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Welding of inconel tubes with P22 headers

Welding of inconel tubes with P22 headers

Welding of inconel tubes with P22 headers

(OP)
What care should be taken when welding inconel tubes N625 with SA-335 grade P22?
In one header, tubes are stub on with full penetration joint through tube wall thickness.
In secon headers tubes are stub in, joint is partial penetration through header wall thickness.
Tube thickness is 1.6 mm and header thickness is 25 mm in both cases.
 

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

RE: Welding of inconel tubes with P22 headers

I would butter the P22 side of the weld joint for either header jpoint configuration , perform PWHT for the P22, and then complete the weld joining the 625 tubes to the P22 header. You want to avoid PWHT exposure to the 625 tubing material.

RE: Welding of inconel tubes with P22 headers

And I would "Safe Nozzle" the Set-In [stub-in] header.  Put 6" to 8" long P22 stubs on the header, PWHT it, and then weld on the Inconel tubes to the stubs.

Or see the Design Engineer will allow you to Set-On to both headers.  Try explaining the PWHT issue to him.  He might listen.

RE: Welding of inconel tubes with P22 headers

(OP)
Metenger and Duwe6,

Thanks for your valuable feed.
Please explain why we avoid 625 inconel from PWHT exposure?
Which welding material is suitable for buttering in this case?
I have checked with designer, he can change the joint configuration to stub on.
Thank you once again.
 

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

RE: Welding of inconel tubes with P22 headers

PWHT is not good for Inconel.  Not extremely bad, but not good.
Butter the joint with 625 filler metal.

Attached is an interesting bit of info on P22 welding, to include a way to avoid PWHT on small connections.

http://www.t-put.com/EN_welding_CrMo.pdf
 

RE: Welding of inconel tubes with P22 headers

For Inconel 625 wrought material, you want to avoid exposure to temperatures where sensitization can occur. What this means is that the corrosion performance of the alloy can suffer, as a result of sensitization (carbide precipitation along grain boundaries).
Alloy additions to 625, like niobium/columbium are used to reduce sensitization. However, from my experience I would avoid exposing this material to any PWHT, which is the reason why you either butter the low alloy side of the weld joint and PWHT. When this operation is completed you can finish the weld used to join the 625 tube to the P22 header or safe end the header using T22 stub tubes, PWHT and weld the T22 tube to the Inconel 625 tube because the thickness of 1.6mm does not require PWHT.
 

RE: Welding of inconel tubes with P22 headers

(OP)
In case, if we weld T22 stubs with P22 headers first and do PWHT as we see Table PW-39.4 (ASME Section I)that PWHT is mandatory requirement when such connections are welded with headers.

When we would weld inconel tubes with T22 stubs, because of lesser nominal thickness, PWHT is not required for circumferential butt welds up to weld nominal thickness 16 mm per Table PW-39.4. That is clear for me.

We would use GTAW for making weld between T22 stubs and inconel tubes, my question is what would be the most suitable wire for GTAW? any recommendation regarding heat input?, travel speed?, we would use preheat 150C.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

RE: Welding of inconel tubes with P22 headers

Regarding wire, I would use Inconel 625 wire (ERNiCrMo-3).

The preheat for the T22 looks acceptable. Try to keep the heat input on the low end, and maintain an interpass temperature of 300 deg C.

RE: Welding of inconel tubes with P22 headers

I'm following this thread with interest, although I'm not able to contribute anything meaningful, but I'd be curious to know what you mean by "butter" the joints?

Cheers

RE: Welding of inconel tubes with P22 headers

Fizza453
As presently configured with the very thin tubes welded to the much more massive headers, I would not expect a long service life should thermal cycling be an operational criteria. Suitably designed stubs are recommended.

RE: Welding of inconel tubes with P22 headers

macmet;
In certain situations post weld heat treatment (PWHT) is required on a dissimilar metal weld joint because the lower alloy side of the weld joint may require PWHT by code, whereas, the higher alloy side may not require PWHT (austenitic or Ni-base steels).  

To meet Code required PWHT for the low alloy side of the weld joint,  the low alloy base material is prepared by depositing (e.g., buttering) two or more weld layers along the weld prep surface using filler metal approopiate for DMW joints, and is subject to PWHT for Code compliance. Once this is completed, the weld joint is completed by joining the buttered side of the weld joint to base material where PWHT is not required.
 

RE: Welding of inconel tubes with P22 headers

Thanks metengr.

As always, much appreciated.

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