Welding Procedure Specification (WPS)

A welding procedure specification (WPS) is a written document providing direction to the welder (or welding operator). It contains all the necessary parameters viz. joints, base metals, filler metals, positions, preheat, PWHT, gas etc. (including ranges, if any) under which the welding process must be performed. These parameters are known as variables (as per ASME Section IX). Three types of variables are mentioned in the code, these are;

  1. Essential Variable
  2. Non essential Variable
  3. Supplementary Essential variable

Essential Variables (For WPS – QG-105.1 & QW-251.2): A change in essential variable is considered to affect the mechanical properties (other than toughness) of the welded joint. Hence the WPS must be requalified, if the essential variable is changed.

Supplementary Essential Variables (QG-105.3 & QW-401.1): A change in the supplementary essential variable will affect the toughness properties of the joint, heat-affected zone, or base material. Hence supplementary essential variables become additional essential variables in situations where procedure qualification requires toughness testing. When procedure qualification does not require the addition of toughness testing, supplementary essential variables are not applicable.

Nonessential Variables (QG-105.4 & QW-251.3): Nonessential variables are those in which a change can be made without requalification of the existing WPS, since it is not considered to affect the mechanical properties of the joint. Though a change in the nonessential variable doesn’t require requalification of the WPS but still it should be properly addressed in the welding procedure specification (WPS).

Some basic facts about WPS:

A welding procedure specification shall contain, as a minimum, the specific essential and nonessential variables that are applicable to the welding process. When the referencing Code, standard, or specification requires toughness qualification of the welded joint, then applicable supplementary essential variables shall also be provided in the WPS.

These variables are listed in tables from QW-252 to QW-257. Please note that for each welding process, there is a separate table containing the list of all variables. For example list of variables (essential, nonessential and supplementary essential) for Shielded Metal Arc Welding (SMAW) is given in table QW-453.

Please see the below table (Table-1) for a complete list of welding processes and their corresponding tables for variables (as per ASME Section IX).

Table-1

Steps to be followed for preparation of WPS:

First of all we need to identify the welding process which is to be used for example weather it’s a SMAW or GMAW or GTAW or any other welding process or it’s a combination of two or more welding processes. Once the welding process is decided then we need to see the corresponding table (QW-252 to QW-257) for the complete list of variables. With the help of the table we can list out all the necessary variables to be used in our WPS.

Once the minimum variables (essential, nonessential and supplementary variable, if any) are decided a preliminary WPS (or proposed WPS also known as pWPS) is prepared.

Based on the proposed WPS, Test coupon (or coupons) is prepared, and the coupon is welded as per the values (or range) provided in the pWPS. All the real time data (observed during the welding of test coupon) are recorded.

After successful welding, test coupon (or coupons) is subjected to destructive test, and if the test coupon (or coupons) meets the minimum code requirement then the same pWPS is finalized and approved for further job. In case of any change same procedure is repeated till the test coupon doesn’t meet the minimum code requirement.

All the real time data during welding of test coupon and destructive test report data is compiled into one document known as Procedure qualification record (PQR).

After successful preparation of PQR, final WPS is prepared and produced to the authorized welding inspector for final approval.

Please click on this link to see a sample WPS Format.

Important Articles in ASME Section IX

Article I           Welding General Requirements

QW-150            Tension Tests

QW-153            Acceptance Criteria-Tension Tests

QW-160            Guided-Bend Tests

QW-163            Acceptance Criteria-Guided Bend Tests

QW-171            Toughness Tests

QW-172            Toughness Tests-Drop Weight

QW-180            Fillet-Weld Tests

QW-182            Fracture Tests

QW-183            Macro Examination-Procedure Specimens

Article II          Welding Procedure Qualifications

QW-200            General

QW-210            Preparation of Test Coupon

QW-250            Welding Variables (Refer Table-1)

Article IV          Welding Data

QW-400             Variables

QW-401.1           Supplementary Essential Variable (Procedure)

QW-402              Joints

QW-403              Base Metal

QW-404              Filler Metal

QW-405              Position

QW-406              Preheat

QW-407              Post Weld Heat Treatment

QW-408              Gas

QW-409               Electrical Characteristics

QW-410               Technique

QW-420                Base Metal Groupings

Table QW/QB-422   Grouping of Base Metals for Qualification

QW-430                F‐Numbers

Table QW-432        Grouping of Electrodes and Welding Rods for Qualification

QW-440                Weld Metal Chemical Composition

Table QW-442         A-Numbers Classification of Ferrous Weld Metal Analysis for Procedure Qualification

