SS Bolts for Incoloy 825 Valve

[pnrngv]

Hi,

Need expert metallurgy advice on galvanic corrosion for using stainless bolts on ASTM B564 N088825 (Incoloy 825) valve body-bonnet bolting.

Project specification allows to use austenitic stainless bolting AISI Type 316 (per A193). However, need clarity with respect to galvanic corrosion.

Thanks

pnrngv

 

[EdStainless]

Why are you using 825 in this system?
The 316 will be less corrosion resistant and weaker.
Is 316 what the valve manufacturer recommends?
Make sure that you use the correct specification, there are different strength levels of 316 hardware.
And use a good anti-gall.

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P.E. Metallurgy

 

[TugboatEng]

Is the valve installed in a corrosive environment or is it handling a corrosive fluid? In most cases the bolts are isolated from the fluid by gaskets so unless you have a leak, galvanic corrosion of the bolts shouldn't be a problem.

 

[MagBen]

825 per B564 is fully annealed, 316 per A193 be slightly cold worked, so strength levels are pretty much comparable. 316 is obvious less corrosion resistant. That said, when both alloy are passivated, their potentials are pretty close (with 825 a little more noble), galvanic corrosion is not a big concern.

 

[pnrngv]

Hi EdStainless


Why are you using 825 in this system?
It is the project specification requirement. This is 3/4" gate valve provided as a Drain valve for 8" Ball Valve.
Specification calls for Inconel (Same as Trim of Ball Valve).

Is 316 what the valve manufacturer recommends?
No. In Project specification, it is specified to provide AISI 316 bolting.


Hi Tuboateng
It is Onshore upstream Gas field. Inconel Gasket are provided for the valve.

 

[EdStainless]

825 is an Incoloy, an iron based alloy. There are about 25 of these grades. And there are about as many Inconels which are Ni based alloys.
If the requirement is for Inconel bolting then you need to look for alloys like 625.
I am not worried about galvanic issues but rather crevice corrosion and chloride stress corrosion cracking of the 316 are what will limit its life.

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P.E. Metallurgy