Essential vs. Nonessential Variables
Inspection Trends / July 201020FeatureBy Albert J. Moore article is the second in a seriesaimed at helping you understand theconcept of Welding ProcedureSpecifications (WPSs), how to write them,and how to use them. This article definesthe differences between Essential andnonessential Variables . Article three willcover qualifying a WPS by testing, andarticle four will help you write a WPS that,in the author s words, will do more thancollect dust. If you look at the label on any fooditem candy bar, cookies, box of browniemix you will see a list of label does not provide the quantity ofeach ingredient, but it does list theingredients in order of the greatest to leastamount used. It would be impossible, basedsolely on the information provided on thelabel, to duplicate the exact recipe themanufacturer welding documents somecontractors provide are a lot like the labelon a box of brownie mix. They list only thebasic information needed to meet theapplicable code, but fail to list importantinformation the welder needs to replicatethe test information should be includedin the welding documentation?
ASME groups the various base metals by P- or S- numbers. AWS B2.1, Specification for Welding Procedure and Performance Essential vs. Nonessential Variables CWIs must review the applicable welding standard to determine which welding parameters are defined as essential, nonessential, and supplementary essential variables
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