FWIW,  when we were looking at changing to stainless steel tubing for hydraulic lines, one concern of the vendor was that ss inside rubber clamps, in the ABSENCE of air, would not form its proper protective coating and corrode. He referenced buried underground, below water table, ss tubing as a particular problem.

I have no further info, and think  there may have been much old wives tale there, as we have had no problems with the ss under the rubber clamps.

kcj

Captdave;
One concern regarding direct burial of ss piping is the potential for MIC (microbiologically influenced corrosion) damage on the OD surface in contact with the ground. I would review soil conditions and determine how the piping was buried (trenched with backfill - gravel or sand).

The piping code that would apply would be ASME B31.3. However, this is geared for design and does not address corrosion issues related to burial.

For information on Corrosion of SS in Soil, please see the following web site;

http://www.euro-inox.org/

After you enter, navigate to the Materials and application and other documents. You will find a technical paper on corrosion of stainless steels in soil.

Always apply coating and CP to buried SS.