1.1   Introduction

API 610 has been written to ensure safe and reliable pumps are used in a dangerous industry. Below we have summarized the major features and requirements of API 610. You should not rely on this paper for your full knowledge of API 610 nor to make a decision as to whether you use, or do not use the API 610 standard.  We recommend that you read and understand the standard before deciding whether to, or how to, apply it to your application.

1.2   Scope

API 610 is a standard that covers the minimum requirements for centrifugal pumps for use in petroleum, heavy duty chemical and gas industry services. It includes pumps running in reverse as hydraulic power recovery turbines.

1.3    Why is API 610 Published?

API 610 has been written to ensure a minimum standard for:

Safety:  

Safety is of prime importance in the petroleum industry. A cracked pump casing, failed bearing or leaking mechanical seal can lead to a major catastrophe.

Reliability:  

After safety, production is of prime importance in the petroleum industry. If production stops, it can cost millions of dollars per day.

Maintainability:  

If a pump is removed for an overhaul, it must be back in service as quickly as possible to ensure safety back up and no loss of production.

1.4   Who Publishes API 610?

The API standards are published by the American Petroleum Institute.

1.5   Who Uses API 610?

Owners and operators of the following facilities typically specify API 610 when purchasing all of their pumps:

  • Offshore Oil Platforms
  • Onshore Oil Fields
  • Oil Processing Facilities
  • Oil Refineries
  • Oil and Petroleum Product Pipelines and Terminals
  • Gas Processing Plants
  • LNG Plants

It is also used by owners and operators of the following facilities to purchase heavy duty (high pressure or high temperature) pumps, not covered by other industry standards:

  • Chemical Processing Plants
  • Power Stations (Boiler Feed Water Pumps)
  • Co-Generation Power Plants

1.6    Pump Types Covered

API 610 covers all types of centrifugal pumps likely to be required in the oil and gas industries, these include:

  • Horizontal and vertical
  • Single stage, two stage and multi-stage
  • Single case and double case (barrel type)
  • Vertical sump and vertical canned (or double case)

2. Features of the API 610 Standard

2.1    Long Reliable Life

API pumps must be designed and constructed for a minimum service life of 20 years and at least 3 years of uninterrupted operation (clause 2.1.1).

In practice there are many API 610 pumps in industry that have been operating for in excess of 40 years and many oil refineries are now reporting MTBF figures in excess of 7 years.

2.2    Casing Design

The pump pressure casings must be designed using the stresses, welding and inspection practices given in the pressure vessel code (2.2.1).

Overhung pumps, between bearings radially split pumps, multi-stage pumps and vertical double case pumps are to be designed with a pressure rating equal to the lesser of 4,000 kPa-g or an ANSI 300# flange rating (2.2.2).

Radially split casings are required if temperature of fluid is above 200 deg C, the fluid SG is less than 0.7 or the discharge pressure is above 10,000 kPa-g (for flammable or hazardous fluids) (2.2.6).

Overhung horizontal single stage pump casings should have centerline supports (2.2.9).

2.3    External Nozzle Forces and Moments

API 610 lists the maximum forces and moments, which the pump nozzles must be able to take, and still give satisfactory performance. Case distortion and shaft misalignment are considered when assessing satisfactory performance (2.4.1).

The pump must meet these requirements without any bearing housing support (3.3.6).

2.4    Rotors

Default impeller design is closed and constructed as a one piece casting. Except on vertical suspended pumps, impellers must be keyed to the shaft and secured by a cap screw or cap nut, which in turn must have a positive mechanical locking method (2.5.1, 2.5.2, 2.5.3)

Shaft run out is limited to 0.001 inch (2.5.6).

Shaft stiffness must limit the deflection at the mechanical seal faces to 0.002 inch (2.5.7). This is most important for long mechanical seal life.

2.5   Wear Rings

Pumps must have renewable wear rings on both the casing and impeller (2.6.1). The minimum wear ring clearances are specified (2.6.4).

2.6   Mechanical Seals

There is now an API standard for mechanical seals, API 682 (2.7).

Both API 610 and API 682 specify seal chamber dimensions. These dimensions help ensure an ideal environment for the mechanical seal.

2.7   Vibration

API 610 specifies maximum allowable vibration levels – nominally 3.0 mm/s RMS unfiltered, at the bearing housing (2.8.3).

2.8   Balancing

Balancing and balance grades are specified for the various pump configurations, these can be summarized as:

Single stage and two stage pumps:   impellers dynamic balanced to Grade G1.0 (2.8.4.1).

Multi-stage pumps:   impellers and major components balanced to grade G1.0, rotors balanced to G2.5 (5.2.4.2)

2.9   Bearings

Minimum L10 design bearing life is 25,000 hours, at rated conditions (table 2.7). In practice most API 610 pumps will have an L10 bearing design life far in excess of this figure.

Bearing housings must have constant level oilers fitted.

2.10   Drivers

Driver power ratings must be at least equal to the following (table 3.1):

Motor kW Percentage of Rated Pump Power <22 125% 22-55 115% >55 110%

2.11   Baseplates

Strict guidelines are given for baseplate design. These design criteria ensure minimal misalignment of pump and driver shafts (3.3.5).

Baseplates must be single piece drain rim or drain pan design, to ensure that any leakage is contained within the baseplate (3.3.1, 3.3.2).

Pump and drive train components must have mounting pads, fully machined flat and parallel. Values are specified for measuring compliance (3.3.3).

2.12   Inspections

The manufacturer must keep quality records for at least 20 years (4.2.1.1).

2.13   Material Inspections

The purchaser should specify which parts are to be subjected to surface and subsurface examination, and the type of examination required (i.e. magnetic particle, liquid penetrant, radiographic or ultrasonic) (4.2.1.3).

The standard lists the appropriate procedure and acceptance criteria for these examination methods (4.2.2).

2.14   Testing

All pressure casings must have a hydrostatic pressure test, with liquid at a minimum of 1.5 times the maximum allowable working pressure (refer to the standard for special provisions) (4.3.2).

All pumps are to be performance tested unless stated otherwise. The standard gives detailed requirements for the testing and tight tolerances on test results (4.3.3).

NPSHR and Complete Unit Tests (i.e. test of pump and driver train complete with all auxiliaries) are optional, to be performed when specified (4.3.4).

2.15   Summary

In summary, the features of API 610 are:

  • Heavy duty casing design
  • Centerline supports
  • Low shaft stiffness ratio
  • Low shaft deflection at the seal faces
  • Long design bearing life
  • Low vibration levels
  • High allowable forces and moments on nozzles
  • Stringent testing requirements