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Glossary

Essential variable

A welding variable whose change requires the welding procedure to be requalified, because it materially affects the mechanical properties of the joint.

Codes separate variables into essential, nonessential and — where notch toughness matters — supplementary essential. Changing a nonessential variable needs a revision to the WPS. Changing an essential one needs a new qualification.

The same physical change can fall into different classes under different codes, which is why “we requalified for that last year” is an answer that has to be checked rather than trusted.