Basic piping engineering and arrangement

Introduction to Piping System A pipe can be defined as a tube made of metal, plastic, wood, concrete or fiberglass. Pipes are used to carry liquids, gases, slurries, or fine particles. A piping system is generally considered to include the complete interconnection of pipes, including in-line components such as pipe fittings and flanges. Pumps, heat exchanges, valves and tanks are also considered part of piping system. Piping systems are the arteries of our industrial processes and the contribution of piping systems are essential in an industrialized society. Fig. 1 illustrates the magnitude of piping required in a typical chemical process plant. Piping systems accounts for a significant portion of the total plant cost, at times as much as one-third of the total investment. Piping systems arranged within a very confined area can be a added challenge to piping and support engineers. Figure 1 The initial design of a piping system is established by the functional requirements of piping a fluid from one point to another. The detailed design is decided by criteria such as type of fluid being transported, allowable pressure drop or energy loss, desired velocity, space limitations, process requirements like free drain or requirement of straight run, stress analysis, temperature of fluid, etc. The supporting of piping systems requires a significant engineering, design, fabrication and erection effort. In some cases, special structures (like structural T or inverted L, cantilevers, U portals, pedestals, etc) must be built solely for the purpose of supporting piping systems. Piping Material The material to be used for pipe manufacture must be chosen to suit the operating conditions of the piping system. Guidance of selecting the correct material can be obtained from standard piping codes. As an example, the ASME Code for Pressure Piping contains sections on Power Piping, Industrial Gas and Air Piping, Refinery and Oil Piping, and Refrigeration Piping Systems. The objective being to ensure that the material used is entirely safe under the operating conditions of pressure, temperature, corrosion, and erosion expected. Some of the materials most commonly used for power plant piping are discussed in the following sections. Steel – Steel is the most frequently used material for piping. Forged steel is extensively used for fittings while cast steel is primarily used for special applications. Pipe is manufactured in two main categories – seamless and welded. Cast Iron – Cast iron has a high resistance to corrosion and to abrasion and is used for ash handling systems, sewage lines and underground water lines. It is, however, very brittle and is not suitable for most power plant services. It is made in different grades such as gray cast iron, malleable cast iron and ductile cast iron. Brass and Copper – Non-ferrous material such as copper and copper alloys are used in power plants in instrumentation and water services where temperature is not a prime factor. Read less