

govern fabrication of a given product in a fabricator's workshop. Most often, however, the

purchaser will simply specify the properties desired in the weldment in accordance with a

code or specification, leaving the fabricator to use a welding procedure that will produce the

specified results. In other cases, the purchaser will prescribe that the fabricator establishes

definite welding procedure specifications and test them to prove that the resulting welds will

meet requirements specified by the purchaser.

Figure 1 pressure use in many industries such as petrochemical, oleo chemical and heavy chemical

industry. The pictures above show the almost complete of pressure vessel.

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2.0 WPS DESCRIPTION

In this section, the WPS provided will be given with description and justification

about all content involve in WPS form that involve . The justification include the applicable

code and detail on welding process. This WPS only can be applied for carbon steel weld on

fabrication of pressure vessel. This WPS can use for certain metal codes with thickness

between 15.3mm. Any metal part with that thickness can be joint with single vee and sing

bevel type. All the WPS is referred to ASME BPVC section 9.

2.1 The codes

In this fabrication of girth weld of nozzle accordance of WPS provided, the ASME

boiler and pressure vessel code (BPVC) section 9 was followed. The ASME boiler and

pressure vessel code embraces its own QA system which revolves around satisfying the rules

of the code.  This demonstrates that an accredited fabricator has some competencies

permitting them to perform a large amount of their own inspection without the involvement

of an Independent Inspection Body, which would be required by other standards for similar

inspections. However, there are no agencies or board stopping by using any of the rules of the

ASME code without being ASME approved. To prove the competence in welding, an

Independent Inspection Body is recommended to approve the WPS and the test.

2.2 Welding process – gas tungsten arc welding

According to the WPS, gas tungsten arc welding is use as their welding process.

GTAW is one of welding process that provide good joining, good penetration and high

quality weld. Actually GTAW or TIG usually applied on stainless steel but carbon steel also

acceptable. Manual welding type mean the weld operation is done by hand weld without any

help from robot or machine. The process is used with shielding gas and without the

application of pressure. The shielding gas used is argon. GTAW can be used with or without

the addition of filler metal. The polarity type can be used with either DC or AC, the choice

depends largely on the metal to be welded. For this application, DCEN is use by using 2%

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thoriated tungsten electrode. Direct current welding is typically performed with the electrode

negative (DCEN) polarity. DCEN welding offers the advantages of deeper penetration and

faster welding speeds. Alternating current provides a cathodic cleaning action (sputtering)

that removes metal oxides from the surfaces of the weld joint, which is necessary for welding

aluminum and magnesium.

2.3 Electrode – Thoriated tungsten

2.4 mm diameter with 7 inch length electrode was used to weld. The tungsten

electrode is made of 2% thorium tungsten that called thoriated tungsten. Thoriated tungsten

electrodes are widely used because they make good welds, deep penetration, long lasting and

quite easy to use. These electrodes are normally sharpened by grinding like pencil pointed as

part of the standard procedure while preparing to perform gas tungsten arc welding (GTAW).

2.4 Shielding gas - Argon

Argon gas with 99.9% purity is use as shielding gas for this type of welding. Argon is

a heavy gas that is obtained from the atmosphere by the liquidization of air. Depending on the

volume of use, argon may be supplied as a compressed gas or as a liquid. Furthermore, the

argon gas can be purchased at much lower prices in the bulk liquid form compared to the

compressed gas form. This gas is the most widely used type of shielding gas for GTAW than

helium. Actually there are several advantages by using argon rather than helium.

a. Good arc starting

b. Produce smooth arc

c. Lower flowing rate than helium

d. Easy on current setting when welding

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2.5 Filler metal – ER70S-G

The A-number and F-number are indicate 1 and 6. F-number is refer to electrodes and

welding rods to reduce the number of welding procedure and performance qualifications. A-

number function is to minimize the number of welding procedure qualifications, steel and

steel alloy filler metals are also grouped according to ASME section 9 tables 3 in appendix.

