Centrifugal Pump Selection

COMPLETE REVISION January 2004

Process Industry Practices Machinery

PIP RECP001 Design of Pumping Systems That Use 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 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 This Practice will be revised, reaffirmed, or withdrawn.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. Printing History September 1995 Issued January 2004 Complete Revision Not printed with State funds

COMPLETE REVISION January 2004

Process Industry Practices Machinery

PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps Table of Contents 1. Introduction .................................. 2 1.1 Purpose ............................................. 2 1.2 Scope................................................. 2

2. References ................................... 2 2.1 Process Industry Practices ................ 2 2.2 Industry Codes and Standards .......... 2 2.3 Other References .............................. 3

3. Definitions .................................... 3 4. Requirements ............................... 4 4.1 General Design Principles ................. 4 4.2 Hydraulic Selection Criteria................ 5 4.3 Net Positive Suction Head Considerations................................... 8 4.4. Heating/Cooling Jacket.................... 11 4.5. Driver ............................................... 12 4.6 Energy Evaluations .......................... 13 4.7. Application of Specific Pump Types ....................... 14

Process Industry Practices

Appendix – Figures ....................... 16 A-1 Pump Operating Ranges as a Function of Flow Rate and Suction Specific Speed, Nss A-2 Pump Operating Ranges as a Function of Flow Rate and Suction Specific Speed, nqs A-3 Vertical Vessel Reference Levels for NPSHA Calculations A-4 Horizontal Vessel Reference Level for NPSHA Calculations A-5 NPSH vs. Flow Rate for Various Speeds at Nss = 9,000 and 11,000 A-6 NPSH vs. Flow Rate for Various Speeds at nqs = 175 and 215

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

1.

COMPLETE REVISION January 2004

Introduction 1.1

Purpose This Practice provides designers with requirements for design of pumping systems that use centrifugal pumps.

1.2

Scope This Practice describes the requirements for general design principles, hydraulic selection criteria, net positive suction head considerations, jacket and driver considerations, and energy evaluations for design of pumping systems that use centrifugal pumps. Fire water pumps should be designed in accordance with the National Fire Protection Association (NFPA) codes and standards and are not covered by this Practice. This document is a complete revision of PIP RESP001, and therefore, revision markings are not provided.

2.

References Applicable parts of the following Practices, industry codes and standards, and references 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 REIE 686 - Recommended Practices for Machinery Installation and Installation Design

2.2

Industry Codes and Standards • American Petroleum Institute (API) – Std 611 - General Purpose Steam Turbines for Refinery Service – Std 610 - (ISO 13709) - Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries • American Society for Mechanical Engineers (ASME) – B73.1 M - Specification for Horizontal End Suction Centrifugal Pumps for Chemical Process – B73.2 M - Specification for Vertical In-Line Centrifugal Pumps for Chemical Process • Hydraulic Institute – ANSI/HI 1.3 - Hydraulic Institute Centrifugal Pump Applications

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2.3

PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

Other References – Irving Taylor, What NPSH for Dissolved Gas?, Hydrocarbon Processing, August 1967, Volume 46, Number 8, pages133-134 – W. Roy Penny, Inert Gas in Liquid Mars Pump Performance, Chemical Engineering, July 3, 1978 – Mao J. Tsai, Accounting for Dissolved Gases in Pump Design, Chemical Engineering, July 26, 1982 – C. C. Chen, Cope with Dissolved Gases in Pump Calculations, Chemical Engineering, October 1993 – Jerry L. Hallam, Centrifugal Pumps: Which Suction Specific Speeds Are Acceptable?, Hydrocarbon Processing, April 1982

3.

