Is it OK to use Galvanized Bolts in SS Valves

[bmoorthy]

Service: NACE Sour, Offshore

Valve material : SS 316L, 31254, 32750, 31803

Is it permitted to use A 193 B7M Galvanized Bolts for SS Valves for Body to Bonnet joint, Valve to piping joints?

 

[gr2vessels]

My answer is no, don't get zinc in contact with stainless steel. Despite of some contrary opinions, I still call two reasons for it;- the localised preferential galvanic corrosion will remove the zinc coating, exposing the B7 bolts to the marine environment and also, in case of hign temperature exposure, the chemical reaction between the zinc and the stainless could be an additional fire hazard. That's valid for the coated washers also.
cheers,
gr2vessels

 

[strider6]

In terms of NACE /ISO requirements the A 193 B7M materials is permitted (see table A.4 of NACE /ISO 15156 part 2) for bolts in Sour Service.
A suggestion could be to use isolating kit to isolate the bolts and nuts from the valve materials and avoid any issue of galavanic corrosion.

S.

http://www.corrosionist.com

 

[Xianglu]

Agree with gr2vessels. In addition, galvanic process may introduce hydrogen cracking to high strength bolts. A 193 B7M Galvanized Bolts are prohibited by some organizations.

Cheers,

 

[ash9144]

Also using dissimilar materials for bolts can have thermal expansion issues. Stainless pipe would expand differently than galvanized steel.

 

[birra17]

Can anybody recommend me what kind of body material is able to work with marine atmosphere? Or what kind of coating may I use due I already have specified Carbon Steel body material.
Thanks,

 

[unclesyd]

birra17,

You need to start a new thread in the Valve Enigneering Forum Forum408 and Red Flag this one.