Piping Arrangements Around Centrifugal Pumps


Centrifugal pumps are one of the most commonly used types of pumps in various industries, including chemical, oil and gas, water treatment, and many others. These pumps have a simple design, are easy to operate, and can handle a wide range of fluids. In this article, we will discuss what centrifugal pumps are, their different types available, and Study of Piping Arrangements for Centrifugal Pumps.

  1. What is a Centrifugal Pump?
  2. Different Types of Centrifugal Pumps
  3. Types of Centrifugal Pumps based on API 610
  4. Location and Height for Centrifugal Pump
  5. Study of Piping Arrangements
  6. Auxiliary Piping
  7. Pipe Support Arrangements
  8. Conclusion

1. What is a Centrifugal Pump?

A centrifugal pump is a mechanical device that uses centrifugal force to move fluids. It works by converting mechanical energy into fluid energy, which moves the fluid from one place to another. The pump consists of an impeller, a casing, and a motor. The impeller is a rotating component that creates a vacuum in the casing, which draws the fluid into the pump. The fluid is then expelled from the pump through the discharge outlet. The figure below explains the simplest centrifugal pump type.

2. Different Types of Centrifugal Pumps

2.1. Single-Stage Centrifugal Pump:

This is the simplest type of centrifugal pump, consisting of only one impeller. It is suitable for low-pressure applications and can handle a wide range of fluids.

2.2. Multi-Stage Centrifugal Pump:

This type of pump has multiple impellers, which are stacked on top of each other. Each impeller increases the pressure of the fluid, making it suitable for high-pressure applications.

2.3. Axial Flow Centrifugal Pump:

This pump has an impeller that directs the fluid parallel to the shaft, which creates a low-pressure area behind the impeller. The low-pressure area draws the fluid into the pump, making it suitable for applications where high flow rates are required.

2.4. Radial Flow Centrifugal Pump:

In this pump, the impeller directs the fluid perpendicular to the shaft, which creates a high-pressure area around the impeller. This pump is suitable for applications where high pressures are required.

2.5. Mixed Flow Centrifugal Pump:

This pump has an impeller that directs the fluid at an angle between the axial and radial directions. This creates a combination of high flow rate and high pressure, making it suitable for applications where both are required.

2.6. Self-Priming Centrifugal Pump:

This type of pump has a special design that allows it to prime itself, meaning it can draw fluid from a lower level without the need for external priming. This makes it suitable for applications where the pump is located above the fluid level

3. Types of Centrifugal Pumps based on API 610

API is the abbreviation for American Petroleum Institute which is the main U.S trade association for the oil and natural gas industry representing organizations involved in producing, refining, distributing, and many other aspects. Centrifugal pumps are one of the most common categories of rotating equipment found in these industries and the American Petroleum Institute created the API 610 standard for
these pumps

API 610 classifies various types of centrifugal pumps which are primarily divided into three groups: OH, BB and VS.

OH – Overhung pumps – The impellers of these pumps overhang a radial bearing and so the support must take care of all forces, including the overhung mass and the rotor dynamic and hydraulic forces. Typical applications include: Produced Water; Feed Pump; Booster Pump; Hydrocarbon Transfer; Condensate.

BB – Between bearing pumps – The impellers of these pumps are suspended between the two supports with the impeller placed horizontally, in the same orientation as the bearings. Typical applications include: Cooling Water; Boiler Feed; Well Injection; Feed Water; Crude Transfer.

VS – Vertically suspended pumps – The casing and impellers of these pumps are submerged in the pumped fluid, suspended on a vertical column below a support plate at the top of the tank to which the motor and thrust bearing are mounted. Typical applications include: Open Drain; Closed Drain; Crude Oil Transfer; Firewater; Seawater Lift.

4. Location and Height for Centrifugal Pump

The piping arrangement around a centrifugal pump’s suction and discharge is critical to ensure that the pump operates within its design parameters and delivers the required flow and pressure. The arrangement should be carefully planned to minimize frictional losses, prevent cavitation, and reduce vibration and noise. General Points to be considered while locating centrifugal pump in the plot plan are as follows:

4.1 General Plot Plan Requirements

  1. The pump layout (distance between pumps) shall be determined with consideration given to the space to install piping (connected to pumps or steam turbines), electric cables, and switch stands.
  2. Hot oil pumps and light oil (vaporizing at room temperature and atmospheric pressure) pumps shall not be installed underneath air fin coolers.
  3. Space shall be provided between pumps handling combustible fluids, for fire fighting as well as for daily operation, maintenance, and inspection.
  4. The casing cover, impeller, and shaft of large-size pumps and multistage pumps are removed for inspection and maintenance. Consideration, therefore, shall be given to providing a laydown area. The necessity of trolley beams or mobile cranes for inspection and maintenance shall be considered.
  5. A common spare pump, where it is installed, shall be located in the middle of the pertinent pumps.