Definitions high stream factor plants: Plants in which the on-stream time must be 97.5% or greater at design capacity intermediate life plants: Plants with an expected economic life of less than 20 years long life plants: Plants with an expected economic life of 20 years or more net positive suction head (NPSH): Total absolute suction head, in feet (meters) of liquid, determined at the suction nozzle and referred to the datum elevation, minus the vapor pressure of the liquid, in feet (meters) absolute. Datum elevation is the suction nozzle centerline for vertical in-line pumps and the top of the foundation for other vertical pumps. net positive suction head available (NPSHA): NPSH, in meters (feet) of liquid, determined by the purchaser for the pumping system with the liquid at the rated flow and the corresponding pumping temperature net positive suction head required (NPSHR): NPSH, in feet (meters), determined by vendor testing with water. NPSHR is measured at the suction flange and corrected to the datum elevation. NPSHR is the minimum NPSH at rated capacity required to prevent a head drop of more than 3% (first-stage head in multistage pumps) caused by cavitation within the pump. purchaser: The agency that issues the order and specifications to the manufacturer relative density: Ratio of the density of one substance to that of a second reference substance, both at the same specified temperature specific gravity: Dimensionless ratio of the density of a fluid to that of a reference fluid. For design of pumping systems, the reference fluid is water at a temperature of 60ºF (15.5ºC).

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

4.

COMPLETE REVISION January 2004

Requirements 4.1

General Design Principles 4.1.1

Pumping system curves shall be developed for all flow paths, piping configurations, and process flow characteristics. Operation in each of the specified flow paths shall be evaluated for viability. The off-design operating cases and the amount of time in each operating case shall be identified.

4.1.2

Pump(s) selected for the system shall a. Provide the head and flow required for all flow paths, piping configurations, and process flow characteristics. b. Be manufactured from materials acceptable to the process. Materials shall be corrosion- and erosion-resistant.

4.1.3

Flow control systems shall ensure control of the flow within the acceptable operating range of the selected pump(s).

4.1.4

Adequate protection shall be provided to prevent or minimize the impact of operating the pump dry or dead-headed. This may include re-circulation, power monitors, or other instrumentation to detect or prevent dry and deadhead operation.

4.1.5

Pump manufacturer shall determine the rated shaft power required by the pump assembly based on the operating conditions provided by the purchaser. Determination of the rated shaft power shall take into consideration the following variables as a minimum: a.

Specific gravity

b

Viscosity

c

Mechanical seal(s)

d. Stuffing box pressure/suction pressure e. Gear assembly f.

Couplings

g. Hydraulic tolerances Other variables shall be taken into consideration as required. Motor driver shall be sized in accordance with Section 4.5.1.5, Table 1 (this Practice), unless the above-mentioned considerations require a larger driver. 4.1.6

Pump(s) shall have a shaft-sealing mechanism designed for all operating conditions. Sealing mechanisms shall have adequate cooling, lubrication, and support systems consistent with process conditions and seal requirements. Seal area / chamber (on the process side) shall be self-venting.

4.1.7

Suction and discharge piping shall be arranged to minimize turbulence that may reduce the pump’s performance or increase maintenance. Comment:

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Refer to PIP REIE 686, Chapter 6, for more information about pump piping layout.

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

January 2004

4.1.8

Arrangement of suction and discharge piping for pumps in wet pit sump installations shall not permit gas entrainment and shall facilitate maintenance of the pump. Comment:

4.1.9

Refer to Hydraulic Institute standards for more information about wet pit sump design.

Critical speeds shall fall at least 20% outside the operating speed range of the pump.

4.1.10 Suction and discharge piping on pumps used in parallel operation is critical to proper operation. The same pipe size and line loss shall be maintained between each pump and the point where the pumps tie together. Design of the piping shall provide equivalent suction and discharge pressures. 4.1.11 Pumps used in parallel shall be identical in design and size, shall be operated at the same speed, and shall be installed with identical impellers. 4.1.12 If a flow orifice is used (to increase the slope of a pump curve as seen by the system), the orifice shall be installed downstream from the pump because it is a part that is subject to wear. 4.1.13 Pump suction line size is typically designed for fluid velocities from 3 to 6 feet per second (1 to 2 meters per second). Acceptable velocities may increase or decrease depending on NPSH margin for the pump selected and system economic analysis. 4.1.14 Recommended pump discharge line size shall be designed for fluid velocities from 3.5 to 10 feet per second (1 to 3 meters per second). 4.1.15 Pump(s) shall use an impeller sized and designed to accommodate all operating conditions. Semi-open or closed impellers shall be used in hightemperature applications to prevent the pump from locking up during warmup and cool-down. 4.1.16 Design data verifying that the design of the pumping system conforms to the design principles as listed in the previous paragraphs of this section shall be developed. Data shall be subject to a formal review by the purchaser before release of the design for procurement/construction. Data and its formal review shall become a permanent record for project, operations, and maintenance purposes. 4.2