QW-450                 Specimens

Table QW-451.1        Groove-Weld Tension Tests and Transverse-Bend Tests

Table QW-451.2        Groove-Weld Tension Tests and Longitudinal-Bend Tests

Table QW-451.3        Fillet-Weld Tests

Table QW-451.4        Fillet Welds Qualified by Groove-Weld Tests

QW-461                  Positions

QW-461.3                Groove Welds in Plate-Test Positions

QW-461.4                Groove Welds in Pipe-Test Positions

QW-461.5                Fillet Welds in Plate-Test Positions

QW-461.6                Fillet Welds in Pipe-Test Positions

QW-462                  Test Specimen Table QW-462.1(a) to QW-462.5(e) Fig QW-463.1(a) to QW-469.2

QW-470                  Etching — Processes and Reagents

Article V                Standard Welding Procedure Specifications (SWPSs)

I hope this article will help all welding professionals and freshers. Please give your valuable feedback. I would like to thank Mr. Goutham Rathinam (AWeldI & CSWIP 3.1-TWI,UK) for helping me in writing this article. Thank you.

47 comments

  1. Hi sir please can you give me some reference for as per EN standard impact valve for subsize 2.5mm thickness and material 304 temperature at -196 degrees C.

    How many joules required ?

  2. I complete the graduation in mechanical engineering from india. I was worked in dimensional inspection in my foundry(i.e. which produces castings of valve bodies). And also I will be more interest to study welding inspection and other ndt courses.I will be seeking the job for my best future.So you can help to me. Please reply to my mail.Thank you sir.

    1. It is indeed a useful information. Your contribution to knowledge dissemination in the field of welding and allied operations, is a feat that deserves commendation. The only area I beg to disagree with you is the Personnel approval. By this, I mean who is responsible for the approval of a WPS. Your writeup confer the authority on an authorised welding Inspector, which I technically disagree with. Professionally speaking, a WPS begins with a Preliminary Welding Procedure, that is expected to be written by a Welding Engineer, who thereafter hands over same to an Inspector for qualification/testing. After the qualification, the documents is returned back to the welding Engineer for final approval. The welding Engineer has the right to either approve or order a requalification. When similar issue was raised during my senior welding Inspector certification programme in TWI UK, where duties and responsibilities of a senior welding Inspector was being taught, we all criticised it but jokingly concluded at the end, that the job of a welding Inspector as it concerns Welding Procedure Qualification, is not far from that of an errand boy.

  3. Thank you for providing this article. It’ll be very useful for welders and pipe engineers.

  4. Nice Information Sir …………………………..can you provide the article regrding Fabrication of Distillation Column

    1. Tanks for this valuable post.now each and everything is cleared for me how to write Wps and which section is followed for that corresponding concern

  5. Nice article. Very informative for those not familiar with the ASME B&PV Code, Section IX.

    I agree with the comments about seeking out a Welding Engineer, the reason being that the process tables for variables are NOT a “How-To-Guide”. As seen in the forward of Section IX, God’s engineering judgement is required. For example, the WPS can increase the range of variables, to within limits for essential variables, and no limits for non-essential variables.

    The creative license and abuse to the Science of Welding and Metallurgical effects to the cast weld metal and base metal Heat Affected Zones, can only be controlled by an engineer who has studied and experienced these issues.

    Of the well over 400 thousand WPSs that I have had to review/comment/approve for the corporation or government entity that I was working for at the time, I typically find a WPSs that try to open up all variables to a level that their welders will not fail an audit. This can set a dangerous precedent for the safety and quality of the welded assembly.

    Remember that the Code is the “minimum requirements” to be meet. The Welding Engineer needs to fully understand the Fit-Firm-&-Function of the assembly to insure that all proper testing has been completed.

    Typically, Engineers not schooled in welding metallurgy become “Welding Lawyers” with respect to the Code. They can quote chapter and verse, but do not posses the level of understanding to ensure their company will not inherit a large level of Risk during the life of the product.

    Seek expert guidance when identify all of the NDT and DT that should be done to the qualification coupon(s). Prepare the WPS and reduce the risk to stray too far from ALL of the variables used. Prepare the Welder Performance Test Procedure, and again use the Code as a minimum. Train the welders on anything that is different with this welding procedure versus other applications of the same welding process(es) and material grouping. Typically, the more the Welder knows, the lower the Rusk to the company.

    Hope this helps us some small way for you and your readers to consider when working with Code requirements.

  6. Dear sir,
    I watched ur vedio about wps. So plz make new vedio about how can write wps seperate Smaw , GTAW,etc

  7. thanks for this information …Kindly please inform us about how prepare the WPS according to API 1104
    & show the diff rents from IX
    Best Regards

  8. Sir there is single typing error in “some basic fact about Wps section. As the paragraph is written above –

    “””These variables are listed in tables from QW-252 to QW-257. Please note that for each welding process, there is a separate table containing the list of all variables. For example list of variables (essential, nonessential and supplementary essential) for Shielded Metal Arc Welding (SMAW) is given in table QW-453.”””

    In last line of this paragraph it should QW-253 instead of QW-453.

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