Underground Application of Plastic Lined Piping Products

There is not single standard, specification, or plant practice that completely covers the subject of underground piping. Since there is no standard practice, this technical bulletin will only provide general guidelines for underground pipe. In general, we do not recommend using flanged or flared pipe in an underground application if an alternative method can be used. Typically, plastic-lined pipe is used to transport corrosive or toxic fluids and with today's ecological emphasis, one cannot afford an underground leak. When a leak occurs underground, a large amount of material may be lost before the leak is detected. This may lead to a multitude of problems including an expensive clean-up. There are times, however, when a plastic-lined piping system has to be buried. Typically, end users of our piping systems have engineering specifications regarding underground piping which deal with the environmental risks. Also, the Local, State, and Federal engineering guidelines which pertain to underground piping, should be consulted. If you are going to use Resistoflex Plastic Lined Pipe in an underground application, we recommend the following: Use CONQUEST® flangeless piping where possible to reduce maintenance requirements and the possibility of leaks. Make sure that all necessary approvals have been obtained. The trench width should be wide enough to accommodate a torque wrench. We recommend the use of a torque wrench with all of our piping. Do not assemble pipes until they are lowered into the trench. Leave the end protectors on until assembly and keep the plastic faces clean. Both of these measures will help prevent damage to the plastic sealing face. The pipe itself has to be protected. There are several recommended systems that will accomplish this: A good pliable epoxy primer followed by two coates tar epoxy, such as Tar Set Standard, to a minimum of 15 mils. If the pipe is to be taped, the pipe should be primed for taping with a primer recommended by the tape manufacturer. The tape should be pressure sensitive adhesive backed polyvinyl chloride, polyethylene, or as approved by the architect/engineer. There are many more systems. To assure maximum corrosion protection of the buried pipeline, cathodic protection is normally specified to supplement the protective coating system. There are several considerations involving cathodic protection including: electrical continuity in the system, the soil resistivity, and types of electrical power available. There are companies who operate worldwide that are experts on galvanic corrosion protection. The system should be pressure tested 1.5 times the rated working pressure. The test pressure should be maintained for 24 hours and then the bolts should be re-torqued if necessary. Ideally, after the first thermal cycles of the system, the bolts should be re-torqued. When the integrity of the system has been assured, then the trench can be backfilled. The backfill material should be free of rocks, cinders, refuse, and other rough materials. The backfill should be layered in and tamped after each layer. The above is a list of some of the major considerations for the underground installation of pipe. Resistoflex Plastic Lined Pipe does not recommend burying plastic lined pipe, however, by following the above recommendations, and strictly adhering to Local, State, and Federal regulations, the likelihood of problems will be minimized.