Friday, August 7, 2015

Essential and non-Essential Variables... they can make ya nuts

Dear sirs, I have a doubt about WPS (Weld Procedure Specification) by API 1104 - 2013. For me is not clear if “is outside diameter an essential variable in wps api 1104”, because of in say “The ranges of specified outside diameters (ODs) and specified wall thicknesses over which the procedure is applicable shall be identified. Groupings are shown in 6.2.2 d) and 6.2.2 e).”, and in 5.4 is not included as an Essential Variables.
Thanks regards

Essential and non-Essential Variables... they can make ya nuts.
We're often familiar with Essential Variable (those variables that, once changed beyond specific limits, require re-qualification of a WPS.), but what is a non-Essential Variable?
These variables may not show up in a table or list telling us what are allowable variations but they are equally important when writing your WPS.  I often find them left off of WPS's and that only leads to confusion when customers, inspectors or Welders try and interpret or apply your WPS.
When a non-Essential Variable is changed no additional testing is required, but the WPS needs to be changed to reflect the new variable.
Some examples would be:
     *Base materials - Although base material Groups can be Essential, the individual material types are considered non-Essential.  You completed a WPS of a specific material and it qualified you to within a Group.  If you want to change (or develop new) your WPS to reflect a different material within the Group
it is simply a matter of paperwork.
     *Joint Type - Once I qualify a specific joint type that test qualifies a large number of joint types.  I only need to change my paperwork to reflect a different joint design.  (You can now see where a single PQR can qualify a large number of WPS's.)
     *Electrode extension - As a Welder I can vary current by as much as 50 amps by simply changing my stick-out.
     *Electrode type - (GTAW)
     *Technique - Can I weave? Can I whip? Am I allowed to oscillate?  All should be addressed.
It surprised me, that Diameter is not be an Essential Variable per Section 5.4 of API-1104.  But listing it on the WPS is required.
“5.3 Welding Procedure Specification
5.3.1 General
The welding procedure specification shall include the information specified in 5.3.2 where applicable.”
So thickness IS an Essential Variable but Diameter is considered a non-Essential Variable.  Both must be listed on the WPS.
Good Question, Good Luck,

1 comment:

WeldingTodayDotCom  said...

Thanks for sharing those non-essential variables of welding. Important for welder to know thos aspects too.