How to write a 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-253.

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.

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A short video lecture on WPS and PQR, Please watch;

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Please click here to download 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)

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A short lecture on how to wright a Welding Procedure pecification (WPS), Please watch;

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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.