4.2 Piping Arrangement Method

Common location of pumps in chemical and petrochemical plant is under the Piperack at grade.
Pumps are to be placed close to and below the vessels from which they take their suction in order
to have net-positive suction head (NPSH) required by the pump. Pumps can be arranged in the plot plan based on the following 3 methods:

(a) Parallel Arrangement of Pumps by Aligning Foundation Surface on Drive Side or Pump Bed End Surface

This arrangement method has so far been used by many plants, enabling power cable routing to be carried out efficiently and economically. Switch stands are aligned, thereby providing a good appearance and ensuring that the operation of each pump can be started easily. Differences in pump size, however, will result in long or short pump connection piping and thereby an irregular pump arrangement, and will also cause small-size pump suction piping to become longer.

Pump arrangement by aligning the pump bed end surface is advantageous in that pump position can be determined even if the determination of pump foundation dimensions is delayed. Recently, this arrangement is increasingly adopted.

(b) Parallel Arrangement of Pumps by Aligning Foundation Surface on Pump Side or Pump Bed End Surface

This method is not so commonly applied for pump arrangements within a onsite area but is frequently used where pump inlet/outlet piping is connected from the sleeper piping, located in front of the pumps, as in the case of offsite piping. Even if pump size remains unfixed, the necessary space on the piping side can be secured easily.
This method also enables valve operation walkway and piping support installation planning to be carried out easily. It is difficult, however, to estimate and secure the necessary operation walkway and maintenance areas located behind the pumps.
Pump arrangement by aligning the pump bed end surface is advantageous in that pump position can be determined even if the determination of pump foundation dimensions is delayed. Recently, this arrangement is increasingly adopted.

(c) Parallel Arrangement of Pumps by Aligning Nozzle Centerline on Pump Discharge Side

This method has recently been commonly employed in the planning of a piping layout within the plant. If a summary of the pumps (nozzle orientation, pump outline) is made available, it is possible to carry out piping layout to a certain extent. Where the pump nozzles are TOP type, the riser piping is aligned on the same line, and piping support planning can be carried out easily.

4.3 Pump Spacing

For general jobs, it is not possible, in many cases, to obtain pump drawings in the plot plan preparation phase, thus making it difficult to estimate distance between pumps.
Final dimensions shall be determined after the completion of the piping layout. In this case, the piping layout shall be planned on the basis of the space between pumps given in Table below according to the pump suction pipe size. However, final spacing has to be revalidated based on Vendor Information.

4.4 Pump Foundation Height

“Pump foundation height” means the height determined at the pump bed underside. Pump foundation height shall be determined in consideration of the following.
(a) Pump type and size
(b) Suction and discharge piping required underside space (drain piping, supports, etc.)

4.5 Pump Maintenance/Inspection Space

Space for pump maintenance and inspection shall be provided on both sides in principle, at least one side of the pump. Space shall be provided also in front of the pump according to the type of pump. The same space may be used for pumps which are located adjacent to each other. Space for lifting shall be provided right above each pump, and no piping shall be routed in the lifting space.

Spacing according to the type of pump is as follows:

(4.5.1) Single Suction, Single Stage, END-TOP and TOP-TOP

(4.5.2) Single suction, Multi Stage , TOP-TOP and SIDE-TOP

(4.5.3) Double Suction, Single Stage, SIDE-SIDE

5. Study of Piping Arrangements

5.1 General Requirements

Line flows shown in the P & ID shall be carefully studied to satisfy process requirements. Then, piping configuration shall be determined, and piping supports shall be planned, in view of ease of pump operation, maintenance, and inspection.

The typical line flow around pumps is as shown below.

