Industrial Pumps for Oil & Gas: API 610, Centrifugal & Positive Displacement

Quick Reference

Industrial pumps transfer fluids through piping systems. Main types: Centrifugal (high volume, low viscosity per API 610), Positive displacement (gear, screw, diaphragm per API 674/675/676), Submersible, and Multiphase (oil/gas/water mixtures). API 610 is the governing standard for centrifugal pumps in petroleum, petrochemical, and natural gas industries.

What Is an Industrial Pump

An industrial pump converts mechanical energy (from an electric motor, diesel engine, steam turbine, or gas turbine) into hydraulic energy to move fluids through a piping system. In practical terms, it creates flow and overcomes system resistance (head).

Industrial Pump

Industrial pumps are found in virtually every process plant: water treatment, oil and gas production, chemical manufacturing, food and beverage, pharmaceuticals, mining, and power generation. Applications range from wellhead water injection at 10,000+ psi to low-head cooling water circulation in power plants. In the oil and gas sector alone, a single refinery may have hundreds of pumps in service at any given time, making them one of the most important (and maintenance-intensive) equipment categories.

Key Parts and Components

Every industrial pump, whether centrifugal or positive displacement, shares a common anatomy. The table below covers the main components.

Component	Function	Notes
Casing	Contains the fluid, sustains operating pressure, directs flow from suction to discharge	Volute type (most common) or diffuser type
Impeller	Rotating vaned element that imparts kinetic energy to the fluid	Material depends on service: cast iron, SS 316, duplex, Hastelloy, etc.
Shaft	Transmits torque from the driver to the impeller	Must resist torsional and bending stresses
Bearings	Support the shaft, absorb radial and axial loads	Grease- or oil-lubricated; key to long-term reliability
Seal	Prevents fluid leakage along the shaft	Packing (traditional) or mechanical seal (modern, better for high pressure and hazardous service)
Suction nozzle	Fluid inlet	Smooth approach needed to avoid turbulence
Discharge nozzle	Fluid outlet	Directs pumped fluid into the discharge piping
Coupling	Connects pump shaft to motor shaft	Compensates for minor misalignment; absorbs shock
Baseplate	Stable foundation for pump and driver	Maintains alignment; simplifies installation
Motor / Driver	Provides mechanical energy	Electric motor, diesel engine, or steam turbine

Types of Industrial Pumps

The two fundamental pump categories are centrifugal and positive displacement. Every pump on the market falls into one of these families.

1. Centrifugal Pumps

A centrifugal pump spins an impeller to convert mechanical energy into kinetic energy in the fluid. The casing then converts that velocity into pressure. Simple principle, enormous range of applications, from crude oil transfer to cooling water circulation.

Centrifugal pump for oil and gas

In oil and gas, centrifugal pumps cover upstream water injection and produced water handling, midstream pipeline transfer of crude and condensate, and downstream refinery circulation and cooling duties.

Why centrifugal pumps dominate the industry: they handle high flow rates with fewer moving parts than PD pumps, which means less maintenance and lower energy cost per barrel moved. The tradeoff is that they struggle with high-viscosity fluids and lose efficiency quickly when operated far from the BEP.

When selecting a centrifugal pump, pay attention to fluid properties (viscosity, corrosiveness, solids), operating conditions (flow, head, temperature), available space (horizontal vs. vertical configuration), and the applicable standard (API 610 for O&G, ANSI B73.1 for chemical service).

The two main challenges are cavitation (covered in detail below) and wear/corrosion when handling abrasive or aggressive fluids, both addressed through proper material selection and operating the pump within its design envelope.

Common Mistake

Neglecting pump-motor alignment after installation. The pump may have been perfectly aligned at the shop, but thermal growth during operation, piping strain, and foundation settling all cause misalignment. Check alignment both cold and hot (after the pump reaches operating temperature), and re-check annually. Misalignment is the leading cause of seal and bearing failures.

2. Positive Displacement Pumps

PD pumps trap a fixed volume of fluid per cycle and push it forward regardless of downstream pressure. This makes them the go-to choice for high-viscosity fluids, precise dosing, or situations where you need a constant flow rate independent of pressure.

