Design Considerations for Equipment and Piping Layout: Straight Talk About Pipes

This is the third in a four-part series on equipment and piping layout.  This article provides guidelines for piping and pipe rack layouts.

The first article provided guidelines for vessels, cooling towers, and compressors. The second article discussed equipment layout considerations for pumps. The series concludes with the special requirements for heat exchangers, valves, and instrumentation.

Is the shortest distance between two pieces of equipment a straight run of pipe?

Pipes connect the tanks, vessels, pumps, and other equipment shown in the equipment layout drawings—and must do it efficiently, taking into account all applicable codes and standards, client requirements, safety concerns, accessibility needs, piping stress factors, possible interferences, and the total installed cost.  In fact, piping can be a major cost factor for any industrial process installation due to material, fabrication, and labor expenses.

Smart piping layout combines the knowledge of experienced piping engineers and process engineers with a good dose of common sense.  For example, moving a pump or tank a few inches from the initial design location could eliminate an otherwise unnecessary elbow and related flanges.

Piping and instrumentation diagrams (P&ID) serve as the roadmap for routing piping between equipment, and identify the locations of related valves and instrumentation. Here are some piping design considerations that must be accounted for.

Thermal expansion and piping stress analysis

A recent series of articles by Matrix discussed piping stresses caused by thermal expansion (and contraction). Movement occurs, for example, when pipes expand as hot liquids pass through. Just as tanks and pumps are anchored to control the direction of thermal expansion, pipes may also need to be anchored to manage the effects of expansion.

Hot piping will typically have expansion loops, often located in the pipe rack, to accommodate pipe expansion. Or a series of elbows may be used to protect equipment from pipe growth.

Piping Layout Guidelines

  • Review the client’s specifications for piping and flange sizes, steam and high-pressure piping, insulation and tracing, fire systems, and clearance requirements for the operation and maintenance of equipment.
  • Arrange piping to allow full access to equipment for operation and maintenance. Ensure that equipment can be removed without also removing block valves and large sections of piping.
  • Piping for vertical vessels should be located radially around the vessel on the pipe rack side, or should align with adjacent equipment. Leave adequate space for access to platforms, ladders, manways, instruments and drop areas.
  • Horizontal vessels and heat exchangers typically have fixed and sliding ends. Design the piping accordingly.
  • Route piping to use existing structures as pipe supports.
  • Avoid long, straight runs of pipe between two anchor points, such as two pieces of equipment.

Maintaining adequate clearances between pipes and equipment is critical. The following guidelines are based on extreme conditions of heat or cold.

  • Provide a minimum vertical clearance of 7 inches between finished grade or platform decking and the bottom of piping, insulation, or support steel.
  • Provide at least 1 inch of clearance between a branch valve and handwheel, and the header insulation.
  • Leave at least 1 inch of clearance between the outside diameter of a vessel and all piping. Include flanges and the insulation thickness to determine the outside diameter.
  • Provide a minimum of 1 or 2 inches of clearance between pipes, based on the outside diameter of each adjacent flange, pipe, or insulation jacket. Provide 2 inches of clearance between a pipe and a structural member.
  • Provide at least 6 inches of clearance between the bottom of a drain valve, and grade or a platform deck, for plug removal and rodding out.

Steam Piping Guidelines

  • Provide drip legs with steam traps. These can present some serious clearance issues in a project, but are often neglected in the original piping layout.
  • Provide traps and/or drains on both sides of steam control valves, depending on the steam type.

Pipe Rack Design

  • Within a process unit, piping should be grouped in overhead pipe racks.
  • Offsite piping is commonly run on sleeper racks.
  • If pipe racks intersect, establish different elevations for lines running north-south versus east-west.
  • Pipes should change elevation when entering or leaving a pipe rack, and at each change of direction, to avoid interference with the routing of future piping and pipe rack expansion.
  • Long runs of rack piping should be guided typically 2 bents (rack support beams) from a change of direction, and every 3 bents after that. Stress-analyzed piping may have different requirements.
  • Use the appropriate type of pipe support to control expansion, such as anchors or guide supports. Insulated pipes should be designed with shoes to prevent the insulation from resting on the support steel.
  • Avoid dead legs, pockets, and gas traps wherever possible. When unavoidable, provide plugged drain valves.
  • Provide readily accessible isolation valves at process unit battery limits.

The fourth and final article in this series will review piping and equipment guidelines for heat exchangers, valves, and instrumentation.

Matrix Technologies is one of the largest independent process design, power systems engineering, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our manufacturing operations management capabilities and manufacturing process control solutions, contact Scott Saneholtz, PE, Senior Manager Process Solutions Department.

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