Pumps are precision machines. If they are subjected to large external forces, they become deformed, vibrate or produce noise, thereby causing overheating of bearings and damage which is likely to result in machine trouble.
Loads applied to individual pumps, therefore, are restricted (allowable load). This must be taken into account in piping arrangement. Where the pump nozzle is located on the top, the following two supporting methods are used: –
The piping is bent at the shortest distance from the pump nozzle and is supported from beneath the point wherein opposite the pump foundation (Fig. 5-7). The piping is raised straight from the nozzle and is supported from above at the topmost corner (Fig. 5-8).
The method of supporting the piping from beneath ensures that the supports can be installed easily; however, this method causes thermal stress to be applied to the pump due to the difference in expansion between the pump and the piping support. The method of suspending the piping from above is limited to the case where support can be easily taken from the pipe rack or the steel structure; however, it is generally difficult to take such support. This method also causes the operation valve to be located high up. In view of thermal stress design, however, this method does not involve the same problem as with the method of supporting piping from beneath. The method adopted will greatly affect the later arrangement of piping in the area around pumps. Basic design policy, therefore, must be established before the layout planning is started. It is necessary to determine the method to be employed based on surrounding conditions, type of pump, ease of operation/maintenance/support, thermal stress calculation, client’s requirements, and other factors.

  1. Individual lines shall be designed so as to be of the shortest possible length. The steam piping connected to the hot oil pump and turbine driver, however, shall be allowed some flexibility so as to avoid problems with thermal expansion/contraction.
  2. Valves and instruments of piping connected to pumps shall be arranged in view of the relationship with the switch stand, to ensure that pump startup and changeover operations can be carried out easily.
  3. The pump suction and discharge piping shall be located in space, not the maintenance/inspection space, in such a manner that valve handles and the like do not interfere with maintenance and inspection.
  4. Small-size piping for pump cooling water shall be located as closely as possible to the pump bed or to the pump foundation side surface, so that maintenance and inspection are not interfered with.
  5. Where piping subject to thermal expansion/contraction is connected to two or more pumps, thermal stress applied to individual pumps shall be equalized.
  6. Care shall be given to centrifugal pump suction lines, because the straight pipe length between the suction flange and the fitting (elbows, tees, reducers) or strainer or valve flange is sometimes specified to prevent the flow from affecting the pump impeller. API 686 “Recommended Practices for Machinery Installation and Installation Design”, specifies that the straight pipe length should be five times the suction nozzle size. However, pump manufacturer recommendations to be sought after during detail design stage of the project.

5.2 Nozzle Orientation

Pump nozzle positions are determined according to the type and structure of the pump available in the Pump GA drawing. Even there is non-standard type of pump, nozzle orientation can be confirmed from the related manufacture of that pump. However, if you find that nozzle orientation can causes change in entire plan and major change in plot plan, this shall be notified to the Rotating Equipment Department and nozzle orientation shall be discussed and mutually agreed to optimize the overall plant cost and piping arrangements.

5.3 Suction Piping

  1. Piping shall, in principle, be given the shortest length so as to minimize pressure loss occurring in the piping system. The number of bends shall also be minimized. Thus, appropriate piping routes shall be determined.
    Piping shall also be constructed so that air pockets (which cause cavitation) are not formed.
    In any case, appropriate piping routes shall be determined after fully studying the conditions in the area around pumps (accessibility and operability) and effects on pumps (measures for thermal stress applied to piping and ground settlement). Piping such as hot oil lines, steam trace piping, and lines to undergo steam purging must be flexible to absorb thermal expansion/contraction.
  2. Figure “A” below shows an ideal configuration of piping, in which the piping distance between each nozzle is minimized. In the case of hot oil piping, differences in expansion occur between the suction piping of pump A and that of pump B, according to the operating conditions of these pumps (pump A: operated, pump B: not operated). This poses problems with thermal stress analysis or causes dust and the like, which accumulates within the piping system, to center on Pump A strainer, which therefore is likely to plug. This configuration, therefore, is not employed for piping handling high-temperature fluids or fluids which are likely to cause plugging (tower bottom, sludge line, etc.).
  3. Figure “B” below illustrates the case where the overhead piping can be easily grouped with other piping and fluids can uniformly flow into pumps A and B. This configuration, however, is slightly disadvantageous in terms of pressure loss and cost, compared with the configuration shown in Figure “A”.

4. Figure “C” below shows an example of a piping configuration of a general oil line; the line penetrates the oil dike to avoid the formation of air pockets, and a sleeper is located at the lowest level. Piping routes such as in off site areas shall be planned with emphasis laid on measures against cavitation and pressure loss.

