Proven welding and jointing methods

There are many ways to weld and join plastics, some more effective than others. Following are some of the proven and preferred methods. Tangit cement and cleaner systems, which are manufactured by Henkel, are suitable for use with UPVC, CPVC and ABS. CPVC and ABS also have individual cements to join them together. A more chemical resistant joining method, which is suitable for both UPVC and CPVC materials, is Dytex cement and cleaner. Dytex cement is ideal if the pipe is to be used with chemicals such as Sodium Hypochlorite (over 6%) and Sulphuric acid (over 70%). UPVC and CPVC can be glued together but the success of the connection is dependent on the application of the pipe. That is, the type of chemicals passing through the pipe and the pressure under which it will be placed. If you need to connect two very different materials, for example steel and UPVC, then you may wish to consider using mechanical couplings, adaptor fittings, or flanges. Polyethylene (PE) pipes are successfully welded together using the Butt Weld method. They can also be successfully connected using electro fusion, socket fusion, Infrared Weld (IR) and compression as well as mechanical joints. Polypropylene (PP) pipes, which are available in a number of material grades including PP-N, PP-R and PP-H, can be welded together in exactly the same manner as PE pipes. In the case of  PP-N pipes, the most appropriate welding technique is Bead and Crevice Free. If you are welding PVDF material together you can use a number of methods including, IR, Bead and Crevice Free, Socket Weld as well as mechanical jointing. All...

Handling Surge Pressure

Surge pressure or water hammer, as it’s more commonly known, is the term used to describe dynamic surges caused by pressure changes in a piping system. If left unchecked, surge pressure can have detrimental consequences. Surge pressure occurs when the velocity of the fluid travelling through a pipe is increased or decreased and may be transient or oscillating. Waves of positive or negative pressure can be generated by a number of factors including: Opening or closing of a valve Starting up or stopping a pump Changing the pump or turbine speed Wave action in a feed tank, and Trapped air The pressure waves travel along at speeds limited by the speed of sound in the medium, causing the pipe to expand and contract. The energy carried by the wave is dissipated and the waves are progressively damped. When oscillatory surge pressure occurs extreme caution is needed as surging at the harmonic frequency of the system can lead to pipes bursting. When designing a piping system, both the pressure excess from water hammer and the hydrostatic load need to be considered. This total pressure must be sustainable by the piping system if it is to be effective. Polyolefins, such as PE, are the most suitable pipes for handling surge pressure. As these pipes are made from a softer material they are more flexible, and can therefore, generally handle the surge more effectively when compared to steel pipes or PVC pipes with rubber joints. The excess pressure is absorbed by the body of the polyolefin pipe instead of the joint. When considering PE pipes, ensure that the means stress is not...