Rotary types:

Type	How It Works	Typical Use	API Standard
Gear pump	Two interlocking gears trap and move fluid	Lube oil, fuel oil, high-viscosity fluids	API 676
Screw pump	One or more helical screws advance fluid axially	Crude oil transfer, multiphase boosting	API 676
Lobe pump	Rotating lobes move fluid gently	Food/beverage, sanitary applications	API 676

Reciprocating types:

Type	How It Works	Typical Use	API Standard
Piston/plunger pump	Piston reciprocates in a cylinder	High-pressure injection, hydraulic systems	API 674
Diaphragm pump	Flexible diaphragm flexes to create suction/discharge	Hazardous chemicals, slurries (fluid never contacts the drive side)	API 675
Metering pump	Precision reciprocating PD pump with adjustable stroke	Chemical injection (corrosion inhibitors, biocides, scale inhibitors)	API 675

3. Submersible Pumps

Submersible pumps sit inside the fluid they pump, so there is no suction lift and no cavitation from elevation difference. Common in well water extraction, sewage handling, and drainage. In oil and gas, Electric Submersible Pumps (ESPs) are a key artificial lift method for high-volume wells.

4. AODD (Air-Operated Double Diaphragm) Pumps

These use compressed air to alternately flex two diaphragms. They are self-priming, can run dry without damage, and handle chemicals, viscous liquids, and slurries well. You see them everywhere in chemical plants for utility and transfer duties.

5. Multiphase Pumps

Multiphase pumps transport a mixed stream of gas, oil, water, and sometimes sand as a single fluid, without a separator at the wellhead. This eliminates the need for test separators, individual flowlines, and associated topsides equipment, which is a major cost saving on offshore platforms and remote onshore fields.

The key design parameter is Gas Volume Fraction (GVF), the ratio of gas to total fluid. A good multiphase pump handles anywhere from near-100% liquid to near-100% gas.

Type	Principle	Best For
Twin-screw	Two intermeshing screws trap and advance the mixture	Consistent flow rate regardless of pressure; handles high GVF and slugging
Helico-axial	Combined axial and centrifugal action via helical rotor	High flow rates, moderate pressure boost
Progressive cavity	Single helical rotor in elastomer stator creates advancing cavities	Highly viscous fluids, high GVF, lower flow rates

Centrifugal vs. Positive Displacement vs. Reciprocating: Comparison

Choosing the right pump family is the first and most consequential decision in the selection process. The table below provides a direct comparison.

Parameter	Centrifugal	Rotary PD (Gear/Screw)	Reciprocating PD (Piston/Diaphragm)
Flow behavior	Variable (depends on head)	Nearly constant (independent of pressure)	Pulsating (requires dampeners)
Typical flow range	1 to 100,000+ m3/h	0.1 to 5,000 m3/h	0.01 to 500 m3/h
Pressure range	Low to moderate (up to ~250 bar multistage)	Moderate (up to ~50 bar)	Very high (up to 1,000+ bar)
Viscosity handling	Poor above ~200 cP	Excellent (up to 1,000,000 cP)	Good (up to ~10,000 cP)
Efficiency at off-design	Drops rapidly away from BEP	Relatively stable	Relatively stable
Solids tolerance	Limited (wear issues)	Moderate (twin-screw can handle some solids)	Good (diaphragm type best for slurries)
Self-priming	No (needs priming)	Yes	Yes
Maintenance complexity	Low (fewer moving parts)	Moderate	Higher (valves, packing, diaphragms)
Best for	High flow, low viscosity, continuous duty	Viscous fluids, lube oil, fuel oil	High pressure injection, precise metering

Selection Rule of Thumb

If the fluid viscosity is below 200 cP and the required flow rate is high, start with a centrifugal pump. If viscosity exceeds 200 cP, or if you need a constant flow rate regardless of backpressure, look at positive displacement. For very high pressures (above 100 bar) with low flow rates, reciprocating pumps are typically the only viable option.

API 610 Centrifugal Pump Types

API 610 (also published as ISO 13709) is the governing specification for centrifugal pumps in petroleum, petrochemical, and natural gas service. If you are buying a centrifugal pump for an oil refinery, gas plant, or offshore platform, API 610 is the standard you will reference.

