Is ADDITION of PWHT for GTAW an essential variable? 3

[timsch]

QW-407.1 states that a separate qualification is required for .... no PWHT. I take this to mean that if an existing WPS has PWHT, a new PQR will be needed to weld to this WPS without PWHT.

On the other hand, what if a user wants to ADD PWHT to some welds that don't require it per an existing WPS? It seems that this could be covered by the statement (2) PWHT within a specified temperature range, but if so, it's not clear.

 

[david339933]

You need to requalify for PWHT.
QW-407.1(a) lists when re-qualification is required for P1-P6, P9-P15F. QW-407.1(b) states when re-qualification is required for material not of the P numbers listed in (a).
If you have a WPS without PWHT, you must re-qualify for PWHT.

 

[timsch]

Thanks for the response, but I'm still not clear why it is specifically stated under both (a) & (b) "no PWHT", rather than something similar to QW-408.5 where it specifically states "addition or deletion" regarding backing gas. The way QW-407.1 is worded, it seems like a one-way street, prohibiting the REMOVAL of PWHT but not the ADDITION.

 

[david339933]

Because (a) and (b) are talking about different materials. Under (a) for example is P1 - Carbon Steel. "A separate procedure qualification is required for each of the following". 1) No PWHT - So you need a WPS qualified for no PWHT. 2) PWHT below the transformation Temp. - so you need a separate qualification for PWHT below the transf. temp. 3) If you need to PWHT above the transformation temp. you need to re-qualify as well.
(b) is for "all other materials" not listed in (a).

QW-407.1(a) is telling you that you need to re-qualify for each item listed (1)(2)(3)(4)(5).

You're right, it doesn't state "addition or deletion" but if you look at the Legend for the essential variables for the process used, it shows the symbol next to QW-407.1 means "change".

 

[Dhurjati Sen]

Dear timsch,

Care to put a few stars for david339933 ?

Regards.

DHURJATI SEN

 

[timsch]

David,

I'm still not fully convinced. The fact that the symbol stands for change doesn't seem to indicate that ANY change requires additional qualification. I base that on the fact that a decent amount of detail is given in QW-4XX.X regarding which changes require additional qualification. If any change was not allowed, additional details wouldn't be needed.

Regarding QW-407.1, for all materials, the change from PWHT to NO PWHT requires additional qualification. This is easy enough to understand; PWHT is for stress relief, and the benefits of this are obvious. If a weld has passed required tests after PWHT, it is not certain that these same tests will be passed if PWHT is not performed.

Alternately, if a weld passes these same tests without PWHT, why would it not pass them after going through PWHT, assuming that the PWHT was done within the limits specified for that material? While I could see that there might be reasons to not allow this, that decision seems to be left to the engineer to determine using sound judgement in this situation based on the wording here.

 

[A clark]

Timsh,

Have you asked your Inspector or the AIS? I'm sure that they can answer your question. Or, have you asked them and didn't like the answer? David has answered your question thoroughly. Accept it and move on.

Allan

 

[weldstan]

PWHT for some materials may not be for stress relief but for other reasons like corrosion resistance or further processing.

 

[pradipgoswami]

Hi Timsch,
This clause has more complications than thought of as there are multiple PWHT scenarios involved in any procedure qualification. This is so as any change of PWHT condition is a mandatory and essential variable under QW-253 and beyond.

A NEW PQR is required for each of the following conditions.
QW-407.1 A separate procedure qualification is required for each of the following:

(a) For P‐Numbers 1 through 6 and 9 through 15F materials, the following postweld heat treatment conditions apply:
(1) no PWHT
(2) PWHT below the lower transformation temperature
(3) PWHT above the upper transformation temperature (e.g., normalizing)
(4) PWHT above the upper transformation temperature followed by heat treatment below the lower transformation temperature (e.g., normalizing or quenching followed by tempering)
(5) PWHT between the upper and lower transformation temperatures

Some explanations are as below:
1. NO PWHT is self explanatory.
2.PWHT below the lower transformation temperature. --Typically refers to Stress Relieve or Annealing.
3.PWHT above the upper transformation temperature (e.g., normalizing)- causes refinement of grain structure changing/improving all mechanical properties.
4) PWHT above the upper transformation temperature followed by heat treatment below the lower transformation temperature (e.g., normalizing or quenching followed by tempering)-Further to the benefits of normalizing this HT improves notch toughness, ductility
(5) PWHT between the upper and lower transformation temperatures(AC3 & AC1)-any temperatures between these ranges will impart different mechanical property conditions both for BM and WM than what's likely to be experienced upon exposure at AC1 & AC3 temperature.

Note there's no shortcut, a new PQR is required under each of the above the conditions..

Thanks.





Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[DekDee]

Timsch,
David and Pradip have given you comprehensive answers - I suggest you take Allan Clarkes advice and "move on".

You seem very intent on this Addition / Deletion of PWHT.
In short it cannot possibly work for this scenario.
If you change from QW407.1 (a)(2) to QW407.1 (a) (3) you have not added (or deleted) PWHT but you still require a new PQR.
Similarly, if you change from QW407.1 (a)(5) to QW407.1 (a) (3) you have not deleted (or added) PWHT but you still require a new PQR.
Regards,
Shane

 

[timsch]

Thank you all for your explanations. I am not pursuing a particular answer with an agenda, just trying to come to an understanding. We have a customer who is asking if they can have PWHT performed in an application where one of our weld procedures that does not have PWHT is to be used. I'm trying to give them an answer, but was confused, obviously. Many times I have struggled with the wording and intent of the code, and this time is no different; I still find the phrasing in this part odd. However, I will take the consensus advice here and accept that, knowing full well that the expertise many of you bring to the table surpasses my own.

Regards,

 

[viper3982]

What if you had two WPS' that are identical save PWHT?

EG: WPS#1;PQR#1: all variables match WPS#2;PQR#2 except for WPS#1 has PWHT.

In that case you would have 2 PQR's that pass with the same criteria but under different PWHT conditions.

EG: if the unit was already welded with WPS#1 PQR#1 non-PWHT'ed...you have PQR#2 which HAS been PWHT'ed.
If all the parameters/variables are the same, you could justify the soundness of the weld as meeting testing requirements EITHER way.

Yes, you would have to re-qualify. Yes, it would still need to meet the requirements as david and pradi were saying.