Hydraulic Selection Criteria 4.2.1

Pump(s) selected for the pumping system shall have head capacity characteristic curves that rise continuously as flow is reduced to shutoff.

4.2.2

If pumping system is designed for pumps to operate in parallel, the head rise to shutoff shall be at least 10% of the head at rated capacity. Comment:

Process Industry Practices

Pumps without a substantial rise in characteristic curve, as flow is reduced, are more susceptible to operating at dead head (shut-in) conditions if such pumps operate in parallel.

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

Comment:

January 2004

Achieving a continuously rising head characteristic curve with low-flow high-head pumps is not always possible. Pumps with this characteristic rarely operate in parallel.

4.2.3

Pump impeller shall have a best efficiency point (BEP) that is between the normal and rated operating points.

4.2.4

Normal operating point flow rate of the pump shall be greater than the minimum continuous flow rate specified by the pump vendor and less than the flow rate at the BEP for the selected pump impeller.

4.2.5

Pump shall be capable of at least a 5% head increase at rated condition with the installation of a new impeller.

4.2.6

Minimum diameter of selected pump impeller shall be 105% of the minimum diameter impeller for the generic pump curve for the specific pump. Comment:

4.2.7

Suction recirculation increases as minimum diameter impeller is approached. This can result in increased NPSHR at the same flow rate and in less predictable performance.

If the pumped fluid has a variable specific gravity, the head required to be developed by the pump shall be based upon the lowest specific gravity and the greatest system differential pressure for the required flow rate. Comment:

“Specific gravity” is used throughout this Practice in lieu of “relative density.” Some commonly used equations would otherwise be affected by the shifting temperature reference used in relative density.

4.2.8

If viscosity corrections are required, head, capacity, and efficiency corrections shall be the responsibility of the pump manufacturer. These corrections shall be calculated in accordance with the “Centrifugal Pump” section of ANSI/HI 1.3.

4.2.9

Pumps with suction specific speeds of NSS greater than 11,000 (ηqs greater than 215) require specific approval by the purchaser. A quotation for such a pump shall include minimum continuous flow rate, maximum operating flow rate, and operating experience. Comment:

Suction specific speed, NSS (S), is an index of pump suction operating characteristics determined at the BEP with the maximum diameter impeller. Suction specific speed is an indicator of the NPSHR for given values of capacity and rotating speed. NSS (S) provides an assessment of susceptibility of the pump to internal recirculation. NSS (S) is calculated by the following equation:

NSS (S)

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COMPLETE REVISION

=

(N)(Q)^1/2 / (NPSHR)^3/4

where NSS (S)

=

suction specific speed

N

=

rotating speed in revolutions per minute

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

January 2004

Q

NPSHR

=

flow rate per impeller eye, in gallons per minute (cubic meters per second) at the BEP with the maximum diameter impeller

=

total flow rate for single suction impellers

=

half of total flow for double suction impellers

=

net positive suction head required in feet (meters) at the BEP for the maximum diameter impeller

Comment:

Suction specific speed, Sderived using cubic meters per second and meters, multiplied by 51.6, is equal to suction specific speed, NSS, derived using U.S. gallons per minute and feet.

