Guidelines for Piping Arrangements for Centrifugal Pumps

January 2004

Process Industry Practices Machinery

PIP REEP004 Guidelines for Piping Arrangements for Centrifugal Pumps

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES In an effort to minimize the cost of process industry facilities, this Practice has been prepared from the technical requirements in the existing standards of major industrial users, contractors, or standards organizations. By harmonizing these technical requirements into a single set of Practices, administrative, application, and engineering costs to both the purchaser and the manufacturer should be reduced. While this Practice is expected to incorporate the majority of requirements of most users, individual applications may involve requirements that will be appended to and take precedence over this Practice. Determinations Determinations concerning fitness for purpose and particular matters or application of the Practice to particular project or engineering situations should not be made solely on information contained in these materials. The use of trade names from time to time should not be viewed as an expression of preference but rather recognized as normal usage in the trade. Other brands having the same specifications are equally correct and may be substituted for those named. All Practices or guidelines are intended to be consistent with applicable laws and regulations including OSHA requirements. To the extent these Practices or guidelines should conflict with OSHA or other applicable laws or regulations, such laws or regulations must be followed. Consult an appropriate professional before applying or acting on any material contained in or suggested by the Practice.

This Practice is subject to revision at any time by the responsible Function Team and will be reviewed every 5 years. This Practice will be revised, reaffirmed, or withdrawn. Information on whether this Practice has been revised may be found at www.pip.org.

© Process Industry Practices (PIP), Construction Industry Institute, The University of Texas at Austin, 3925 West Braker Lane (R4500), Austin, Texas 78759. PIP member companies and subscribers may copy this Practice for their internal use. Changes, overlays, addenda, or modifications of any kind are not permitted within any PIP Practice without the express written authorization of PIP.

PIP will not consider requests for interpretations (inquiries) for this Practice.

Not printed with St ate funds

January 2004

Process Industry Practices Machinery

PIP REEP004 Guidelines for Piping Arrangements for Centrifugal Pumps Table of Contents 1. Introduction..................................3 1.1 Purpose ............................................. 3 1.2 Scope................................................. 3

2. References ...................................3 2.1 Process Industry Practices ................ 3

3. Definitions ....................................3 4. General Piping Configuration ..... 4 4.1 Typical Arrangements........................ 4 4.2 Pump Suction Piping ......................... 4 4.3 Pump Discharge Piping ..................... 5

5. Support of Piping Systems .........5 5.1 5.2 5.3 5.4 5.5 5.6 5.7

Equipment Allowables ....................... 5 Design Considerations....................... 5 Cold Spring ........................................ 5 Expansion Joints................................ 5 Piping Alignment ................................ 6 Supports ............................................ 6 Field Welds........................................ 7

Process Industry Practices

6. Operation and Maintenance Considerations ........................... 7 6.1 Accessibility ....................................... 7 6.2 Piping Vents, Drains, and Gauge Connections....................................... 8 6.3 Permanent Inlet Strainers.................. 9 6.4 Temporary Inlet Strainers .................. 9 6.5 Warm-up Lines .................................. 9 6.6 Minimum Flow Bypass....................... 9 6.7 Self-Priming Pumps......................... 10 6.8 Pumps Operating in Parallel............ 10

Appendix – Typical Piping Arrangements – Figures.......... 11 Figure 1.

End suction, top discharge overhung centrifugal pump preferred installation Figure 2. End suction, top discharge overhung centrifugal pump alternate installation. Figure 3. Top suction, top discharge centrifugal pump preferred installation Figure 4. Top suction, top discharge centrifugal pump alternate installation for large diameter piping Figure 5. Side suction, side discharge centrifugal pump preferred installation

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January 2004

Figure 6.

Side suction, side discharge centrifugal pump alternate installation for suction piping with elbow installed in the same plane as the shaft Figure 7. Vertical inline side suction, side discharge centrifugal pump preferred installation Figure 8 Vertical inline side suction, side discharge centrifugal pump alternate installation Figure 9. Examples of reduction at pump suction for side suction pump piping Figure 10. Examples of reduction at pump suction for end suction pump piping Figure 11. Examples of suction and discharge valve orientation

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January 2004

1.

Introduction 1.1

Purpose This Practice provides guidance for designers in the layout of piping systems around centrifugal pumps.

1.2

Scope This Practice is a compilation of graphics and narrative guidelines for the layout of piping for centrifugal pumps. This Practice covers piping considerations that affect operability, maintainability, hydraulic performance, and piping flexibility for centrifugal pumps. It includes typical piping layout drawings for each configuration routinely found in the process industry and considered good practice. This document also references other industry standards that apply to installation requirements, allowable nozzle loads, and methods of piping flexibility analysis. This document does not address auxiliary piping (lube oil piping, seal piping, etc.) or non-metallic piping systems.

