post weld heat treatment

[leedrong]

Dear All

We are just about to perform PWHT of Heat Exchanger Shell have 20 mm thickness ,2000 mm Dia ,6000mm in length,SA240-321 Material.
PWHT temprature and hodilg time is 900 degree centigrade for 4 ours minmum.
We have no experience PWHT like this high temperature for long time for the fabricated shell.
We will use bracing to protect deformation but we worry about bundle insertion work after PWHT due to the clearance
is 5mm between shell and bundle.
Anybody have PWHT experience for such a fabricated shell at high temperature for 4 hours ? and could give us good technical advice to ensure bundle insertion after PWHT without trouble?

 

[metengr]

leedrong;
I would not recommend any PWHT for SA-240 Type 321 SS. This is a Ti stabilized austenitic stainless steel, and I see no reason to perform this type of heat treatment after welding. Typically, this material is supplied in a solution annealed condition (heat treatment at 923 deg C to 1093 deg C followed by rapid cooling or quenching). A stabilization anneal is conducted at 843 to 899 deg C for up to 5 hours, depending on thickness.

With your situation, I would be hard pressed to perform a stabilization anneal unless the original material was not properly solution annealed. I would review the material test reports before committing to any stabilization anneal heat treatment of a fabricated shell.

 

[leedrong]

Many Thanks Mr.Metengr

We already proposed not perform PWHT to client but rejected.
Specification crealy says that all welds of equipment shall be post weld heat treated and blocked and suppoted as necessary to avoid any deformation or damage.

 

[metengr]

Prepare to perform possible local weld build-up/machining with a boring bar to true-up the shell ID after the stabilization heat treatment.

 

[TJonesy]

Hi Leedrong,
I would check into localized PWHT (electric heaters) on the welds only since you stated that only the welds need to be PWHT. There are alot of company's that do this, and the documentation should satisfy your customer. If you plan on sticking the unit into a furnace, I agree with Metengr, your gonna have a mess

 

[vesselguy]

Leedrong,
If I were you, I would challenge your Client on their specification in reqards to the blanket statement "all welds to be PWHT." One should not say that without qualification based on material spec and service. Metengr is correct that 321 (a P8 material) don't require PWHT after welding. Aged material may required annealing but that's another issue that is not applicable here.

 

[PAN]

Leedrong,
Please inform your design and operationg condition of this heat exchanger.

 

[leedrong]

Hi~! Gentleman .

Design condition of equipment is as followings.

* Dt( centigrade ) : 560 /530 ( Shell side /Tube Side )
* O.t( Centigrade ) : 450 /420
* DP (kg/cm2G ) : 7 /10
* OP (kg/cm2G ) : 4 / 8

Material is all sus 321

We failed to pursuade client not perform PWHT and we are preparing jig for Heat treatment now.

 

[Sinbading]

hi leedrong,
i agree with Metengr,
please tell me process of PWHT ,thank you!