There are two types of pipes mainly used for different medium transporting: Type one is the metal pipes; Type two is the plastic ones. Among the metal pipes, the steel pipe has been playing a leading role for a long history because of its low price and high stiffness and strength. Therefore the steel pipe also has some disadvantages like bad performance in wear resistance, easy to be worn off, not easy to get connected and so on, so people always want to develop some new kinds of pipes to replace it. Although the stainless steel pipe and the copper or aluminium ones have a better corrosion resistance in certain cases, but the cost is too high for the long distance transporting project. Since the begin of their industrial production, the plastic pipes have been widely used in kinds of areas, especially in water supply and drainage pipelines construction, they are taking the place of the traditional steel pipe in a great amount. However, the single plastic pipes have their own fatal drawbacks in: One poor thermal resistance, the temperature can not be higher than 60℃ for a long term use; Two bad stiffness and bad compression resistance, so they cannot replace the traditional steel pipe widely. For this reason, many research departments and companies are competitively developing new types of the pipes in a better performance and a better price.
UHMWPE(Ultra High Molecular Weight Polyethylene)floating Pipe and Steel Lining-UHMWPE Composite Pipe
Ultra high molecular weight polyethylene is an excellent engineering plastic, it has the highest properties in wear resistance, impact resistance and low temperature resistance in all kinds of the engineering plastics, especially for its wear resistance and self-lubrication, which are all superior to the other plastics. However its melt viscosity is high with a poor fluidity because of the ultra high molecular weight (about 1.5 million ~ 4 million ) of UHMW-PE, so the extrusion speed of the pipe is slow, which leads to a long production period. Characteristics of the UHMWPE pipe:
1. Impact resistance of the UHMWPE pipe. It has the best abilities in environmental stress cracking resistance and scratching resistance in all kinds of plastics, in which its impact strength in the normal temperature is more than 9 times higher than PE100, while the temperature goes down minus 30 ℃, the impact resistance is 15 times higher than PE100; the cracking resistance ability of the UHMWPE is about one times higher than PE, and when the temperature goes down, the impact resistance of the UHMWPE gets higher. Its extraordinary flexibility makes it can defense kinds of impact from external forces and withstand the crustal deformation without a composite with the steel pipe, therefore safer and more reliable than steel pipe.
2. Wear resistance of the UHMWPE pipe is 3~6 times higher than that of steel pipe, 1.3 times higher than that of PE pipe, so it can make a better transporting for the slurry in a small particles.
3. UHMWPE pipe is in a saturated molecular group with a very stable chemical ability, it can resist to kinds of corrosive medium and erosive organic solvent, so it can be more corrosive than other plastics like PE, polypropylene, nylon, ABS ect.
4. UHMWPE pipe holds a non-adhesive ability and its chemical and physical polarities are lower than normal plastics, for example, the polarity of PE is 9 while that of UHMWPE is only 1, which is surely lower than that of metal materials, so it doesn’t work to it for the normal adhesive agent. So do the scaling materials. As long as the slurry velocity of flow reaches 2.3 ~ 4.6 m/s, scaling can not be formed. Even if the scaling layer is formed after a long time accumulation, it will not be solid and can be removed easily. And it is not need to add any corrosion inhibitor for the acid pickling, after which the surface can be as smooth as new without causing any damage to the pipe wall.
5. Theoretically speaking, service life of the UHMWPE pipe can be up to several hundred years, because the aging rate and embrittlement speed of UHMWP5. Theoretically speaking, service life of the UHMWPE pipe can be up to several hundred years, because the aging rate and embrittlement speed of UHMWPE is very slow, to use it underground for 50 years, its mechanical ability just goes down about 20%. With a same UV resistance ability with PE100, the aging property of UHMWPE is superior to PE100 pipe for about 1/4. E is very slow, to use it underground for 50 years, its mechanical ability just goes down about 20%. With a same UV resistance ability with PE100, the aging property of UHMWPE is superior to PE100 pipe for about 1/4.
6. The friction coefficient of the UHMWPE pipe is just 1/6 of that of the new steel pipe, 1/5 of normal PE pipe, 1/20 of rubber pipe and 1/2 of polypropylene pipe. The flow coefficient “C”of UHMWPE pipe is 160, for the new steel pipe, its flow coefficient is just 130, however the coefficient of old steel pipe goes down to 95, and the “C” coefficient of the steel pipe even down to 60~80 when it is used in the dad conditions of slurry transporting. What’s more, the wear resistance, non-adhesion and corrosion resistance of UHMWPE can make the wall surface keep smooth, leading to a flow capacity 50% higher than steel pipe, and make the transporting system keep a good flowing condition in a low pressure for a long time.
