Thermal stabilization of SS347/ SS321 1

[rkg]

Thermal stabilization of stabilized grades of aust. SS(SS347/SS321) and associated welds is increasingly being specified (which means heating to 815-900 deg. C followed by cooling in air).
1.What advantages does stabilization have?
2.Further, what could go wrong in previous installations where SS347/ SS347H was used without stabilization?
3. Can it be said definitively that thermally stabilized piping installations operating at high temperatures would perform better in service than those not subject to this heat treatment.
4. What should be the heating rates and soaking times? Some people/ specifications recommend minimum four hours soaking irrespective of thickness.
5. Is it justified to apply thermal stabilization heat treatment to all applications of SS347/SS321 subject to pressure and temperature? It is to be noted that getting this treatment at Mills costs additional money while buying materials.

 

[EdStainless]

This will vary some what by product form.
If you have material stabized then the specified straightness/flatness no longer applies. For light gage tubing products (walls under 0.100") times of 10min are enough to produce adaquate stabalization.

In my experience, stab. helps the most when you are at the lower end of the temperature range. As you get hotter the material will stab. in service just fine.

Properly stab. material will resist intergranular carbide formation. This may be critical, or not, depending on your application.

We have seen a lot of 321 recently that has so little C that it will not hardly stab., it doesn't need to. Even without the Ti there would not be a significant amount of carbide formation.

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[NickelMet]

The thermally stabilized grades 321/347 are also recommended for mitigation of polythionic acid attack. You can refer to NACE RP0170 for some (but not a whole lot) of information.

~NiM