The term "Piping Designer" as used in this document refers to that person responsible for the overall plant layout, the Plot Plan, the equipment location, the pipe routing, the development of the CAD models, the piping isometrics. It does not refer to the Piping Material Engineer or the Pipe Stress Engineer who each are involved in the "design" of a piping system but in a totally different means and manner.
What does the Piping Designer need to know?
Piping design is more than just knowing how to turn on the computer, how to find the piping menus and the difference between paper space and model space.
So, appropriately, what else does the designer need to know about piping design besides how to operate a keyboard and a mouse or connect a piece of pipe to a fitting?
Here is a list of the most basic of things that a good piping designer should know.
Thinking about every one of these items should become as natural as breathing for a good piping designer.
• Pipe, Fittings, Flanges and Valves – All designers need to know and understand the broad spectrum of items that make up the "vocabulary" of the piping language. This includes the many types of fittings, the many different schedules, the wide variety of common piping materials, the flange class ratings and the types and function of the different valve designs.
• Relationship of other Engineering groups – All designers need to know and understand the relationship, activities and contribution of all the other engineering and design groups on the project. These include: Process, Civil, Structural, Mechanical Equipment, Vessels & Tanks, Electrical and Instruments/Control Systems. These groups have a responsibility for contributing to Piping's success just as Piping has a responsibility for contributing to their success.
• Piping Execution – All designers must understand how piping design progress is linked to P&IDs, equipment vendor drawings, instrument vendor drawings, stress analysis and structural support design in order to identify areas where the piping design is being held up.
• Process Documents – All designers need to be able to read, understand and know how to use the two major documents produced by the Process Engineering team. These documents are the PFD (Process Flow Diagram) and the P&ID (Piping and Instrument Diagram). The PFD is used by the more experienced Piping Designer early in the project for plot plan development before the P&ID's are available. The P&ID's are used by Piping Designers of all levels during activities throughout the Detailed Design phase of the job; the drawing production phase and any possible field follow up.
• Process Variables – All designers must know and understand the four basic process variables: pressure, temperature, flow and level, and the instrumentation used to regulate and/or measure these variables.
• Process Plant Equipment – All designers need to know and understand what the different types of equipment are. They also need to know and understand the piping related issues there are for each type of equipment. They must know which types of equipment have the nozzles fixed by the manufacturer and which types of equipment need to have the nozzles located (by the piping designer). The designer also needs to know and understand the operational, maintenance and installation/construction issues for each type of equipment.
• Equipment Operation and Internals – All piping designers need to understand the equipment process function and the equipment internals in order to orient process and instrument nozzles/connections, and locate manway, platform, ladder and staircase access.
• Equipment piping – All piping designers need to know the right and the wrong way to pipe up (connect pipe to) different kinds of equipment and for maintenance/disassembly space requirements. This includes pumps, compressors, exchangers, filters or any special equipment to be used on a specific project.
• Allowable pipe spans – All designer need to know and understand the span capabilities of pipe in the different schedules for a wide variety of common piping materials. When a new project introduces a new material with severely reduced span capabilities; supplemental training may be required.
• Expansion of pipe – All piping designers must understand that they need to treat a piping system as though it is alive. It has a temperature and that temperature causes it to grow and move. That growth and movement must be allowed for and incorporated in the overall design. Not just of that specific line but for all other lines close by. The process of expansion in a pipe or group of pipes will also exert frictional forces or anchor forces on the pipe supports they come in contact with.
• Routing for flexibility – All piping designers must understand how to route pipe for flexibility. Routing for flexibility can normally be achieved in the most natural routing of the pipeline from its origin to its terminus. Routing for flexibility means (a) do not run a pipe in a straight line from origin to terminus and (b) building flexibility into the pipe routing is far cheaper and more reliable than expansion joints.
