We have a problem where we have to replace steam piping which is buried under the ground every year.  The piping is black iron and we get tired of replacing it.  Any suggestions out there?  We have tried stainless, still leaks - we tested the soil and was acididc a few years ago, , we put some lime down in the soil, it lasted a little longer but when the piping had to replaced, it was a mess...

Do you keep the line hot year round, or is it out of service and cold for extended periods? Low pressure lines corrode much faster than high pressure (and temp) ones underground.

What kind of insulation are you using? Something like Foamglas works well underground, as moisture has no effect on it. Fibreglass and cal-sil just suck up water and hold it against the pipe. The corrosion rate, when the lines are cold, is just spectacular.

There are pre-fab insulated piping systems, but I've always found them extremely expensive, long delivery, and didn't stand up very well. The field joints on the insulation jackets always seem to be a problem. Leaks show up in the jackets after a couple of years (almost always at a jacket field joint), and the vendor and contractor point at each other as to who's at fault. The owner of the line typically winds up eating the repair cost - big surprise.

We insulated the steam lines in Foamglas, then heavy roofing paper (mostly to keep the dirt out from between the cracks in the insulation), and direct buried them. These have lasted for years, going on decades now - as long as they're kept HOT.

The only other solution to your problem involves a tunnel, or a duct with some ventilation. That's expensive up front, and often there isn't room in the ground to allow for it.

We have had good luck with steam piping(API Cast Steel Valves) installed in concrete chases/trenches/small tunnels (whatever you want to call them) which are just big enough to place the piping in the trench, weld it up, insulate it, properly guide, anchor and support it.  Some of these systems have lasted up to 50 years (maybe longer?).  The piping is seamless A53 grade B, insulated with foamglass and covered with perforated aluminum jacketing.  We are running at 60 psig, 420F and return all of our condensate.  We have tried to stay away from preinsulated piping for the reasons mentioned by TBP, I will tell you though that we do have a 5000ft ricwil system that is about 40 years old, just starting to cause us problems because of the outer casing failing and condensate piping forming tubercules and failing from the inside out.  This system doesn't even have any sacrificial anodes, that we know of.  Today's systems do have sacrificial anodes which will help out alot.  If you do go the preinsulated piping route, stick with a drainable-dryable class A system.  Also would stay away from foams.  Let me know if you want any of our standard specs for chase systems.

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