Define the Service
A supplier cannot select the correct valve from size and pressure class alone. The following 18 input groups should be included in the request for quotation:
- Fluid name and composition
- Gas, liquid, vapor, or mixed-phase condition
- Design and operating pressure
- Design and operating temperature
- Lowest possible temperature
- Maximum pressure difference across the closed valve
- Hydrogen sulfide, carbon dioxide, chloride, and water content
- Solid-particle size, hardness, and concentration
- Expected opening and closing cycles
- Required opening or closing time
- Manual, pneumatic, electric, or hydraulic operation
- Fail-open, fail-close, or fail-in-place action
- Fire-test, low-emission, sour-service, or cryogenic requirements
- Full-bore, pigging, DBB, or DIB requirements
- Flanged, butt-weld, socket-weld, or threaded ends
- Indoor, outdoor, buried, offshore, or marine installation
- Inspection and document requirements
- Packing and long-term storage requirements
The maximum line pressure and the maximum pressure difference across the valve are not always the same. The second value affects operating torque and actuator size.
“Natural gas” is also too general. Wet sour gas, dry sweet gas, hydrogen-rich gas, and gas containing particles may need different materials, seats, seals, tests, and cavity-pressure controls.
A complete API 6D ball valve RFQ should list every condition that may change the valve design, testing scope, or price.
Choose the Main Standard
The purchase order should state one main valve standard, its edition, required addenda, and project-specific additions. Do not list several standards without explaining which one has priority.
API 6D: API Specification 6D covers pipeline and piping valves, including design, materials, manufacturing, testing, marking, and documentation. The 25th edition has later updates, including Addendum 3 issued in March 2025.[1]
API publishes addenda and errata after the main edition. The contract should name the exact issue instead of stating only “latest API 6D.”[2]
When an API Monogram is required, check the legal company name, manufacturing address, product scope, and license status in API’s official directory.[3]
API 608: API 608 applies to defined metal ball valves with flanged, threaded, and welding ends. API published the 7th edition in 2025.[4]
API 608 and API 6D are not interchangeable. The project engineer should choose the standard that matches the valve type and service.
ASME B16.34: This standard covers pressure-temperature ratings, materials, dimensions, testing, marking, and nondestructive examination for many cast, forged, and fabricated valves. ASME currently lists the 2025 edition.[5]
ISO 17292: ISO 17292 covers metal ball valves for petroleum, petrochemical, natural-gas, and related industrial applications. Its size, pressure, and end-connection limits must be checked before it is used as the governing standard.[6]
Set the Test Rules
Pressure testing should follow the main valve standard and the purchase order. ISO 5208 is intended to be used with a valve product standard; where requirements differ, the product standard takes priority.[7]
API 598, API 607, API 608, and API 641 have different purposes. They should not be grouped together as one general “API test certificate.”[8]
The order should state:
- Test standard and edition
- Test medium
- Test pressure
- Test duration
- Valve position
- Pressure direction
- Allowed leakage
- Leakage measurement method
- Witness or hold points
- Required test records
Fire testing: A fire-tested valve is checked for pressure containment and permitted internal and external leakage during and after a defined fire exposure. ISO 10497 is an international fire type-test standard for valves.[9]
The fire-test certificate must match the actual valve type, body construction, seat design, stem sealing, size range, and pressure class. A certificate for a small two-piece floating valve does not automatically qualify a large three-piece trunnion valve.
Low-emission testing: ISO 15848-1 covers valve type testing for fugitive emissions.[10] ISO 15848-2 covers production acceptance testing.[11]
A packing supplier’s certificate does not prove that the complete valve has passed a low-emission test. Stem diameter, stem finish, packing chamber, pressure, temperature, and operating cycles all affect leakage.
Choose Forged or Cast Construction
A forged body is shaped under pressure before machining. A cast body is made by pouring molten metal into a mold.
Forged construction is often selected for compact high-pressure valves, low-temperature service, critical isolation, or projects that require forged pressure-containing parts.
Forging can provide controlled mechanical properties, but it does not remove every risk. Forgings can still have:
- Laps and cracks
- Internal inclusions
- Wrong heat treatment
- Excessive hardness
- Poor impact toughness
- Material mix-ups
- Machining damage
Large cast bodies may be more practical for some sizes and pressure classes. The choice should depend on pressure, temperature, material, body shape, inspection level, cost, lead time, and maintenance requirements.
See the detailed forged versus cast valve body comparison for the main manufacturing and inspection differences.
Choose Floating or Trunnion Design
Floating ball valves: The ball can move slightly under pressure and is pushed toward the downstream seat. This design is commonly used where size, pressure, seat load, and torque remain within the manufacturer’s proven range.
