Weldoverlay for flange gasket facing

[nickypaliwal]

What is the primary reason for weldoverlay on gasket facing of flange?

Is it crevice, galvanic or uniform corrosion?

 

[EdStainless]

It is usually used to fight crevice corrosion.
Since CC is worse the tighter the crevice is, at seals it is very severe.
In many cases a common stainless like 316L will handle the working fluid, but they overlay seal surfaces (this includes valve trim) with Ni-Cr-Mo alloys.

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P.E. Metallurgy, Plymouth Tube

 

[nickypaliwal]

Considering it is for Crevice Corrosion then why is SS316 which is more prone to crevice corrosion, is used to overlay on carbon steel surfaces ?

Also, does CO2 content affect the crevice corrosion to that extent that overlay is only asked for more corrosive services, where Carbon steel bare is not used for piping/vessels. Same is not asked for systems with carbon steel and corrosion allowance.

 

[EdStainless]

316 is much better than CS, and Ni alloys are better than 316.
The idea is just to go up a step in corrosion resistance. If you go too far then you also have to worry about galvanic corrosion issues.
CO2 is an issue because it lowers pH, which makes corrosion more sever.

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P.E. Metallurgy, Plymouth Tube