5. Figure “D” shows an example of LPG piping. LPG produces vapor inside the piping according to the ambient temperature. Gravity piping, therefore, shall be employed; the piping shall be sloped at a rate of about 1/50 so that vapor produced can be returned to the tank. Care shall thus be taken in avoiding the formation of vapor pockets. Where the settlement of tanks is expected, the level of gravity lines shall be determined so that free draining (no pocket) can be ensured even after settlement.

5.4 Valve Installation Location

(a) The valve located on each suction line is used to isolate fluid flow, for pump change-over operation, maintenance, inspection, and strainer cleaning. This valve, therefore, shall be brought as close as possible to the pump suction nozzle, so that the formation of liquid pockets within the route from the valve to the pump suction nozzle can be minimized, as shown in Figures below.

(b) Where a gate valve is installed on a horizontal suction line, if the valve handle is located vertically, an air pocket is formed in the valve bonnet. The handle, therefore, should be installed horizontally with, however, consideration given to the accessibility. Where a valve is installed on vertical piping, its handle should be oriented toward the passage in line with other pump piping valve handle orientation, within, however, the range in which the handle does not interfere access way.
(c) Where it is difficult or impossible to operate the valve from the ground due to the height at which the valve is installed, a valve operation platform shall be provided. Use of a chain shall otherwise be studied. In this case, the valve shall be located in such a manner that the chain does not come into contact with the pump/motor rotating shaft. In some cases, the chain comes into contact with some other installation, and sparks are thereby produced, thus causing the pump to ignite. Some clients, therefore, do not accept the use of chains, also from the standpoint of frequency of valve operation.

(d) An operation walkway as shown in Figure below may be provided for pump piping which is connected to the offsite sleeper piping, in view of valve operability and accessibility. The valves shall be located along the operation walkway. Also, each valve shall be located in such a way that its front and rear can be easily supported from the ground; space for supports shall be provided beforehand. In addition, where the walkway is intended to serve as both valve operation platform and passage, it shall be brought as close as possible to the pumps, within, however, a range not interfering with the maintenance of the pumps.

5.5 Strainer Installation Position

A strainer is installed on the pump suction pipe. In this case, space to pull the wire mesh must be provided, for strainer cleaning. Wire mesh pull out withdrawal direction and space necessary for working differ according to the type of strainer. It is necessary, therefore, to fully understand the strainer structure and to perform piping arrangement. Strainer installation direction is sometimes restricted according to, in particular, fluid flow direction.

(a) Where T-strainer (angle type) is used:
This type of strainer must always be installed at locations where the piping bends 90° as shown in Figure-A below. Figure-B below shows examples of piping using a T-strainer.

(b) Where T-strainer (straight type) is used

This type of strainer must be installed in a straight run of piping. The wire mesh can be pulled in any direction from the piping. Where this type of strainer is installed on vertical piping, it may be located with the orientation that may prove to be convenient to wire mesh pull out. Where installed on horizontal piping, it should be located laterally. Figure “B” below shows examples of piping using a T-strainer (straight type). When installed downward, T-strainers require a drain on the cover flange, but inconvenience such as drain blockage is apt to often occur.

(c) Where Y-strainer is used:

This type of strainer can also be installed on a straight run of piping as with the piping using a T-strainer (straight type) The wire mesh can be pulled in any direction from the piping. Strainer installation position and wire mesh pulled direction are the same as those of T-strainers (straight type). Figure “B” below shows examples of piping.

5.6 Reducer Installation Location

For a reducer to be installed at the horizontal portion near a nozzle, an eccentric type shall be used; it shall be installed in such a manner that the flat side is located upward, in order to avoid the formation of air pockets.

5.7 Discharge Piping

(1) Piping Route
Discharge piping routes may, in principle, be designed in the same manner as the “piping route” for suction piping set forth in above sections. Discharge piping, however, is not subject to severe control of pressure loss unlike suction piping; the presence of air pockets is permitted. Emphasis, therefore, shall be laid on operation, in piping planning.

(2) Valve Installation Location
The valve installation position is basically the same as that set forth in Item 6.47 above. As shown in Figures “A” and “B” below, however, the discharge piping check valve should be installed horizontally in view of the structure of check valve and ease of support installation.
It is possible to make a piping arrangement, in which a swing check valve, dual plate check valve or similar check valve is installed on vertical piping. In this case, however, consideration shall be given to the block valve being located high up; the block valve should be located at a point which is easily accessible from the motor switch stand. In general, the piping arrangement shown in Figure “B” is suitable for medium- and small-size pumps. If the block valve position is likely to become higher, however, the line shall first be lowered as shown in Figure “A”. Thus, a piping arrangement which ensures that the valve can be operated easily, shall be adopted.

