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 5.3.2.4 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
Rafael

Rafael,
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,
PWC

"Scare a moose, scare a moose, will you do my fan Van Gogh"

Paul

I find myself rejecting a lot of welds. I don't want to fail them and find out that I misinterpreted something. When there is undercut in small amounts throughout the length of the weld I'm still not clear on what they mean by "...in two inches up to 12 inches..." (AWS-D1.1, Table 6.1(7))  so I find myself pretty much disregarding the 1/32nd undercut rule, unless the weld is less than 2 inches long. And I just use 1/16.
David N.

All right, here we go...
Table 6.1 (7), Undercut:
"shall not exceed 1/32 in. except...Shall not exceed 1/16 in. for more than 2 in. in 12 in." (artistic liberties taken liberally)
So, undercut that is not more than 1/32" is acceptable. Period!  Also, undercut greater than 1/32" that does not exceed 1/16" and it's accumulated length comes to 2" or less is also acceptable.
Example 1: You're looking at a 3" weld. It's got 1/16" of undercut (depth) for 2" of its length. It's acceptable.
Example 2: A 3" weld is part of a 3 on 6 intermittent fillet weld. Imagine 3 of those fall with in 12". One 3" weld has undercut and the undercut is 1/16" (depth) for 3/4" (length). Another 3" weld is undercut  at 2 places. The undercut is 1/16" deep for 3/4" and again for 1/2"‎ of length.  The last 3" weld has 1/32" for its entire length. These 3 welds falling with in the same 12" of a joint length would be acceptable (Total length of undercut greater than 1/32" deep equals 2").
Now my head hurts.
PWC

Ahh... finally it makes sense.  Now I'll have to read it until it's burned into my brain.  I never put it together that they were talking about intermittent welds.  I wonder if everyone else assumed I understood that, or if they don't know either.
Thank you!  You have saved me much self-doubt!
David N.

No, no, no... I simply used intermittent welds as an example. If you had a weld that was 8" long, the same rules would apply.If it had undercut its entire length that did not exceed 1/32"‎ it's acceptable.  Along that same weld, at one location the undercut is 1/16" deep for 1/4", then 1/16" deep for 1/2", then again for 1", then again for 1/4", that weld would still be acceptable. (as long as the individual undercuts greater than 1/32" but not over 1/16" do not total more then 2" of length in any 12")
Again, my head hurts.
PWC

Holy crap! I understand even better now! So the length they are talking about is how far along the weld the undercut runs.  That is the biggest part I wasn't grasping before. That's so simple... And now quite embarrassing. No wonder nobody could explain it to me, it should have been obvious. Every time I read about the two inches, I was thinking it had something to do with the length weld, not the length of the undercut portion.

I guess I am finding the downfall in studying by myself! I couldn't get past my initial understanding. Kind of like when you learn the words to a song incorrectly, and even after you find out the correct words, you still sing them wrong out of habit... Okay, fine. Maybe it's nothing like that!
David N.

That is Exactly what it's like.
"Scare a moose, scare a moose, will you do my fan Van Gogh"
PWC