API 610 vs API 674 vs API 618: Selecting the Right Equipment Standard

API 610, API 674, and API 618 govern three distinct classes of rotating equipment used across oil and gas, petrochemical, and gas processing facilities, and confusing their scope is a common early-stage engineering error. API 610 covers centrifugal pumps. API 674 covers reciprocating positive displacement pumps. API 618 covers reciprocating compressors. A specification that cites the wrong standard for a given machine class rarely raises a flag at the data sheet stage. The error surfaces later, when a vendor’s proposal fails technical bid evaluation or a package unit fails an EPC contractor’s document review.

This confusion carries a real cost. A wrong-standard call on a metering pump package can push a six-week procurement cycle past twelve weeks once the vendor re-quotes against the correct data sheet. Engineers specifying equipment for GCC, India, and Southeast Asian facilities need a fast way to route each machine to its governing standard before the requisition goes out. This article resolves the API 610 vs API 674 vs API 618 selection question directly: what each standard covers, where the boundaries sit, and how to apply it correctly.

What API 610, API 674, and API 618 Actually Govern

API 610 governs centrifugal pumps for petroleum, petrochemical, and natural gas facilities, covering horizontal and vertical configurations classified as OH, BB, or VS types. API 674 governs reciprocating positive displacement pumps, primarily power pumps used in pulsating, high-pressure duty. API 618 governs reciprocating compressors, a gas-handling machine class outside the scope of either pump standard.

The API 610 vs API 674 vs API 618 scope confusion usually starts with a false assumption that “API pump standard” is a single document. API maintains separate standards for each equipment mechanism because failure modes, materials, and testing regimes differ between a centrifugal machine and a reciprocating one. Centrifugal pumps fail through cavitation, seal wear, or bearing degradation under continuous rotational load; reciprocating pumps and compressors fail through valve wear, rod packing leakage, or pulsation-induced fatigue under cyclic load.

API 610, currently in its 12th Edition, applies to centrifugal pumps handling liquid petroleum, petrochemical, and natural gas process fluids. API 674 applies to reciprocating positive displacement pumps, most commonly power pumps used for chemical injection, produced water reinjection, and metering duty beyond centrifugal flow-smoothness limits. API 618, now in its 5th Edition, applies to reciprocating compressors used for gas compression services, a separate machine class handling a compressible fluid rather than a liquid.

The practical implication for a specifying engineer: if the machine moves liquid using rotational impeller action, API 610 applies. If it moves liquid using a reciprocating piston or plunger, API 674 applies. If it moves and compresses gas using a reciprocating piston, API 618 applies. Misrouting any one of these at the requisition stage invalidates the vendor’s technical proposal against the correct code basis.

Scope and Applicability by Equipment Class

API 610, API 674, and API 618 each define scope boundaries by equipment mechanism, not by service duty alone. API 610 subdivides centrifugal pumps into OH (overhung), BB (between bearings), and VS (vertically suspended) types. API 674 subdivides reciprocating pumps by power frame configuration. API 618 subdivides reciprocating compressors by cylinder arrangement and control approach.

API 610 Scope: Centrifugal Pump Types

API 610 classifies centrifugal pumps into three families based on rotor support. OH types are overhung pumps with the impeller cantilevered beyond the bearing housing, common in general refinery service below 75 kW. BB types are between-bearing pumps, used for higher-head, multistage services such as boiler feed and pipeline injection. VS types are vertically suspended pumps, typically used for sump, condensate, or cooling tower applications where a dry-pit installation is impractical.

API 610 is technically aligned with ISO 13709, and many GCC and Southeast Asia EPC data sheets reference both interchangeably. Confirm which edition the purchaser’s specification calls for before issuing the requisition.

API 674 Scope and the API 675 Distinction

API 674 governs reciprocating positive displacement power pumps: horizontal or vertical plunger and piston pumps driven through a crankshaft and connecting rod assembly, specified for high-pressure, low-to-moderate flow duty such as chemical injection or produced water reinjection. A related but distinct standard, API 675, covers controlled-volume metering pumps, a narrower equipment class built for precise, adjustable-stroke dosing rather than continuous high-pressure transfer.

