Stainless Steel Tube Sheet (for Filters) welding to Carbon Steel Thick Shell (Subjected to PWHT)

[Kunal88]

I would appreciate an advice on the subject. i have thick Wall Filters (2" thick) having design temperature and pressure as 250 Deg F and 890 psig. Since, the thickness of the vessel qualifies the same to be subjected to PWHT as per code requirements same would be performed. But, the catch is these filters have tube sheets that bear the metallurgy as SS 304 which needs to be welded to these shell.
Question is how would the welding of SS tube sheet be performed on the vessel which has to undergo PWHT?

Letting the SS tube sheet inside shell will subject the same for sensitization.

Can you please advise what shall be the procedure to perform the same. These tube sheets are close tolerance with shell so buttering may cause fitment issues for tube sheets.

Can someone please advise?

 

[Dhurjati Sen]

Dear Kunal88,

Why do you think SS would sensitize at 250⁰C ?

Why don't you try 309 filler wires?

Regards.

DHURJATI SEN
Kolkata, India

 

[weldstan]

You will get sensitization of the 304 during PWHT. Why not use 304L for the tube sheet? Because the dissimilar metals weld will be subject to PWHT, the use o Nickel based filler metal alloys is recommended.

 

[Kunal88]

These are not solid tube sheets and i am using SS 304L tube sheets to be welded on Carbon Steel. I am not worried about sensitisation at 250 Deg F but when these Tube sheets will be subjected to a temperature of 610 Deg C i.e. PWHT temperature there would definitely be chances of Sensitization of stainless steel.
I was planning of using UCS-56 (f)(5) repair but that is valid only if PWHT is required by code but since i have a few vessels which are in Amine Service (PWHT is a service requirement) i cannot use UCS-56(f)(5).
The only thing i can think off is buttering the inside surface of shell with 309L and subjecting the vessel to PWHT. After completion of PWHT welding the SS tubesheet on top of the buttered surface.Since, the weld is between SS i guess we can get rid off getting PWHT done again.
Please advise if i am thinking correctly or i am wrong somewhere.

 

[weldstan]

Very little sensitization will occur on the 304L tube sheet during PWHT. You may also butter the carbon steel side of the joint and complete the weld after PWHT as you described.

 

[Dhurjati Sen]

Dear Kunal88,

As per your original post, if fitment is not an issue, you are thinking correctly.

Do ensure that the hardness of the SS to SS weld does not exceed the acceptable limit.

Regards.

DHURJATI SEN
Kolkata, India