The F-number groupings are based essentially on their usability characteristics, which

determine the ability of welders to make satisfactory welds with a given process and filler

metal. The A-number is based on chemical composition of the deposited weld metal.

The filler metal used to joint as added metal to joint the metal with base metal

thickness 15.3 mm according to WPS. The filler metal code is design by AWS to show the

specification such as strength, type and chemical composition in the filler metal. ‘ER’ letter

means the electrode or filler rod. ‘70’ show that the filler rod have tensile strength that can

stand to 70000 psi and ‘S’ is solid filler rod without any flux in it. Some filler rod have

tubular shape contain with flux and ‘G’ is chemical composition of the filler rod; 0.05% C,

0.31% Si, 1.07% Mn and 0.05% P, 0.82% Ni (refer to Kobelco consumable table in

appendix). This filler rod was categorized in high tensile steel and low temperature steel. In

addition, the rod is suitable for DCEN polarity and shielded by argon gas.

2.6 Base metal

Carbon steel is use to fabricate the pressure vessel. According to WPS provide, P-

Number is 1 and group number is 1 or 2. Base metals are assigned P-numbers in ASME

Section IX (QW/QB-422 table at appendix) to reduce the number of welding procedure

qualifications required. For ferrous base metals having specified impact test requirements,

group numbers within P-numbers are assigned. These assignments are based on comparable

base metal characteristics such as composition, weldability, and mechanical properties. This

list is an ascending sort based on specification numbers.

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Table 1 P- Number assignment (courtesy of ASME)

2.7 Joint design – single vee and single bevel

Welder can use this WPS for single vee and single bevel joint. If welder want to use

the specification for other joining type such as double vee, company need to produce new

WPS for that joining. The root face at the both joining with gab 3 - 4.5mm produce excellent

penetration and reinforcement and normal practical variations in voltage, current, welding

speed, and edge preparation cause minimum damage to the backing. For this joint, low

amount of filler wire is needed and also low current input can apply at the first pass of the

weld. However single pass weld only can aaply when the thickness of the metal is 4mm and

below.

2.8 Preheating

The minimum temperature for preheating is 26 degrees and maximum is 200 degrees

Celsius. The temperature for preheating is depending on the thickness of the joint. If thick

material 15.3 mm accordance of WPS, maximum temperature of preheat is required.

Preheating is important to reduce cooling rate of the metal after welding. In addition, the

purpose of preheat is to reduce risk of hydrogen cracking and reduce the hardness of the weld

heat effected zone that contribute to cracking. Sometime the base metal contains moisture

that can produce porosity effect on weld after. So preheating will needed to reduce and give

zero moisture to get high quality welding. Preheat method is flame heating on the base metal

using LPG.

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2.9 Electrical characteristic

The polarity in the WPS is direct current electrode negative or straight polarity for

GTAW. This polarity is suitable for steel such as mild steel and stainless steel with using the

thoriated tungsten as the electrode because the heat concentration is 70% on metal and 30%

on electrode. According to ANSI/AWS standard, the electrode must be use in Direct Current

Electrode Negative (DCEN) only. The polarity to use with a particular electrode is

established by the electrode manufacturer.

The current use actually is not constant. For this type of fabrication, the current

adjustment is depend on thickness of the metal to be joint. The welder should know hoe to

control their travel speed during welding to get proper heat input. Refer to WPS, the heat

input is quite slow because the limitation of the GTAW. Even though, GTAW with DCEN

polarity produce good arc and deep penetration. According to AWS, the current range; 90 to

200 A should use 2.4 mm diameter electrode. This parameter is important to follow to avoid

the electrode become melt due to high heat input.

