GB/T 24925-2019: What a Chinese Cryogenic Valve Test Report Actually Contains

GB/T 24925-2019, 低温阀门 技术条件 (Cryogenic valves — Technical conditions), is the current Chinese national standard for cryogenic valves, and it can be read in full, free of charge, on China's national standards public service platform. When a Chinese supplier issues a cryogenic valve test report, this is the document behind it.

A valve built and tested to this standard meets a coherent set of numbers. It will not automatically meet the numbers in a European or American specification, because this is a self-developed national standard rather than an adoption of an international text.

This article sets out what GB/T 24925-2019 covers, the tests it defines, and the one clause that explains why a Chinese cryogenic valve often arrives without a fugitive emissions result.

Read it and you can compare a Chinese cryogenic valve quotation against your specification on the numbers rather than on the label.

A European buyer opens a quotation for cryogenic ball valves, finds a test report with a column of figures and no ISO reference anywhere on it, and asks the supplier to redo the documents to ISO 15848.

The supplier has not made a mistake and the buyer has not been misled. The two sides are working to different documents, and only one of them is in the other's specification.

What does the standard cover?

Cryogenic gate, globe, check, ball and butterfly valves from DN15 to DN1200 and PN16 to PN400, over a medium-temperature span of −196 °C to −29 °C, with flanged, wafer and welded ends.

PN16 to PN400. DN15 to DN1200. Class 150 to Class 2500. One document covers that whole field, across a temperature span from −29 °C to −196 °C.

Note that the warm end is −29 °C, not −50 °C. The ISO 28921 series and the withdrawn BS 6364 both open at −50 °C. The Chinese standard opens at −29 °C, so the two families overlap from −50 °C to −196 °C and diverge in the band between. That is not a defect in either; it is the scope to read when you put two certificates side by side.

What does the test table require?

Numeric acceptance criteria for every item: packing seal ≤ 100 ppmv and flange gasket ≤ 50 ppmv over 900 s, seat leakage at 100 × DN mm³/s (200 × DN for check valves) over 300 s, at least 20 low-temperature cycles (23 for check valves), and a maximum manual operating force of 360 N.

Table 1 of the standard sets the low-temperature performance and test items:

CWP is the cold working pressure — the reference pressure for the test.

Three observations about this table are more useful than the numbers themselves.

The check valve gets a harder seat test and a longer cycle requirement. 200 × DN against 100 × DN, and 23 cycles against 20. Both figures move together, in the same direction, because a check valve has no operator to seat it. The standard treats the check valve as a separate case rather than folding it into the same row.

The stem limit and the body-joint limit are not the same number. 100 ppmv at the packing, 50 ppmv at the flange gasket. That is the same relationship the ISO arrangements use — a looser stem limit and a tighter body-joint limit — but these are the Chinese standard's own figures. Do not carry either of them across as an ISO class.

360 N is a number your specification can be checked against. It is the ceiling for a manually operated valve, and it is the kind of figure that most datasheets do not print.

Why is the fugitive emissions test missing?

Because clause 5.2.3 of the standard makes it something that is performed only when the purchase contract requires it.

This is the single most useful clause in the document for an overseas buyer. A Chinese cryogenic valve that arrives without a fugitive emissions result has not necessarily failed to meet a requirement — the standard makes that test contract-driven, so the default is that it is not done.

Two consequences follow.

It is contract-driven, not unavailable. Ask for the test in the contract, in the terms of the standard that will be applied, and it becomes part of the order. That is a different instruction from asking for "a low-emission valve", which names no test at all.

The report will carry the marking of the standard it was tested against. A fugitive emissions test on a Chinese valve may be reported against GB/T 40079-2021, the Chinese modified adoption of ISO 15848-1:2015. Its marking prefix is GB FE rather than ISO FE. If your specification says ISO FE - BH - CO3, expect a document reading GB FE - BH - CO3 - GB/T 40079 — the same family of class requirements under a different label. That mismatch is written about in more detail in ISO 15848 Explained: Reading BH, CO3 and SSA0 on a Valve Certificate.

What other provisions appear in a Chinese cryogenic valve?

Six: cryogenic treatment, anti-static construction, cavity pressure relief, surface finish, non-destructive testing, and a bonnet-extension table the standard sets but this article does not quote.

Cryogenic treatment. For austenitic stainless steels used below −100 °C, the standard calls for at least two cryogenic treatments of the body, bonnet, closure, seat and stem before finish machining. It defines cryogenic treatment as immersing the part in liquid nitrogen to −196 °C, holding for 2 hours to 4 hours depending on thickness, then letting it return to ambient. This is a dimensional-stability step, not a cleaning step.