2.

References Applicable parts of the following Practices shall be considered an integral part of this Practice. The edition in effect on the date of contract award shall be used, except as otherwise noted. Short titles will be used herein where appropriate.

2.1

Process Industry Practices (PIP) – PIP REIE686 - Recommended Practices for Machinery Installation and Installation Design – PIP RESE002 - Allowable Nozzle Loads on Rotating Machinery

3.

Definitions axial stop: Mechanical restraints used to control axial or longitudinal movement of the piping in one or two directions without providing complete fixation breakout spool (also known as dropout spool ): A short, flanged length of pipe immediately connected to the pump piping flanges. Lengths vary with the size of the pipe but typically range from 6 inches (15 cm) to 3 ft (1 m). The purposes of this spool are to facilitate pump installation, allow piping modification to reduce pipe strain, isolate the pump, facilitate commissioning activities such as flushing or blowing lines, and allow removal of temporary inlet strainers. cold spring : The intentional misalignment of piping during assembly to produce a desired initial displacement and stress hangers: All devises used to suspend a piping system and also to support the weight of the same. Examples include suspended rods, base-type support units, anchors, etc. Hangers are included in the more general term “pipe supports.”


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January 2004

isolation block valve (also known as block valve or isolation valve): A valve used to isolate a pump preparatory to maintenance owner: The party who owns the facility wherein the pump system will be used restraints: All devices used to restrict or limit the free expansion of a piping system and yet support none of the weight. Examples include guides, sway braces, sway struts, and snubbers. Restraints are included in the more general term “pipe supports.” short radius elbow: A fitting used to change the direction of the piping system 90 , having a radius equal to 1.0 times the nominal pipe diameter °

standard long radius elbow: A fitting used to change the direction of the piping system 90 , having a radius equal to 1.5 times the nominal pipe diameter °

supports: The entire range of devices used to suspend, support, guide, anchor, and restrain the movement of piping systems. Examples include hangers, restraints, guides, anchors, sway struts, shock and sway suppressors, etc.

4.

General Piping Configuration 4.1

Typical Arrangements Typical piping arrangement sketches for various pump types are provided in the Appendix of this Practice.

4.2

Pump Suction Piping 4.2.1

Pump suction piping should be arranged in accordance with PIP REIE686, Chapter 6 - Piping, such that the flow is as smooth and uniform as practicable at the pump suction nozzle.

4.2.2

The use of tees, crosses, valves, reduced port valves, strainers, near-runsize branch connections, and short radius elbows should be avoided near the suction nozzle.

4.2.3

Suction valves should be full port and of the same size (or larger) as the pump nozzle on condition that net positive suction head (NPSH) margin is available in accordance with PIP RESP001 (see Appendix Figures 1 through 4).

4.2.4

The pump suction piping should have a straight run of five pump suction nozzle diameters between the suction flange and first elbow, tee, valve, reducer, permanent strainer, or other obstruction in accordance with PIP REIE686 , Chapter 6. Comment :

4.2.5

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Temporary suction strainers, flanges, drains, and pressure indicator connections may be included within the straight run suction piping requirement.

The suction pipe size should be larger than the pump suction nozzle or should be as a minimum equal to the pump suction nozzle.



January 2004

4.3

5.

4.2.6

For horizontal suction piping, eccentric reducers with the flat side on top should be used to avoid pocketing of vapors in the suction line. For top suction pumps, the reducer should be concentric (see Appendix Figures 1 through 4).

4.2.7

The last pipe elbow in the suction line to a pump should be a standard long radius elbow.

4.2.8

For double suction pumps, the last pipe elbow in the suction line to the pump should be perpendicular (not in the same plane) to the impeller shaft (see Appendix Figure 3).

Pump Discharge Piping 4.3.1

A check valve should be installed in the discharge line of all pumps in accordance with PIP REIE686, Chapter 6 - Piping , unless no possibility exists for a flow or pressure surge (such as water hammer) under any condition.

4.3.2

The check valve should be located between the pump discharge flange and the discharge block valve.

Support of Piping Systems 5.1

Equipment Allowables The support and flexibility of the suction and discharge piping systems should be designed to limit nozzle loads to less than those specified in PIP RESE002.

5.2

5.3

Design Considerations 5.2.1

The design of pump piping support systems should account for all possible operating conditions. The potential effect of operating upsets and transients on nozzle loads, internal misalignment, and external coupling misalignment cannot be ignored.

