A propane cylinder does not spoil, but its certification runs out. US Department of Transportation rules require cylinders to be requalified on a schedule that starts the day they are manufactured, and a cylinder past that date cannot legally be filled. The date is stamped into the collar, the ring of metal around the valve.
The rule, in one sentence
49 CFR § 180.205(c) states that no cylinder may be filled with a hazardous material and offered for transportation in commerce unless that cylinder has been successfully requalified and marked in accordance with the subpart. Propane is a hazardous material for these purposes, which is why a refill attendant checks the collar before touching the valve, and why a station that turns you away is following federal law rather than being difficult.
How long you get
The Utah State Fire Marshal's filling guidance gives the version most consumers meet in practice: DOT cylinders must be inspected and requalified within 12 years of the date of manufacture, and every 5 years after that.
The regulation itself is more particular. Under 49 CFR § 180.209, requalification periods for DOT 4-series cylinders, the family that includes ordinary grill and RV tanks, run 5, 7, 10, or 12 years depending on which test the requalifier uses and the conditions the cylinder is kept in. External visual inspection buys 5 years. A volumetric expansion test on a cylinder that is externally coated against corrosion and used only for non-corrosive gas can buy 12. The stamp on your collar reflects whichever method was actually used, so read it rather than assuming.
Reading the collar
Two kinds of marking matter:
- The manufacture date. Usually a month and year, often as digits split by a letter code, stamped when the cylinder was made. The first clock runs 12 years from here.
- Requalification marks. Added each time the cylinder passes. These carry the date, the identification number of the facility that did the work, and a code for the method used. The most recent one, not the manufacture date, is what a filler goes by on an older tank.
Only an approved facility may apply those marks. Section 180.205(b) prohibits anyone from representing that a requalification has been performed unless they hold a current approval issued under the relevant part. A cylinder that fails must be rejected for repair or condemned.
Check the valve too
An in-date cylinder can still be unfillable if it has the wrong valve. Every newly manufactured cylinder between 4 and 40 pounds has been required to carry an overfill prevention device since October 1, 1998, and since April 1, 2002 cylinders without one cannot be refilled at all.
The quick check is the handle. A triangular handwheel, usually with the letters OPD on it, means the cylinder has the device. A round or star-shaped handle means it predates the requirement. Some early OPD valves were made before the lettering was required, so if the handle is triangular but unmarked, ask rather than guess.
Your options when it is out of date
- Have it requalified. An approved facility inspects the cylinder and, if it passes, stamps a new date. This makes sense for larger cylinders and for tanks in good condition, where the cost is small next to replacing the steel.
- Exchange it. For a standard grill cylinder this is usually the cheaper path, because an exchange cage takes your expired tank and gives you a current one. You give up whatever propane is still inside, and you receive less gas than a refill would put in. The tradeoff is laid out in refill vs. tank exchange.
A filler who tops up an out-of-date or non-OPD cylinder is breaking federal rules, and the requalification interval exists because steel that has been dropped, dragged, and left in the weather for a decade is worth looking at before it is put back under pressure. If a station refuses your tank, the tank is the problem.
Find somewhere to sort it out
Refill counters are generally staffed by someone trained to inspect a cylinder, and many propane dealers requalify on site. Exchange cages will take an expired tank off your hands.