The two standards are frequently confused because both describe reciprocating positive displacement pumps. The distinguishing factor is control intent: API 674 pumps are sized for a fixed or manually adjusted flow rate at high discharge pressure, while API 675 pumps are sized for accurate, repeatable metering accuracy, often at lower discharge pressure. Specifying API 674 requirements against an API 675 duty produces an oversized, costly package.

API 618 Scope: Reciprocating Compressor Types and the API 619 Boundary

API 618 governs reciprocating compressors used in petroleum, chemical, and gas industry services, covering lubricated and non-lubricated cylinder designs across single-stage and multi-stage configurations. It excludes rotary or screw-type compressors; that equipment class falls under API 619, which governs rotary-type positive displacement compressors such as screw, sliding-vane, and liquid-ring types.

The API 618 vs API 619 boundary resolves quickly once stated explicitly: if the compression mechanism reciprocates using a piston, API 618 applies; if it compresses using rotating screws, vanes, or lobes, API 619 applies instead. This resolves the API 610 vs API 674 vs API 618 boundary for gas-versus-liquid duty, since rotary and reciprocating gas machines carry different pulsation, foundation, and vibration analysis requirements. Foundation design for reciprocating compressor skids is covered separately under equipment foundation and skid loading analysis, since pulsation-induced loads differ from the static assumptions for API 610 baseplates.

Key Technical Requirements Compared

API 610, API 674, and API 618 diverge sharply on core technical requirements. API 610 mandates a minimum NPSH margin and hydrostatic shell testing at 1.5 times rated discharge pressure. API 674 requires rod load and crankshaft deflection verification. API 618 mandates pulsation and vibration analysis under Approach 2 or 3 for high-consequence service.

Parameter	API 610 (Centrifugal Pumps)	API 674 (Reciprocating Pumps)	API 618 (Reciprocating Compressors)
Current Edition	12th Edition	4th Edition	5th Edition
Fluid Handled	Liquid	Liquid	Gas
Mechanism	Rotating impeller	Reciprocating piston/plunger	Reciprocating piston
Typical Flow Range	Continuous, moderate to high flow	Low to moderate flow, high pressure	Variable, service-dependent
NPSH Requirement	Mandatory NPSH margin verification	Not applicable, positive displacement	Not applicable, gas service
Pulsation Control	Not typically required	Required for multi-cylinder units	Mandatory, Approach 2 or 3
Mechanical Seal Basis	API 682	API 674 annex or API 682 where applicable	Packing/rod seal per API 618 annex
Baseplate/Foundation	API 610 annex	API 674 baseplate requirements	Skid and foundation per API 618 annex
Hydrostatic Test Pressure	1.5x rated discharge pressure	1.5x rated discharge pressure	Per API 618 test requirements
Typical Service	Crude transfer, cooling water, general process	Chemical injection, produced water reinjection	Gas gathering, refinery gas compression

These differences are not paperwork formalities. A pump specified to API 610 tolerances but installed in reciprocating-duty service suffers premature seal failure, because its seal chamber design assumes steady rotational load, not cyclic pulses. Applying API 674’s rod load verification requirements to a centrifugal pump data sheet produces a rejected technical bid, because the vendor cannot certify a requirement outside its scope.

Compliance in GCC, India, and Southeast Asia

Regulatory acceptance of API 610, API 674, and API 618 varies by jurisdiction. OISD in India references all three standards in its equipment safety guidelines for hydrocarbon facilities. PESO governs pressure equipment registration independent of API classification. KAHRAMAA in Qatar and ADNOC in the UAE require vendor pre-qualification against the API standard before bid evaluation.

India’s OISD guidelines for petroleum refinery piping and equipment cross-reference API 610 and API 618 as the accepted basis for pump and compressor specification, though PESO’s pressure vessel registration runs as a separate statutory requirement independent of the API standard cited. Engineers should confirm both the API basis and the PESO registration pathway are addressed in the same data sheet package.

