Is my gas cylinder out of date?
A propane bottle, a welding cylinder or a fire extinguisher carries a stamp saying when it was last requalified and which test was used. This reads it, straight from 49 CFR 180.213.
It will not tell you the expiry date, and nor will the stamp. How long a requalification lasts depends on the specification the cylinder was built to, which is stamped somewhere else entirely. That is the regulation’s own structure, and this page shows every period it allows rather than picking one.
This one runs on your own device. It is worked out in your browser, so there is nothing to send and nothing to log. Where a tool on this site does send something out, that page says so and names where it goes.
What you are looking at
The regulation is precise about the arrangement:
“Each cylinder successfully passing requalification must be marked with the RIN set in a square pattern, between the month and year of the requalification date. The first character of the RIN must appear in the upper left corner of the square pattern; the second in the upper right; the third in the lower right; and the fourth in the lower left.”
So the month is on the left, the year on the right, and the four characters of the requalifier’s identification number are stacked two-by-two between them. The test symbol follows. The RIN identifies who did the work, not when, and this page does not need it.
The regulation gives one symbol two meanings
Paragraph (f) of 180.213 lists what each symbol stands for. Two of those paragraphs give the same letter:
| Symbol | Paragraph | Means |
|---|---|---|
S | 180.213(f)(4) | the proof pressure test |
S | 180.213(f)(6) | DOT 8 series cylinder shell requalification only |
Same letter, two meanings, two paragraphs apart, in the
regulation that defines them. A cylinder stamped S has had one of two
different things done to it and the stamp does not say which. The tool above reports both
and does not choose, because choosing would be inventing the distinction the regulation
left out.
In practice the two rarely collide — (f)(6) is about acetylene cylinders of the DOT 8 series, and a person holding one usually knows. That is an argument for why it has survived, not for pretending it is not there.
Why the stamp cannot tell you when it expires
180.209 Table 1 sets the requalification period, and it sets it by the specification the cylinder was made to:
| Specification | Requalification period |
|---|---|
3 | 5 years |
3A, 3AA | 5 or 10 or 12 years |
3AL | 5 or 12 years |
3AX, 3AAX | 5 years |
3B, 3BN | 5 or 10 years |
3HT | 3 years |
3T | 5 years |
4AA480 | 5 or 10 years |
4B, 4BA, 4BW, 4B-240ET | 5 or 7 or 10 or 12 years |
4D, 4DA, 4DS | 5 years |
4E | 5 or 10 or 12 years |
Foreign cylinder ( see ยง 173.301(j) of this subchapter for restrictions on use) | 5 years |
6 of those 12 rows give more
than one period. The common propane and LPG specifications —
4B, 4BA, 4BW, 4B-240ET — allow
five, seven, ten or twelve years, and which one applies depends on sub-paragraphs of
180.209 that turn on how the cylinder is used and what it holds.
This is not a gap in the regulation. It is a regulation that declines to compress four different situations into one number, which is more honest than the alternative and much less convenient. The tool above lists every resulting due date rather than picking the most likely, for the same reason the piano page shows every overlapping table.
What this page is not
It reads a stamp. It is not an inspection. A cylinder can be within date and unfit, and the person who fills it is the one who decides. Rust, dents, gouges, fire damage and a damaged foot ring all condemn a cylinder regardless of what the collar says.
It also covers only cylinders marked under the US regulation. A cylinder stamped to a European or UN standard carries a different arrangement, and this page does not guess at it — the same position the boat page takes on hull numbers from before 1984.