Welding 3" Thick 347 SS to Carbon Steel 3

[iam42]

Hi Guys,

I have a job coming up that requires us to weld 3" thick SA182-347 to SA106 Gr. C Pipe. I am no metallurgist but I have read enough in here to scare me a little with regards to Re-Heat Cracking on thick sections. I am not sure if this is a major factor but the design temp for this joint is 550°F

My Plan at the moment is to butter the CS weld bevel with ERNiCr-3 and then PWHT the CS pipe. I then plan to weld the joint with ER347 in a similar manner to a standard 316 or 304 joint.

Is my plan flawed and doomed to failure?

If so, can some kind sole please suggest a better approach.

Many Thanks

 

[EdStainless]

You may need a thicker layer of Ni than the drawing suggests.
That is the correct basic approach.
But the risk is in the details.

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P.E. Metallurgy, Plymouth Tube

 

[iam42]

Thanks Ed,

I was planning on putting a minimum of 1/4" overlay/butter on the CS weld prep.

Do you think that is adequate?

Thanks

 

[metengr]

Yes, this thickness of butter layer is acceptable for the carbon steel side of the weld joint. You may need to perform an intermediate stress relief of the 347H weld joint to avoid cracking. I would weld the entire joint using ERNiCr-3 to avoid stress relaxation cracking potential.

 

[iam42]

Thanks for the input metengr,

I am afraid I have already purchased 160lb of 347 weld wire.

Is there anything I can do during welding that will reduce the risk of cracking if I use the 347 weld wire?

Thanks again.

 

[metengr]

Not knowing your original condition of the 347H SS pipe, the main issue with stress relaxation cracking with thick section components will be the condition of the 347H pipe material. If it was cold worked as part of fabrication, you may have local problems after welding with the 347H heat affected zone.

If the pipe was supplied in a fully solution annealed condition or had a stabilization treatment, welding should not be a problem after the butter layer and PWHT have been performed on the carbon steel side of the weld joint, as long as the delta ferrite level is acceptable to avoid hot cracking.

I would hope you are qualifying a welding procedure specification for this project.

 

[EdStainless]

The risks with a thick SS weld are mostly related to hot tearing or cracking.
Checking your FN on your filler is a first step.
Watching heat input and temperatures is critical.
You are doing a full thickness qualification, right?


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P.E. Metallurgy, Plymouth Tube

 

[iam42]

Thanks Guys,

Metengr/Ed,

I will be qualifying the WPS next week. The actual material that will be used for the job is a forging and not pipe so I am hoping that it will be supplied in a fully solution annealed condition.

Due to the very short lead time on this I have had to make do with 1 1/2" thk plate for the PQR.

Guys, I really do appreciate the time and thought you put into your answers.

Many Thanks

 

[metengr]

You are fine regarding your approach, there is no need to perform a full thickness qualification for the WPS per Section IX.

 

[weldstan]

Welding 347 filler metal into a Nickel base filler metal is almost guaranteed to hot crack in the first pass against the nickel base filler. As a general rule of thumb, never weld stainless filler into nickel base filler - weld nickel base filler into the stainless steel.

 

[EdStainless]

The problem that Stan is talking about is that for passes against the Ni filler you will pick up enough Ni so that the FN will become low, maybe zero. The result is a tendency to hot tear/crack.
Watch this when you do your qual, you need a pass schedule that minimizes the dilution of the 347 by the Ni.

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P.E. Metallurgy, Plymouth Tube

 

[iam42]

Thanks Weldstan & Ed,

Now I am more confused (not that difficult to do). Would it be better to use a 309 wire for the buttered layer?

Thanks

 

[metengr]

Based on your service temperature limit for the weld joint, the 309 would work for the butter layer, followed by the 347. My preference would have been ERNiCr-3 for the entire weld joint.

 

[iam42]

Thanks Metengr,

I just wish I had started this post before buying the consumables.

If anyone is interested, I will post the results of the testing after completion.

Thanks again to all for the contributions.

 

[weldstan]

Agree with metengr.
A recent example of welding ER347 into a ENiCrMo-3 weld overlay to weld 347 internals to the heavy wall carbon steel overlayed vessel. The ER347 was specified by either the manufacturer's Welding Engineer or the Engineering Company. Regardless or who specified it, the welds could not be completed without cracking after numerous repair attempts. For this weld, I would have recommended the use of ERNiCrMo-10 or ERNiCrMo-3. While I had no involvement with this vessel, I did casually mention the improper choice of filler metal and they finally made the welds correctly - after 5 months of failure.

 

[iam42]

Guys,

I am not really sure about the mechanism of the cracks that I could possibly encounter. Is the concern with cracking in the Weld Metal or will it be along the HAZ or Base Metal?

Thanks

 

[metengr]

Mostly weld metal cracking followed by 347H base metal HAZ cracking (much less risk to no risk if base metal was supplied in a solution annealed condition).

 

[iam42]

Hi Guys,

I presented my preWPS to our customer, 309 butter on the carbon steel and 347 fill and cap to complete the joint. Their response was that they want the full joint welded with 309. They explained to me that this is how their last spool was welded by a previous supplier and they want to keep consistency.

As I mentioned before, I'm not a metallurgist so I am not sure if there is any metallurgical reason to avoid this.

Ed, Stan and Metengr, do you know of any reason why 309 filler would be a poor choice for this complete joint.

Thanks

 

[metengr]

The only limitation of 309 is the service temperature of the welded joint. If it is below 800 deg F, you are fine with 309 filler wire.

 

[iam42]

Thank you very much Metengr, I think this is what I will go with.

I really do owe you a beer for all your help.