SS vavle in CS piping

[302Hugo]

I'm not familiar with corrosion engineering, and I can't remember the rules along using SS in CS piping, and vise versa. I beleive the general rule of thumb is that you want to have more CS than SS, correct?

I am installing a valve in CS piping, but I can only procure a SS body valve. Would it be ok to use this or will I see potential corrosion? Do the connecting nuts/studs have to meet a certain requirement? The fluid will be crude at about 70C.

 

[unclesyd]

I don't know about crude but we have SS valves in steam condensate service. I haven't ever heard of any problems.
On some of the system we use SS bolts and nuts, not because of having to, but due to the area. Outside the battery limits of each building (5) we use CS studs and nuts.

 

[Metalguy]

The CS/SS area ratio (anode/cathode) depends in part on the electrical conductivity of the solution, but even with a good electrolyte the area of the cathode doesn't have a linear effect on the anode corrosion rate.

Any corrosion would probably happen close to the interface, which is why coating a few inches of the cathode side (where possible) is so effective.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[EdStainless]

Just to make it clear, to suppress galvanic corrosion you coat the SS. I have seen people put in a 6" or 12" length of SS pipe on either side of the valve with the ID coated.

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Plymouth Tube

 

[Jmoore1]

It is very common in low temperature environments to have SS valves in CS service as the Carbon steel can become very brittle at those low temperatures, especially in water service where valves are often used in throttling and can be chewed up quite quickly. Where I work we dont isolate CS and SS because we havent seen any issues (albeit I do live in a very very dry environment.)

 

[alseng]

SS is good for H2S, CO2 environment. the only downside that its soft, we usually use SS fittings & valve materials in downhole pumps.

 

[strider6]

You should consider:

-external surface in contact with atmosphere

-internal surface in contact with fluid (crude)

SS is a general classification and depensing on fluid composition, operating temeperature and external exposure (marine, rural..) you need to select the correct type of SS.

Vic



Corrosion Control