• Weight and loads (live loads and dead loads) – All piping designers need to understand the effects of weight and loading. They need to know and understand that everything has a weight. They need to be able recognize when there is going to be a concentrated load. They need to have access to basic weight tables for all the standard pipe schedules, pipe fittings, flanges, valves for steel pipe. They also need to have the weight tables for other materials or a table of correction factors for these other materials vs. carbon steel. They need to be able to recognize when downward expansion in a piping system is present and is adding live loads to a support or equipment nozzle.
• Standards and specifications – All piping designers need to understand the content and application of the client and engineering company standards and specifications used on the project. In particular the designer must have intimate knowledge of the primary standards and specifications he/she will use; these being pipe supports and piping classes.
• Vessel piping – All piping designers also need to understand about the connecting, supporting and guiding of piping attached to vessels (horizontal or vertical) and tanks. They need to know that nozzle loading is important and does have limitations.
• Rack piping – All piping designers need to understand that there is a logical approach to the placement of piping in (or on) a pipe rack and the setting of rack elevations. It does not matter how wide or how high the rack or what kind of plant, the logic still applies. Starting from one or both outside edges the largest and hottest lines are sequenced in such a manner that allows for the nesting of any required expansion loops. Another good guideline is; Process lines on the lower deck(s) and Utility Lines on the upper deck(s). The spacing of the lines must also allow for the bowing effect at the loops caused by the expansion.One rule of thumb for setting the distance between piping levels is three times the largest pipe size.
• Expansion loops – All designer need to understand and be able to use simple rules and methods for sizing loops in rack piping. This should include the most common sizes, schedules and materials.
• Cold spring/Pre-spring – All piping designers should understand the basics rules of cold spring and pre-spring. They need to understand what each one is along with when to and when not to use each.
• Design production methods – All piping designers need to be able to make all types of piping documents (sketches, layouts, detail piping plans, isometrics, etc) using different methods. These methods include first and most important, manually. Every piping designer must be able to go to the field or sit in front of a client and make proper, intelligent, and understandable piping sketches. They must also be able to produce detailed final drawings manually. Today, piping designers also need to know (or be able to learn) a wide range of electronic 2D or 3D design tools.
• Fabrication and Construction methods – All piping designers need to understand shop spool fabrication, modularization and field erection construction methods, and be able to determine "shop' and "field" material splits, shipping box sizes, field welds and field (or final) fit-up welds.
• Heat Tracing – All piping designers need to understand the purpose of process heat conservation, know the different methods (Jacketing, Tracer Tubing or Electric), Tracer commodity (Steam, Oil, Hot Water, etc.) and Tracer system requirements and be able to design heat tracing circuitry.
• Deliverables – All piping designers need to understand the purposes of each of the piping deliverables, such as plot plans, key plans, piping plans and sections, and isometrics.
• Drawing Content – All piping designers must understand how to present their designs. Drawing content and dimensioning practices must be well thought out in order to clearly communicate the designs to construction personnel.
• Economics – All piping designers must be aware of economics. For instance, move a piece of equipment to reduce costly high pressure and alloy piping runs; reduce the number of fittings and welds, and eliminate unnecessary supports whenever possible to save on material, fabrication and erection costs.
Any person that has this type of training, this type of knowledge and then consistently applies it is indeed a piping designer. He or she will also be a more valuable asset to their company and to themselves in the market place. On the other hand anyone who does not know or does not apply the knowledge about these issues while doing piping work is nothing more than a piping drafter or a CAD operator.
Acknowledgements: Thanks to Richard Beale: Co Author of the book "The Planning Guide to Piping Design" (Gulf Publishing) for his insightful input and editorial contribution.
About the Author
James O. Pennock has more than forty-five years in the process plant design profession. He has been involved in both home office and job site assignments on refinery, chemical, petrochemical, power and other projects. His experience ranges from entry level designer to engineering manager. Much of this was with Fluor. He is also the author of the book "Piping Engineering Leadership for Process Plant Projects." He is now retired, living in Florida, USA and does only occasional consulting work.