Section IX QW-256: Gas Purity

Date 06-16-2015 18:12

If I have a WPS/PQR for GTAW (Orbital or Manual) autogenous fusion-only welding that specifies "high purity argon min. 99.996%" for both the torch and backing gas, do I have to generate a new WPS/PQR if I want to use a higher grade argon (ultra high purity 99.999%)

The way I read Table QW-256, paragraph QW-408.2, a change in the gas percentage is an essential variable. Thoughts?

By js55

Date 06-16-2015 20:18

That isn't what is meant by gas percentage. You do not have to re-qualify per Section IX.

By Superflux (****)

Date 06-17-2015 01:09

Since it does not say percentage of mixture, it kinda could be interpreted either way.
I'd never raise the issue, but think what fun it would be just to razz someone...

By fschweighardt (***)

Date 06-17-2015 02:47

If it says 99.996% MIN you should be fine

By Jovi Zhu (**)

Date 06-19-2015 07:04

Agree with js55.

That is purity other than percentage.

By aevald

Date 06-19-2015 16:45

Hello FloridaSnook, argon purity speaks to having trace elements of other components in the gas besides just Argon and as such you are given a percentage of purity.

Fschweighart, highlighted "MIN" in his comment to say that when you are using a gas of a higher than minimum purity you will be within allowable limits and good to go.

If you had a mixed gas and you were looking at percentage and purity it would be slightly different due to having a list of gases and listing a percentage of each one. The actually purity of the gas combination would be relative to the additional elements contained within the mix other than the listed gases. The percentages of the gas mix would be relative to the accuracy of the percentage of the gases contained within the combination. I hope that I haven't confused this for you. Best of luck and regards, Allan

By Jovi Zhu (**)

Date 06-21-2015 07:00

Section IX QW-408.2 recommends the use of AWS classification of SFA-5.32 to specify the shielding gas composition.
So...in the case of this post, if the WPS specify SG-A of SFA-5.32 , then gas purity change from 99.997% to 99.999% is not considered a esstential variable and do not require requalification of the WPS.

However, since QW-408.2 says "may", the use of SFA-5.32 classifications is not mandaory. The way the WPS specifies is OK. I assume that the qualification test was done with a specified 99.996% purity Ar~

Note that the backing gas is another esstential variable as dictated by QW-408.9 for groove welds of certain materials~ By specifying "high purity argon min. 99.996% for both the torch and backing gas", the WPS has specifed two variables of Section IX. Whether QW-408.9 is esstential or not depends on the welds and materials.