Comment:

Industry has extensive published documentation indicating that pumps with high NSS (S), defined as 11,000 (215) and greater, have reduced reliability. Refer to Hallam (1982). At off-design (off-BEP) conditions, these pumps are susceptible to both suction and discharge recirculation, which may result in high vibration and poor seal life. Pumps with high NSS (S) should not be accepted for services with widely varying operating flow rates. If no reasonable alternative to a high NSS (S) pump exists, steps should be taken to ensure pump operation at or very near the BEP. Consider a controlled bypass or a complete shutdown if the pump is used in a batch operation. Vibration instrumentation should be considered for proper monitoring of these steps.

Comment:

Inducers have been applied successfully to as much as 30,000 NSS (580 S), although the more common range is 15,000 to 25,000 NSS (290 to 480 S) . When considering inducers, particular attention should be devoted to the NPSHR curve shape and the pump manufacturer’s experience. Care should be given when selecting inducers for pumps that have a large range in flow rate because a narrow flow range is preferred for inducers.

4.2.10 Normal and rated flow rates of pumps shall be within the acceptable range in accordance with Figures A-1 and A-2 (for SI and U.S. Customary units, respectively). Pumps with flow rates outside this range require specific approval by the purchaser. Pumps with flow rates outside this range require Figures A-1 and A-2 (for U.S. Customary and SI units, respectively), provided in the Appendix. Pumps with flow rates outside this range require specific approval by the purchaser. Comment:

Process Industry Practices

Figures A-1 and A-2 may not apply to inducer designs.

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

Comment:

COMPLETE REVISION January 2004

As shown in Figures A-1 and A-2, the acceptable range of flow rates is reduced as higher suction specific speed pumps are applied. It is recognized that the damage that may occur to a pump at high suction specific speeds is also a function of the energy density level of the pump. Therefore, Figures A-1 and A-2 should be considered as a general guide.

4.2.11 Pump manufacturer shall state the minimum continuous flow rate required by the pump and whether this flow rate is based on hydraulic stability or thermal limitations. 4.2.12 Determination of the minimum continuous flow rate of the process shall take into consideration normal, abnormal, start-up, and shutdown conditions. Comment:

Pump operation below the stated minimum continuous stable flow rate causes increased process fluid recirculation within the pump, which may result in increased noise, high vibration level, and bearing and/or seal failure. Pump operation below the stated minimum continuous thermal flow rate may result in gasket failure, seal failure, or flashing in the pump casing.

4.2.13 If process conditions or operating practice cannot ensure the minimum continuous flow rate required by the pump, a minimum flow bypass or instrumentation to the alarm or to shut down the pump shall be provided. 4.2.14 Unless otherwise specified, minimum flow bypass shall be routed to the suction vessel. 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. 4.2.15 Bypass routed to the pump suction line shall be connected at a point that is a minimum distance of 10 pipe diameters upstream of the pump suction flange. Comment:

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

4.2.16 Size of the suction vessel, thermodynamic properties of the pumped fluid, and amount of fluid to be recirculated shall be taken into consideration to determine whether a cooler is required in the bypass line. 4.3

Net Positive Suction Head Considerations 4.3.1

Requirements for calculating NPSHA and for margins between NPSHA and NPSHR shall be strictly applied. Additional margins shall not be applied without specific approval of the purchaser.

4.3.2

NPSHA shall be calculated assuming the following: a. 110% of rated pump capacity b. Lowest liquid level in the suction vessel

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

January 2004

c. Operating condition with the lowest NPSHA Comment:

The operating condition with the lowest NPSHA typically has the highest temperature, vapor pressure, and viscosity and typically has the lowest liquid level.

4.3.3

On vertical vessels, lowest liquid level shall be defined as the bottom tangent line with pump inlet piping connected at the bottom of the vessel or at the takeoff level if the inlet line to the pump is not connected to the bottom of the vessel (see Appendix Figure A-3). On horizontal vessels, lowest liquid level shall be defined as the bottom inside level (see Appendix Figure A-4).

