Every valve with a moving stem has a potential leak path through its packing. One valve leaking a few hundred ppm of methane is easy to dismiss, but a gas plant has thousands of them, and stem leaks tend to grow as packing wears and thermal cycles loosen glands. Fugitive emission standards exist to qualify valve designs that stay tight over their service life. This article explains how ISO 15848, API 622, API 624 and API 641 fit together and how to specify low emission valves ISO 15848 classes on a purchase order.
Why methane emissions from valves matter
Methane is a potent greenhouse gas. According to the IPCC Sixth Assessment Report, its global warming potential is roughly 80 times that of CO2 over 20 years and about 30 times over 100 years. Reducing methane leakage is therefore one of the fastest ways for producers to cut their emissions footprint, and it features in initiatives such as the Global Methane Pledge and the UNEP Oil and Gas Methane Partnership (OGMP 2.0). The UAE has a net-zero by 2050 target and several regional producers have announced methane-reduction goals, which are increasingly reflected in project specifications.
Beyond climate reporting, there are practical reasons. Leaking stems release toxic H2S in sour service, waste product, create hazardous-area concerns, and trigger repairs found in leak detection and repair (LDAR) surveys using EPA Method 21 or optical gas imaging. In hot desert service, high daytime temperatures and wide day-night swings also cycle the packing thermally, which is exactly the stress these standards simulate.
ISO 15848-1: type testing and classification
ISO 15848-1 is a type test performed on a representative valve to classify the design. The result is a class designation such as ISO FE BH - CO1 - SSA 0 - t(-29 °C, 200 °C) - Class 300 - ISO 15848-1. Each part means something specific.
Tightness classes
Stem leakage is measured either with helium, using a vacuum or total leak rate method, giving classes AH, BH and CH, or with methane, giving classes AM, BM and CM. Class A is the tightest and C the least tight. In practice, class AH is typically achieved only with bellows-sealed stems, while well-designed packed valves commonly reach BH. Body seals, such as bonnet gaskets, are checked by sniffing. Helium and methane results are not interchangeable, so the purchase order must state which one is required.
Endurance classes
Endurance defines how many mechanical cycles the valve completes during the test, combined with thermal cycles. For isolating valves, CO1 is 205 mechanical cycles, CO2 is 1,500 and CO3 is 2,500. For control valves, CC1 is 20,000 cycles, CC2 is 60,000 and CC3 is 100,000. Most isolating valves in hydrocarbon service are specified at CO1 or CO2; frequently operated valves justify CO2 or higher.
Temperature classes and SSA
The test temperature, for example t(-46 °C), t(RT) or t(200 °C), defines the range over which the classification is valid. The SSA number records how many stem seal adjustments were made during the test. SSA 0 means the gland was never retightened.
ISO 15848-2: production acceptance testing
Part 2 is a production test applied to a sample of valves from an order, normally at room temperature with helium. It confirms that production valves are built like the type-tested unit; it does not replace Part 1. Specify the sampling level and the production tightness class, and do not accept a Part 2 report as proof of design qualification.
API 622, API 624 and API 641
API 622 type-tests the packing itself in a test fixture, not a complete valve. The test runs 1,510 mechanical cycles and five thermal cycles up to 260 °C with methane at 600 psig, and includes a corrosion evaluation of the packing against stem material. It qualifies the packing product, which is then used in a valve test.
API 624 type-tests rising-stem valves, such as gate and globe valves to API 600, 602 and 623, fitted with API 622-qualified packing. The test uses methane at 600 psig (or the valve rating if lower), 310 mechanical cycles and three thermal cycles to 260 °C, with a maximum stem leakage of 100 ppmv. API 641 applies a similar methane approach and 100 ppmv limit to quarter-turn valves, including ball valves, plug valves and butterfly valves.
| Standard | What is tested | Test medium | Result |
|---|---|---|---|
| ISO 15848-1 | Valve design (type test) | Helium or methane | Tightness, endurance and temperature class |
| ISO 15848-2 | Production valves (sample) | Helium, usually room temperature | Production acceptance |
| API 622 | Packing in a fixture | Methane | Packing qualification |
| API 624 | Rising-stem valves | Methane | Pass/fail at 100 ppmv |
| API 641 | Quarter-turn valves | Methane | Pass/fail at 100 ppmv |
What makes a valve low emission in practice
Certificates follow design. The features that usually separate a qualified valve from a standard one are:
- Fine, consistent stem surface finish and tight straightness and diameter tolerances
- Die-formed flexible graphite rings with braided anti-extrusion end rings, or engineered PTFE sets for lower temperatures
- Corrosion-inhibited graphite to protect the stem from pitting under the packing
- Live-loading with disc springs to keep gland stress as packing consolidates
- Deep stuffing boxes, adequate gland bolt size and accurate gland follower guidance
- Bellows seals where AH tightness or highly toxic service justifies them
Actuated valves also need attention: side loads from a poorly aligned actuator can wear packing unevenly and undo a good test result.
How to specify low emission valves
- State the standard and full classification, for example ISO 15848-1 BH-CO1-SSA 0 with the required temperature class, or API 624 / API 641.
- Say whether helium or methane classes are acceptable.
- Require that the type-test certificate covers the offered size range, pressure class, stem seal design and packing material.
- Ask for ISO 15848-2 production testing and define the sample size.
- Request the API 622 report for the packing used in API 624 valves.
- Combine requirements with sour service, fire test (API 607 or API 6FA) and low-temperature needs, and check that the qualification remains valid for all of them.
Sending an RFQ for low emission valves
Include valve type, standard, size, class, materials, the required ISO 15848 or API classification, test medium, endurance class, temperature range and the documents you expect. Our guide on RFQ documentation for oil and gas equipment lists typical certificates. Then send us your RFQ and we will match offered valves to the qualification you need.
Frequently asked questions
Is ISO 15848 or API 624 better for a gas project?
Neither is universally better. ISO 15848-1 gives a richer classification and allows tighter helium classes, while API 624 is a fixed pass/fail methane test common in refining and North American specifications. Many project specifications accept either, or require ISO 15848-1 class BH with a stated endurance class.
Does a valve need retesting if the packing supplier changes?
Generally yes. Both ISO 15848-1 and API 624 qualify a specific design, including the packing arrangement. Changing the packing material or supplier, stem finish or gland design can invalidate the qualification, so ask the manufacturer to confirm that production valves match the tested configuration.
Can a gland-packed valve achieve tightness class AH?
It is difficult. Class AH is usually associated with bellows-sealed stems. Well-designed packed valves with live-loading commonly reach BH, which is the class most often specified for hydrocarbon isolating valves.
What does SSA mean in an ISO 15848 classification?
SSA stands for stem seal adjustment. It records how many times the gland had to be retightened during the type test. SSA 0 means no adjustment was needed, which indicates a more robust seal design.