Check:
- Maximum valve size and pressure class
- Seat load at full pressure difference
- Breakaway torque
- Seat deformation
- Stem strength
- Body-cavity pressure relief
- Required leakage rate
For clean service requiring tight shutoff, review the available forged soft-seated ball valve range.
Trunnion-mounted ball valves: The ball is supported by upper and lower bearings or trunnions. The seats move to seal against the ball.
This design is commonly used for:
- Large sizes
- High pressure
- Pipeline isolation
- Emergency shutdown
- Powered actuation
- DBB or DIB service
The drawing should show the trunnion bearings, seat springs, seat directions, drains, vents, sealant-injection points, and cavity-pressure relief method.
A detailed API 6D trunnion ball valve guide can help buyers prepare the required data sheet and drawing review.
Choose the Body Type
Side-entry: A side-entry valve usually has a two-piece or three-piece bolted body. Check body seals, bolting, tightening procedure, fire-resistant sealing, and maintenance access.
Top-entry: Internal parts can be removed through the top opening. In-line maintenance does not mean maintenance under pressure. The valve must be isolated, drained, and depressurized before opening.
Fully welded: A fully welded valve has no bolted split joint in the main pressure-containing body. It can reduce external body-joint leak paths, but welding heat, distortion, weld examination, repair limits, and seat protection must be controlled.
For buried or gas-transmission service, compare split-body and fully welded ball valves before selecting the body construction.
Define SPE, DPE, DBB, and DIB
SPE: Single piston effect. Excess body-cavity pressure can push the seat away from the ball and relieve pressure toward the lower-pressure side when the required pressure difference is reached.
The manufacturer should provide the seat effective area, spring load, relief direction, cavity-to-line pressure difference, and test method.
DPE: Double piston effect. The seat can be pressure-energized from either side. Two DPE seats may trap pressure in the body cavity, so an external relief device may be required.
DBB: Double block and bleed. Two seating surfaces isolate pressure from both valve ends, and the cavity between them can be vented or drained.
DIB-1: Both seats are bi-directional.
DIB-2: One seat is uni-directional and the other is bi-directional.
The RFQ should state the required pressure direction, seat arrangement, bleed point, leakage limit, and test method. Do not approve a valve only because these abbreviations appear in a catalog.
For compact isolation systems, review the available DBB compact manifold design, but confirm its actual isolation and bleed test before purchase.
Check the Bore and Ends
“Full bore” should be confirmed on the approved drawing. Check the ball port, seat opening, body bore, weld-end bore, internal steps, drain position, and any stem intrusion.
The smallest opening is the real restriction.
For piggable pipelines, state the pig type and minimum passage size. Cleaning pigs and intelligent inspection tools may have different limits.
A reduced-bore valve can lower cost and weight, but it also reduces flow area and increases local velocity. Review the full-bore versus reduced-bore comparison before approval.
Flanged ends: ASME B16.5 covers pressure-temperature ratings, dimensions, materials, tolerances, marking, and testing for flanges from NPS 1/2 through NPS 24.[12]
For larger flanges, the project may require ASME B16.47 or another applicable standard.
Butt-weld ends: ASME B16.25 covers welding bevels and end preparation for piping components.[13]
Confirm the pipe outside diameter, actual wall thickness, inside diameter, bevel, root face, bore transition, material, welding procedure, and post-weld heat-treatment requirement.
Soft seats and seals can be damaged by field welding heat. The manufacturer should state the maximum permitted body temperature and whether extended ends, heat sinks, or removal of internal parts are required.
Face-to-face length: ASME B16.10 standardizes dimensions for defined valve types and sizes.[14] Special or compact valves may use a nonstandard length, so the drawing must be approved before pipe fabrication.
Select the Materials
Common forged body materials include:
- ASTM A105 carbon steel
- ASTM A350 LF2 low-temperature carbon steel
- ASTM A182 F316 or F316L stainless steel
- ASTM A182 F51 duplex stainless steel
- ASTM A182 F53 or F55 super duplex stainless steel
- Nickel alloys
ASTM A105 covers carbon-steel forgings for piping applications.[15]
ASTM A350 covers carbon- and low-alloy-steel forgings that require notch-toughness testing for piping components.[16]
ASTM A182 covers forged or rolled alloy- and stainless-steel flanges, fittings, valves, and valve parts.[17]
The material grade alone is not enough. Also check:
- Heat-treatment condition
- Impact-test temperature and result
- Hardness
- Corrosion conditions
- Hydrogen sulfide
- Chloride level
- Welding and repair limits
- Bolting and small-bore fittings
- Seat, seal, bearing, and spring compatibility
A low-temperature body does not make the complete valve suitable for low temperature. The stem, bolting, seats, seals, lubricant, actuator, and accessories must also work at the minimum design temperature.
