The precise transfer of chemicals and additives is critical in the oil and gas, petrochemical, water treatment, and other industries. Single-stage metering pumps are essential to ensure precise transfer and minimize additive consumption. Various international standards have been developed to ensure the safe, stable, and precise operation of these pumps . The most important of these is API 675 .
This standard, developed by the American Petroleum Institute (API), is considered the authoritative source of information for the design, manufacture, testing, and monitoring of variable displacement pumps. This article introduces API 675 and discusses its objectives, technical requirements, scope, benefits, challenges, and application recommendations for each pump.
History and purpose of API 675
Date
API 675 was first published in the 1990s to establish a uniform regulatory framework for the design and manufacture of metering pumps for the process industry. Subsequent editions have been technically revised and harmonized with the metric system and other international standards. The primary objective of developing this standard was to establish uniform purchasing specifications for manufacturers and buyers, thus ensuring mutual understanding of technical and quality requirements.
Goal
API 675 aims to achieve the following objectives:
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Specify requirements for the design, manufacture, and testing of variable displacement positive displacement pumps.
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Ensure accurate, stable and repeatable pump operation.
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Improve the operational reliability of your equipment and facilitate maintenance
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Creating a common technical language between buyers and manufacturers
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Improving pump reliability and service life in critical industrial applications
Scope and limitations
Inquiry
API 675 pumps are typically used in applications requiring low flow rates and high precision. Examples of such applications include:
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Injection of chemicals such as corrosion inhibitors, defoamers or antiscalants
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Adding catalysts or additives to process units
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Dosing control in water and wastewater treatment plants (e.g. introduction of chlorine, acids or alkalis)
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Injection of additives into oil and gas pipelines
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For precise addition of sensitive components in the pharmaceutical and food industries
End
API 675 applies only to variable-displacement piston pumps . Centrifugal, rotary, or continuous-flow pumps are not covered by this standard. Furthermore, this standard may not apply to some simple diaphragm pumps and non-hydraulic mechanical drives.
Key concepts of API 675
1. Control period (reduction coefficient)
Pumps that comply with API 675 must operate at approximately 10% of their rated capacity while maintaining accuracy. In other words, if a pump is designed for 100 liters per hour, it must also operate with acceptable accuracy at 10 liters per hour. This property is important for processes that require variable flow rates.
2. Accuracy and repeatability
Accuracy indicates how close the actual performance is to the specified value, while repeatability determines the pump’s ability to repeatedly deliver the same performance under the same conditions. According to API 675, accuracy should be within ±1%, while repeatability is typically around ±3%.
3. My line
The relationship between the set and actual flow rate should be linear, meaning any change in the set flow rate results in a proportional change in the output flow rate. This property improves pump controllability in an automated system.
4. Positive return mechanism
The positive return mechanism ensures that the piston or diaphragm returns to its original position at the end of each stroke. This is necessary to maintain a precise flow rate during each pumping cycle and avoid flow fluctuations.
5. Intake and exhaust valves
API 675 designs must use robust, corrosion-resistant, and fast-acting check valves to prevent backflow and volume failures.
6. Safety valve
The pumping system must be equipped with a pressure relief valve or bypass circuit to prevent damage to the pump and piping if the outlet pressure is too high.
7. Compression and separation of liquids
Appropriate seals, especially in diaphragm pumps, can prevent the leakage of hazardous or corrosive fluids. Diaphragms are typically made of corrosion-resistant materials such as polytetrafluoroethylene (PTFE), fluororubber (FKM), or synthetic rubber.
8. Building materials
All parts that come into contact with the fluid must be made of materials compatible with its chemical and thermal properties. Common materials include 316 stainless steel, Hastelloy, PVC, PVDF, and PTFE.