7. With a relatively high tensile yield strength and elongation break, the thermal deformation temperature of the UHMWPE pipe is tens of degrees higher than the normal plastics, however its brittleness temperature goes down nearly limitless, together with a 100% coefficient of elongation, the pipe can bear relatively great stress in a large range of temperature, while absorbing impulse load and the water pressure fluctuation when shutting it down.
8. The welding process of UHMWPE pipe is easy, convenient and effective, and the strength of the welding line even surpasses the pipe body, which is providing a convenient for installation of the long distance pipeline, especially for installing the middle-high and high pressure pipes. Needs no anti-corrosion treatment, the UHMWPE pipeline can be handled and laid conveniently and it allows the changing of the pipeline direction according to the terrain changes. The installation cost of the UHMWPE pipe is usually just one fifth of that of steel pipe and steel-plastic composite pipe.
9. Cost Effective of UHMWPE Pipe. Especially for pipes in middle large diameters used in low pressure pipeline, the total project cost is definitely less than the cost for a seamless pipeline project, and also less than that for the composite pipeline project and alloy metal one, but service life of the UHMWPE pipe is more than 5 times longer than that of steel pipe, and 3 times longer than composite pipe.
10. UHMWPE pipe is applicable to be used as crude oil gathering pipeline because most of the pipelines have been laid in some remote areas with some disadvantages like a complicated land features of terrain and a great changeable climate and so on. With the advantages in light weight, easy installation, high ability in low temperature resistance, anti-aging, the UHMWPE pipe is more outstanding when used for the oil gathering pipeline project.
11. Thermal Insulation Property: heat conductivity coefficient of UHMWPE pipe is much lower than that of steel pipe, because of which, except for some special requirement, the insulation measures doesn’t need to be taken to the UHMWPE pipe generally.
UHMWPE-Steel Composite pipe solved the disadvantage in cannot withstand high pressure of plastic pipes, by compositing steel pipe together with UHMWPE pipe, the pipe is not only high pressure resistant but also wear resistant which can bear the pressure more than 10MPa.
Information Abstracted from chinabaike.
The main material for PEX pipe is HDPE, which makes use of the high energy ray or chemical initiator to transfer the linear molecular structure to be space net structure. The pex pipes could work under 0.2 to 2.0Mpa pressure rate under temperature of -75℃ to 110℃.
Pex pipes have excellent ECRS, thermostability, creep resistance, tear resistance and notch crack resistance, overcoming the sensitivity of common polyethylene to filling material, such as fortifier, conductive filler, and fire retardant additives, etc.
The pex pipes using no matter chemical methods or mechanical methods to make HDPE cross linking, which largely improve its performances of polyethylene. After cross linking, the heat resistance and strength, anti-aging, anti-ECRS, electrical insulation, fire resistance, permeability, creep resistance, etc. But its disadvantage is inferior to wear resistance and pressure bearing capability.
polyethylene-aluminum Composite pipe
The outside and inside surface of polyethylene-aluminum Composite pipe is HDPE pipe or pex pipe layer, and the middle is welding tube of aluminum plates. The aluminum tube will b adhered with the polyethylene lining layers by adhesive. The disadvantage is that the internal polyethylene is easy to be pulled off with aluminum pipes after long time working.
Plastic lining Steel pipes
Plastic pipes, like PVC pipes, PP pipe, PE pipes have very good corrosion resistance, but with lower pressure bearing capability. Although the pex pipes give the solution to the heat resistance and anti-aging, the ring stiffness and pressure rate is comparatively lower, and it has poor property of gas and liquid separating. The above problems limited its wide application. The GRP/FRP pipes has lower costs, but with poor wear resistance. The plastic lining aluminum pipes and steel pipes have higher pressure rate, but easy to separate after long time working due to the different linear expansion coefficients between the metal pipes and plastic pipes. The UHMWPE plastic lining steel pipes, manufactured by Shandong Buoy&Pipe Industry perfectly found solution to this challenging problem. The UHMWPE lining have good wear and corrosion resistance inside, and the outside steel pipes helps to bear higher working pressure.
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