Plastic pipework

Abstract: A method and apparatus for welding PVC pipe which includes a means to clamp and apply welding heat so that plastic pipes may be welded while under external pressure adapted to offset internal pressures. The method includes the steps of placing a clamp about a splice to be welded, tightening the clamp and applying heat through the clamp to the plastic in sufficient quantities to cause the plastic to fuse. The steps are carried out by utilizing an apparatus comprised of a clamp which is adapted to encompass the area to be welded and apply a constricting force to that area while heat is transferred through the clamping means to the plastic.

Abstract: The invention relates to a hard polyethylene pipe with high impact resistance, which solves the problem that the hard PVC pipe has low impact strength, has brittleness, and is easy to leak, permeate and crack. The technical scheme to solve the problem is that: the hard polyethylene pipe is prepared from the following components in part by weight: 220 to 280 parts of PVC, 6 to 10 parts of heat stabilizer, 0.7 to 1.3 parts of lubricant, 2.1 to 2.9 parts of titanium pigment, 10 to 20 parts of impact modifier, 2 to 4 parts of processing aid and 3.5 to 6.5 parts of calcium carbonate; and the hard polyethylene pipe is prepared by the following steps: firstly, evenly mixing the components to prepare a mixture; secondly, heating the mixture to between 105 and 145DEG C, and cooling the mixture to between 30 and 55DEG C; standing the cooled mixture at a normal temperature of between 18 and 25DEG C for 8 to 12h; extruding the mixture at a temperature of between 130 and 220DEG C with an extruder; and cooling at a temperature of between 10 and 22DEG C. The hard polyethylene pipe has good toughness and impact resistance, chemical resistance, and difficult leakage, seepage and crack, and is innovation on pipes.

Abstract: A large-scale pipeline test rig at Deltares, Delft, The Netherlands has been used for filling and emptying experiments. Tests have been conducted in a horizontal 250 mm diameter PVC pipe of 258 m length with control valves at the downstream and upstream ends. This paper investigates the accidental simultaneous closure of two automatic co ntrol valves during initial testing of the test rig. The simulta neous closure of both valves has induced upsurge and downsurge at the same time. Large water hammer and column separation have caused failure of pipe supports and leakage at pipe joints . The incident was caused by a fault in an electronic conversion b ox due to power failure. Afterwards the downstream end automatic valve has been modified to a manually operated valve to a void the accidental simultaneous closure of the valves. The accidental transient event has been fully recorded with pressu res, flow rates and water levels. The measurements of the acc ident are presented, analyzed and discussed in detail. Photog raphs show the damages to the system.