The standard classifies centrifugal pumps into three families and 17 specific configurations. Understanding these designations is essential for specifying the correct pump for each service.

Overhung (OH) Types

In overhung pumps, the impeller is mounted on the end of the shaft, cantilevered beyond the bearing housing. These are the most common pump types for general process duty.

Type	Name	Description	Typical Application
OH1	Foot-mounted, flexibly coupled	Standard horizontal end-suction pump on a baseplate	General process, cooling water, condensate
OH2	Centerline-mounted, flexibly coupled	Casing supported at the shaft centerline for thermal stability	Hot services (above 175 degC): hot oil, boiler feed water
OH3	Vertical in-line, flexibly coupled	Suction and discharge nozzles in-line; saves floor space	Space-constrained installations, moderate duty
OH4	Rigidly coupled, close-coupled	Impeller mounted directly on the motor shaft; no coupling	Low-cost, compact applications; utility water
OH5	Close-coupled, with integral bearing	Similar to OH4 but with an integrated bearing frame	Moderate-duty chemical process

OH1 vs. OH2

The key difference is the casing support. OH1 mounts on feet at the base of the casing, which means thermal growth can cause misalignment. OH2 supports the casing at the shaft centerline so that the pump grows upward symmetrically, maintaining alignment at high temperatures. For any service above 175 degC (350 degF), always specify OH2.

Between Bearings (BB) Types

In BB pumps, the impeller(s) sit between two bearing housings. This provides superior rotor stability and allows for multistage designs at higher pressures and speeds.

Type	Name	Description	Typical Application
BB1	Axially split, single stage	Horizontally split casing for easy maintenance access	Large-volume crude transfer, pipeline service
BB2	Radially split, single stage	Barrel-type casing for high-pressure containment	High-pressure process, hydrocarbon service
BB3	Axially split, multistage	Horizontally split with multiple impellers in series	Moderate-pressure multistage (boiler feed water)
BB4	Radially split, single-casing multistage	Single barrel casing with multistage rotor	High-pressure injection (water injection, pipeline)
BB5	Radially split, double-casing multistage	Inner cartridge inside an outer barrel	Very high pressure; boiler feed, high-head injection

When to Use BB Types

BB1 and BB3 (axially split) are easier to maintain because the upper half of the casing lifts off to expose the rotor. However, for pressures above approximately 100 bar, you must use radially split designs (BB2, BB4, BB5) because the axially split joint cannot seal reliably at those pressures. BB5 is the premium choice for critical high-pressure, high-temperature multistage service.

Vertically Suspended (VS) Types

VS pumps hang vertically into a pit, sump, tank, or vessel. The motor sits above the mounting plate, and the pump extends downward into the fluid.

Type	Name	Description	Typical Application
VS1	Vertical sump, single-casing	Single-casing pump suspended in a wet pit	Cooling water intake, drainage
VS2	Vertical sump, diffuser type	Diffuser-type casing for higher head	Deep-well pumps, large cooling water systems
VS3	Vertical sump, double-casing	Double-casing (barrel) for high-pressure containment	High-pressure well pumps
VS4	Vertical sump, line-shaft driven	Long line shaft connects motor above to pump below	Deep-set pump in wells, dewatering
VS5	Vertical sump, cantilever	No submerged bearings; shaft cantilevers from above	Corrosive or abrasive sumps where submerged bearings would fail
VS6	Vertical sump, submersible motor driven	Motor submerged with the pump	ESP (Electric Submersible Pump), borehole applications
VS7	Vertical sump, axial flow	Axial (propeller) type for very high flow, low head	Large circulating water systems, flood control

Key Takeaway: API 610 defines 17 pump configurations across three families (OH, BB, VS). Selecting the right configuration depends on the service conditions: OH types for general process duty, BB types for high-pressure or multistage service, and VS types for submerged or vertical installations. Always match the configuration to the temperature, pressure, and installation constraints of your specific application.

Pump Curves and Performance Parameters

Understanding Pump Curves

Every centrifugal pump ships with a set of performance curves. You need to read them; the datasheet alone is not enough.