ISO 28921-1 covers the design, manufacturing, and production testing of isolation valves for low-temperature service.[18]
For LNG and similar applications, review purpose-built forged cryogenic ball valves rather than modifying a standard ambient-temperature design.
Check Sour-Service Limits
“NACE compliant” is not enough. The project should state which sour-service standard applies and provide the real operating environment.
ISO 15156 is used for material selection in hydrogen-sulfide-containing oil and gas production environments.[19]
ISO 17945 addresses metallic materials resistant to sulfide stress cracking in corrosive petroleum-refining environments.[20]
Check:
- Hydrogen sulfide partial pressure
- Presence of a water phase
- Fluid pH
- Chloride level
- Temperature
- Material hardness
- Cold work
- Welding and heat treatment
- Plating
- Bolting and spring materials
Control Material Traceability
The approved bill of materials should list the exact material for the body, closure, ball, stem, trunnion, seat rings, springs, bearings, seals, bolts, drains, vents, and injection fittings.
The traceability chain should connect:
- Valve purchase order
- Material supplier
- Material certificate
- Heat number
- Cut forging
- Machined part
- Assembly record
- Valve serial number
- Final data book
During a factory audit, use at least three random checks as an internal audit method:
- One raw forging in the material store
- One valve under machining or assembly
- One completed and tested valve
For each sample, check the heat number, drawing revision, inspection record, and final identification. Three samples are not an industry-mandated quantity, but they provide a practical way to test whether the traceability system works at different production stages.
Positive Material Identification can help detect alloy mix-ups, but it does not replace mechanical tests, heat-treatment records, impact tests, hardness results, or full material certificates.
Choose Seats and Ball Coatings
Soft seats: Common materials include PTFE, modified PTFE, reinforced PTFE, PEEK, and nylon.
Do not accept a quotation that says only “PTFE seat.” Ask for the exact grade, filler, temperature range, pressure limit, chemical compatibility, creep resistance, rapid gas decompression resistance, and expected cycle life.
ISO 23936-2 gives requirements and procedures for qualifying elastomers used in oil and gas production equipment.[21]
Metal seats: These may be required for high temperature, abrasive solids, erosive flow, or severe cycling.
The ball and seat should be treated as a matched pair. Check:
- Base materials
- Coating process
- Coating thickness
- Hardness
- Porosity and bonding
- Surface finish
- Ball roundness
- Lapping method
- Allowed leakage
A harder coating is not always better. A brittle or poorly bonded coating can crack or separate from the base metal.
Review the available forged metal-seated ball valves when soft seats cannot handle the process conditions.
Check the Stem, Torque, and Actuator
The torque sheet should include:
- Break-to-open torque
- Running torque
- End-to-close torque
- Pressure difference
- Temperature
- Seat material
- Fluid condition
- New and aged conditions
- Safety factor
- Maximum allowed stem torque
Check the strength of the stem, stem-to-ball connection, gearbox, coupling, bracket, keys, bolts, and actuator as one system.
The actuator should be large enough to operate the valve but not so large that it can damage the stem or mounting parts.
For a pneumatic actuator, use the minimum available air pressure. For a spring-return actuator, compare the actuator output and valve torque through the complete stroke.
For an electric actuator, check starting torque, running torque, duty cycle, motor protection, gear limits, travel stops, and control signals.
Qualify the Chinese Manufacturer
Verify the relationship between the company that quotes, manufactures, exports, receives payment, holds certificates, and provides the warranty.
Check:
- Chinese legal company name
- English trading name
- Business-license address
- Actual factory address
- API license holder where required
- ISO certificate holder
- Export company
- Bank-account holder
- Warranty provider
A trading company is not automatically unacceptable, but the buyer must know where the valves are designed, machined, assembled, and tested.
Review the manufacturer’s stated facilities on the company information page, then verify important claims through licenses, production records, equipment checks, and an on-site or third-party audit.
Outsourcing is also not automatically a problem. The manufacturer must control its forging mill, heat-treatment supplier, coating company, laboratory, NDE provider, and actuator supplier.
Audit the Factory
A practical audit should inspect real materials, parts, and records.
