PE pipe is a new type of water supply pipe produced by extrusion moulding process with polyethylene resin as the main raw material. There are three kinds of connection modes: hot melt, electric melt and mechanical connection. PE water supply pipe has the advantages of corrosion resistance, non-scaling, good hydraulic conditions, light weight, long service life (50 years of service life), good flexibility (breaking elongation up to 500%, strong adaptability to uneven settlement of foundation), good impact resistance and seismic performance. Moreover, the construction connection is simple, convenient and fast. Compared with spheroidal graphite cast iron pipes and steel pipes of the same caliber, PE pipes below DN300 have a high cost performance ratio.

In recent years, the application of PE water supply pipe in water supply projects has increased rapidly, and it has become the preferred material for water supply projects. However, PE pipe also has some shortcomings, such as high temperature resistance, sun exposure, higher longitudinal elongation of lower pipeline (nearly 3%, more than 10 times of steel pipe), metal detector can not locate, higher maintenance cost after high failure of PE water supply pipe, etc. Measures should be taken actively in design and construction.

Common Faults and Reasons in Construction and Installation

1.1 Inadequate material management

(1) Frequent bursting and leakage of PE pipes after 3 months of opening water in a newly installed PE pipeline were checked. PE pipes and fittings were not supplied by the same manufacturer, and a batch of PE pipes and fittings were not produced by the same manufacturer in the same batch. The chemical properties were inconsistent, and the bonding at many hot-melt joints was not reliable.

(2) Due to the influence of freezing rain and snow weather and spring transportation, PE pipes were delayed in the renovation site of a PE pipeline. After emergency repairs of various PE pipes in stock, water leakage occurred in many joints of the pipeline, which caused heavy losses to construction units and owners. It was found out afterwards that the leakage was due to the mixing of PE pipes from different manufacturers.

(3) In autumn, a newly installed PE pipe bursts longitudinally after it is opened to water. After investigating PE pipes stored in the open air, the quality of PE pipes deteriorated and brittle after high temperature exposure in summer.

1.2 PE pipe damaged by internal stress after thermal expansion and cold contraction

(1) PE pipe contraction and extension device: at about 2:00 p.m. of the dn200pe water supply pipe just installed in the afternoon of July 2006, the expansion device at the interface with the cast iron TEE was cracked, and the water gushed out lasted for more than 2km and the water leakage loss exceeded 2000m3. The test results show that the stretcher can withstand 12 kgf/crn2 stress (1 kgf/cm'=0.1MPA) and the stretcher is a qualified product. The cause of the accident is that PE pipe has a large coefficient of thermal expansion and cold contraction, and the pipe backfilling has not been laminated and compacted, resulting in PE pipe contraction and expansion after cooling at night.

(2) PE pipe shrinkage causes ductile iron pipe socket to pull off: on a winter day in 2006, at about 0:00 p.m., the ductile iron pipe connected with the newly installed dn200PE pipe pulled off the socket from the socket and the socket spacing exceeded 12 cm, resulting in water flooding nearby construction sites. Water leakage exceeded 1500 cubic meters. The accident was caused by the shrinkage of PE pipe in winter, which caused the ductile iron pipe to be pulled out, resulting in leakage of water in the pipe.

(3) In the spring of 2007, when the DN200 and DN50 straight pipes in a residential area were connected by diameter change, the dn50PE pipes were twisted and bent from the diameter change after thermal expansion and elongation. Under the impact of high-speed water flow for a long time, cracks and leakage occurred at the bend.

(4) During the Spring Festival, the joint of PE pipe water meter bursts after the water accumulated in a water supply pipe gallery freezes.

1.3 Unreasonable Pipeline Installation

(1) Users of DN50 branch pipes newly installed with dn100PE pipes in winter have little water pressure during the day and at night. Preliminary analysis shows that the pipeline leakage, after repeated investigation and analysis, section excavation inspection failed to find the original Gang. Finally, the pipe joints were sawed off, and it was found that the excessive welding at the hot-melt joints resulted in radial necking of water supply and drainage, and the pipeline was almost blocked by water flow, resulting in long-term water-free for users. The pressure test records of this section of pipeline are all qualified, and it is difficult to find them without flow analysis. The hot-melting time of PE pipes in summer and winter should be carefully controlled. It is easy to form radial necking when the welding time is too long to affect the flow rate. On Hot Melt Docking Time Hot Melt Socket Connection

(2) Water leakage occurs after opening tees with cast iron clamps on a PE main pipe. It was found that the shrinkage of PE main pipe after cooling resulted in the dislocation of the attached clamp and water leakage at the tee. Cast iron clamp is not suitable for PE pipe opening tee connection branch pipe. Standard PE tee pipe fittings and fuse sleeve connection are recommended.

(3) The bottom of a dn200PE pipe leaks after one and a half years of installation. The reason for inspection after excavation is that the base of the pipe is not made of sand cushion, and the residual flat iron and scrap cast iron pipe breaks through the PE water supply pipe.

(4) A PE pipe passes through the sewage well from the inside of the casing, brittle fracture occurs only 8 months after installation. The reasons for the investigation are as follows: the casing is not tightly sealed and the domestic sewage with high temperature is immersed in PE pipe for a long time, resulting in the brittle fracture of PE pipe after denaturation.

(5) After the excavation of a leaky pipeline, carefully observe that there is a little sediment adhering to the hot-melt joint, which leads to water seepage of the pipeline joint. The installation of PE pipe in this section coincides with the blowing sand weather, and the sewage cross flow and debris are easy to adhere to the hot-melt welded pipe joints.

(6) When the water meter is removed during the maintenance of a PE pipeline, the pipelines at both ends are dislocated and can not be installed. The reason for inspection is that the concrete is poured unilaterally during the pouring of pipe piers and piers, which causes the pipe to be distorted and distorted.

(7) When a water supply pipeline opens three-way, because the main pipe valve closes and stops water not strictly, there is wired flowing water at the three-way interface of the welded fuse sleeve, and the weld seam has seepage phenomenon.

PE water supply pipe in construction

Above are some faults caused by mistakes in the construction and installation of PE water supply pipes. In order to avoid re-construction and bring economic and manual losses, it is necessary to strictly follow the standards in the construction process.