API 6D pipeline valves: project specification guide
API 6D is widely referenced for pipeline and piping valves, but a standard number alone does not complete the purchase specification. The project must define the valve type, service, pressure-temperature basis, materials, bore, end connections, operation, testing and supplemental requirements.
TAZ Engineering & Export Team · · 13 min
Define the pipeline duty and valve function
State whether the valve provides mainline isolation, station isolation, bypass, pigging, emergency shutdown or non-return duty. Include normal position, operating frequency, closing time, maximum differential pressure and consequences of failure.
Valve type should follow the required function and pipeline operation. Full-opening or through-conduit requirements, pig passage and cavity behaviour need explicit confirmation in the datasheet.
Set pressure, temperature and materials basis
Provide design pressure and temperature, minimum design metal temperature, fluid composition, corrosion allowance and external environment. Select body, bonnet, trim, seals, bolting and weld overlay as a system.
For sour, corrosive or low-temperature service, add the relevant materials standard and project restrictions. Do not treat a general API 6D statement as evidence for special-service qualification.
Specify ends, bore and dimensions
Define flanged or welding ends, standard, schedule or bore, facing, face-to-face or end-to-end dimension and pup-piece requirements. Review transitions for pigging and pressure drop.
The approved drawing should show port, seat, cavity, drain, vent, injection and lifting arrangements. Field connection details need review before manufacturing release.
Address sealing and cavity pressure
Specify seat arrangement, sealing direction, double-block or isolation requirements, cavity relief philosophy and any bleed or vent connections. Terminology should be tied to a measurable design and test method.
Soft-seat material must fit pressure, temperature, fluid and decompression conditions. Metal-seated designs need an agreed leakage criterion and coating or overlay basis.
Size actuation for the governing case
Provide maximum differential pressure, line pressure, operating time, power supply, fail position, emergency operation, hazardous-area classification and control interface. Actuator torque should include valve factors and agreed margin.
Review stem and mounting interface, gearbox, stops, local indication, limit switches and partial-stroke requirements. Record the final torque sheet in the dossier.
Define testing and supplemental evidence
State required shell, seat, backseat where relevant, functional and supplemental tests with standard, pressure, medium, duration and acceptance. Add fire-safe, fugitive-emission, antistatic or high-pressure gas testing only when required.
Use an ITP and traceable test reports. The final MRB should connect materials, assembly, testing, coating, marking and release records to each valve or defined batch.
Checklist
- pipeline function
- design pressure and temperature
- minimum metal temperature
- fluid and corrosion basis
- full-bore and pigging requirement
- seat and cavity philosophy
- end connections and dimensions
- actuator torque basis
- test and qualification matrix
- traceable final dossier