External valve leakage can occur at the stem or shaft seal and body joints. Buyers need to distinguish a packing-material test, a valve type test and production acceptance. The standard named in the requisition determines what was measured and how the result is classified.
01 / Routes
Select the route that matches the valve and project specification.
ISO 15848-1 evaluates external leakage of stem/shaft seals and body joints of isolating and control valves intended for volatile air pollutants and hazardous fluids. Its official scope excludes end-connection joints and certain other effects. API maintains separate routes for quarter-turn and rising-stem valve designs.
A project may specify one route because its classification, temperature cycles, mechanical cycles and acceptance language fit the owner’s programme. Do not combine designations from different systems into an invented hybrid class.
| Route | Typical design scope | Procurement question |
|---|---|---|
| ISO 15848-1 | Type-test classification for isolating/control valves. | Required tightness, endurance and temperature class. |
| API 641 | Quarter-turn valve type testing. | Offered ball/butterfly/plug design coverage and edition. |
| API 624 | Rising-stem valve type testing with graphite packing. | Stem, packing, body-joint and design coverage. |
| Production test | Order-specific acceptance where specified. | Method, sample/extent and relation to type qualification. |
02 / Seal system
Packing performance depends on the hardware around it.
Stem finish, straightness, diameter, gland geometry, packing chamber, surface condition, fastener load and thermal expansion all influence leakage. The body-joint gasket and bolting are part of the external-leakage system as well.
Replacing packing with a familiar low-emission product does not automatically transfer a qualification. The tested design and the standard’s extension rules control the claim.
03 / Certificate
The certificate should tell you what was cycled and measured.
Look for the valve manufacturer and model, standard edition, laboratory, test report, valve size/rating/material, stem or shaft details, packing/gasket identification, temperature range, mechanical cycles, thermal cycles, measurement method and result/classification.
If the order includes several sizes and materials, ask for a coverage matrix. A certificate for a small carbon-steel test valve may not cover a large stainless configuration merely because the packing name is the same.
- Tested assemblyValve model, drawing, size, class and materials.
- Seal detailsPacking set, gasket, stem/shaft and gland arrangement.
- Test programmeTemperature and mechanical cycles, adjustments and method.
- ResultMeasured leakage and classification/acceptance.
- Offered coverageDocumented extension from tested design to supplied item.
04 / Field life
A type-test pass is not a maintenance-free promise.
Installation loads, thermal transients, stem damage, corrosion, solids and packing adjustment affect field leakage. Preserve the manufacturer’s installation and maintenance instructions and any permitted gland-adjustment limits.
For critical services, build a leak-detection and repair programme around the plant’s regulatory and operational requirements. The valve certificate is one input, not the whole programme.
05 / RFQ
Specify the standard, class and evidence before quotation.
Identify the applicable standard and edition, required temperature/endurance/tightness classification or acceptance, production testing extent, approved adjustments and document package. Require deviations in the proposal.
Where methane or another specific test medium is required, state it. Do not assume that one standard’s medium, measurement method or class can be translated directly into another.
Valve fugitive-emissions qualification shall comply with [standard, edition and required class]. Supplier shall provide the complete report reference and a design-coverage matrix for each offered model, including packing, gasket, stem/shaft, size, rating, material and temperature range.
Sources / editorial control
Source basis
- ISO 15848-1:2015. Official current scope page; includes stated exclusions.
- API Standards Plan. Confirms API 641 second edition (2023) and API 624 second edition (2023).
- API refining publications catalogue. Official catalogue descriptions for API 641 and related valve standards.
Review limit: This overview does not reproduce classification limits or test procedures. Use licensed standards and the complete laboratory report for acceptance.