For pipeline construction application, there are 16 points t

Time:2014-09-11 13:02

Whether a construction project stands or falls all depends on various details. Therefore, based on my personal experience and the experience of others, , the problems that should be avoided in the construction of water supply and drainage pipelines are summarized as below with reasons and solutions also provided. Let everyone use this as a reference !

I. Rain pipes shouldn not be connected with expansion joints or coupling.

Reason: The walls of rain pipes are relatively thin and a vacuum is easily formed in the pipeline during a rainstorm, causing the pipe to flatten or even crack by the air pressure.

Solution: When installing the pipes, they must be connected with bell-and-spigot joints. The bell-and-spigot joint have two main functions: First, for connecting the pipes; Second, it is used for ventilation and overflow, and offsetting expansion allowance.

II. PE and PVC-U pipes cannot be used for hot water

Occasions for usage:

1. Normally, the temperature of water flowing through the PE pipes should not exceed 40℃;

2. Normally, the temperature of water flowing through the PVC-U pipes should not exceed 45℃;

Case: A customer from Ma On Shan chose our PVC-U supply pipes D501.0MPa, which were connected to the pipeline of a solar heater without consideration of the circumstance of hot water return. Because the pipes were often loaded with hot water, it finally resulted in the D50 pipes becoming seriously deformed by heat with the outside diameter expanding to 110.

III. Water supply pipes should not be backfilled and concealed without the premise of a pressure test.

Reason: This test can be used for testing hardness and air tightness, thereby avoiding pipeline leakage which results in greater loss.

Solution: After being installed, water supply pipes should first be tested like above in accordance with the related technical instructions. Once the condition of leakage is ruled out, then the pipes can be backfilled and concealed.

IV. The supply pipeline with a great drop cannot function without a venting device

Reason: When the pipeline drop is great or the distance is large, a water hammer or vacuum will be formed inside the pipeline, causing the pipeline to flatten or crack.

Solution: Exhaust valves should be installed to eliminate any water hammer or vacuum.

The role of exhaust valves: 1. eliminating water hammer; 2. supplying air to remove negative pressure.

Case: In the construction that occurred in places like Quzhou, Changshan county or Lishui county, vacuums and negative pressure were formed inside the pipes because exhaust valves were not installed, causing the pipes to flatten and break.

V. In the summertime, the pressure test for PE supply pipes should not be performed at noon or in the afternoon

Reason: PE pipe material has a property to very easily absorb heat from the atmosphere, thus raising the temperature of water inside the pipes to around 50℃. Therefore, when the test is done at high temperatures, the pressure test for the pipes should be calculated by choosing the corresponding reduction factor based on the actual water temperature. (as follows in this table)

Case: For the rural secondary water supply project in Cixi, the pipes were installed in the summer and the pressure test was done in the afternoon when the air temperature was higher. The pipes were exposed to strong sunlight and absorbed a great amount of heat, causing the water temperature to rapidly increase. Thus the pipes were cracked when the test started. However, when the test was done in the morning when the air temperature was relatively low, the pipeline functioned normally.

VI. When installed under floors, PP-R hot water pipes should be fitted with clamps

Reason: PP-R material has a greater linear expansion coefficient, indicating less influence from thermal expansion when filled with hot water. The result is that the pipes embedded under floors are deformed and hunched up, thus raising the floors.

Solution: Pipes must be fixed with a certain number of pipe clamps depending on practical situations.

Case: A user from Linping, Hangzhou installed the hot water pipes under floors without using clamps, the pipeline expanded when filled with water, causing all the floors to raise up.

VII. In winter, electrical casing should not be bent with overexertion

Reason: The toughness of electrical casing will drop greatly at low temperatureand will crack the pipes when bending.

Solution: In winter when the temperature is relatively low, it is preferable to rub the part to be bent to produce heat, then bend it with a spring.

VIII. Before the welding of PE or PP-R pipes, it is necessary to clean the heating plate, the die head surface, and the pipe end to be welded

Reason: When welding PE or PP-R pipes, weld defects will be formed due to the impurities on the heating plate, the die head surface, and the welded end of pipes, causing pipeline leakage.

Solution: The heating plate, the die head surface, and the pipe end to be welded must be cleaned before welding.

Case: Gaotai County Running-water Company used our PE D315 supply pipes, of which the surface to be welded was not cleaned, causing leakage to occur in the pipeline after welding.

IX. A flat flared end should not be used for PVC supply pipes D110 or above

Reason: The large-diameter PVC supply pipe has a large taper on the flat flared end and it is hard to completely insert the pipes and flat end into the flat flared end, resulting in leakage at the joints.

Solution: The PVC supply pipes D110 or above usually use a lapped joint or socket to be connected.


X. PP-R hot water pipes should not be exposed to the outdoors for a long period of time.

Reason: PP-R material has poor aging resistance.

Solution: Concealed laying or the addition of a protective layer

Case: A user from Xiaojiang Township, Xinchang County used the PP-R pipes as outdoor pipes to connect a solar heater, which cracked after only two years of outside use.

XI. In high-rise buildings, PVC-U drainage pipes should be fitted with energy dissipators.

In high-rise drainage, water has a high potential energy which can damage elbow and horizontal branches very easily. Therefore, when PVC-U drainage pipes are used in high-rise buildings greater than or equal to 20m, the vertical pipes should be provided with energy dissipaters for every six floors.

XII. Coupling expansion joints should not be used in horizontal pipes

Reason: Coupling expansion joints have a poor sealing performance, easily causing horizontal pipe leakage .

Solution: Horizontal pipes normally use expansion joints, preventing the pipeline from leaking.

XIII. The welding temperature of PE or PP-R pipes should not be too high

Reason: Due to the characteristics of various materials, and their material degradation at high temperatures, carbonization can take place.

Solution: 1. Normally, the welding temperature of PE pipes is 200℃~240℃; 2. PP-R is normally 200℃;

Case: A company in Anqing City used our PE pipes D50 products and were consequently welded at 300℃. One year later, a large leakage occurred to the welded junction. Lianyungang Guanyun Hotel chose the PP-R pipes D63, which were also welded at 300℃, and a leakage occurred at the junction when a pressure test was done.

XIV. Reinforcement measures should be taken at the bend of large-diameter PVC-U pipes

Reason: The water impact force at the bend is greater, which can easily damage the pipeline.

Solution: A cement block is provided at the bend as reinforcement.

XV. Water should be drained from PE-RT pipes in a timely manner when not being used

Reason: Water will freeze and expand, breaking pipes at low temperatures.

Solution: Water must be drained in a timely manner from the pipeline when not being used.

XVI. Normal PP-R hot water pipes are not recommended for high temperature radiators, especially for small household boilers, in which case PP-R stable static pipes are recommended

Reason: The water temperature of high temperature radiators are generally greater than 70℃. Long-term usage will shorten the life of the pipes. The heating temperature of small household boilers is relatively high, the water is often boiled, and the pipeline is short, in which water temperature is changeable, seriously affecting the normal use of pipes.

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