Design Considerations for Equipment and Piping Layout: Locating Valves and Special Equipment
This is the last article in a four-part series on equipment and piping layout. This article reviews guidelines for locating various types of valves, and also considers the equipment needs of heat exchangers, fired equipment, and instrumentation.
The first article provided guidelines for vessels, cooling towers, and compressors. The second article discussed equipment layout considerations for pumps. Piping and pipe rack guidelines were covered in the third article of the series.
Properly Locate Each Valve Based on Its Application
Valves come in all shapes and sizes. Based on the application and the fluid in the piping, the valve required for the job could be a gate, ball, butterfly, globe, check, safety/relief valve, or control valve. Some valves are operated manually, by turning the handwheel or pulling on an overhead chain. Others open and close using motors and solenoids.
Piping engineers have a lot to consider when locating valves for the equipment and piping layouts discussed in the previous articles. They often work closely with the process engineers to select the correct valve for each application. Some general location guidelines that apply to most valves are listed below:
- Review the valve manufacturer’s installation recommendations to determine if the valve should be mounted vertically or horizontally. Also review the owner/client requirements. Take care to never install the valve upside down or backwards.
- Frequently operated valves should be easily accessible from grade, platforms, or permanent ladders. If the bottom of the handwheel of a horizontal valve is more than 6 feet above grade, such as for a seldom-used valve, use valve extensions, chain operators, or a platform for access.
- Focus on personnel safety for anyone walking near valves or operating them. Make sure handwheels and chains do not present a safety hazard. Keep valve handwheels out of operating aisles wherever possible. Avoid tripping hazards and head bangers. Valves that handle steam, acids, and caustics should be located below eye level to prevent eye and facial injuries.
- Provide enough clearance for servicing and replacing valves. Also provide at least 4 or 5 inches clearance around a valve handwheel for easier use by an operator.
- Use lug type valves unless directed otherwise by the client.
Pressure safety valves protect equipment from over-pressurization. Generally, they are installed so they drain freely into the flare header.
- If the safety valve can’t be serviced during operation, it’s necessary to install block and bypass valves, with the block valves being locked or car sealed open.
- Also, the block valve handwheels should be installed in the horizontal not vertical position. This will prevent a mechanical failure of the valve from blocking the line.
Valves often have specific piping layout needs, such as a minimum number of diameters of straight pipe before and after the valve. Complying with the “rules of thumb” and the laws of physics can prevent “water hammer” conditions that lead to valve failure.
Heat Exchangers Run Hot and Cold—Relatively Speaking
A heat exchanger is a piece of equipment with two fluids flowing in opposite directions in order to exchange heat through a solid boundary or surface. Common types of exchangers include shell and tube, double pipe or fin tube, plate and frame, and air coolers.
The basic rule for flow through an exchanger is that the fluid being heated must flow up, while the fluid being cooled flows down. That means that hot fluids enter at the top of the exchanger, while cold fluids enter at the bottom.
- Exchanger elevations are typically determined by piping layout or system hydraulic requirements. Ensure proper clearance between the drain on the lower piping and grade.
- The channel nozzles in a bank of exchangers should line up whenever possible.
- Bundle pulling must be from the end of the exchanger opposite the pipe rack.
- Exchangers with removable tube bundles should have a clearance for maintenance equal to the bundle length plus 20 feet from the tube sheet.
- Air-cooled exchangers are normally located on the top of pipe racks, with platforms provided for tube sheet access. Air coolers with multiple bays require the inlet piping to be symmetrical to equalize the flow to each bay.
- Design the piping so that the channel end of the exchanger can be removed without removing the isolation valves.
- Provide a bypass line between the cooling water supply and return lines to prevent freezing when the exchanger is out of service.
Be Careful with Fired Equipment
Fired equipment includes heaters, incinerators, and boilers. Fired equipment should be located, if practical, so that gases from process areas and hydrocarbon areas cannot be blown into the open flames.
- Review the owner/client specifications to properly set the height of heater stacks relative to other equipment and platforms. Maintain at least 7 feet of clearance from the bottom of the heater to the high point of the grade.
- Provide sufficient clearance and access for the easy removal of tubes, burners, fans, and other related equipment.
- Locate fired heaters around the outside of a unit plot, and adjacent to an unrestricted road.
- Provide access for firefighting on all sides.
Many instruments, such as flow meters, have piping design requirements so they can operate correctly and accurately. Industry standards, vendor literature, and owner specifications all provide guidance.
- Control valves with actuators should be installed with the centerline 2 feet above grade. Provide a minimum of 12 inches of distance (or the manufacturer’s recommended distance) above the actuator.
- Provide a minimum of 2 feet of clearance from the connection taps on an orifice flange to adjacent piping, equipment, or steel.
This fourth article in the series concludes our overview of the process involved in equipment and piping layout. We hope this information will guide you in designing your next industrial project.
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, (419) 897-7200 x509.