FN in stainless steel piping

[Corgas]

Dear Colleagues, I need your opinion(s) one more time.

Recently I came across some new welds in stainless steel piping (built to ASME B31.3) with some degree of magnetism.

I have not used ferrite scope yet, but I will very soon. I've requested WPS/PQR to determine FN according to WRC-1992 FN diagram.

I know that ASME Section II, part C A6 pretty much describes what WRC established and from my previous life most refiners consider acceptable FN between 3 & 11.

Question 1) Does ASME B31.3 address ferrite content in weld deposits?

Question 2) If I find a FN > 11. What impact will have on corrosion properties and cryogenic properties?

Any links will be greatly appreciated.

Thanks,

Corgas

 

[metengr]

Corgas;

Question 1) Does ASME B31.3 address ferrite content in weld deposits?

No. This is recommended by the design engineer or engineering specification.

Question 2) If I find a FN > 11. What impact will have on corrosion properties and cryogenic properties?

A FN of 11 is too high for austenitic weld deposits. The corrosion resistance will be lower and even more important, the notch toughness will be reduced because of the increased ferrite content.

 

[EdStainless]

It depends an the thickness and the service.
If this is acidic service then residual delta ferrite will cause accelerated corrosion of the welds. In neutral or alkaline service it will have no impact on corrosion resistance.
The toughness would be an issue on thick pipe (say above 0.300"). I don't think that you could tell on thinner material.

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Plymouth Tube

 

[MikeMet]

You may be stressing over nothing. Welds in stainless steel piping will be slightly magnetic due to retained ferrite. Same way cast austenitic stainless steels are slightly magnetic. Only if fully solution annealed after welding will they be truly non-magnetic. Even at FN 11 the weld can have adequate corrosion resistance, it depends on alloy content.