information on pwht effects on 321 stst overlay 1

[bigbro]

we have been asked to supply a vessel 70mm thick in 1501 490b lt50 carbon steel c/w 321 stainless steel overlay on the bottom dish.
will the pwht of the vessel affect the 321 properties?

 

[metengr]

I presume you are talking about 321 stainless steel cladding on carbon steel? Literature from Avesta Polarit does discuss microstructural stability of Type 321H material. Exposure to elevated temperature service for many tens of thousands of hours will result in some minor embrittlement from sigma phase but not to the extent of other austenitic stainless steels.

The 321 grade of stainless steel is stabilized with Ti so you don't readily form the chromium carbides that result in reduced corrosion resistance and sigma phase formation along grain boundaries. Also, the duration and temperature of PWHT is such that little change will occur.

 

[SJones]

Run an ASTM A262 intergranular corrosion test on a test piece subjected to the PWHT cycle of the vessel. You may be (un)pleasantly surprised.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[stanweld]

I would love to see your 321 Weld Overlay Procedure. Agree with Steve. Be ready for an unpleasant surprise.

 

[EdStainless]

This is often why 321 is used for overlay in place of 304, you can PWHT the CS without sensitization.
I have seen this work out great. Of course I have also seen some disasters. Watch the procedures.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[bigbro]

Just to clear up a point we would be using a 347 stainless steel SAW consumable to overlay the dish head.

 

[metengr]

This is also a stabilized grade of austenitic stainless steel except with colubium-tantulum. Does your corrosion resistant weld overlay (CRO) procedure call for a 1st layer of 309 on the carbon steel followed by 2 layers of 347 for the CRO? If not, I would use 309 weld metal over the carbon steel, PWHT, and deposit the 347 weld metal over the 309 to finish the CRO with no final PWHT.