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;
- Essential Variable
- Non essential Variable
- 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).
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.
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-210 Preparation of Test Coupon
QW-250 Welding Variables (Refer Table-1)
Article IV Welding Data
QW-401.1 Supplementary Essential Variable (Procedure)
QW-403 Base Metal
QW-404 Filler Metal
QW-407 Post Weld Heat Treatment
QW-409 Electrical Characteristics
QW-420 Base Metal Groupings
Table QW/QB-422 Grouping of Base Metals for Qualification
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
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-461.3 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.