Welding Q&T'ed Ni-Cr-Mo Alloys 1

[tc7]

I was told to plan out a new PQR to SMAW and GTAW SA-543 to SA-543 and also SA-543 to SA-541 Grade 5 forgings. The specs are for mat'ls already in the Q&T condition. What is the typical post weld on these? Is it typical to return to the Q&T condition? or simply stress relieve?

SA-543 principles are:
C=.2
Ni=2.75/3.90
Cr=1.5/2.0
Mo=.4/.6
Mg=.4/.7

SA-541 Grade 1 principles are:
C=.35
Ni=.4
Cr=.25
Mo=.1
Mg=.4/.9

What is suggested welding rod(s) and fillers for each combination??

Since the SA-541 has a much higher carbon (.35 max) than the SA-543 (.20 max) what issues should I be aware of or concerned about?

Thanks any advice or referrals are appreciated

 

[metengr]

tc7;
Please re-review your material above. What is the specific Type and Class of material for SA 543, is it Class B or C and Type 1, 2 or 3? The post weld heat treatment can be performed provided you remain BELOW the original tempering temperature that was specified by the material specification. I reviewed ASME SA-543, and the minimum tempering temperature is 1100 deg F, so you want to PWHT at 1050 deg F (max).

For the filler metal to join SA 543 to itself, I would suggest

SMAW process; SFA 5.5 E10018M
GTAW process; SFA 5.28 ER100S-1

For joining SA 541 to SA 543, I have a problem with your post. What exactly is the material Grade? Is is Grade 5, which I believe you meant because you are joining to SA-543, which is a nickel-bearing steel. Grade 5 only has 0.23 max C. Just trying to help you here.

 

[tc7]

Good morning Met-
I see you were up late last night? or maybe you're on the west coast. Or you don't sleep at all?

Anyway, I apologize for being sloppy with my material grades & types. Truth is I don't have drawings or firm design as yet and I do not know the types and sizes of welds yet either. Presumably it is some type of Sect VIII vessel or device.

I expect the SA-543 to be Type B Class 2 (and the Mn content is .4/7 not Mg as stated);
I expect the SA-541 to be Grade 1 (and the Mn content is .4/.9, not Mg as stated);
All subject to change I am sure.

And as you mention there is a difference in carbon content between these two and I am curious as to known problems that may result from this mismatch and nesessary precautions if any aside from proper preheat, slow cooling, and a proper PWHT.


I presume from your PWHT and filler suggestions that re-heat treating the welded area of these materials to the original purchased Q&T condition is not expected or typical? It puzzles me that we take a high strength material and use a high strentgh weld rod, then diminish the strength of the Q&T condition in the most critical areas of the vessel. I presume the Code calculations account for this reduced strength (I may post that question on the ASME forum) but what strength level do I strive for in a PQR tensile test?

Thanks.

 

[metengr]

tc7;
I do sleep, but not as much as most people. I have a lot of fun with helping other engineers. Anyway, regarding your questions;

- the Q&T materials endorsed by ASME can be welded with little sacrifice in bulk properties, provided good welding practices are followed. Namely, watching heat input and controlling preheat and interpass temperatures, and post weld heat treating below the original tempering temperature.

If you review ASME Section VIII, Div 1 Part UCS you will see that for these low alloy, nickel bearing steels PWHT is required, and ranges from 1000-1100 deg F, depending on your P-No and Group No.

The selection of filler metal is not something that the Code necessarily provides specific guidance. The main concerns are strength and ductility with knowing the service limitations (like notch toughness for MDMT). So, you need to select your filler metal knowing that you can pass tensile and bend testing requirements and notch toughness (if necessary), specified by Section IX.


Getting back to your OP; for SA-543 Type B, Class 2, your UTS range is 115-135 Ksi min, and the max carbon is 0.20%. In this case, I would change the weld electrode to 12018M for SMAW, and ER120S-1 for GTAW. This material is a P-No 11B, Group 10.

Now for the SA-541 to be joined to SA-543, why would you be using a Grade 1? I would think that you would be using a Grade 5 to match the other nickel-bearing steel. Until you get this resolved, I won't provide any other information to confuse the issue.

 

[tc7]

Met-
I was not the selector of the components, I am only reacting to specs given to me by the materials group. It may be a matter of what materials are available in the time needed? Or perhaps to allow transition to yet a higher carbon steel down stream? I cannot get that feedback right now. But that difference in carbon content is exactly what prompted my concern and question. Would you anticipate extreme difficulty in welding this combination?

 

[metengr]

tc7;
No. You might have to make an adjustment in preheat requirements, but that is about it.

 

[tc7]

Thankyou again Met-

I am just now noticing that in addition to the mismatch in carbon content, there could be a significant mismatch in tensile strength as well and it seems too large a difference to assume it was deliberate. I'll raise the flag on that to be sure we're not getting bad information.
VR
tc7