API 675 Metering Pump for Oil & Gas, Petrochemical & LNG: Doseuro PDP Series

API 675 is a standard issued by the American Petroleum Institute for positive-displacement metering pumps with adjustable flow rate used in process operations within the oil & gas and petrochemical industries. Unlike conventional commercial dosing pumps, API 675 establishes a framework covering metering accuracy, pump head calculation documentation, wetted-part materials, and pre-shipment testing procedures. The objective is to ensure that each dose injected into the process line has minimal deviation and repeatable consistency, even when system pressure fluctuates.

In a refinery or petrochemical complex, process chemicals are injected at dosages calculated by the process engineer: corrosion inhibitors, demulsifiers, scale inhibitors, pH-adjusting agents, and hydrate inhibitors for gas pipelines. Dosage errors can damage product quality, accelerate equipment corrosion, or inflate chemical costs — which is why compliance with a metering standard such as API 675 becomes a technical requirement in many project specifications.

A metering pump is a positive-displacement pump: each cycle displaces a defined volume of liquid. Flow rate is adjusted through two parameters — stroke length and frequency of the displacement mechanism. This allows the operator to set very small, consistently repeatable doses — something a centrifugal pump cannot achieve.

By drive mechanism, metering pumps fall into several main families: solenoid (electromagnetic) for small doses and rapid on/off cycling; mechanical diaphragm using a cam or eccentric to drive the diaphragm; hydraulic diaphragm using hydraulic oil to actuate the diaphragm for leak-free, high-pressure operation; and piston/plunger in direct contact with the process fluid for very high pressures. In oil & gas process environments requiring high pressure and stable accuracy, piston/plunger and hydraulic diaphragm configurations are generally preferred — and this is the technical foundation of process pump series manufactured to API 675, such as the Doseuro PDP.

Within the Doseuro (Italy) catalog, the PDP is the process metering pump series manufactured to the API 675 standard with ATEX certification, targeting oil & gas, petrochemical, and LNG applications. With ATEX, the pump is permitted for installation in classified hazardous areas — a typical characteristic of gas processing facilities, storage tanks, and hydrocarbon pipelines. The API 675 framework standardises the metering calculation and control approach for additive injection duties that require stable, accurate dosing.

The wetted pump head material is selected according to the chemical properties of the additive: SS316L for oil-based chemicals and moderately corrosive fluids, or engineering plastics PVC / PP / PVDF / PTFE for strongly corrosive media. For control, the pump can be operated manually or accept a 4-20mA signal to automatically adjust the dose in response to flow, pH, or ORP sensors in the system — suitable for continuously operating process lines.

Specific flow rate and pressure figures depend on the model and actual operating conditions (viscosity, back pressure, temperature), so selecting the PDP configuration must begin from the plant’s specific process requirements.

Doseuro offers multiple series for different applications, from chlorine dosing in water treatment to high-pressure process additive injection. Understanding the relationship between series helps select the right equipment rather than defaulting to the highest-specification series for every application. The PDP sits in the oil & gas process segment, while water treatment or high-concentration chemical dosing in standard industrial plants may be better served by the SR series at a more appropriate cost level.

When the requirement is oil & gas process service with explosion protection and a standardised metering framework, the PDP is a sound choice. When very high pressure is needed but the API 675 framework is not mandatory, the piston SR type A (AP-A variant up to 230 bar) may be an alternative worth considering.

A reliable process dosing system requires alignment across three layers: pump head material compatible with the additive, a drive mechanism that meets the pressure range requirements, and a control loop that tracks the process. For strongly corrosive additives, PVDF or PTFE is preferred; for oil-based chemicals, SS316L is generally adequate. The 4-20mA signal enables the pump to be integrated into the control system, automatically adjusting the dose in response to main-line flow rate or pH/ORP sensors, helping to reduce chemical consumption and stabilise quality.

Beyond the equipment itself, the critical factor is calculating the correct dose under actual operating conditions — back pressure, viscosity, and temperature all affect the actual flow rate delivered. This is why it is advisable to work with an experienced metering pump specialist to select the model and pump head configuration, rather than relying solely on catalog specifications.