Curve	What It Shows	Why It Matters
Head vs. Flow (H-Q)	Discharge head at each flow rate	Core selection tool; overlay this on your system curve
Efficiency	Pump efficiency across the flow range	Peaks at the Best Efficiency Point (BEP); stay close to it
Power	Brake horsepower at each flow rate	Determines motor sizing
NPSHr	Required NPSH at each flow rate	Must stay below NPSHa to avoid cavitation

The system curve is a plot of total system resistance (static head plus friction losses) against flow rate. Where the system curve intersects the pump’s H-Q curve is your operating point. That operating point must fall between 80% and 110% of BEP for reliable long-term operation.

The pump affinity laws govern how changes in impeller speed affect performance: flow changes proportionally with speed, head changes with the square of speed, and power changes with the cube of speed. This is why variable frequency drives (VFDs) are so effective at saving energy: a 20% speed reduction cuts power consumption by nearly 50%.

Key Performance Parameters

Parameter	Symbol	Definition	Unit
Flow rate	Q	Volume of fluid delivered per unit time	m3/h, GPM
Total Dynamic Head	TDH	Total energy added to the fluid (suction to discharge)	meters, feet
Best Efficiency Point	BEP	Flow rate at which the pump operates at peak efficiency	m3/h, GPM
Brake Horsepower	BHP	Power input to the pump shaft from the driver	kW, HP
Pump Efficiency	eta	Ratio of hydraulic power output to mechanical power input	%
Specific Speed	Ns	Dimensionless number relating speed, flow, and head; indicates impeller geometry	-
Minimum Continuous Stable Flow	MCSF	Lowest flow at which the pump can operate without recirculation damage	m3/h, GPM

Field Note

Select pumps to operate between 80-110% of BEP (Best Efficiency Point) at normal operating conditions. Running a pump at 50% of BEP to “have margin” actually causes more damage than running near BEP - recirculation inside the impeller causes heating, vibration, and premature bearing failure. If your process genuinely needs a wide flow range, consider a VFD instead of oversizing.

NPSH: Net Positive Suction Head

NPSH is one of the most important, and most commonly misunderstood, parameters in pump engineering. Getting it wrong causes cavitation, which destroys impellers and costs far more than the engineering time to calculate it properly.

NPSHa (Available)

NPSHa is the energy available in the fluid at the pump suction flange, above the vapor pressure. It is a property of the system, not the pump, and is calculated as:

NPSHa = (P_surface - P_vapor) / (rho x g) + H_static - H_friction

Where:

• P_surface = absolute pressure at the liquid surface (atmospheric for open tanks, vessel pressure for closed systems)
• P_vapor = vapor pressure of the liquid at pumping temperature
• rho = fluid density
• g = gravitational acceleration
• H_static = elevation of the liquid surface above (+) or below (-) the pump suction centerline
• H_friction = friction losses in the suction piping (including strainers, valves, bends)

NPSHr (Required)

NPSHr is the minimum suction head the pump needs to avoid cavitation. It is a property of the pump, determined by the manufacturer through testing (per HI 1.6 or API 610 test protocol). NPSHr increases with flow rate: it is lowest near shutoff and highest at maximum flow.

NPSH Margin

The fundamental rule: NPSHa must always exceed NPSHr at the operating point, with a safety margin. API 610 specifies a minimum margin, but experienced engineers add more to account for:

• Strainer fouling (increases suction friction losses over time)
• Process upsets (temperature excursions raise vapor pressure, lowering NPSHa)
• Pump degradation (NPSHr increases as impeller wear rings open up)
• Measurement uncertainty (suction piping pressure losses are estimates)

Pro Tip

The NPSH margin in the datasheet is the minimum; always design for more. A pump that “just meets” NPSH requirements at commissioning will cavitate within a year of operation. A common industry practice is to maintain NPSHa at least 1.5 to 2.0 times NPSHr, or NPSHa minus NPSHr of at least 1.0 to 1.5 meters, whichever is greater.

Cavitation

Cavitation occurs when local pressure inside the pump drops below the liquid’s vapor pressure. Vapor bubbles form, travel to higher-pressure zones, and collapse violently, pitting the impeller and eroding the casing.

