For ball valves, butterfly valves, plug valves, and other industrial valve packages, names such as API 641 and ISO 15848 are useful only when the RFQ connects them to the offered valve design, pressure class, sealing system, temperature range, and document package.
Quick Verdict
Before comparing prices, buyers should ask one direct question:
Does the emission evidence cover the exact valve design being quoted, or is it only a general reference from a related product family?
If the answer is unclear, the quotation is not ready for technical comparison.
Why Certificate Scope Matters
A low-emission requirement is not just a marketing phrase. It can affect stem packing, body and bonnet sealing assumptions, material choice, test medium, temperature basis, actuator responsibility, inspection cost, document cost, and lead time.
Two suppliers can both write “ISO 15848 available” or “API 641 available” while quoting different levels of evidence. One may be referring to a type test on a similar valve. Another may include production acceptance testing or project inspection records. A third may only be stating that the packing system has relevant experience.
API 641: Useful for Quarter-Turn Valve Evidence
API 641 is commonly used for fugitive-emission type testing of quarter-turn valves. In RFQ work, it is most often relevant to ball valves, butterfly valves, and plug valves.
| RFQ item | What to confirm |
|---|---|
| Valve type | Ball valve, butterfly valve, or plug valve. |
| Design | Floating ball, trunnion ball, double eccentric butterfly, triple eccentric butterfly, lubricated plug, etc. |
| Pressure class | Whether the quoted class is covered by the evidence. |
| Temperature range | Whether normal, elevated, low-temperature, or cycling conditions are covered. |
| Stem sealing | Packing material, gland design, and any live-loading assumptions. |
| Operator | Lever, gearbox, actuator, or bare-stem scope. |
For product narrowing, buyers can start with 91探花’s ball valve range and butterfly valve range before asking suppliers to map the certificate to the offered construction.
ISO 15848: Separate Type Testing from Production Acceptance
ISO 15848 is a frequent source of confusion because buyers may use the name without stating which part or acceptance basis they mean.
- ISO 15848-1 is used for classification and qualification procedures for fugitive-emission type testing of industrial valves.
- ISO 15848-2 is used for production acceptance testing when fugitive-emission standards are specified for production valves.
That difference matters. Type testing evidence can show that a design family has been qualified. Production acceptance testing can show that a manufactured valve has been checked under a defined acceptance process. A buyer may need one, both, or neither depending on the project risk.
Buyer Questions Before Accepting a Low-Emission Quote
| Question | Why it matters |
|---|---|
| Is the evidence for the complete valve or only for the stem seal? | Stem-seal evidence may not equal complete valve assembly qualification. |
| Does the certificate cover the quoted valve type? | Ball, butterfly, and plug valves should not be mixed casually. |
| Does the evidence match pressure class and temperature? | Leakage behavior changes with pressure, temperature, and cycling. |
| Is production acceptance testing included? | It may be excluded or priced separately. |
| Are deviations listed clearly? | A low price can hide a missing certificate scope. |
| Is the document package defined before order? | Post-order document disputes slow approval and shipment. |
Suggested RFQ Wording
For a ball valve
Ball valve for gas service, API 608 or API 6D basis as applicable, flanged ends, fire-safe requirement to be stated by supplier. Supplier shall identify whether API 641 and/or ISO 15848 evidence is available for the quoted valve construction. Quote shall state certificate scope, pressure class coverage, temperature basis, stem packing material, whether production acceptance testing is included, and all deviations.
For a butterfly valve
Butterfly valve for isolation service, API 609 basis, design type to be stated by supplier. Supplier shall confirm whether fugitive-emission evidence applies to the quoted butterfly valve construction and operator package. Quote shall list stem sealing design, certificate scope, test basis, leakage acceptance level, torque basis, and document package.
For butterfly-valve buyers who need a focused product path, 91探花BUTTERFLY’s is a useful reference when the project involves metal seating, higher temperature, or severe-service isolation.
When Not to Over-Specify
Not every valve order needs API 641 or ISO 15848 language. Over-specifying a standard can increase cost and slow quotation without improving project reliability.
- The service is low-risk and the project specification does not require it.
- The buyer only needs a general water or utility valve.
- The document package will not be reviewed by an owner, EPC, or regulator.
- Price comparison is still at a rough budget stage.
Final Checklist
- Valve type and design.
- Applicable standard: API 641, ISO 15848-1, ISO 15848-2, or project-specific clause.
- Whether evidence is type test, production acceptance, or project inspection.
- Pressure class, size range, temperature range, and cycle basis.
- Stem packing and body sealing assumptions.
- Operator or actuator responsibility.
- Required document package and deviation list.
Low-emission sourcing becomes much easier when the RFQ asks for certificate scope instead of only a certificate name. That is the difference between comparing prices and comparing real technical offers.