A drain valve and a pipe are sometimes installed on check valves to drain the trapped liquid at low point.

(3) Reducer Installation Position
Unlike suction piping, discharge piping does not pose large problems with pressure loss. The reducer, therefore, may be installed at any position between the pump nozzle and the check valve.

6. Auxiliary Piping

(1) Drain and Purge Connection
(a) To prevent air ingress due to mis-operation or other causes, no drains are provided near the pump of the suction piping, as a general rule. However, where fluids easily causing plugging, fluids solidifying at room temperature or other similar fluids are handled, a purge connection, which concurrently serves as a drain, shall be installed as near as possible to the block valve on its upstream side. In general, the necessity of a purge connection is indicated in the P&ID concerned.

(2) Pressure Gage Installation Position
Pressure gages shall be installed in the orientation and at the height which ensure that the graduations can be easily read and which do not interfere with block valve operation.

(3) Temperature Instrument Installation Position
Where there is a spare pump, the line of the pump which is not operating forms dead space, therefore, a local temperature indicator shall be installed on the common line. Where temperatures cannot be read by such a local temperature indicator, a temperature indicator shall be installed on the ground using a capillary tube.
A temperature indicator shall otherwise be installed on each line, which connects each pump. Such measures shall be studied and confirmed with the Instrumentation and Control Engineering Department.

(4) Pump cooling piping: Mainly used to cool bearings and lube oil coolers; sometimes used to cool motors

(5) Vent and drain piping: To fill and draw liquid into/from the pump casing, and also to draw liquid from the base drain connection.

(6) Mechanical seal piping: Sealing liquid piping at the bearing of pumps provided with a mechanical sealing mechanism (The discharge liquid of the pump is used for mechanical sealing.)

(7) Flushing oil piping: Piping used to flush sludge and the like, which accumulates at the bearing of pumps handling fluids containing sludge (prevention of abrasion of bearing due to sludge)

7. Pipe Support Arrangements

The type of piping support must be planned, designed and selected in accordance with the relevant standard and as per the requirements for the layouts. Following type of supports are normally used:

(1) Where pump alignment is necessary, adjustable supports shall be used. In the case of large-diameter piping, pump alignment may be difficult when only one point very close to the pump nozzle is supported using an adjustable support.
(2) Where piping supports involving thermal expansion are used, studies shall be conducted on the installation of stoppers, guide supports and the like in order to reduce force and moments applied to pump nozzles due to thermal expansion. Thus, the optimum support types shall be selected. In this case, supports shall be provided with strength and rigidity which prove to be fully resistant to external force.

(3) With respect to pump installation on soft ground and piping connected to large pumps, consideration shall be given to the relative settlement between the pump and the piping, and studies shall be carried out on the integration of pump foundations with piping support foundations (possibility of integration of foundations, civil design information submission time, etc.).
(4) For the pumps whose piping must be removed for maintenance and inspection, the piping supports shall be of a structure which ensures ease of removal and installation.
(5) Figure below shows the types of piping supports.

(6) Piping supports in the area around the pump shall be brought as close to the pump nozzle as possible to ensure that the piping load is minimally applied to the pump nozzle.
(7) Supports (guides and stoppers) used to reduce force and moments applied to the pump nozzles shall preferably be located along a straight line which runs through a fixed point of the pump, to ensure that the thermal expansion rate between the binding point and the nozzle is minimized. See the figure below for such example.

8. Conclusion

In this article we discussed about various types of centrifugal pumps including pump types based on API 610. The piping around centrifugal pumps is important for a number of reasons. It provides a means of connecting the pump to the equipment that it is designed to serve. It also helps to distribute the fluid evenly throughout the pump and to prevent the fluid from cavitating. As a Piping Engineer or designer, one must learn about all the important aspects related to Pumps like pumps locations in plot plan, maintenance & access requirements, process requirements in order to apply best piping arrangements around pump. This article is an effort to best describe some of the important factors so that reader can independently apply it when it comes to design piping arrangements around pumps. Any comments , suggestions or queries are welcome.

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