Variables used in WPS
Depending on their influence on obtaining a desired weldment, the welding variables are then classified and listed. Some of them are listed as "Essential variables", some of them as "Supplementary Essential variables" and the others as "Non Essential Variables".
Essential variables
Essential variables when changed beyond the allowable limits while welding, alter the prescribed weld properties. Hence, production welds with such altered variables should not be continued without requalification and certification.
Supplementary essential variables
Still more number of variables from the above list are declared as essential in case where a procedure qualification is applied for eg. a weldment going for notch toughness applications. These are called supplementary essential variables.
Non essential variables
Those welding variables which when changed during welding (within logical limits) do not cause to alter the desired weld properties. They are just altered in the WPS. Hence production welds with such altered parameters could be continued without any requalification of the welding procedure.