Design and construction requirements in API 675
API 675 specifies precise requirements for every phase of pump design and construction. The most important of these are:
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Housing and frame:
These must have sufficient mechanical strength to withstand pressure and vibration and be made of durable materials. -
Moving parts:
The design should minimize wear and vibration. Bearings and crankshafts should be easy to lubricate and maintain. -
Coupling and motor:
The power transmission from the motor to the pump must be smooth and slip-free . A flexible, shielded coupling is recommended. -
Hydraulic systems:
The design must transfer pressure and flow evenly and avoid hydraulic shocks. -
Valves and flow paths:
The correct selection of valve type, material and size is critical for reliable operation. -
Instruments and equipment:
For real-time monitoring of pumps, devices for measuring pressure, temperature and operating status are essential. -
Safety:
Each pump must be equipped with a pressure relief valve, an emergency stop system and, if necessary, a diaphragm leak alarm.
Testing and inspection
One of the most important requirements of API 675 is testing and inspection to ensure that the pump meets the specified specifications. Key tests include:
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Hydrostatic pressure test:
The pump and pressure-bearing components must be tested at a pressure of at least 1.5 times the rated pressure to ensure the strength of the pump body. -
Functional testing:
Includes flow tests at various setpoints to verify the accuracy, linearity, and repeatability of pump performance. -
Leak test:
Check the overall tightness of the system to ensure that no fluid leaks occur at vulnerable points. -
Material testing:
Verification of material certification and its conformity with project requirements. -
Documentation:
All test results, drawings and specifications must be made available to the buyer.
Example of a pump that complies with API 675
Many well-known pump manufacturers worldwide produce metering pumps according to API 675. For example:
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The HYDRO series hydraulic diaphragm pumps feature
an accuracy of ±1%, an adjustable capacity from 10% to 100% of the rated flow, and a two-layer safety system to prevent leakage. -
The X9 series piston pumps feature
digital controls and are designed to fully meet the requirements of API 675 for the oil and gas industry . -
Hydra-Cell and Hemmen pumps are characterized by
their compact size, the ability to operate continuously under high pressure, and the full compliance with the requirements for precision, tightness, and safety.
Advantages of using API 675 compliant pumps
1. High-precision material injection:
ensures accurate flow rate for sensitive operations with an error of less than ±1%.
2. Performance stability:
The pump can be operated over a wide pressure and flow range without significant performance changes.
3. Increased safety:
The safety and control system and the sealed design reduce the risk of accidents.
4. Long service life and easy maintenance:
Due to the use of durable materials and standardized design, the pump has a long service life and is easy to maintain.
5. Confidence in industry contracts:
API 675 is a global standard that enables customers worldwide to purchase products with confidence in their quality.
Problems and limitations of implementation
While compliance with API 675 offers many benefits, it also brings challenges:
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Increased production costs:
The use of special materials, detailed testing, and extensive documentation increase the final price. -
High technical knowledge required:
Design, modification and maintenance of pumps according to API 675 require experienced specialists. -
Difficulties in obtaining parts:
Some spare parts must be manufactured to exact standard specifications and their procurement can take a long time. -
Exceptions must be specified:
Certain requirements may not apply to some projects; these requirements must be specified in the contract between the buyer and the manufacturer.
Practical advice on purchasing and selecting individual pumps according to API 675 standard
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The exact version of the standard must be specified on the order (e.g. API 675 3rd Edition).
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Flow rate, operating pressure, fluid type, temperature and materials in contact with the fluid must be fully specified.
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Any permissible deviations or exceptions must be agreed upon in writing between the buyer and the manufacturer.
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Use a certified manufacturer with experience in manufacturing API pumps.
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The final inspection (factory acceptance test) is carried out before delivery in the presence of a representative of the buyer.
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The buyer must be provided with, among other things, material certificates, drawings, test results and maintenance instructions.
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A regular maintenance and inspection program should be carried out according to the manufacturer’s recommendations.
Finally
API 675 is one of the most comprehensive and recognized standards for positive displacement pumps, guaranteeing the precision, safety, and reliability of every pump. Compliance with this standard in the design, manufacture, and operation of pumps not only improves the quality of industrial processes but also reduces the costs associated with failures, leaks, and production downtime.
In critical industries such as oil and gas, petrochemicals, and water treatment, the use of pumps compliant with API 675 is a technical and economic requirement. Understanding the concepts and requirements of this standard is critical for purchasers and engineers to select the right equipment and maximize performance.