Application characteristics of PE pipe engineering
(1) Good sanitary performance and thermal insulation performance. Good corrosion resistance, no chemical action on all ions in the water, no rust, not only for hot and cold water systems, but also for direct drinking water systems. The thermal conductivity of PE pipe is 0.21W/m · k, which is only 1/200 of that of steel pipe. In general, insulation is not required. When used for hot water pipes, insulation and energy saving effect are obvious. The expansion force generated when the temperature changes is also small, which is suitable for direct burial and concealed laying in the wall and floor surface
(2) Good heat resistance and long service life. The high working temperature of pipes can reach 95 ℃, and the long-term service temperature under 1.0MPa pressure is 70 ℃. The service life under normal temperature can reach more than 100 years.
(3) Convenient installation and reliable connection. The pipe is not only simple in production process, less equipment investment and light in weight. Its weight is only 1/9 of steel pipe and 1/10 of copper pipe, reducing the construction intensity of workers. The pipe material is processed with the same raw material, with good hot melting function, easy and reliable installation, the strength of the connection part is greater than the pipe body, and the pipe structure does not affect the flow. In addition, the pipeline resistance is small, the inner wall of the straight pipe is smooth and will not scale, and the sectional area of the pipe fittings will not change when connecting.
(4) The waste materials of pipes and pipe fittings can be recycled. After cleaning Ultra wear-resistant composite pipe It can be directly used to produce pipes and pipe fittings after crushing.
PE pipes are mainly used in cold and hot water systems, direct drinking water systems and heating systems (including floor radiation heating).
The main disadvantage of PE pipe is that its rigidity and impact resistance are worse than those of metal pipes. Civilized construction shall be paid attention to during storage, transportation and construction; In the design and construction, special attention should be paid to the setting of supports, proper selection of expansion devices, and correct laying of pipes; Poor UV resistance, aging under long-term direct sunlight; Under the same outer diameter, the effective flow section is smaller than other pipes.
3. Discussion on some problems in engineering application
3.1 Selection principle of PE pipe
(1) Correctly distinguish the use of pipes and reasonably select cold and hot water pipes. Cold and hot water pipes have different wall thickness, different pressure resistance and different prices. The cold water pipe or hot water pipe shall be specially noted during design. The pressure bearing of PE pipe has two remarkable characteristics: first, with the temperature of water in the pipe rising, its allowable pressure will drop sharply; The second is that the bearing time increases, and the allowable pressure also decreases significantly. Considering the long-term service life of the pipeline and abnormal factors in construction and actual use, for safety needs, the nominal pressure level selected for the cold water pipe is the large working pressure of the system multiplied by 1.5 times the safety factor, and the hot water pipe multiplied by 3.0 times the safety factor. The pressure grade of the selected pipes must meet the pressure bearing capacity at the working water temperature.
(2) The current code for design and construction acceptance of building water supply and drainage indicates that the plastic pipe diameter specification is the nominal outer diameter, the symbol is De, and the unit is mm. The pipe diameter specification of super wear-resistant composite pipe plastic pipe is different from the nominal diameter DN (mm) described in the Standard for Water Supply and Drainage Drawings. Special attention should be paid to the pressure level and pipe diameter specification in design calculation, material supply and construction organization.
Anti pipe use. PE pipe has low oxygen index and belongs to combustible material. The super wear-resistant composite pipe shall not be used in the fire water supply system.
3.2 Arrangement and laying of PE pipe
PE pipe laying should be concealed. If it is directly embedded in the wall or laid in the building surface, its friction can be used to overcome the expansion force caused by the temperature difference of the pipeline. In addition, it is beneficial to heat insulation and avoid aging.
Concealed laying methods include direct buried concealed laying (including embedded wall laying and floor surface laying) and indirect buried concealed laying (including laying in pipe shaft, ceiling, behind decorative plate and floor overhead layer).
When the pipe is embedded in the wall and laid in a concealed manner, it is required to reserve a groove with the cooperation of civil engineering. The depth of the size is De ＋ 20 mm, and the width is De ＋ (40 ～ 60) mm.
Concealed laying of pipes in the ground layer shall be constructed according to the drawing. If there is any change, it shall be noted on the construction drawing to avoid damage during ground decoration.
3.3. Installation, connection, pressure test of pipes and methods for penetrating walls, plates and foundations
(1) Installation and connection of pipes. PE pipe fittings of the same material shall be connected by hot melting, and the concealed part shall be free of screw thread and flange connection
Hot melt connection is applicable to plastic plastics of the same material. Melt and bifurcate the originally closely connected molecular chains of the material, heat them for a certain time, connect and fix the two parts, and establish joint pressure in the fusion zone.
Hot melt connection includes butt type hot melt connection, socket type hot melt connection and electric melt connection. The last two methods shall be adopted for water supply pipeline of super wear-resistant composite pipe building.
(2) Pressure test of pipeline. The test pressure of the cold water pipe is 1.5 times of the working pressure of the pipe system, but not less than 1.0 MPa; The test pressure of the hot water pipe shall be twice the working pressure of the pipe system, but shall not be less than 1.5 MPa
(3) The practice of pipe passing through walls, slabs and foundations. When the hot water pipe goes through the wall, the steel casing shall be set in coordination with the civil engineering. The cold water pipe can have a hole reserved through the wall, and the hole size is 50 mm larger than the outer diameter; When the pipeline passes through the floor or roof, the steel casing shall be set, and the casing shall be 50 mm higher than the ground, and strict waterproof measures shall be taken; When the pipeline passes through the foundation wall, a metal casing shall be set. The clear distance from the reserved hole on the foundation wall to the casing shall not be less than 100 mm.