Check:
- Material separation and heat-number marking
- Quarantine area for rejected parts
- Drawing revision used at each machine
- Machine capacity for the offered sizes
- Critical dimension records
- Gauge and torque-tool calibration
- Seal storage and shelf-life control
- Assembly cleanliness
- Test-bench pressure and size capacity
- Pressure-gauge range and calibration
- Serial-number control
- Document review and release process
Do not accept a general statement such as “500 valves per month” without checking whether the capacity covers the order’s real sizes, materials, pressure classes, coatings, tests, and documents.
Check Production Capacity
Capacity should be calculated from the project’s actual valve mix, not from a factory’s total monthly output.
For illustration, assume a project requires 120 applicable valves and the factory can machine, assemble, and test 10 of those valves per week. The theoretical production period is 12 weeks. Adding a 20% planning allowance for inspection holds, rework, machine maintenance, and schedule variation increases the practical planning period to about 15 weeks.
This calculation is only an internal planning example. The actual production rate must be supported by machine loading, test-bench availability, subcontractor capacity, and approved drawings.
An illustrative project schedule may look like this:
| Stage | Example Duration |
|---|---|
| Drawing and document approval | 2–4 weeks |
| Forging procurement | 6–10 weeks |
| Machining | 3–5 weeks |
| Ball coating and lapping | 2–4 weeks |
| Assembly and testing | 1–2 weeks |
| Final documents and packing | 1–2 weeks |
| Typical total when stages overlap | About 14–22 weeks |
This 14–22 week range is an example, not a standard delivery promise. Large sizes, duplex materials, special coatings, cryogenic testing, late drawing approval, or holiday shutdowns can extend the schedule.
Review the manufacturer’s trunnion ball valve production timeline and compare it with the actual order requirements.
Verify the Track Record
A useful project reference should show:
- Project country and year
- Valve type
- Size range
- Pressure class
- Body and seat materials
- Fluid service
- Actuator scope
- Quantity
- Inspection level
- Document scope
A supplier that has delivered Class 150 carbon-steel floating valves has not proved that it can supply Class 1500 duplex trunnion valves for sour gas.
Ask for evidence such as redacted purchase orders, approved drawings, inspection releases, test reports, shipping documents, completion letters, or reference contacts.
Where available, also review FAT first-pass rate, nonconformance reports, late documents, shipping delays, field leakage, warranty claims, and corrective actions.
A published DN600 PN63 DIB-1 forged trunnion valve project record can be used as an example of the details a buyer should request, but the evidence should still be checked independently.
Control Inspection and Testing
The Inspection and Test Plan should list each manufacturing stage, procedure, acceptance rule, record, and inspection point.
Typical stages include:
- Drawing approval
- Material review
- Forging inspection
- Heat treatment
- PMI and hardness testing
- Nondestructive examination
- Machining and dimensions
- Assembly
- Shell test
- Seat test
- DBB, DIB, or cavity-relief test
- Torque and functional test
- Actuator test
- Coating and marking
- Packing and final release
A hold point means production cannot continue until the required approval is received.
Each test report should identify the valve serial number, size, pressure class, procedure, medium, pressure, duration, allowed leakage, actual result, test bench, gauge, date, operator, and inspector.
A general certificate without a serial number does not prove that a specific valve was tested.
Compare the factory’s hydrostatic, pneumatic, and cryogenic test equipment with the actual order requirements.
Control Documents and Changes
Agree the document list before production starts.
The package may include:
- Approved data sheet
- General arrangement drawing
- Cross-sectional drawing
- Bill of materials
- Seat-action diagram
- Pressure-temperature rating
- Torque and actuator calculations
- Quality plan and ITP
- Material certificates
- Heat-treatment and impact-test records
- PMI, hardness, and NDE reports
- Pressure- and leakage-test reports
- Fire- and emission-test qualifications
- Calibration records
- Nonconformance reports
- Operation and maintenance manual
- Spare-parts list
- Final manufacturing record book
A medium-size order can produce a large number of records. For example, an order of 50 serialized valves may require at least three individual records per valve:
- One assembly record
- One pressure-test report
- One final inspection record
That alone produces 150 valve-specific records: 50 valves × 3 records. Shared drawings, procedures, material certificates, coating reports, calibration certificates, and the final data book are additional documents.
This example shows why document preparation must be included in the production schedule. Physical completion does not mean the order is ready for shipment.
Require written approval before changing the factory, forging source, material, heat treatment, seat grade, seal grade, ball coating, subcontractor, drawing, test procedure, actuator, gearbox, or delivery date.
A technically similar substitute is still a change.
