Types of Variables for Welding Procedure Specifications
ASME IX has tabulated each welding variables for different welding processes and subdivided them into essential, supplementary essential and nonessential variables.
If you want to watch a video discussion of these variables, you can click this video as well!
Essential Variables
According to QW-251.2 of ASME IX, the essential variables are considered to have an effect to the mechanical properties of the weldment and therefore shall require requalification of the WPS.
Examples of these variables are:
Supplementary Essential Variables
According to QW-251.2 of ASME IX, the supplementary essential variables are required for metals which the referencing code or standard (for example ASME B31.3, ASME B31.1 etc.) requires toughness tests in addition to the essential variables for each welding process.
These are the variables that will be essential if impact tests are required. Impact tests are required depending on the base metals, for low temperature applications and for metals that have the possibility to reach their ductile-brittle phase.
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Example of these variables are:
The last two variables are essential when toughness tests are required since a lack of heat input may render the material brittle and thus fail the said tests.
Nonessential Variables
According to QW-251.3, nonessential variables are described as the variables if changed, maybe made in the WPS without requalification.
The following variables are considered nonessential:
If you love more free stuff and want to know more, you can also check out my videos here regarding the fundamentals of WPS and PQR. This is where I discuss these variables as well.