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I have consulted on and dug up many multimillion-dollar failures of pipe insulation systems. It can get muddy! Most of my professional engineer peers ignore the fact that at some time, piping systems will be underwater — not a good situation.
I suggest you hire a geotechnical engineer to tell you at what depth groundwater will be present. In some areas of the country, it will be safer to install pipe aboveground.
As a general rule, the hotter the pipe, the greater chance the insulation system will fail. Another common error is to backfill with sand. This creates a place for rainwater to collect. It is OK to place sand a few inches around the piping, but the remainder of the backfill should be the original dirt. I wouldn’t recommend loose-fill products, either.
Thermal expansion of the pipe must be carefully designed; I prefer a U configuration. Any manufactured expansion device must be in a manhole. Do not put hot pipe and cold pipe in the same trench; I have seen too much PVC piping destroyed by the heat from the hot pipe. Before the trench is filled in, carefully (with a mirror on a stick) inspect the underside of the insulation system for holes in the water barrier.
In absolutely dry soil, you could insulate the pipe with old copies of Plumbing Engineer; however, if the piping is anywhere where it rains, I wouldn’t recommend this approach!
• Southern Louisiana. This project was a church facility near a river. The grass above the underground pipe was burnt from the heat of the steam piping and the basically nonexistent insulation.
The lawyers wanted to know if the insulation was installed per the specs; the answer was yes. When a nun flushed a toilet, the water was very hot. The “chilled water” was 110 F due to being in the same trench with the failed insulated steam pipe.
We dug up the heavy clay soil and found that the pipe insulation had dissolved in many locations due to the failed water barrier on the insulation and the heat from the steam pipe. The ground was very wet.
Due to the high groundwater on this site, the piping was rerouted above the ground. The contracting firm was off the hook because it had followed the engineer’s spec. The engineer, however, was not so fortunate.
• Southern Michigan. The steam pipe (700 F) was 20 inches in diameter and almost 17 miles long. The pipe thermal expansion was quite a few feet in total. The insulation was applied in the field and only a single layer. In some areas, the pipe was 15 feet belowgrade; in others, the water table was 3 feet belowgrade.
When they turned the steam on, the pipe expanded much more than the insulation exposing the bare pipe. Groundwater hit the 700 F pipe and exploded, sending the pipe insulation 30 feet into the air in areas that had not yet been backfilled. It was quite expensive to fix.
• Quebec. Another steam pipe job with single-layer, field-applied insulation in a paper plant. One area that was abovegrade was a 3-inch gap with bare pipe; the pipe had expanded more than the insulation. It was suggested that the workmanship was faulty.
The pipe insulation manufacturer sent its No. 1 technical service person to the site. We had a little contest. The technical service person and a local insulation contractor employee each insulated a 6-foot section of pipe. We then put the two test sections to a water leak test. Both failed. The contractor was not to blame; it was a faulty design that failed.
• Central Kansas. This was a maximum-security prison; the state’s attorney general hired me. There were a few miles of buried hot water pipe at a campus-style facility with sidewalks connecting the various buildings. Everywhere you looked, little clouds of moisture were coming out of the ground; there was no question as to where the piping was buried.
The state provided us with a backhoe operated by an inmate, plus several inmates with shovels. It was a typical loose-fill insulation application with 4x4 pipe supports. The insulation was saturated with water, and the pipe was corroded.
The entire system was replaced with a conduit system.
• Western Iowa College. The PVC conduits were factory-supplied with kits for waterproofing the conduit joints. After the system failed, an inspection showed that the contractor had sealed the visible areas but left the hidden areas unsealed. So, the college replaced the whole system.
The next system featured PVC conduit with urethane foam insulation. The heating pipe was buried next to the chilled water pipe. When I was called to inspect the newly failed system, the chilled water PVC pipe had “melted” or softened up from the heat from the failed hot water pipe.
Once again, the joint workmanship was lousy and everything had to be replaced.
• Rhode Island College. This was a large campus with thousands of feet of a buried conduit system. It was winter and steam gushers were everywhere on campus due to the failure of the underground steam pipe insulation system.
There were many manholes in the system for valves and expansion devices. The design engineer specified sump pumps in all the manholes; however, school officials felt that pumps in every manhole were an unnecessary expense so they were not installed (a very costly error). The manholes filled with groundwater and rainwater. The naked ends of the conduit system in the manholes filled with water and destroyed the insulation.
It was a very expensive mess; the school had to buy a bunch of sump pumps.
• California University. This was a beautiful campus with brick walkways and expensive landscaping. The heating pipe was installed in concrete trenches — 4-feet wide and 3-feet deep with a concrete slab cover. Somebody (without thinking) specified self-stick asphalt jacketing for the insulation cover.
The other error was the insulation thickness was only 1 1/2 inches; it should have been 3 inches or a different attachment. The self-stick jacket was too hot and the insulation fell off the pipe — an expensive but straightforward aspect of the problem.
In this article, we have tried to show the things not to do when designing and installing insulated underground piping. There are some excellent products and systems that work on the market for this application if you do your research.
William A. Lotz, a consulting engineer in St. Albans, Vt., has a degree in mechanical engineering and is a licensed PE in eight states. His work career includes several years with insulation manufacturers and insulation contractors — plus many more years as a consulting engineer designing and troubleshooting pipe insulation problems. Lotz has more than 300 articles in the trade press and recently published his first book, “Moisture Control and Insulation Systems in Buildings, Chilled Water Pipes and Underground Pipes.”