Plastic pipes

UT for Plastic Pipe extrusion. State of the art, 20 chapters inch 30 Fig.,... 

As early as 1966, natural gas was available to all of the lower 48 states in the United States. During the period 1967—1990, the U.S. transmission system grew from 362,700 km to 450,800 km. Over this same time period, the distribution mains increased from 867,800 km to 1,347,000 km. As plastic pipe and reUable joining technology became available, the use of plastic pipe expanded to include the distribution of gas in low pressure systems. By 1990, approximately 24% of the U.S. distribution system was based on plastic pipe (1). 

Liquids. Liquids usually are moved through pipelines (qv) by pumps. Special alloys, plastic pipe and liners, glass, and ceramics are widely employed in the chemical industry for transport of corrosive hquids. Care is required in making the connections, to prevent exposure of unprotected metal such as flanges and bolts to the corrosive material inside the piping. 

Example 10 Response to Instantaneous Valve Closing Compute the wave speed and maximum pressure rise for instantaneous valve closing, with an initial velocity of 2,0 m/s, in a 4-in Schedule 40 steel pipe with elastic modulus 207 X 10 Pa, Repeat for a plastic pipe of the same dimensions, with E = 1.4 X 10 Pa. The liquid is water with P = 2.2 X 10 Pa and p = 1,000 kg/m. For the steel pipe, D = 102,3 mm, b = 6,02 mm, and the wave speed is... 

Plastic Pipe In contrast to other piping materials, plastic pipe is free from internal and external corrosion, is easily cut and joined, and does not cause galvanic corrosion when coupled to other materials. Allowable stresses and upper temperature limits are low. Normal operation is in the creep range. Fluids for which a plastic is not suited penetrate and soften it rather than dissolve surface layers. Coefficients... 

Support spacing must be much closer than for carbon steel. As temperature increases, the allowable stress for many plastic pipes decreases very rapidly, and heat from sunhght or adjacent hot uninsulated equipment nas a marked effec t. Successful economical underground use of plastic pipe does not necessarily indicate similar economies outdoors aboveground. 

ASTM and the Plastics Pipe Institute, a division of the Society of the Plastics Industry, have established identifications for plastic pipe in which the first group of letters identifies the plastic, the two following numbers identify the grade of that plastic, and the last two numbers represent the design stress in the nearest lower (0.7-MPa (lOO-lbfiin ) unit at 23°C (73.4°F). 

Further information on the design of thermoplastic piping can be found in the Plastics Pipe Institute s Technical Report TR-21. 

For several years now, cable ducts have been manufactured from plastic pipes, which are watertight and form a continuous run of piping. In laying the ducts, low points can occur in which condensed water or water penetrating from the ends can collect. In many cases this water has led to corrosion damage in lead-sheathed cables. Lead-sheathed cables must therefore only be used in such ducts with an additional PE sheath of type A-PM2Y. Cathodic protection of these cables is not possible because of their complete insulation by the plastic pipe. 

PBDs may occur on plastic surfaces with no metal substrate, for example the wall of a plastic pipe conveying charged material, in this case the double layer forms between the inner charged wall of the pipe and a countercharge which accumulates on the outer wall via conduction or via corona discharge. in the latter case both layers of charge reside on nonconductive sur-... 

PLATE 6. Approximately l-m-long spontaneous PBD on plastic pipe. 

All-plastic nonconductive pipe such as polyolefin is not recommended for handling nonconductive or semiconductive liquids except where it can be shown that the advantages outweigh any risks associated with external static ignition or leakage via pinholes, or where tests have demonstrated that the phenomena will not occur. Burying an all-plastic pipe prevents external... 

Where nonconductive and semiconductive liquids must be transferred through plastic piping systems, mitigating strategies include... 

Combinations of these strategies might be considered. For example, in many cases the presence of an external conductive layer on a plastic pipe will not by itself eliminate puncturing of the internal plastic wall, and if the layer does not provide containment it will not prevent external leakage. 

Nonconductive plastic pipe should not be used for transfer of ignitable powder or for any powder transfer through electrically classified areas. Hazards comprise brush discharges, PBDs and external sparks due to induction. Charge accumulation is discussed in 5-3.2.1. 

Industrial equipment is a continuing area of development for plastics. Pipes, pumps, valves and sight glasses, made from such materials as PVC, PTFE and poly-4-methylpent-l-ene, have become well established on account of their corrosion resistance. The nylons are used for such diverse applications as mine conveyor belts and main drive gears for knitting machines and paper-making equipment. These and other materials are widely used where such features as toughness, abrasion resistance, corrosion resistance, non-stick properties, electrical insulation capability and transparency are of importance. 

A 200 mm diameter plastic pipe is to be subjected to an internal pressure of 0.5 MN/m for 3 years. If the creep rupture behaviour of the material is as shown in Fig. 3.10, calculate a suitable wall thickness for Ae pipe. You should use a safety factor of 1.5. 

Underground transmission lines are preferred in places where rights-of-way are severely limited because they can be placed much closer together than overhead lines. They are also favored for aesthetic reasons. They may be directly buried in the soil, buried in protective steel or plastic pipes, or placed in subterranean tunnels. The conductors are usually contained within plastic insulation encased in a thin metallic sheath. The conductors enclosed in steel pipes may be immersed in oil, which may be circulated for cooling purposes. For all types of underground lines, the capacitance is higher than for overhead lines, and the power transfer capability is usually limited by the resistive losses instead of the inductance. Wliile not exposed to environmental... 

One design that is used for installation convenience, but can also allow higher efficiency, is an induced draft fan that pulls in extra air to cool the flue products to temperatures that can be safely vented through plastic pipe. Because of the fan, long horizontal venting runs arc possible with this system. 

For process water, steel pipes are used unless iron pickup is to be minimized. Plastic pipes (polyethylene and polyvinylchloride) are used but they sometimes need external protection from solvents present in industrial atmospheres, ultraviolet radiation (including sunlight), freezing and mechanical damage. 

Plastic pipes Pipes made from plastic materials such as unplasticised p.v.c.. Polythene, ABS and GRP are now widely used for carrying domestic cold water, wastes and rain water. Joining varies according to pipe diameter and service condition, but is generally relatively simple (see Section 18.6). 

Condensed water will run down the evaporator fins to a collection tray below the coil. From there, drain pipes will take this water to a drain. If plastic pipe is used, it should be black to exclude daylight, or slime will grow inside the tube. Drain pipes passing through rooms below freezing point need to be fitted with trace heaters. 

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