4.3.4

For existing vessels, and if selection of pumps is limited, the liquid level may be taken as one of the following: a. Elevation of the minimum operating liquid level if vessels have level control b. Elevation of the low alarm setting if vessels have level control c. Elevation of the automatic shutdown level if vessels have a level controller, low-level alarm, and automatic shutdown device

4.3.5

NPSHA shall exceed NPSHR by a minimum of 3 feet (1 meter) from minimum continuous flow to 110% of rated operating point. Use of an inducer to meet this requirement shall require approval of the purchaser. Comment:

3-feet (1-meter) minimum margin is desirable because NPSHR of individual impellers may vary significantly. NPSHR is determined under ideal pump operating conditions, and at the stated NPSHR, the pump is already in cavitation with a 3% head loss. Cavitation damage can result in high-energy density impellers at head losses less than the normal 3% used in standardized testing.

Comment:

Using the equation in Section 4.2.9 of this Practice and the 3-feet (1-meter) margin specified in Section 4.3.5 above, the minimum acceptable NPSHA can be estimated with the following expression: NPSHA ≥ [(N/ Nss)^4/3 * Q^2/3 ] + 3 (U.S. Customary units) NPSHA ≥ [(N/ S)^4/3 * Q^2/3 ] + 1 (SI units) With an assumed pump speed, the minimum NPSHA can be estimated and used to determine the preliminary elevation of the suction vessel.

4.3.6

If the margin between NPSHA and NPSHR at 110% of rated operating point is less than 5 feet (1.5 meters) or if an inducer is used, NPSHR testing shall be performed.

4.3.7

If the pumped liquid has dissolved or entrained gas, the NPSHA used to select the pump shall be half of the calculated NPSHA.

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

COMPLETE REVISION January 2004

Comment:

Some common liquids in which the NPSHA may be adversely affected by dissolved gases include carbon dioxide, hydrogen sulfide, amine, etc.

Comment:

Published articles related to this topic are as follows: Taylor (1967), Penny (1978), Tsai (1982), and Chen (1993).

4.3.8

NPSHA used to select the pump shall be indicated on the data sheet.

4.3.9

For uncontrolled applications, i.e., cooling tower pumps, in which the pumps can run out to the end of the curve, NPSHA shall exceed NPSHR by a minimum of 3 feet (1 meter) from minimum continuous flow to the end of the curve. Comment:

Uncontrolled pumps typically operate at the end of the curve because of overly conservative system design factors. This results in a pump with a greater head requirement than actually exists in the installed system. This head requirement can be a significant source of unreliable operation.

4.3.10 NPSHR reductions or corrections for hydrocarbon liquids and hot water are unacceptable. 4.3.11 Elevation of suction vessel shall be set to meet the requirements for margin between NPSHA and NPSHR specified in Sections 4.3.5 through 4.3.9 above. Comment:

Figures A-5 and A-6 provided in the Appendix give to the engineer establishing suction vessel elevation an appreciation of the NPSHA that must be provided at various flow rates and pump speeds to meet NSS (S) limitations. For planning purposes, the preliminary vessel elevation should be based on the NPSH requirements shown in Figures A-5 and A-6, with NSS of 9,000 (S of 175) as a reasonable approach. This allows the selection of a pump without exceeding the NSS ≤ 11,000 (S = 215) limit (see Section 4.2.9). Raising the suction vessel may be more economical than using a larger, slower speed or a double suction pump. For example, for pumps with identical process conditions, a pump that operates at 1,770 RPM versus 3,560 RPM increases cost from 40% to 100%. A pump that operates at 1,180 RPM versus 3,560 RPM increases cost from 100% to 300%. Drive motors that operate at 1,180 RPM are also significantly more expensive compared with motors that operate at 1,770 RPM or 3,560 RPM. Some suction vessels can be raised to provide adequate NPSHA at a reasonable cost. By adequately addressing these issues, the overall cost effectiveness and reliability of the pump will be enhanced.

4.3.12 If significant changes are made to the piping layout, the NPSH calculations shall be repeated with the actual layout.

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January 2004

Comment:

4.4.

