Why can polyurethane insulation composite pipe be buried directly?

Why can polyurethane insulation composite pipe be buried directly? The benefits of using the direct burial method are self-evident, but this method puts forward higher requirements for the insulation pipeline, mainly its maintenance and service life problems, which is particularly harsh
for the anti-corrosion of the insulation pipeline.
The high-density polyethylene sheath pipe outside the polyurethane insulation layer is its ** protection, most of the plastic is difficult to be degraded in the natural environment, especially the high-density polyethylene is more resistant to corrosion under environmental conditions after being buried in the ground, even if it is wet, microorganisms, and even in the acid and alkali salt medium is still relatively stable; In addition, its water-vapor transmittance is extremely low, which can effectively protect polyurethane insulation pipes
.
Due to the closed cell structure, the polyurethane also plays a certain protective role in the outer wall of the working steel pipe, so that it is protected from the corrosion of the outer wall of the steel pipe from the
external environment.
This composite insulation pipe solves the two major problems of anti-corrosion insulation, and the service life in the underground can be more than 20 years, and it does not need to be maintained
during the operating year.
Of course, this is only an ideal situation, and there have been many problems in practical applications that have caused a decrease
in service life.
The main reasons for its emergence are as follows
.
(1) The insulation layer is eccentric, that is, the polyurethane insulation layer is different from the steel pipe, forming an uneven insulation thickness, which can soften the outer layer of plastic and be damaged
.
(2) Improper use and damage, susceptible to damage during transportation and installation, insufficient depth from the ground after burial or soft upper soil and road, resulting in damage
to the load vehicle after being crushed.
(3) improper interface treatment, in the process of pipeline laying and installation, the welding of the two pipes is not tight to cause water leakage, or the operation is not serious in the process of "filling the mouth" and causing damage
caused by the infiltration of external sewage into the insulation layer.
(4) The use of plastic and polyurethane insulation pipe is unreasonable, such as the use of sorting and messy recycled plastic, after extrusion molding plastic pipe can not be fully plasticized and lead to the deterioration of
the outer pipe.
The low density of polyurethane insulation pipe causes low strength and has been damaged during handling, and the system contains free acid that is too high, resulting in corrosion of the outer wall of the steel pipe
.