5.2.2

All identifiable system thermal or pressure upsets should be specified before starting engineering and procurement of the pump and design of the piping system. These abnormal conditions can result in higher loads being imposed on the nozzles than under the normal operating situations and can cause coupling misalignment after only one cycle of upset load.

5.2.3

If differential settlement is anticipated, the pump foundation should be extended to provide support for the suction piping.

Cold Spring Cold spring (cold pull) should not be used as a design method to deal with anticipated thermal growth and operational pipe strain.

5.4

Expansion Joints Expansion joints should not be used unless the owner’s approval is obtained for each expansion joint proposed.


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5.5

January 2004

Piping Alignment Piping alignment should conform to PIP REIE686 , Chapter 6 - Piping .

5.6

Supports 5.6.1

General 5.6.1.1 Piping should be adequately supported and controlled to meet the design requirements of the pump. This removes the static load, allows identification of piping fit problems during installation, and allows easier removal of the pump for maintenance. 5.6.1.2 Only those supports specified as a result of the piping analysis should be provided (see PIP RESE002). 5.6.1.3 Piping design requirements should include allowable flange loadings, thermal growth, etc. These requirements are set by the pump manufacturer, the industry standards, or the owner. 5.6.1.4 The dead weight of the piping and process fluid should be entirely supported by pipe hangers or supports.

5.6.2

Springs 5.6.2.1 Spring supports should be designed to provide the required support for the weight of the pipe, the insulation, and the contents during operation and hence relieve the load on the pump nozzle and allow free thermal expansion of the pipe. 5.6.2.2 Adding more supports or moving existing supports may be necessary if resonant vibration appears in the piping. Comment : Spring supports for liquid-filled piping systems may be difficult to install because the system is empty at the time of installation and the spring design load reacts against a liquid-filled system.

5.6.3

Adjustable or Rigid Supports 5.6.3.1 Adjustable supports should be used to account for field variations in installed dimensions and for changes over time. 5.6.3.2 The first piping support next to a horizontal nozzle should be an adjustable support. 5.6.3.3 Rigid supports may be used to limit the movement of a line to prevent excessive deflection. 5.6.3.4 A rigid support is not satisfactory where thermal expansion may cause the pipe to move away from the support.

5.6.4

Restraints 5.6.4.1 Restraints should be installed to control deflections caused by induced loads (such as thermal expansion, wind, etc.) in the

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January 2004

pump piping system, thus avoiding excessive loads on pump nozzles. 5.6.4.2 Restraints should be used to direct the pipe thermal movement away from the equipment and into other portions of the piping system that have enough flexibility to absorb the movement without becoming overstressed or without overloading other connections. 5.6.4.3 A guide should be used to permit only axial movement while preventing lateral movement. 5.6.4.4 An axial stop should be used to permit lateral movement while preventing axial movement.

5.7

6.

Field Welds 5.7.1

The piping design should include a provision for a final piping field weld to permit piping installation in accordance with the machinery flange fit-up requirements in PIP REIE686 , Chapter 6 - Piping .

5.7.2

On larger pipe, the final field weld should be farther away from the machine to allow for ease of installation.

5.7.3

Following the final field weld, the pipe-to-pump nozzle flange alignment should comply with PIP REIE 686 .

Operation and Maintenance Considerations 6.1

Accessibility 6.1.1

Piping should be arranged to allow adequate access to the pump without requiring excessive dismantling of the piping system.

6.2.2

The coupling between the pump and its driver should be easily accessible to align the pump and driver.

6.2.3

Pump seal access should be considered because seal failure is the most common cause for maintenance.

6.1.4

Axially split pump casings should not have overhead obstructions.

6.1.5

Radially split pump casings should have clear access to the end of the pump for normal maintenance.

6.1.6

If necessary, access can be provided by designing the piping to be removable. It is best, however, to design the piping to be self-supporting in a manner that minimizes the need for piping removal during normal maintenance activities.

6.1.7

The guidelines for accessibility contained in PIP REIE686 , Chapter 6 Piping , should be carefully followed.

6.1.8

Isolation valves should be provided in the inlet and outlet process piping.


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6.1.9

January 2004

Any temporary or permanent strainer should be located between the inlet isolation block valve and the pump inlet connection. Comment:

Depending on service , process integrity may require double block and bleed valves on vents and drains.