Generally, this recalculation is not required unless the piping diameter or equivalent length is changed significantly to increase pressure drop.

Heating/Cooling Jacket 4.4.1

The pump shall have a heating/cooling jacket if conditions require it as stated in Section 4.4.2. Comment:

The following are the types of jackets typically used on centrifugal pumps:

a. Stuffing box jacket b. Seal chamber jacket (fully jacketed only) c. Pump casing jacket d. Bolt-on or external steam jacket (casing) e. Bearing housing cooling jacket (Oil sump fin tube is preferred. Cast bearing housing jackets are acceptable only with purchaser’s approval.) Comment:

4.4.2

Jackets are used to remove or add heat to the local area to which they are applied. High-temperature liquids that flash if heat is added, such as through rubbing friction or mechanical seals, require cooling. High-temperature liquids that solidify if the temperature decreases require the addition of heat, especially during startup when piping and pumps are at ambient temperature. Jackets must be hydrostatically tested before the pump is shipped. Leakage to the atmosphere could be hazardous in some processes.

A heating/cooling jacket shall be used in the following conditions/applications: a. Temperature of pumped fluid is above 300ºF (150ºC) unless metal bellow-type seals are used. b. Temperature of pumped fluid is above 572ºF (300ºC). c. Boiler feedwater pumps d. Dead-ended seal chambers e. Liquids with low flash points f. Products with high melting points

4.4.3

Cooling/heating jackets or inserts for seal chambers shall be provided by the pump vendor if specified by the purchaser.

4.4.4

If the temperature of the pumped fluid is greater than 350ºF (175ºC), the pump and seal vendors shall be jointly consulted about using cooled flush or running the seal chamber dead-ended with jacket cooling.

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

4.4.5

4.5.

COMPLETE REVISION January 2004

Cooling/heating jackets for seal chambers shall have connections arranged so that the entire passageway can be mechanically cleaned, flushed, and drained.

Driver 4.5.1

Electric Motor 4.5.1.1 For applications in which the pumped fluid has a variable specific gravity, the rated power of the motor shall be based on the greatest specific gravity. 4.5.1.2 If viscosity corrections for the pumped fluid are required, the power requirements specified in Sections 4.5.1.4, 4.5.1.5, and 4.5.1.6 shall be increased an appropriate amount by the pump manufacturer. Start-up at cold temperature when the viscosity of the pumped fluid is higher than viscosity under operating conditions shall be taken into consideration. 4.5.1.3 Use of a variable speed motor may be considered under one or more of the following circumstances: a. If the process operating conditions have a large range in operating flow rates or if a significant portion of the flow is recirculated b. In slurry service if reduction in pump speed reduces erosion and eliminates throttling valves c. If the process does not require a constant head, which is typically controlled by throttling d. If routine operation of the pump results in operating power of less than 50% of rated power, which will result in excess heat and inefficient operation of the motor Comment: The primary benefit of variable speed pumps is the reduction of energy requirements because of the elimination of throttling and minimized erosion in slurry pumps. Variable speed pumps may also provide benefits in systems requiring a wide range in flow. Variable speed pumps in constant flow and head system service have no advantage. 4.5.1.4 If the end-of-curve power is less than 5 hp (4 kW), the next standard size larger motor shall be used. Comment: The purpose of this requirement is to overcome startup problems caused by slow acceleration of small motors overcoming inertia and drag of seals. Seal drag increases as suction pressures increase. Failure to consider these factors can result in

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

January 2004

tripping the driver before operating speed is reached. 4.5.1.5 Driver power shall, as a minimum, be equal to the rated shaft power at the rated point multiplied by the percentage listed in Table 1. Table 1. Electric Driver Sizing Rated Pump Power Bhp < 30 30-100 > 100