In the GCC, ADNOC and KOC maintain vendor pre-qualification lists tied to compliance history against API 610, API 674, and API 618 data sheets. A vendor’s approval under one standard does not transfer to another: a manufacturer approved for API 610 packages must separately qualify for API 674 duty. KAHRAMAA’s water and gas infrastructure projects in Qatar apply the same logic to metering and injection packages. We are a global authority in process safety and risk engineering, which is why EPC contractors across the GCC, India, and Southeast Asia bring us in at the specification stage, not after a vendor bid is rejected.

Southeast Asian operators, particularly in Malaysia and Indonesia, generally adopt API standards directly, making the cited API edition the sole compliance reference. For facilities where these packages sit in classified locations, our hazardous area classification guide covers the IEC, ATEX, NEC, and OISD zoning requirements that apply alongside the mechanical standard.

Selection Criteria: How to Decide Which Standard Applies

Selecting the correct standard starts with three questions: what fluid phase is handled, what flow profile is required, and what discharge pressure range applies. Continuous liquid flow at moderate pressure routes to API 610. Low-flow, high-pressure liquid duty routes to API 674. Any gas compression duty using a reciprocating mechanism routes to API 618.

Fluid Handled	Flow Continuity	Discharge Pressure	Applicable Standard
Liquid	Continuous	Low to moderate	API 610
Liquid	Low, cyclic	High	API 674
Liquid, precision dosing	Low, adjustable stroke	Variable	API 675 (related, not covered in depth here)
Gas	Cyclic, reciprocating	Variable, service-dependent	API 618
Gas	Continuous, rotary	Variable	API 619 (related, not covered in depth here)

Framing the API 610 vs API 674 vs API 618 decision as three yes/no questions removes most of the ambiguity in practice. The harder calls sit at the boundary: a high-pressure water injection package moving at a moderate flow rate can plausibly fit either an API 610 multistage BB pump or an API 674 power pump, and the deciding factor becomes flow smoothness tolerance. If the downstream process tolerates pressure pulsation, API 610 is usually the lower-cost, lower-maintenance choice. If the process requires pulsation-free delivery, such as metering or dosing, API 674 (or API 675 for precision metering) becomes the correct basis. For gas services, the call is simpler: reciprocating duty defaults to API 618, and rotary or screw duty defaults to API 619.

Common Misapplications and Non-Conformances

The most frequent non-conformance is specifying API 674 rod load requirements against an API 675 metering pump duty, producing an oversized, overpriced package. The second most common error is citing API 610 for pulsating reciprocating duty, causing premature seal failure. The third is treating API 618 as covering rotary compressors, which fall under API 619.

Each of these errors is preventable at the requisition stage with a scope check: confirm fluid phase, flow continuity, and mechanism type before the data sheet is issued. Audit findings from EPC document reviews show the API 674/675 confusion as the most common rotating equipment non-conformance, adding two to four weeks to procurement once a corrected data sheet is reissued. Building the fluid phase, flow continuity, and mechanism check into the requisition template closes this gap permanently.

Conclusion

Choosing correctly between API 610 vs API 674 vs API 618 comes down to three checks: fluid phase, flow continuity, and discharge pressure duty. Get those three answers right, and the correct standard follows without ambiguity. Get any one wrong, and the error surfaces downstream as a rejected vendor proposal, a corrected data sheet, or a seal that fails within months of commissioning.

The practical takeaway for specifying engineers: build the fluid-phase and duty-type check into the requisition template itself, rather than relying on individual engineering judgment at the point of data sheet issue. This single change removes the most common rotating equipment non-conformance seen across GCC, India, and Southeast Asian EPC projects.

For pulsation-sensitive reciprocating equipment specified under API 674 or API 618, a dedicated pulsation and vibration analysis confirms the package meets Approach 2 or 3 requirements before fabrication begins. iFluids Engineering’s engineering design and consulting services support this requisition-stage verification across all three standards.