This article provides information about welding procedure specification(WPS) based on the requirement of ASME Code Section IX. The code defines it as "A WPS is a written qualified welding procedure prepared to provide direction for making production welds to Code requirements".
The WPS may be used to provide direction to the welder or welding operator to meet the code requirement. The WPS should include all essential, nonessential and supplementary essential variables i.e. joint design, base material, filler metal, position, preheat and post weld heat treatment, gas composition, electrical characteristic, etc.. These variables have been provided in the article II QW-250 thru QW-280 of ASME Code Section IX.
A welding engineer or any knowledgeable and competent person in the welding metallurgy with appropriate experience can write a WPS.
How to write a WPS?
There is the standard form for the WPS in ASME Code Section IX (Form QW-482). This form can be copied and used. The welding engineer may use different sources such as welding handbook etc. Each field in this form must be completed. This WPS is written with the knowledgeable persons but still we need to proof the written WPS produce a weld with desired mechanical property.
The written welding procedure specification must be qualified by mechanical testing that is called procedure qualification record (PQR).
The WPS specifies ranges, and when you need to use related WPS out of the specified ranges, you need to revise your WPS and re-qualify it.
There are many grouping systems in ASME Code Section IX in purpose to reduce the number of WPS's and PQR's. These groupings are P numbers, A numbers, F numbers. These numberings are grouping similar material or filler metal with specific characteristics and cause to reduce the number of WPS's. This grouping reduces the costs.
The ranges indicated in the article IV ASME Code Section IX. The article IV should not be read directly; you should refer to specified paragraph when referred in the QW-250 thru 280 for the ranges. The article IV in ASME Code Section IX formed from hundreds of paragraphs which are not related to each other and each paragraph numbered and must be read when referred from other places in the code.
For example, in SMAW (QW-253), for thickness range, it refers you to the Article IV paragraph 403.8, you can find thickness range in this paragraph. It will refer you to another table that you can obtain thickness range based on your test coupon thickness.