Refrigerant Cylinder Retest & Requalification (DOT/ISO/GB): What the Stamped Date Actually Requires

Sun, 20 Sep 2026 · QUZHOU HUAFU NEW REFRIGERATION MATERIAL CO., LTD.

Refrigerant Cylinder Retest and Requalification (DOT/ISO/GB): What the Stamped Date Actually Requires

A cylinder is not a container you keep. It is a pressure vessel with an expiry, and the expiry is stamped on it.

1. What the stamped date means

Every refillable pressure cylinder carries a test date (and often a retest interval). The interval is not a recommendation — it determines whether the cylinder may lawfully be filled.

⇒ The interval is framework-specific. A cylinder that is within date under one jurisdiction’s rules may be out of date under another’s.

2. How to actually check a cylinder at receipt

1. Locate the test date (stamped or on the shoulder) and any retest interval marking.
2. Work out the next due date from the interval applicable to that cylinder specification.
3. Confirm the cylinder still has a legible stamp — an unreadable stamp is not evidence of compliance.
4. Confirm the UN number / proper shipping name matches the gas in it.
5. Record the test date in your receiving file, so the next shipment can be checked against it (receiving checks).

Step 5 is the commercial one. A supplier that sends cylinders without disclosing the test date leaves you unable to verify compliance — and that inability is itself the finding.

3. Why cylinders are requalified at all

Requalification is a hydrostatic test (or an approved equivalent): the cylinder is pressurised beyond its service pressure and its permanent expansion is measured.

⇒ Requalification certifies the vessel, not the gas. A cylinder that just passed retest says nothing about the quality of what was filled into it — those are two separate verification chains.

4. The interaction with filling limits

The fill limit for a liquefied gas is set against a reference temperature so the cylinder is not liquid-full at that temperature. A cylinder approaching its requalification limit and a cylinder that is overfilled are different failure modes:

• Overfill → hydraulic pressure on warming (no vapour space)
• Expired vessel → loss of pressure integrity

⇒ Both are prevented by reading the marks, and both are invisible without them — the fill limit itself is set at a reference temperature (filling ratios and temperature compensation).

5. What to put in a purchase specification

Ask for, in writing:

1. Test date (or next due date) of the cylinders to be supplied.
2. Cylinder specification / standard (e.g. DOT specification, ISO standard, GB standard).
3. Water capacity (WC) and tare weight (TW) — the two numbers that make net product verifiable.
4. Valve outlet standard and number (outlet standards by market).
5. UN number and proper shipping name.

⇒ Items 3 and 4 are the ones most often omitted, and they are exactly the ones that let a receiver verify a shipment without opening it.

6. Disposition of out-of-date cylinders

An out-of-date cylinder is not scrap — it is a cylinder that must be requalified before being filled. The commercial consequence for a buyer is simple: an out-of-date cylinder cannot be lawfully filled, so a shipment arriving with out-of-date cylinders cannot be topped up in the destination market until requalification.

⇒ This is why the test date belongs on the order, not discovered at receipt — and why an out-of-test cylinder has to be kept out of the storage bay until it is requalified (storage and segregation).

What we can provide

For this article’s subject — the vessel’s own date — what can be put in writing before the cylinders move is: the requalification (test) date of each cylinder group, the next due date under the framework those cylinders are marked to, and the cylinder specification/standard the dates belong to.

That is the set a receiver can act on without opening a cylinder: the date is either inside its cycle or it is not. Quantity and product identity are different checks, and they have their own evidence (net weight and COA at receipt).

Contact us with: the gas, the cylinder type, and the destination market.

Sources

• 49 CFR 180.205 / 180.209 — US DOT periodic requalification of cylinders and requalification intervals (PHMSA / eCFR).
• 49 CFR 180.213 — requalification markings (requalifier’s registered symbol, test date).
• ISO 6406 / ISO 10460 (ISO) — periodic inspection and testing of seamless / welded steel gas cylinders.
• ADR 6.2.1.5 (UNECE) — periodic inspection intervals for pressure receptacles.
• TSG 23-2021 §9.3 — Gas Cylinder Safety Technical Regulation (SAMR, China) — periodic inspection cycles.
• GB/T 13004-2016 / GB/T 13075-2016 — Periodic inspection and evaluation of seamless / welded steel gas cylinders (SAMR/SAC, China).

Prepared by Quzhou Huafu New Refrigeration Material Co., Ltd — a warehousing and filling operation (storage and cylinder filling/repacking), not a manufacturer.