Common causes: excessive suction lift, high fluid temperature, partially blocked suction strainers, or sharp bends in the suction piping.

Symptoms: crackling noise (sounds like gravel in the pump), fluctuating discharge pressure, vibration spikes, and visible pitting on the impeller eye.

Prevention: maintain adequate NPSHa (with margin), minimize suction piping losses, keep fluid temperature stable, and use a VFD to avoid running the pump far off its BEP. If the layout cannot provide enough NPSHa, consider using an inducer (a small axial impeller installed ahead of the main impeller) or switching to a pump with a lower NPSHr.

Pump Sealing Systems

The shaft seal is the most maintenance-intensive component on a centrifugal pump. In oil and gas service, the seal must contain hazardous fluids at elevated temperatures and pressures while allowing the shaft to rotate at thousands of RPM. API 682 defines mechanical seal requirements for API 610 pumps.

Mechanical Seals (API 682)

Arrangement	Description	Application
Arrangement 1	Single mechanical seal	Non-hazardous services; water, cooling fluids
Arrangement 2	Dual unpressurized (tandem) seals with buffer fluid	Moderate-risk services; the buffer fluid absorbs minor leakage and enables leak detection
Arrangement 3	Dual pressurized seals with barrier fluid	Hazardous, toxic, or flammable fluids; barrier fluid at higher pressure than process prevents any process leakage

API 682 also defines seal piping plans (Plan 11, 13, 21, 23, 32, 52, 53A/B/C, 54, etc.) that specify the auxiliary systems for cooling, flushing, quenching, and pressurizing the seal chamber.

Traditional Packing

Braided packing rings compressed by a gland into a stuffing box. Still used on some water and utility services where minor controlled leakage is acceptable. Not suitable for hazardous or high-temperature service. Requires regular adjustment and is being phased out in favor of mechanical seals on most new installations.

Sealless Pumps (API 685)

For the most hazardous services, sealless pumps eliminate the shaft seal entirely:

• Magnetic-drive (mag-drive): An outer magnet set on the motor side drives an inner magnet set on the impeller side through a containment shell. No dynamic seal. Limited by temperature (containment shell material) and power (eddy current losses in the shell).
• Canned-motor: The motor rotor is enclosed in a sealed can, directly coupled to the impeller. The process fluid lubricates the bearings. Higher efficiency than mag-drive but more complex to maintain.

Sealless Pump Limitations

Sealless pumps cannot run dry because the process fluid lubricates the bearings. Loss of flow causes immediate bearing damage. Always install low-flow protection (flow switch or power monitor) and make sure there is adequate minimum flow recirculation. Also, sealless pumps have lower efficiency than sealed pumps of equivalent size due to eddy current losses (mag-drive) or rotor/stator gap losses (canned-motor).

Materials of Construction

Material selection drives pump life and maintenance cost more than almost any other factor. Get it wrong and you are replacing impellers every turnaround; get it right and the pump runs for a decade between overhauls.

API 610 Material Classes

API 610 defines standard material classes (previously called “material class” and now aligned with ISO 13709 designations) for wetted pump components. The table below summarizes the most commonly specified classes.

Material Class	Casing	Impeller	Shaft	Typical Service
S-1 (C-6)	Carbon steel	Carbon steel	Carbon steel or 4140	Non-corrosive hydrocarbons at moderate temperature
S-3 (C-6)	Carbon steel	12% Cr steel	4140 or 410 SS	Mildly corrosive hydrocarbons, produced water
S-4 (C-6)	Carbon steel	CF8M (316 SS cast)	316 SS	Moderately corrosive services
S-6 (A-8)	316 SS	316 SS	316 SS	Corrosive chemicals, acids, seawater
S-8 (D-1)	Duplex SS	Duplex SS	Duplex SS	Severe chloride corrosion, offshore seawater
A-7	Alloy 20 (CN7M)	Alloy 20	Alloy 20	Sulfuric acid service
C-6	Ni-Al Bronze	Ni-Al Bronze	Monel	Seawater fire-fighting pumps

