Reference profile
- Designation
- API 676
- Title
- Positive Displacement Pumps — Rotary
- Issuing body
- American Petroleum Institute (API)
- Current edition
- 3rd Edition (Reaffirmed 2020)
- Status
- Active; international benchmark standard for heavy-duty rotary positive displacement pumps.
- Category
- Rotary Positive Displacement Pump Standard
Overview
API Standard 676 covers the minimum requirements for rotary positive displacement pumps and pump units for use in the petroleum, petrochemical, and natural gas process industries.
Rotary pumps excel in transferring high-viscosity fluids (heavy crude, bitumen, asphalt, lube oil, fuel oil), handling multiphase oil/gas mixtures, and providing smooth, pulse-free flow regardless of discharge pressure variations.
Scope & Applicability
Covers
- Pump Types: Twin-screw (timed non-contacting rotors), triple-screw (untimed), progressive cavity (PCP), external/internal gear, lobe, and sliding vane pumps.
- Casing & Rotor Construction: Heavy-duty pressure casings, replaceable liners, alloy rotors/screws, external timing gears, and external bearings isolated from process fluid.
- Overpressure Protection: Integral or external safety relief valves (PSV/Bypass valves) designed to protect the casing against overpressure.
- Heating Jackets: Steam or thermal oil heating jackets for high-viscosity or temperature-sensitive fluids (asphalt, wax, bitumen).
- Testing Requirements: Hydrostatic testing (1.5x MAWP), performance testing with viscous fluids, NPSH verification, and dynamic balancing.
Does NOT cover (exclusions)
- Reciprocating positive displacement pumps (plunger/piston)—covered by API 674.
- Controlled volume metering pumps—covered by API 675.
- Centrifugal process pumps—covered by API 610.
- Field overhaul and screw re-profiling—refer to vendor specialized manuals.
Key Requirements
Rotary Pump Type Selection (Twin-Screw vs Triple-Screw vs Gear)
- Twin-Screw Pump (Timed Non-Contacting): Ideal for heavy crude, bitumen, multiphase oil/gas/water mixtures, and dirty fluids. External timing gears prevent screw-to-screw contact.
- Triple-Screw Pump (Untimed): Power rotor drives idle rotors directly via fluid film lubrication. Excellent for clean lubricating fluids (lube oil, hydraulic oil, fuel oil) at high speed.
- Gear & Lobe Pumps: Compact choice for moderate-flow, high-viscosity chemical or polymer transfers.
External Timing Gears & Isolated Bearings
- Isolated Timing Gears: For Timed Twin-Screw pumps, timing gears and bearings must be isolated from the process fluid chamber and lubricated by an independent oil bath.
Overpressure Protection & Relief Valves
- Integral Relief Valve: Rotary positive displacement pumps generate continuous flow regardless of discharge pressure. An integral or external bypass relief valve is mandatory.
Inspection & Hydrostatic Testing
- Hydrostatic Test: Pressure-retaining casings must be tested at a minimum of 1.5x MAWP for at least 30 minutes.
- Performance Test: Factory performance testing under simulated viscosity and temperature conditions to confirm slip and capacity.
Technical Details
Volumetric Efficiency vs Viscosity: Q_actual = Q_theoretical - Q_slip. As viscosity increases, slip decreases rapidly, resulting in higher volumetric efficiency for viscous fluids.
Multiphase Gas Handling (GVF): Timed Twin-Screw pumps can handle Gas Volume Fraction (GVF) up to 95% to 98% intermittently without vapor locking.
API 682 Seal Chamber Envelope: Mechanical seal chambers must accommodate standard API 682 cartridge seals and flush plans (e.g. Plan 11, Plan 32, Plan 52/53).
Engineering Notes
- Always specify steam or thermal oil heating jackets for asphalt, bitumen, wax, or heavy fuel oil services to heat the casing and melt solidified liquid prior to pump startup.
- Size suction piping 1 to 2 pipe sizes larger than the pump suction nozzle when handling high-viscosity fluids to minimize friction head loss and prevent cavitation.
- Select Timed Twin-Screw pumps over gear pumps for fluids containing abrasive solids or variable multiphase gas content.
Related Standards
Source, Edition & Status
- Publisher
- API
- Edition Year
- N/A
- Industries
- Refinery, Petrochemical, Chemical
- Content Status
- reviewed
- Last Reviewed
- 2026-07-01
- Last Updated
- 2026-07-01
- Verified By
- Engineering Reviewer
- Official Link
- www.api.org
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