PWHT Requirement for welding of SS410/SS410S

[jerin james]

Dear All,

Please note that we are currently manufacturing a tube bundle which is a replacement for one of the end users.
The complete bundle is SS410 material (Tube-SA 268 TP 410 ,tubesheet -SA 182 F 6 a Cl 2, baffles,Sliding bar and support plates-SA 240 410S). The existing equipment(bundle & shell) is not subject to PWHT . However our welding engineering has raised the concern that the bundle needs to be subject to PWHT because of clauses in tables UHA 31-1 & UHA 32-1.

The baffle thickness is 10mm Thk and there is 6mm fillet welding of baffle to sliding bars. The sliding bar is 26mm Thk which is welded to the tubesheet (groove welding-13mm up and down). tube (19.05 OD *1.65mm thk) to tubesheet (170mm Thk) is strength welded (1.2mm weld).

I would like to have your advise on PWHT requirements because of welding of SS410/SS410S.

Thanking you .

Regards
Jerin

 

[0707]

IMO for this kind of material PWHT is not required, tubes can be welded to tube sheet with a preheat and by TIG process with ER309.

Regards

luis

 

[EdStainless]

Is the material 410 or 410S? the S is low enough in C that PWHT would not be a concern. If it is straight 410 then double check the actual C and check the hardness of some welds and HAZs.
If they are higher than you like then a tempering treatment may be in order.

0707, I have also seen this welded with 41081 or 41086 filler as both are very low C, or even one of the stabilized grade fillers (low C + Cb and/or Ti).

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P.E. Metallurgy, consulting work welcomed

 

Be careful mashing SS410 and SS410S together. As similar as they are in composition, they are quite different materials when it comes to welding (and more significantly, post-weld heat treatment).
ASME IX recognizes this by assigning them different P-numbers; they are also treated differently in the ASME construction codes.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[jerin james]

Dear Luis,
@0707

Thanks for your reply .

The clauses in table UHA 31-1 & UHA 32-1 , says we have to have carbon content less than 0.08% if we have to exclude PWHT ..is my understanding correct ?? The tube (SA 268 TP 410) and tubesheet (SA 182 F6a cl2) suppliers are not able to comply to 0.08% max .

Thanks
Jerin

 

[jerin james]

Dear @Edstainless,

Tube and tubesheet is 410 while baffles and sliding bars are 410S .

My main concern here is ordering the baffles and sliding bars with additional SPWHT cycles because QC is saying entire bundle requires PWHT ..as the baffles are non pressure parts, can we not exempt entire bundle from doing PWHT ?

Thanks
Jerin

 

[0707]

EdStainless I agree with you, but my experience with ER309 is good if the operating temperature of the exchanger is bellow 340ºC and if we are dealing with straight tubes of course.

luis

 

[EdStainless]

0707, Agree, the only thing that I don't like about 309 in this case is that depending on weld dilution you end up with various phases in the welds, and that can fluctuate. Of course the large CTE mismatch is also an issue in some cases.
Just saying that there are good alternatives.

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P.E. Metallurgy, consulting work welcomed

 

[jerin james]

@Edstainless & @0707, Kindly advise your stand on requirement of PWHT for welding of non pressure parts (sliding bars/tie rods etc. fabricated from SS410S) . Reference from the code would be appreciated or else if you can explain with regards to Table UHA 32-1 would be very helpful.

Thanks
Jerin

 

Generally speaking, 410 is an alloy where NOT matching the filler metal is my preferred approach. 410 filler has the problem of higher hardness than the base metal and therefore more susceptibility to cold cracking. It also has a very wide freezing range so it can be prone to solidification cracking.
If extreme temperature cycling over long service time is not in play then 309L is a good choice. Unless dilution is extreme then you should be able to join any combination of 410 and 410S.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[jerin james]

@ironic metallurgist ,

Our welding engineer has advised to use NiCrMo-3 for welding instead of SS410. Operating temperature of tube side fluid is 260 Deg C & Shell side fluid is 366 Deg C.

Please advise your thoughts on requirement of PWHT for welding of NON-PRESSURE parts in line with code.

Thanks
Jerin

 

I don't consider this to be an extreme environment in terms of temperature cycling, but Inconel is always a good option.
With martensitic SS I look for strategies that avoid PWHT. I would have to know the configuration (thickness, joint type) and the materials being joined.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[jerin james]

@ironic metallurgist
Tube material -268 TP 410 , tubesheet - SA 182 gr F6a cl2 .

Tubesheet thickness -174mm , tube thickness - 2.11mm ,tube to tubesheet joint - strength welded .

Sliding bar is 410s material (26mm thk), is welded to the tubesheet .

Pls let me know if you need further details .

Thanks
Jerin

 

[EdStainless]

IM, while I agree with avoiding PWHT on these grades, if the 410 is higher C then the HAZ will end up much harder than desired. Often the PWHT for these alloys looks like a tempering.
I can live with the NiCrMo-3 as a filler, maybe not needed but it will work.


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P.E. Metallurgy, consulting work welcomed

 

Your 174mm (7 inch) thick tubesheet is the common element in both types of welds, and it is the controlling factor in applying UHA-32-1. The tubesheet and tubes are pressure boundary, while the sliding bar is a direct attachment to pressure boundary.

UHA-32-1 Note (a) permits exemption from PWHT only up to 1.5" (38 mm) when certain conditions* of preheat and examination are met.

It appears your welding engineer is correct, and that you are required to PWHT - a bit of a tricky proposition for a heat exchanger. If this were new construction I would look into buttering options for the very thick tubesheet.

* Interestingly it is unclear in the latter part of Note (a) if the same non-air hardening filler metal is still required. Technical judgment suggests it should be.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[jerin james]

@ironic metallurgist

The tube to tibesheet weld is only 1.2mm .please see attached joint details. Hope it clarifies . Tube and tibehseet shall be procured with carbon content 0.11%.

Kindly advsie your thoughts .
Thanks
Jerin

 

[jerin james]

@edstainless ,

It would be really helpful if you can explain based on table UHA 32-1 .

Thanks
Jerin

 

jerin,

Preheat and PWHT requirements are determined by the thicker base metal, not the weld dimension. (A small weld can actually exacerbate the HAZ hardness and cold cracking risk.)

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

(because small welds on a thick base will cool very fast and reach higher hardness)

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[jerin james]

@ironic metallurgist, @EdStainless

Agreed about the weld dimension buut what about the tube thickness which is 1.65mm.Isnt that the base metal in our case?

Thanks
Jerin