General Materials Guide

Material	Key Properties	Typical Applications
Cast Iron	Good mechanical strength, cost-effective, limited corrosion resistance	Water, sewage, non-corrosive fluids; general service centrifugal pumps
Carbon Steel	Higher strength and thermal stability than cast iron; requires corrosion protection	High temperature/pressure applications; pipeline and boiler feed water pumps
Stainless Steel (304/316)	Excellent corrosion resistance; Type 316 adds molybdenum for chloride environments	Corrosive liquids, sanitary applications; chemical/food processing, pharmaceuticals
Duplex Stainless Steel	High strength, superior chloride-induced corrosion resistance	Severe corrosive environments; offshore and subsea applications
Nickel Alloys (Hastelloy, Inconel, Monel)	Exceptional corrosion resistance in acidic/alkaline environments; high temperature resistance	Chemical processing, nuclear power, aerospace
Titanium	Exceptional corrosion resistance, lightweight, high strength-to-weight ratio; expensive	Desalination plants, offshore platforms, chemical processing
Plastics/Composites (PP, PVDF, FRP)	Excellent corrosion resistance, lightweight; lower temperature/pressure limits	Highly corrosive fluids; chemical processing, wastewater treatment
Ceramics/Tungsten Carbide	Extreme hardness and wear resistance; brittle, can be costly	Abrasive fluids, slurry applications; seals, bearings, impeller trim

When choosing materials, check the fluid’s chemical compatibility first (use NACE MR0175/ISO 15156 for sour service with H2S), then consider operating temperature and pressure, abrasive content, and any regulatory requirements (e.g., FDA compliance for food-grade pumps). Always balance upfront cost against expected service life; a duplex impeller costs more than carbon steel but may last three times as long in seawater service.

Pump Selection Guide

Step-by-Step Selection Process

Pump selection boils down to five questions:

1. What are the fluid properties? Viscosity, temperature, corrosiveness, and solids content narrow the pump type immediately. High viscosity or solids? Think positive displacement. Clean, low-viscosity liquid at high flow? Centrifugal.
2. What flow rate and head do you need? Plot your system curve (static head + friction losses at various flows) and overlay candidate pump curves.
3. What is the available NPSH? Calculate NPSHa from your piping layout and verify the pump’s NPSHr sits well below it, with margin.
4. What is the operating environment? Ambient temperature, hazardous area classification, and space constraints all affect pump configuration and material choices.
5. What does the total cost of ownership look like? A cheaper pump that eats seals every six months is not cheaper. Factor in energy, spare parts, and downtime.

Which Pump for Which Service

Service	Recommended Pump Type	Why
Crude oil transfer (pipeline)	Centrifugal (BB1 or BB3)	High flow, moderate head, continuous duty
Water injection (high pressure)	Centrifugal multistage (BB4 or BB5)	Very high head, continuous duty, seawater compatible
Lube oil circulation	Gear pump (PD) or screw pump	Viscous fluid, constant flow needed
Chemical injection (corrosion inhibitor)	Metering/diaphragm pump	Precise dosing, low flow, hazardous fluid
Cooling water	Centrifugal (VS1 or OH1)	High flow, low head, low cost
Condensate return	Centrifugal (OH2)	Moderate flow, high temperature
Slurry/produced sand	Centrifugal with hard trim or diaphragm PD	Abrasion resistance is the priority
Wellhead multiphase	Twin-screw or helico-axial	Handles gas/oil/water mixture, variable GVF
Boiler feed water	Centrifugal multistage (BB3 or BB5)	High pressure, high temperature, critical service
Sour hydrocarbon (H2S)	Centrifugal with NACE materials + Arr. 3 seal	Hazardous fluid, zero-leak requirement

Key Takeaway: Pump selection for oil and gas service must balance hydraulic requirements (flow rate, head, NPSH), fluid properties (viscosity, corrosiveness, solids content), and compliance with industry standards like API 610 for centrifugal pumps. Always target operation near the Best Efficiency Point (BEP) for reliability and longevity, and select materials per NACE MR0175 for sour service.