Rated Pump Power kW < 22 22-75 > 75

Multiplier % of Rated Shaft Power 125 115 110

4.5.1.6 If the end-of-curve power is greater than 100 hp (75 kW), the motor shall be sized to cover the end-of-curve power or 110% of rated power, whichever is less. For applications that are expected to operate at the end-of-curve, such as cooling-water circulating pumps, motors shall be sized to operate at the end-of-curve. 4.5.1.7 The motor and coupling shall be sized to meet any specified future increase in power or head requirement. 4.5.1.8 The motor shall have adequate power for initial run-in on water with the pump throttled to 50% of rated capacity. If this requirement results in an increase in motor size, the larger motor shall be quoted as an alternate. Comment: The purpose of this requirement is to verify that the motor is adequately sized for water runs. However, if a larger motor must be furnished solely for water runs, it should first be verified that a water run is planned, and if so, alternate methods of accomplishing the water run should be investigated before deciding to use the larger motor. If water runs are not planned for startup, other methods of ensuring cleanliness of the system must be used such as a blowdown with compressed air. 4.5.2

Steam Turbine 4.5.2.1 Steam turbine drivers shall conform to API Std. 611. 4.5.2.2 Steam turbine power rating shall be 110% of the greatest calculated power requirement of the pump at any operating condition.

4.6

Energy Evaluations 4.6.1

Selection of pumps and drivers shall take into consideration cost of energy in the plant in which they are to be installed along with a payout period consistent with the design life defined in the project premises.

4.6.2

Efficiency of pump/driver used for the selection described in Section 4.6.1 shall be the efficiency that occurs at the normal operating flow rate and at

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the resulting head for the diameter of the impeller selected. Hours per year of pump operation shall reflect the design stream factor. 4.7.

Application of Specific Pump Types 4.7.1

ASME B73.1M and B73.2M Pumps Unless otherwise specified, application of ASME B73.1M and ASME B73.2M pumps shall be limited in accordance with Tables 2, 3, and 4: Table 2. ASME Pump Limitations Characteristic Maximum Temperature - °F (°C) Maximum Discharge Pressure - psig (kPa) Maximum Suction Pressure - psig (kPa) Maximum Rotative Speed - RPM

Limitation 300 (150) 275 (1,900) 75 (500) 3,600

Table 3. ASME Vertical in-Line Pump Limitations Type of Pump: Horizontal ASME AA through A-70 Vertical in-Line ASME Flow - Max., GPM (Cubic Meters/Hour ) Head - Max., Feet (Meters)

Intermediate Life Plants ASME Standard ASME Standard

Long Life, High Stream Factor Plants 600 (135) 400 (120)

Table 4. ASME Horizontal Pump Limitations

Type of Pump: Horizontal ASME A-80 through A-120 Flow - Max., GPM (Cubic Meters/Hour ) Head - Max., Feet (Meters)

4.7.2

Intermediate Life Plants ASME Standard ASME Standard

Long Life, High Stream Factor Plants 2,000 (450) 200 (60)

API 610 Single Stage Pumps Unless otherwise specified, application of API 610 single stage pumps shall be limited in accordance with Tables 5 and 6. Table 5. API Overhung Pump Limitations Type of Pump: Overhung API Horizontal or Vertical Flow - Max., GPM (Cubic Meters/Hour) Head - Max., Feet (Meters)

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Intermediate Life Plants 5,000 (1,140) 1,000 (300)

Long Life, High Stream Factor Plants 3,000 (680 ) 700 (215)

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PIP RECP001 Design of Pumping Systems That Use Centrifugal Pumps

Table 6. API High-Speed, Integrally Geared Pump Limitations Type of Pump: High-Speed, Single Stage, Integrally Geared, API Flow - Max., GPM (Cubic Meters/Hour) Head - Max., Feet (Meters)

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Intermittent Service or Intermediate Life Plants 350 (80) 5,000 (1,525)

Long Life, High Stream Factor Plants 250 (57) 4,500 (1,370)

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Appendix – Figures

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Process Industry Practices

PIP RECP001 STEERING TEAM BALLOT – COMPLETE REVISION Design of Pumping Systems That Use Centrifugal Pumps 11/20/03

Appendix – Figures

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Process Industry Practices