Compare the Bids
Compare every quotation on the same technical basis.
| Item | Supplier A | Supplier B | Supplier C |
|---|---|---|---|
| Main standard and edition | |||
| Valve and body design | |||
| Bore and end connection | |||
| Body, ball, stem, and seat materials | |||
| SPE, DPE, DBB, or DIB arrangement | |||
| Fire and emission qualification | |||
| Sour or low-temperature service | |||
| Actuator and accessories | |||
| Tests, inspection, and documents | |||
| Delivery, packing, and warranty | |||
| Technical deviations |
Total cost should include the valve, actuator, accessories, spares, special tests, third-party inspection, documents, export packing, freight, insurance, customs cost, site support, and schedule risk.
For illustration, Supplier A quotes USD 100,000 and Supplier B quotes USD 108,700. Supplier A appears about 8% cheaper, but its quotation excludes:
- Third-party inspection: USD 6,000
- PMI: USD 3,000
- Special testing: USD 5,000
- Final document package: USD 4,000
After adding the missing USD 18,000, Supplier A’s evaluated cost becomes USD 118,000. It is then about USD 9,300 more expensive than Supplier B’s complete quotation.
This is a calculation example, not an industry price benchmark. Its purpose is to show why quotations must be normalized before the lowest bidder is selected.
Use a Qualification Score
A buyer can use an internal scorecard after all pass-or-fail requirements have been checked.
| Area | Example Weight |
|---|---|
| Technical compliance | 25% |
| Material and traceability control | 15% |
| Manufacturing capability | 15% |
| Testing capability | 15% |
| Similar project record | 10% |
| Document control | 10% |
| Delivery capacity | 5% |
| Commercial terms | 5% |
As an internal example, the buyer may require a minimum total score of 70 out of 100, while material traceability and test capacity remain pass-or-fail items. A supplier scoring 85 overall should still fail if it cannot trace the valve body to its original material certificate.
The 70-point limit and the weights above are sample internal rules, not API or ISO requirements. Each project should set its own limits according to valve risk.
Control Delivery and Site Work
Packing should protect the valve during transport and storage. Require dry internal surfaces, corrosion protection, strong end covers, actuator supports, lifting points, center-of-gravity marks, seaworthy cases where needed, and clear spare-parts identification.
At site, check:
- Crate and moisture damage
- Flange and weld-end condition
- Nameplate and tag number
- Actuator and accessories
- Storage position
- Pipe alignment
- Flow direction where required
- Welding temperature limits
- Travel stops and operating direction
- Fail action and feedback signals
- External leakage after installation
The contract should state whether the warranty starts at shipment, delivery, installation, commissioning, or plant start-up. It should also define response time, failure analysis, repair approval, retesting, spare parts, and transport responsibility.
For spare parts, inspection records, or technical support, review the available industrial valve service scope.
Common Failures
Actuator too small: The RFQ gives line pressure but not the maximum pressure difference. The actuator works without load but cannot open the valve in service.
Heat number lost: The material certificate is correct, but the marking is not transferred after machining. The factory cannot prove that the finished body matches the certificate.
Wrong seat arrangement: The project requires DIB, but the supplier uses its standard SPE design. The mistake is found after material purchase.
Late documents: The valve passes FAT, but missing material, impact, NDE, or calibration records prevent shipment release.
Welding damage: A soft-seated butt-weld valve is installed without controlling body temperature, damaging the seat before commissioning.
Final Checklist
- Service conditions and maximum pressure difference are complete.
- The main standard, edition, addenda, and extra requirements are fixed.
- The valve, seat, body, bore, and end designs are approved.
- SPE, DPE, DBB, DIB, and cavity relief are clearly defined.
- The full bill of materials is approved.
- Material traceability has been demonstrated on real parts.
- Fire, low-emission, sour, and low-temperature claims are within the qualified scope.
- Valve torque, stem strength, and actuator output are approved.
- The legal company, factory, certificate holder, exporter, and warranty provider are known.
- Similar project records have been checked.
- The test bench can handle the required size and pressure.
- The ITP, document list, production schedule, packing, and warranty are agreed.
- All technical deviations are closed before production.
Conclusion
A reliable EPC valve order should connect five records: the approved data sheet, bill of materials, material certificates, serial-numbered test reports, and production schedule. Use at least three random traceability checks during the factory audit, compare bids after adding every excluded cost, and plan production from real machine and test capacity rather than a claimed monthly total. A 50-valve order may create more than 150 valve-specific records, while a typical complex order may require about 14–22 weeks when engineering, forgings, machining, coating, testing, and documents overlap. Suppliers that cannot prove these points should remain unqualified.
Engineering Notice: Final valve selection, material approval, pressure-temperature rating, seat design, actuator sizing, inspection scope, and acceptance criteria must be approved by qualified project engineers. This article does not replace the project specification or the full text of the applicable standards.