Industry Standards Reference

Pump Standards

Standard	Title	Scope
API 610 (ISO 13709)	Centrifugal Pumps for Petroleum, Petrochemical, and Natural Gas Industries	Design, materials, manufacturing, testing for centrifugal pumps in high-temperature/high-pressure O&G service
API 674	Positive Displacement Pumps - Reciprocating	Reciprocating PD pumps (plunger, piston) for petroleum and petrochemical service
API 675	Positive Displacement Pumps - Controlled Volume (Metering)	Metering/dosing pumps for precise chemical injection
API 676	Positive Displacement Pumps - Rotary	Rotary PD pumps (gear, screw, lobe) for petroleum and petrochemical service
API 682	Pumps - Shaft Sealing Systems	Mechanical seal requirements for API 610 pumps; defines arrangements, materials, and piping plans
API 685	Sealless Centrifugal Pumps	Sealless (mag-drive / canned motor) centrifugal pumps for hazardous process service
ANSI/ASME B73.1	Horizontal End Suction Centrifugal Pumps for Chemical Process	Single-stage, end-suction horizontal pumps, the workhorse of chemical plants
ANSI/ASME B73.2	Vertical In-line Centrifugal Pumps for Chemical Process	Same scope as B73.1 but vertical in-line configuration
ANSI/HI	Hydraulic Institute Standards	Broad guidelines covering design, installation, operation, and maintenance for all pump types
ISO 5199	Centrifugal Pumps - Class II	Intermediate-duty centrifugal pumps for general industrial service
ISO 2858	End-suction Centrifugal Pumps (16 bar)	Dimensional interchangeability standard for end-suction pumps
ISO 9905	Centrifugal Pumps - Class I	Stringent requirements for heavy-duty industrial centrifugal pumps

In practice, if you work in oil and gas, API 610 is the default centrifugal pump spec and API 674/675/676 cover PD pumps. For chemical plants, you will more often see ANSI/ASME B73.1. ISO standards appear on projects outside North America or when the client specifies them.

Installation and Commissioning Guidelines

Proper installation is as important as proper selection. A well-chosen pump installed poorly will fail just as fast as a poorly chosen pump.

Installation Checklist

1. Foundation and baseplate: Grout the baseplate on a level foundation. The foundation mass should be at least 3 times the combined weight of pump, driver, and baseplate to dampen vibration.
2. Alignment: Perform both angular and parallel alignment using dial indicators or laser alignment tools. Record readings. API 610 specifies maximum allowable misalignment values.
3. Piping connections: The piping must not impose strain on the pump nozzles. Support the piping independently. Use expansion joints or loops where thermal growth is expected. Eccentric reducers (flat side up) on horizontal suction lines prevent air pockets.
4. Suction piping: Keep suction piping as short and straight as possible. Provide at least 5 pipe diameters of straight run before the pump suction nozzle. Avoid high points that trap gas.
5. Baseplate leveling: Level the baseplate to within 0.05 mm/m (0.001 in/ft) before grouting.
6. Coupling installation: Follow the coupling manufacturer’s instructions for gap and alignment tolerances. Install the coupling guard before starting the pump.

Commissioning Steps

1. Pre-commissioning checks: Verify rotation direction (bump the motor briefly), check bearing lubrication levels, confirm all temporary strainer/startup strainers are installed, and verify all instrumentation is functional.
2. Initial startup: Fill the pump casing and suction line completely (vent all air). Open the suction valve fully. Open the discharge valve slightly (about 20-30% for centrifugal pumps, or per manufacturer recommendation). Start the motor.
3. Post-start monitoring: Check for vibration, bearing temperature, seal leakage, suction and discharge pressures, and motor current. All parameters should stabilize within the first few minutes.
4. Hot alignment check: After the pump reaches normal operating temperature (typically 2-4 hours of running), shut down briefly and re-check alignment. Adjust if needed. This is the final alignment.
5. Performance verification: Compare actual operating parameters (flow, head, power, vibration) against the datasheet. Document all readings for future reference.

Critical Safety Note

Never operate a centrifugal pump with the discharge valve closed for more than a few seconds. The energy imparted to the fluid converts to heat, which can cause the fluid to flash, the seal to fail, or the casing to overpressure. Always make sure a minimum flow recirculation line is installed on pumps that may operate against a closed discharge (e.g., boiler feed water pumps with automatic control valves).