Anti-static construction. The maximum resistance of the discharge path is 10 Ω. It matters most on cryogenic ball valves, where a soft seat can otherwise insulate the ball from the body.

Cavity pressure relief. Double-seated valves are to be provided with a pressure-relief hole of at least 3 mm diameter — the same trapped-cavity failure mode the older European standard addressed.

Surface finish. Stem-to-packing contact surface Ra ≤ 0.4 μm; stuffing box Ra ≤ 1.6 μm.

Non-destructive testing. Radiographic, penetrant, ultrasonic and magnetic-particle testing are called up to the JB/T 6440, JB/T 6903 and NB/T 47013 series. Referenced standards include JB/T 7248, JB/T 12003, GB/T 26480 and GB/T 229.

The standard's bonnet-extension table is not quoted here. Those figures exist only in secondary summaries, and the full text is free to read. The check is cheap enough that a number should not be printed before it has been read in the source.

What changes the outcome of an enquiry?

One line: naming the test. A cryogenic test to GB/T 24925-2019 plus a fugitive emissions test to GB/T 40079-2021 at a named class, documented and reported, is a specification a supplier can answer with a document. "Low-emission cryogenic valve" is not.

A Chinese supplier working to GB/T 24925-2019 is working to a document with a defined scope, a test table with durations and leakage rates, a cycle requirement and an operating-force ceiling. What it does not do by default is produce a fugitive emissions result.

When does this go to a human?

Five boundaries for Chinese cryogenic valve enquiries: any duty below −101 °C (−150 °F), where automatic coverage ends unconditionally; any duty in the −29 °C to −50 °C band, where the two standard families do not agree on scope; any requirement for a fugitive emissions result where the purchase contract does not name the test; any enquiry where the specification names ISO 15848 classes and the report cites GB/T 40079 without the class string; and any duty whose acceptance criterion is a standard number and never a number.

• Any duty below −101 °C (−150 °F), where this site's automatic coverage ends unconditionally. Note that GB/T 24925-2019 reaches −196 °C, so the standard can cover a valve whose duty sits outside the selector's range. The certificate can exist for the valve and the duty is still a handover here
• Any duty in the band between −29 °C and −50 °C, where the two standard families do not agree on scope, and which document governs depends on the project rather than on the valve
• Any requirement for a fugitive emissions result where the purchase contract does not name the test
• Any enquiry where the specification names ISO 15848 classes and the supplier's report cites GB/T 40079 without the class string
• Any duty where the acceptance criterion is a standard number and never a number

What people assume, and what the standard says

Common questions about Chinese cryogenic valve documentation

Is the standard really free to read?

Yes, in full, on China's national standards public service platform. This is a standard China developed itself, which is why the platform can publish it. Chinese standards that adopt an ISO text do not get the same treatment, because of ISO copyright.

My supplier sent a test report with no ISO reference. Is it wrong?

Probably not. Check which standard it cites and compare the numbers. If your specification requires a fugitive emissions result and the report shows none, the purchase contract is where that gets fixed.

Does a Chinese cryogenic valve meet an ISO 15848 class?

Only if it has been tested and reported to the Chinese adoption of that standard, GB/T 40079-2021, with the class string. The cryogenic standard on its own does not produce an ISO 15848 class.

Where do the 20 cycles come from?

From the low-temperature cycle-life requirement in Table 1 of GB/T 24925-2019 — 20 cycles for gate, globe, ball and butterfly valves, and 23 for check valves.

Can I specify this standard for a European project?

You can specify any standard you and the supplier agree, but a specification normally names the standard the site's own rules recognise. The useful move is to state the acceptance criteria as numbers and let the standard reference follow from them.

What this article does not cover

Note that this article does not select a cryogenic valve, does not determine compliance with any standard or regulation, does not provide certification or qualification advice, and does not quote commercial terms. It sets out the scope, the test table and the key clauses of GB/T 24925-2019, and states how a Chinese cryogenic valve test report reaches a buyer.

Where the next constraint sits

The other side of the same question is the document a European specification usually names instead, and why its requirements moved — BS 6364: Withdrawn in 2015 — What a Cryogenic Valve Specification Should Name Instead.

Where a fugitive-emissions result is what the specification actually wants, the string GB FE - BH - CO3 - GB/T 40079 has to be decoded before it can be set beside ISO FE - BH - CO3. ISO 15848 Explained: Reading BH, CO3 and SSA0 on a Valve Certificate does that field by field.

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