PWHT requirements for 304H prefabrication 1

[AlbeBersani]

Hello to everybody,
we are managing a prefabrication in 304H grade.
Client ask a PWHT at 890°C for 1 hour per inch, then 2.4 minutes/mm.
Max welded thickness involved is 35mm, then 84 minutes of holding time, after a requirements of heating rate of 83°C/hour from ambient temperature (then more then 10 hours of heating).
Our concern is about the possibility of sensitization of this kind of material with high carbon content, at these required temperature and times.

Have someone experirence or references to give us an help to discuss this matter with our client ?

Many thanks,

Alberto

 

[IdanPV]

1. ASM Handbook, "Heat Treating", Thomas J. Lienert (Editor), Vol. 4, ASM International: "Heat Treating of Stainless Steels"

2. Relieving stress in stainless steels, World Pumps, January 2013.

 

[GD2]

Op,
What's the construction Code? Code provides PWHT requirement. Typically it goes by P-Nos for ASME PVC. Then compare between the two and ask your client to review.

GDD
Canada

 

[IdanPV]

This material is defined as P-No. 8 and Group No. 1.

According to ASME VIII-1, Table UHA-32-3, PWHT is neither required nor prohibited for joints between austenitic stainless steels of the P-No. 8 group.

 

[jt1234]

We do solution annealing on all P8 formed head to remove residual stress due to past experience of cracking head in ethylene plant. It can either be the entire head solution annealed or only solution anneal the formed segments to remove residual stress due to forming. The final assembly welding will not be solution annealed.
Just curious what's the purpose of doing PWHT at that temperature ?

 

[EdStainless]

At the specified temp you will form Cr carbides, but it is high enough that you will not get sensitization.
The killer is Cr depletion along the carbides. If it is hot enough for the Cr to diffuse quickly then you will not see the depleted zone.
The heating rate restriction is ridiculous.
We would usually go into a furnace at 800F and aim to heat at 200-250F/hr.
(this is for heavier material, similar to yours. with light material <0.100" we go into a 1600F furnace and heat to 1950F in a few minutes)
High temp stress relief or annealing does not permanently remove residual stress.
After a rapid cooling you will have a lot of residual stress, but it will be highly random.
There will not be concentrations at bends, welds, and other transitions.

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P.E. Metallurgy, consulting work welcomed

 

[GD2]

Op,
Essentially, you will be doing a solution-annealing for the 304H, which is a practise used for 300 series SS. What cooling rate will you use? Furnace, air or water cooling? Ask/decide with the customer.

GDD
Canada