STABILIZING AND ANNEALING OF SS321 TUBES 2

[mombu]

Dear all,
I hope someone could help me about the following:

I have SS321 tubes with OD 25.4 mm (1") and thk 2 mm which shall be bent as "U" tubes.

The requirement of NACE Standard RP0170-2004 and Client (Protection of Austenitic Stainless Steels and Other Austenitic Alloys from Polythionic Acid Stress Corrosion Cracking During Shutdown of Refinery Equipment ) claims the additional stabilizing heat treatment @900°C for 2-4 hours before welding.

There is an additional requirement of ANNEALING HEAT TREATMENT usually perfomed by the mills @1050°C approx. per ASTM Spec A 213.

My questions / doubts / concerns are:

1) As said, the tubes will be bent to hairpins by cold working. After bending the tubes should usually be solution annealing treated by resistors at 1050°C for few seconds (15 sec. approx.)..this is also requested by a Client's specification.
Could the solution annealing negatively affect the stabilizing treatment??

2) Some mills say that the correct procedure is to perform the solution annealing at 1050°C for few seconds only (15-20) after bending (U-bends+200mm),and that this does not negatively affect the stabilizing and does not compromise the performed stabilizing.
Other source think that, after bending, the "U" tubes (U-bends+200mm),shall receive the stabilizing heat treatment @900°C for approx. 30 minutes only. NO other treatment shall be done.

Which one is wright??

3) the tubes will be welded to the tubesheet in SS321.
The tubesheet will be stabilizing @900°C.
Regarding the welding between tubes and tubesheet, I think there is NO concerns during the welding of the tubes since the ends of tubes do not receive any additional treatment or cold working after those received at mill so the welding between tubes and tubesheet is done between stabilized parts . Is my though correct??

The concern is about the U bends / HAZ after the cold working and solution annealing.


Have you already faced this kind of problems in the past??

What do you suggest to do??

awaiting for your precious help I thank everybody in advance.

Regards

mombu

 

[metengr]

mombu;
For 321 ss tube fabrication and this includes u-bending, a solution treatment is required by ASTM A 213 specification after all fabrication is completed (forming skelp into tube, long seam welding, etc). A stabilization heat treatment (if specified by the Purchaser) is always subsequent to solution treatment for these types of austenitic stainless steel grades (321, 347, etc). The stabilization treatment is performed at a temperature lower than the solution treatment temperature. So, why would you stabilize first and solution treat? This makes no sense.

Regarding installation of solution treated and stabilized 321 ss tubes into a tubesheet with seal welding; nothing more needs to be done after seal welding.

 

[mombu]

Dear ,

thanks a lot for your reply.
I agree with you but my main concern is the following:

- the tubes ( as straigth) will be at mill
1) solution annealing treated at 1050°C
2) stabilized at 900°C for 2-4 hours

- a client specification claims the U-bends + 300mm of straigth legs shall be solution annealing treated ;

Information got from sub-suppliers are in conflict each other since some suppliers say that after bending the U-bends+300 mm CAN BE solution annealing @1050°C by resistors or few seconds (as requested by client's spec.) and this does not compromise the stabilizing done at mill
WHILE
other sub-suppliers say that after bending the U-bends+300 mm SHALL RECEIVE ONLY an heat treatment in furnace @900°C for 30 minutes and NO stabilizing heat treatment by resistor shall be done otherwise the stabilization done at mill would be compromise;

Metengr; WHAT WE HAVE TO DO ??
we have now to inform the client about our procedure and, if we can not perform the stabilizing after bending as requested by the Client's Spec. we have to inform the that in liue of what they requested we will perform a stabilizing of U-bends infurnace.

Could you help me??

Thanks a lot in advance for your time.

Mombu

 

[metengr]

Mombu;
The post bending thermal treatment should be performed at 900 deg C for 30 minutes and would not compromise the original mill anneal and stablization thermal treatment.

 

[EdStainless]

There are two ways to get there.
metengr gave you the best one, fab tubes, solution anneal, stabilize, bend, stabilize the bends.
The other approach is to solution anneal the tubes and then bend them, then stabilize the entire u-bent tube.

There is no reason to go to anneal temp on the ubends.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[mombu]

Dear Edstainless / metengr,
you have been very helpful !! Thank you !

Now I will contact again the tube suppliers and further duscuss....

I will keep you informed about.

thanks again

mombu