Underground Stainless

[TangoCleveland]

We are replacing an underground water drain line from a process air system at 165 psig. Existing line is Carbon Steel. Customer plans to use a stainless water drain line in direct burial installation. Two questions arise in my mind -
1) is there any galvanic potential between 304SS and carbon steel?
2) Will soil chlorides give us a problem with buried stainless?

This is a rush job; any information will be helpful.

Larry

 

[Metalguy]

1. Yes, usually large.
2. Depending on the Cl level, amount of moisture, wetting&drying, pH, temp. and the SS alloy, YES, you can easily expect thru-wall pitting and possible MIC attack in/near welds.

 

[unclesyd]

Our plant site had numerous S/S lines, 2" to 16", underground. As stated above it depends on the environment around the pipe. There are some lines 304 S/S that are 50 years old with no problem. We have lost others at times as low as five years. The lines that are in acidic service (waste) are especially venerable if they get a leak. No product lines, either S/S or C/S, were ever below ground.

We had all the problems mentioned by “Metalguy” with the worst being Chloride induced SCC on the exterior. It wasn’t always evident until you attempted to make a repair.
All the waste lines have been or are being brought above ground and the ones that had to remain underground have been changed to double containment.

 

[TangoCleveland]

Metalguy & unclesyd,
Thanks for confirming my suspicions.

Larry