How to Order a Pump

When you send an RFQ to a pump vendor, the more complete your data, the faster and more accurate the proposal. Incomplete data sheets are the number-one cause of wrong pump selections. At minimum, provide the following:

Parameter	Details to Provide
1. Type of Pump	Centrifugal, positive displacement, submersible, etc.
2. Fluid Characteristics	Type (water, oil, chemical, slurry); temperature (min/max/operating); viscosity; corrosiveness (pH, chemical composition); solids content (size, concentration); specific gravity
3. Flow Rate	Required flow rate in GPM or m3/h (rated, normal, minimum, maximum)
4. Total Dynamic Head (TDH)	Total lift height including static lift and friction losses (feet or meters)
5. Pressure Requirements	Suction pressure (at pump inlet); discharge pressure (at pump outlet plus system requirements)
6. Power Supply	Voltage, phase, frequency to verify motor compatibility
7. Operating Environment	Ambient temperature; hazardous area classification (explosion-proof ratings); outdoor/indoor location
8. Connection Type	Flanged, threaded, etc.; size for suction and discharge ports
9. Material of Construction	Preferred materials for pump casing, impeller, shaft, and seals
10. Sealing Requirements	Mechanical seals or packing; specific seal arrangement (API 682 Arr. 1/2/3); seal piping plan
11. Regulatory/Certification	Industry or governmental standards (API 610, API 674/675/676, ANSI, ISO, NACE MR0175)
12. Additional Features	Control/monitoring (sensors, controllers, remote monitoring); special coatings/treatments; accessories (baseplates, coupling guards, vibration monitors)
13. Documentation/Support	Required documentation (manuals, performance curves, CAD drawings); after-sales support services

Missing even one of these parameters (especially fluid temperature or viscosity) can result in a pump that looks right on paper but fails in the field.

Frequently Asked Questions

What is the difference between centrifugal and positive displacement pumps?

Centrifugal pumps use a rotating impeller to convert mechanical energy into kinetic energy and then pressure, delivering high flow rates at moderate pressures. Positive displacement (PD) pumps trap a fixed volume of fluid per cycle and push it forward, delivering constant flow regardless of discharge pressure. Centrifugal pumps are best for clean, low-viscosity fluids at high flow rates; PD pumps excel with viscous fluids, precise metering, and high-pressure applications.

What is NPSH and why does it matter for pump selection?

NPSH stands for Net Positive Suction Head. NPSHa (available) is the absolute pressure at the pump suction minus the fluid vapor pressure, determined by your system layout. NPSHr (required) is the minimum suction head the pump needs to avoid cavitation, determined by pump design. NPSHa must always exceed NPSHr with a safety margin (typically 1-2 meters or per API 610 requirements). Insufficient NPSH causes cavitation, which damages the impeller and reduces pump life dramatically.

What are the API 610 pump type designations (OH, BB, VS)?

API 610 classifies centrifugal pumps into three families: OH (Overhung) types OH1-OH5 where the impeller is cantilevered beyond the bearings; BB (Between Bearings) types BB1-BB5 where the impeller sits between two bearing housings for better stability; and VS (Vertically Suspended) types VS1-VS7 for submerged or vertical applications. Each designation defines a specific configuration suited to particular services, pressures, and installation requirements.

What seal types are used in API 610 pumps?

API 610 pumps primarily use mechanical seals per API 682. The main arrangements are: Arrangement 1 (single seal) for non-hazardous services, Arrangement 2 (dual unpressurized/tandem seal) for moderate-risk services where leakage monitoring is needed, and Arrangement 3 (dual pressurized seal) for hazardous and toxic services where zero leakage is required. Sealless alternatives (magnetic-drive and canned-motor pumps per API 685) are available for highly toxic or dangerous fluids.

How do I select the right pump for an oil and gas application?

Start with fluid properties (viscosity, temperature, corrosiveness, solids content) to narrow the pump type. Plot your system curve (static head plus friction losses) to determine required flow and head. Calculate NPSHa to verify the pump will not cavitate. Check API 610 material classes for compatibility with the process fluid. Select a pump that operates between 80-110% of its Best Efficiency Point (BEP) at normal conditions, and size the motor with adequate margin. Always consider total cost of ownership (energy, spare parts, and downtime), not just purchase price.