For buried systems SS piping is often coated and/or protected by CP. In cases of agressive soil conditions, hazadous materials, or very long required lifetime, both coating and CP are used.
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Corrosion never sleeps, but it can be managed.
If you do not know precisely what your soil conditions are throughout the length of the pipe system, I would advise the use of CP. I have seen rapid pitting failurs in unprotected 316 SS and 304 SS piping in both a gas utility's riser connection to the meter/regulator at individual home locations ($5 million USD replacement cost in 1979 dollars), in miles of fuel gas piping at a major Air Base (over 25 million USD repalcement cost in 1980 dollars)and a number of international incidents with equally staggering costs for replacement.
There has been much research done into the requirements for cathodic protection of stainless steels compared to carbon steels over the past 30 years. Under most situations, it is likely to be OK to use standard carbon steel design guidelines.
Care should be taken however in selecting the CP system to be used, depending on the grade of stainless steel to be used, the soil conditions, and the life of the asset. Stainless steels can suffer from hydrogen embrittlement, so care must be taken to avoid over protection of the steel and the resultant Hydrogen evolution that occurs.
A competent corrosion engineer should be able to assist you.
The ferritic or dual phase ferritic/matensitic alloys can have issues with hydrogen. This is not a factor with the austenitic grades.
This is one area where you need to hire a pro.
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Corrosion never sleeps, but it can be managed.
projacktowl,
1. Stainless steel is specified for the process side environment - not the "buried" side from a corrosion standpoint, hence, coated carbon steel cannot be used.
2. The problem with S.S. in buried service is that full polarization may not be achieved throughout the length of the burial without application of CP.
I'm sorry for the second question I asked. I made a mistake. Let me re-phrase it.
Would the passivation process of the stainless steel pipe (outer surface) be compromised, when it is buried underground and with application of CP (impressed / sacrificial)?
With proper application of CP, the stainless steel surface exposed to the soil will remain in the passive state. Impressed current CP systems have been used on large complex underground stainless piping systems and sacrificial anodes have been used to protect short, simple underground systems in plants on projects in which I have been involved.
I once saw a situation where some burried stainless tubing was protected by wrapping it in aluminum foil.
Does that seem like an acceptable method to protect the tubing?