6.1.10 Block valves requiring attention, observation, or adjustment during normal operation should be located within reach from grade or platform. 6.1.11 Block valves used for operation of the system may be chain-operated when the bottom of handwheel is more than 7 ft (2.1 m) above the high point of finished surface or operating platform. 6.1.12 Chain wheels should not be used on screwed valves or valves smaller than NPS 3. 6.1.13 An impactor-type chain wheel should not be used on valves smaller than NPS 4. 6.1.14 Chain-operated wrenches should not be used on any type of valve. 6.1.15 Block valves used only for process shutdown and located less than (15 ft) (4.6 m) from an access level do not need to be chain-operated unless they cannot be reached by a portable ladder. 6.1.16 Stems of globe and gate valves with solid wedges should be oriented above the valve body centerline. 6.1.17 Stems of gate valves with split or double disc-type gates should be oriented vertically upward. 6.1.18 Stems of valves in hot service, such as heat transfer fluids, should be in the horizontal position. 6.1.19 Sufficient room should be allowed for the operation of handles or levers on valves. 6.1.20 Hand-operated control valves should be located so that they can be adjusted while associated instruments can be read.

6.2

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Piping Vents, Drains, and Gauge Connections 6.2.1

Vents and drains should be provided in accordance with PIP REIE686 , Chapter 6 - Piping .

6.2.2

Adequate drains should be provided on the piping to perform routine maintenance on pumps.

6.2.3

Drains should be located at the lowest point in the piping near the pump.

6.2.4

Drain connections should not be placed in angle sections of reducers.

6.2.5

Dead legs in piping should be avoided. When a dead leg is unavoidable, it should be provided with drains.

6.2.6

Provisions should be made for the installation of a pressure gauge in the suction piping between the strainer and the pump suction flange.



January 2004

6.2.7

6.3

A pressure gauge should be installed in the pump discharge piping between the check valve and block valve. Gauge isolation and bleed valves should also be provided.

Permanent Inlet Strainers Permanent strainers should be provided according to PIP REIE686 , Chapter 6 Piping .

6.4

6.5

Temporary Inlet Strainers 6.4.1

Temporary suction strainers should be provided for initial startup according to PIP REIE686 , Chapter 6 - Piping .

6.4.2

A means (typically a break-out spool) should be provided to remove the temporary suction strainers.

6.4.3

A means of determining whether a strainer is plugged should be provided. This is of particular importance on high-energy pumps.

Warm-up Lines Pumps handling hot materials greater than 300 F (150 C) or handling high pour point materials should have warm-up lines in accordance with PIP REIE686 , Chapter 6 - Piping . °

6.6

°

Minimum Flow Bypass 6.6.1

If the minimum continuous flow rate required by a pump cannot be assured, a minimum flow bypass or instrumentation to alarm or shut down the pump should be provided. Comment:

Sealless pumps require minimum flow protection at all times including at start-up and during upset conditions.

6.6.2

Unless otherwise specified, minimum flow bypass should be routed to the suction vessel.

6.6.3

If the system provides adequate cooling for the recirculated fluid, consideration may be given to routing the minimum flow bypass to the pump suction line.

6.6.4

A bypass routed to a pump suction line should be connected at a point that is a minimum distance of 10 pipe diameters upstream of the pump suction flange. Comment:

6.6.5


Bypass control is often used on high specific speed pumps, such as axial flow pumps, because the power requirement decreases with increased flow.

Size of the suction vessel, thermodynamic properties of the pumped fluid, and amount of fluid to be recirculated should be taken into consideration to determine whether a cooler is required in the bypass line.

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6.7

6.8

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Self-Priming Pumps 6.7.1

Suction piping for self-priming pumps should be designed to minimize friction loss and reduce the volume of air that must be evacuated in the suction pipe.

6.7.2

Piping elbows and suction piping lengths should be minimized.

6.7.3

The suction pipe size should be the same size as the pump suction nozzle.

6.7.4

During the priming cycle, air is evacuated from the suction line at a very low pressure at the pump discharge. If the application requires a discharge piping system that incorporates a check valve to prevent backflow or to stop water hammer, an air bleed line or vent should be installed between the discharge flange and the check valve to ensure that the pump will prime. The air bleed line should not be installed below the liquid level or should not contain any liquid traps to impede airflow from the pump. An air release valve may be installed to allow the air to escape and seal once the pump is primed.

Pumps Operating in Parallel 6.8.1

The pressures on the suction and discharge sides of each pump in parallel should be essentially equal.

6.8.2

If two or more pumps are fed from one common suction intake or discharge into a common header, suction and discharge manifold piping should be symmetric.

6.8.3

Pumps operated in parallel should have block valves to allow individual pumps to be taken out of service.

6.8.4

Each pump operated in parallel should have a check valve installed in the discharge line to prevent backflow under operating conditions.



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Appendix – Typical Piping Arrangements – Figures


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Guidelines for Piping Arrangements for Centrifugal Pumps

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