2.10 Welding technique

Welder should do the weaving or string technique during the weld. With the string

bead method, weld beads are deposited in a straight line. With the weaving bead method,

weld beads are deposited in a zigzag formation. The use of string beads reduces the amount

of heat input, because the forward weld travel speed is faster. Therefore, the string bead

technique should be used instead of the weave bead technique. The exception to the string

bead requirement occurs when welding in the vertical position. In this case, a partial-weave

technique may be used to facilitate welding. However, the total weave shall not be greater

than twice the electrode diameter.

The cup size is 8mm in diameter. The cup size is depending on filler rod size and gas

flow rate use for shielding the metal from oxidation. High flow rate of shielding gas need

suitable gas cup size to prevent metal oxidation and weld deposition such porosity and poor

weld shape. This happen cause of the gas pressure concentration is too narrow and hit the

molten filler rod and gas trapped in it. If gas cup size is too big, the oxidation will occur due

to gas separation and lack of pressure to shield the metal from air.

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Metal cleaning is very important before do any welding operation. Surface cleaning

on weld area should be done to avoid any contaminant such as oil or grease, metal particle,

paint or others that not the base metal component. Furthermore, the surface of the groove

needs to be smooth and not too rough. All the contaminant may cause the welding defect and

discontinuity such crack due to gas trapped, poor joining cause the oil and grease.

3.0 PQR DESCRIPTION

This is the justification of the WPS provided in this report. The justification is contain

the detailed of the test involve and has third party inspector endorsement. Before the WPS is

endorse, the welding coupon provided by fabricator need to be tested. The PQR is the testing

report that approves the pre-WPS is acceptable and can legal to use.

3.1 Tensile test

Since a large proportion of design is based on tensile properties, it is important that

the tensile properties of the base metal, the weld metal, the bond between the base metal and

weld metal, and the HAZ conform to the design considerations of the weld. Where butt joints

are used, the weld metal needs to develop the minimum tensile properties of the base metal.

Tensile strength of weld metal or weld joints is obtained by pulling a specimen to failure. The

example of the specimen can referred to tensile test speciment in appendix. According to

ASME section 9 for thicknesses up to and 25 mm, a full thickness specimen shall be used for

each required tensile test. The tension test specimen shall be pulled at two points under

tensile load. The tensile strength shall be calculated by dividing the ultimate total load by the

least cross-sectional area of the specimen as calculated from actual measurements made

before the load is applied.

For tensile test have its acceptance range. In order to pass the tension test, the

specimen shall have a tensile strength over than ASME section 9 has decide.

a. The tensile strength is not less than minimum tensile strength of the base metal. Refer

to table 2 ASME section 9.

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b. The tensile strength is not less than the minimum specified tensile strength of the

weaker of the two, if base metals of different minimum tensile strengths are used.

c. If the specimen breaks in the base metal outside of the weld or weld interface, the test

shall be accepted as meeting the requirements, provided the strength is not more than

5% below the minimum specified tensile strength of the base metal.

For this report, two specimens, SA-333 grade 6 has been tested for this test.

According to the PQR the ultimate total load 10500 kg approximately has been applied for

tensile stress purpose. Refer to result record, the test is acceptable. The specimen was broken

at the base metal and the tensile strength is obtained with 515.11 MPa over than minimum

tensile stress (415 MPa) provide by ASME section 9 . By refer to table 2 ASME section 9 at

appendix this result have proved that the weld is stronger than base metal

3.2 Guided bend test

One of the most common tests used in the development of welding procedures is the

bend test. The bend test is used to check the relative ductility of welded joint or weld test

specimen. The specimen is usually bent in a special guided test jig. The specimens are

subjected to strain at the outer fiber by bending the specimen to a specified radius that is

based on the type of material and specimen thickness. Codes generally specify a maximum

allowable size for cracks in a bend specimen. Cracks and tears resulting from a lack of

ductility or discontinuities in the weld metal are evaluated for acceptance or rejection to the

applicable code requirements.

