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:
There are companies who operate worldwide that are experts on galvanic
- 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
- 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
- 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.
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.
- 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.
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