Naphthenic acid resistance of chromized 316

[kevlar49]

Does anyone have experience with the Naphthenic acid corrosion resistance of chromized 316 valve bodies. The situation is that 317 valve bodies are too hard to get 30+ week lead time. 316 is easier but api 581 estimates at worst case 3:1 increase in corrosion rate. Inspection does not want to put valve bodies on a special inspection plan; they would prefer that we either say it will last the design life of the pipe or use 317. Other refiners use 316 valve bodies already; I think our policy might be a bit overly conservative.

I could make the 316 valve body thicker, but wanted to see if using a chromizing (similar to pack carburization) process would obviate the need for going to a thicker size. Are some thermal distortion challenges associated with this?

Any thoughts?

 

[0707]

The Mo content gives the resistance to naphthenic corrosion of austenitic stainless steels. SS317 Mo content of 3.5 To 4% is much superior of the normal SS316. As on the valves is where you have more velocity you have to take care with your option. Maybe hot spraying your SS316 steel with molybdenum would help resistance to naphthenic corrosion.

Good luck

luis