Guided-bend test specimens shall be prepared by cutting the test plate or pipe to form

specimens of approximately rectangular cross section. The cut surfaces need to design the

sides of the specimen. There are two surfaces shall be called the face and root surfaces, the

face surface having the greater width of weld. The specimen thickness and bend radius are

shown in figure 3 courtesy of ASME section 9 at appendix.

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The transverse side bend test is use for thickness is less than 25mm according to

ASME section 9. The weld is transverse to the longitudinal axis of the specimen, which is

bent so that one of the side surfaces becomes the convex surface of the bent specimen.

Transverse side-bend test specimens shall conform to the dimensions shown in figure 4

courtesy of ASME section 9 at appendix. To accept the test some requirement need to

achieve before proceed to other test.

a. The weld and heat-affected zone of a transverse weld bend

specimen shall be completely within the bent portion of the

specimen after testing.

b. The specimen should have no open discontinuity in the weld or

heat-affected zone exceeding 3mm measured at any direction of the

convex surface.

c. Eye contact discontinuities such as crack occurring on the corners of

the specimen during testing shall not be considered unless there is

record or evidence that proved from lack of fusion, slag inclusions,

or other internal discontinuities.

3.3 Hardness test

This is a very common testing method and essentially characterizes

the strength properties of the material. The test consists in applying a

standard indenter placed on a ground, polished and etched surface of the

specimen for specified period. The specimen undergoes localized plastic

deformation in the immediate vicinity of the indenter. A variety of

indenter geometry and material and corresponding loads have been

standardized.

In the Vickers hardness test, an indenter of a definite shape is pressed into the work

material, the load removed, and the resulting indentation measured. The full load is normally

applied for 10 to 15 seconds. 3 major component need to test according to ASME section 9 ;

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base metal, HAZ and weld metal. The hardness number is calculated by dividing the load by

the surface area of the indentation. The indenter for the Vickers test is made of diamond in

the form of a square-based pyramid as figure 2. The depth of indentation is about one-seventh

of the diagonal length. The Vickers hardness value is preceded by the designation (HV). The

Vickers hardness number is the same as the diamond pyramid hardness number (DPH).

Figure 2 The shape on the specimen surface after 10 second indented

3.4 Charpy V-Notch impact test

According to ASME section 9,charpy impact test is not necessarily unless it is

required by other section or codes. The Charpy impact test is a pendulum type single-blow

impact test where the specimen is supported at both ends as a simple beam and broken by a

falling pendulum as figure 4 in appendix. The energy absorbed, as determined by the

subsequent rise of the pendulum, is a measure of the impact strength or notch toughness of a

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material. The tests results are usually recorded in foot-pounds. The type of notch and the

impact test temperature are generally specified and recorded, in addition to specimen size (if

they are sub-size specimens, smaller than 10 mm × 10 mm).

3.0 CONCLUSION

In the development of WPS, the initial procedure test is required. The engineer might

be consider testing a limited number of specimens to reassure both himself and the client that

the materials are worthy of prequalification. Qualification is a significant factor in the cost of

most fabrications; therefore, one must take advantage of prequalification whenever

permissible. This is why engineers often will specify a desired procedure in terms of more

than one process, each of which is prequalified separately or they will combine the results of

several procedures into a single “hybrid” procedure, which can then be offered (with

supporting data) to considered WPS is readily qualified.

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4.0 REFFERENCES

1. Welding Technology For Engineers edited by Baldev Raj, V Shankar and A K

Bhaduri (2006).

2. ASME Boiler and Pressure Vessel Code (BPVC) Section 9 handbook (2007)

3. American Petroleum Institute (API) Recommended Practice 577 Welding Inspection

and Metallurgy First Edition, (October 2004)

4. The Practical Welding Engineer Handbook by J. Crawford Lochhead and Ken

Rodgers.

5. Welding Inspection Handbook by AWS Third Edition (2000)

6. http://www.ckworldwide.com/technical_specs.pdf

7. http://www.esabna.com/euweb/oxy_handbook

8. http://www.locknstitch.com/PreheatWeld.htm

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