Piping design is the basic material flow within or outside the plant. It’s a critical element in pharmaceutical plants, oil industries and other heavy scale industries. A simple miscalculation can cause a disastrous outcome resulting in casualties.
Pipes experience thermal stresses that result in movements and expansion. This movement can place significant strain on the piping, supports and attached equipment.
Pipes
Piping systems transport a wide range of fluids. Pipes themselves can be made from a variety of materials including metals and plastics. They are often lined to prevent damage from chemicals in the fluids. Linings can also be used to improve flow properties or meter accuracy. It is important that piping designers know how to identify and define pipes, as well as the type of lining and coatings required.
Pipes are usually classified into different categories based on the material and manufacturing process. For example, pipe is categorized as seamless or welded and further characterized by the method of welding (with filler metal or without). Pipe sizes are standardized by schedule, which loosely corresponds to the nominal diameter up to a maximum of NPS 12, after which the OD stays the same while the wall thickness changes.
All piping design activities should be conducted in accordance with the appropriate codes and standards. The more familiar a piping designer is with codes and standard templates, the less time they will spend re-working the same information across the project.
Piping designs should be conducted in coordination with other engineering and design groups to ensure the system is fit for purpose during construction and operation. This is particularly true for equipment GA drawings, pipe stress analysis and structural support design.
Fittings
Using the right pipe fittings for your project will keep the flow of water, oil or other liquids running smoothly. Pipe fittings come in many different shapes and sizes. Some have matching male and female ends to connect two pipes of the same diameter, or threaded ends to join a larger pipe to a smaller one. Some have an o-ring base like AN fittings and require special port machining to seal properly.
Couplings join lengths of pipe or tubing with a male component that fits over the female component for a tight seal. Often used in copper piping systems, couplings are either slip-to-slip or threaded.
Elbows change the direction of a pipe line. They are available in straight 90-degree or 45-degree angles, and in short arcs (street elbow) and long arcs such as a long-sweep elbow which makes a more fluid sweeping turn to reduce resistance and turbulence. A reducing tee changes the size of a branch line coming off a main line, and it is shaped like the letter T with two parallel ports and one perpendicular.
Caps and plugs close off pipe ends temporarily or permanently. They can be glued, soldered or screwed on, depending on the type of pipe and fitting. Solvent welding is used with PVC, CPVC and ABS to partially dissolve and fuse the adjacent surfaces of pipe and fitting.
Valves
Whether shutting off or allowing flow, valves are a major component of the piping system. They’re a large portion of the total cost, and they can make or break process efficiency. It’s important to identify the correct valve type at the design stage of a project. Different types of valves are identified by symbols on the Process and Instrumentation Diagram (P&ID).
Valve materials can have a significant impact on piping performance especially when dealing with aggressive or abrasive fluids, caustic washdown chemicals and other specialized processing conditions. Choosing the correct valve material is important and can often require evaluation of not only the internal “wetted” parts but also the exterior body components such as the bonnet and stem.
Generally speaking, there are four types of valves. They’re usually categorized by how they function and how they’re controlled:
Supports
Pipe supports are a vital part of piping system design. They ensure that the pipe is adequately supported and restrained to prevent excessive vibration, sagging, nozzle damage, and other issues. They also help prevent thermal expansion and contraction of the pipe.
Pipes are supported by hangers or supports of various types on which they rest. These supports are typically made of steel structural members like angle, channel, I-beam, wide flange beam etc. The support location requirements are taken into account while selecting the type of support.
The support must be capable of carrying the dead weight load, as well as restraining the piping system against thermal and dynamic loads. It should also be able to control lateral movements. It should also be able to protect the piping from thermal stress, weight and steelwork deflections.
There are two kinds of supports in a piping system: primary and secondary. The former is a relatively constant and predictable load that is caused by gravity. The latter is a variable load that changes with conditions. This kind of load includes sudden water or steam pressure, thermal expansion and contraction, vibration, and wind.
The selection of the appropriate support for a particular line is based on the pipe size, construction material, operating temperature, pipe insulation thickness, hydro and air testing, and other factors. It is also influenced by the layout of equipment at grade.