Propane tank inspection stamp: reading the marks on a cylinder collar

Searches for the inspection stamp on a propane tank almost always concern a portable cylinder, the kind used for grills, heaters and forklifts. These cylinders are built to Department of Transportation specifications, and the marks stamped into the collar are how a filler decides whether the cylinder can be refilled. Larger ASME tanks carry a nameplate instead, and they work differently.

The specification and the serial number

Among the marks you will find the DOT specification the cylinder was built to and a serial number. These identify the cylinder and the rules that apply to it. They do not change over its life, and they are what a requalifier refers to.

The manufacture date

The date of manufacture is stamped as a month and a year. It starts the clock: the first requalification is due a set period after that date, a period fixed in the federal regulations for the cylinder’s specification. Fillers are expected to check it before filling, which is why a cylinder can be refused even though it looks fine.

The requalification mark

When a cylinder is requalified, the requalifier adds a new date along with its identification number, and in some cases a letter indicating the method used. The method matters because it can change how long the requalification is valid. The most recent requalification mark, not the manufacture date, is the one that counts once a cylinder has been requalified.

Why there is no inspection sticker on most cylinders

Many people look for a dated sticker, as on a fire extinguisher. Portable propane cylinders are tracked by stamped marks instead. Some exchange programs and requalifiers add labels, but the authoritative information is the stamp, and a sticker does not replace it.

What a refill station checks

Beyond the dates, a filler looks at the cylinder’s condition: dents, corrosion, damage to the collar or the foot ring, and the valve. Modern small cylinders must have an overfill prevention device, and an older valve without one is usually refused. A refusal is not a judgment on the owner. It is the filler following the rule.

What to do with an out of date cylinder

Three choices in practice: exchange it through a cylinder exchange program, have it requalified by a firm authorized to do so, or dispose of it through a channel that accepts propane cylinders. Requalification is not something an owner can do, and filing or altering marks is never an option. The parties involved in each kind of tank are covered in who inspects what.

Larger tanks have a nameplate

Residential and industrial ASME tanks carry a nameplate with the code stamp, the maximum allowable working pressure, the capacity and the manufacturer’s details. There is no requalification date on it, because those tanks are inspected in service under other rules. The overview of propane tank inspection explains how each family is handled, and the inspection planning page covers keeping track of dates across a fleet.

For a fleet of forklift cylinders, the dates are worth recording when the cylinders arrive. A spreadsheet with the serial number and the last requalification mark avoids the surprise of a cylinder refused on a busy morning, and it shows quickly which ones are due in the coming year.

Why the marks can be hard to read

Collars are painted over, dented, rusted or worn by years of handling, and stamps are small. Several requalification dates can sit side by side on an older cylinder, sometimes from different requalifiers. The rule of thumb is to look for the most recent date and the identification number next to it, and not to guess. If the marks cannot be read with confidence, a filler will treat the cylinder as out of date, and the safe course is to have it looked at by an authorized requalifier or exchanged. Repainting a collar so heavily that the marks disappear creates the same problem for the next person who has to read them.