Weld Qualification for P No Groups 4

[metalseng]

I have some questions regarding the P No grouping used in ASME B & PV Code (IX). I am going to use specific examples to explain my question. Please note that my questions are not about qualifying welding procedure for certain alloys but I am using them as examples.

First a simple hypothetical situation:
(P No 4 and Group 1 materials)
I want to a WPS for welding A387 Type 12 Class 1 plate to the same. The minimum tempering temperature for this is 1150F and the minimum tensile strength is 55 ksi.
Now I want to a WPS for welding A182 Type 11 Class 3 to the same. The minimum tempering temperature is 1150F (as above) but the minimum tensile strength is 75 ksi (as opposed to 55 ksi for A387 Type 12 class 1). The question is can I use a WPS qualified for A182 Type 11 Class 3 to weld A387 Type 12 Class 1.
The general question -Do I have to qualify the alloy (within a certain P no and Group) with maximum strength in order to use the qualified WPS for any alloy within the same Group?

Now let’s make this bit more complicated.
I want to weld A202 Class B to the same. The minimum tensile strength specified is 85 ksi and this is an as-rolled plate. However, ASME B & PV code IX lists this under Pno 4 and Group No 1 (same as the above-mentioned two alloys). Does that mean I can use the WPS qualified above (which may have a PWHT) to weld this (as- rolled)?
Though ASTM A202 has been superseded and I used it as an example,my general question is how to deal when alloys within a certain P no and Group no combination have different tempering temperatures.

Summing everything, do we have to have several PQRs (different strength levels and PWHT) for alloys even though they fall under same P No and group no? I tried to find how the code addresses this, but I could not find anything. I would appreciate if anyone could clarify this and specify the section of the code that deals with this.

Thank You.

 

[weldtek]

P numbers, and where supplementary essential variables apply, group numbers, are only one piece of the puzzle. The short answer to your question is, if all other essential variables remain the same then yes you can use the same PQR to qualify the WPS. That's a big IF. If you haven't already done so review QW 25x

 

[DVWE]

A few things to note:

1. Code has raised the minimum tempering on these materials to 1200 F. Don't know if that's important to you or not...I realize you have only given an example here.

2. The bigger issue is when filler metal is under matched with base metal. I've read this somewhere I just need to re-find. If higher ksi values are needed, the only real option you have is to change base material, right? Therefore, it's not an issue as long as the material is the same P-No. and when required Group number. However, you should read QW-420.1 which basically states that all things need to be considered by the manufacturer.

3. Section IX addresses PWHT in QW-407. Refer to QW-252 thru 265 for individual process requirements. I personally believe that time and temperature should always be considered, whereas the code is a bit open in that area (when impact testing is not required). For example, below the lower transformation temperature, is pretty wide open. If you know the PWHT requirements of the production joint, you should try to match that as close as possible with the WPS qualification, time and temperature.

 

[DVWE]

I was thinking of QW-153 - Acceptance Criteria for Tension Tests. Take a look at that.

 

[metalseng]

Thank you for the replies.
I think those answers clarify the issue of PWHT.


Still I do not understand how to go about materials in the same P no and group combination but with different minimum tensile strength values although the PWHT/(tempering in base metal) are same. I am asking the same question again:
"Do I have to qualify the alloy (within a certain P no and Group) with maximum strength in order to use the qualified WPS for any alloy within the same Group?"

Thanks Again.

 

[DVWE]

So in other words, you have a WPS which was qualified with 55ksi to 55ksi base metals, and now you want to use that WPS on 75ksi to 75ksi production weld joints. Correct?

 

[metalseng]

I am asking whether qualifying a WPS for 75 ksi material will be enough to cover welding a 55 ksi material?

Thanks

 

[DVWE]

Absolutely. Especially if the PWHT is similar, and the same filler metal can be used. Think about it. You've just proven that the filler metal is good to at least 75ksi. You can also order your material with simulated PWHT to ensure that minimum tensile can still be met after PWHT. Review QW-153. If your WPS was qualified with the combination (75ksi to 55ksi), then it only needs to meet the minimum tensile of the weaker material.

 

[metalseng]

Thank you for the clarification. I agree.

By my concern is about the point when you say: "The filler wire(weld) for high strength (ex-75ksi) PQR is too hard (strong) for low strength alloy (ex-55ksi)".

Suppose I am creating my own P no Group for similar alloys but not covered by the Code. How do I set the lower and upper strength limits, provided other factors (weldability, chemistry, PWHT) are fine? Is there a guideline for range of strength for the gouping? Perhaps allowable ratio between (the range of strength)/ (min strength)?

Thank you for you patience.

 

[DVWE]

One thing to keep in mind is that there are other filler metals available if matching tensile strength is of concern. In this example, E8018-B2 and also E7018-B2L could be used. Like I said earlier, it's a bigger problem when the filler metal is under matched. For example, E8018-B6 and SA-217 Gr C5 (90ksi). Now take the SA-387 Gr 12 for example, where there is an established tensile range (65-85ksi) then you definitely don't want to exceed the tensile with the filler metal (if such was available).

As far as establishing these ranges, perhaps someone else could shed some light on. I'm not too sure about that. I know that ASME recognized materials are listed in section II part D, and their associated stress values established by ASME.

 

[GRoberts]

ASME Section IX QW-420.1

"These assignments"(i.e. P numbers)"are based essentially on comparable base metal characteristics, such as composition, weldability, brazability, and mechanical properties where this can logically be done. These assignments do not imply that base metals may be indiscriminately substituted for a base metal that was used in the qualification test without consideration of compatibility from the standpoint of metallurgical properties, postweld heat treatment, design, mechanical properties, and service requirements."

Basically, they are saying that given the rules in Section IX, you can still do some things that shouldn't be done, and it is up to you not to do them.

 

[metalseng]

Thanks for reply and insight.

Cheers.

 

[robsalv]

I understand that a change in filler metal is considered a change in essential variable. Does using a different strength filler metal constitute a change in essential variable then?



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[weldtek]

robsalv,
Review QW25x for the applicable process.

 

[robsalv]

Thanks Weldtek.

I'm not an ASME IX user and have only had a cursory exposure to it over the years... but I dragged out a copy and had a quick look where you directed... it would appear that the filler metal strength isn't an essential variable since it doesn't drive an F number change.



- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[weldtek]

robsalv,
In most cases that's true, but, you must also consider the A #. Ref QW 442 also. Also, bear in mind that the above statement does not hold true for HF or CR overlays. See QW 25x.1 for those.

 

[SBlowers]

Experts,

The WPS what we have is for P No 1 Group No 1 or 2 to P No 1 Group No 1 metals. We require to weld P-1 Group 2 materials specifically SA516-70 to SA106 Grd C. Is the original WPS qualify for this job?

Thanks....Blowers

 

[metengr]

SBlowers;
Please start a new post. The answer to your question is yes, provided the WPS is not qualified for notch toughness (impact testing).

 

[SBlowers]

Thanks metengr....

 

[katty11]

genteleman i have a question, i am building numerouse reators I will use one aas an example, we are using SA387 GR.11 CL2 (P4) with a SS304 clad overlay (1/8th). I have concerns about sensitizing ss304 at PWHT temperature. should i be concerned or Austenitic stainless steels which tend to sensitized during welding and not PWHT?

I have heard that Sensitization can be reversed and material restored to full corrosion resistance by a full solution treatment after fabrication. Also, since sensitization problem is time/temperature dependent, thin materials, which are welded quickly, are not usually a problem.