Updated: November 13, 2026
Learning how to read a propane tank date takes less than a minute once you know which stamp matters. On a standard U.S. grill cylinder, the original month and year are stamped into the metal collar. If the cylinder has been requalified, a newer mark adds a requalifier ID, another month and year, and sometimes an E or S that determines the next interval.
Quick Answer: How do you read a propane tank date?
Find a four-digit month-year stamp on the collar, such as 06 21 for June 2021. A U.S. DOT grill cylinder in acceptable condition must be requalified within 12 years of its manufacture date. After requalification, an E mark is valid for five years, an S mark for ten years, and a qualifying mark with no letter for twelve years under current PHMSA guidance. Damage, leaks, severe rust, or unreadable required markings can make a cylinder unacceptable even when its date is still current.
Key Points
- The manufacture date is normally a month and two-digit year stamped on the collar: 06 21 means June 2021.
- TW is tare weight and WC is water capacity; neither is the date.
- The original U.S. qualification period is 12 years for the common DOT grill cylinder covered here.
- After requalification, E means a five-year interval, S means ten years, and no letter means twelve years.
- Use the newest valid requalification mark, not simply the newest random number on the collar.
- A current date never overrides a leaking valve, fire damage, bulge, deep dent, cut, crack, missing collar or foot ring, or serious corrosion.
Where is the propane tank date stamped?
Look on the protective metal collar surrounding the valve. The original manufacture or test date is stamped directly into that collar on most 20-pound steel grill cylinders. Requalification marks may be stamped on the collar or cylinder shoulder, or applied on an approved label.
Use a flashlight and rotate the disconnected, upright cylinder outdoors until you find a month-year pair. Do not sand, grind, drill, or strike the collar to make a faint mark easier to see. If required markings cannot be read, let a propane dealer or approved requalifier inspect it.
What do the numbers and letters on the collar mean?
The collar is an identification plate, so several codes sit close together. The date is the month-year pair; TW, WC, DOT specification, service pressure, serial number, and manufacturer symbol serve different purposes.
| Example marking | Meaning | Is it the date? |
|---|---|---|
| 06 21, 06-21, or 0621 | Manufactured or originally tested in June 2021 | Yes |
| TW 17.2 | Tare weight: empty cylinder plus permanently attached valve, in pounds | No |
| WC 47.6 | Water capacity used by fillers to determine safe propane capacity | No |
| DOT-4BA or DOT-4BW | U.S. DOT cylinder specification | No |
| 240 | Service pressure in psi on a common steel cylinder | No |
| RIN/VIN plus 04 22 E | Approved requalifier ID; requalified April 2022 by external visual inspection | Yes—requalification date |
TW is useful for checking fuel: place the disconnected cylinder upright on a scale and subtract TW from the total weight. The result is approximately the pounds of propane remaining. The site’s guide to 20-pound propane tank runtime walks through that calculation and explains why an exchange cylinder may not contain a full 20 pounds.
When does a U.S. propane grill cylinder need requalification?
A common DOT propane cylinder must be requalified within 12 years of manufacture, then again at the interval established by the requalification method. Calculate from the month as well as the year.
| Most recent valid mark | What it means | Next interval | Example |
|---|---|---|---|
| Original manufacture date | First qualification at manufacture | 12 years | 06 21 → due no later than June 2033 |
| Requalification date followed by E | External visual inspection | 5 years | 04 22 E → due no later than April 2027 |
| Requalification date followed by S | Proof-pressure test | 10 years | 04 22 S → due no later than April 2032 |
| Requalification date with no letter | Volumetric expansion test | 12 years | 04 22 → due no later than April 2034 |
These are current U.S. PHMSA intervals for the cylinder type discussed here. Other countries use different rules, and unusual cylinders or special permits can differ. A qualified filler makes the final refill decision after checking the specification, dates, condition, and valve.
How do you read a requalification stamp?
Identify three pieces together: the approved requalifier’s ID, the month and year, and the method letter if one appears. A loose date without the required requalifier identification is not enough to prove that the cylinder was properly requalified.
PHMSA’s example shows a mark such as V123456 0422 E. V123456 is the approved visual requalifier’s identifier, 0422 is April 2022, and E means external visual inspection. That example would require another requalification by April 2027.
Older cylinders can carry several marks. Start with the original date, then find the newest complete and legible requalification mark. Do not add five years automatically to every requalification: the method letter controls whether the interval is five, ten, or twelve years.
How can you tell whether a cylinder is refillable today?
Use a two-part check: the date must be within its allowed interval, and the cylinder must pass a condition inspection. Either failure is enough for a refill station to refuse it.
- Confirm the cylinder type. This guide covers portable U.S. DOT grill cylinders, not permanently mounted ASME tanks.
- Find the original month and year. If it is less than 12 years old, continue to the condition check.
- If it is older than 12 years, find the newest complete requalification mark. Note E, S, or no letter and apply the correct interval.
- Inspect the cylinder cold and outdoors. Check the body, bottom, collar, foot ring, valve, and pressure-relief device.
- Let the filler decide. A trained dispenser must visually inspect the cylinder before filling and can reject it even if your date math is correct.
| What you find | What to do |
|---|---|
| Date is current; cylinder is undamaged and markings are legible | Take it to a qualified refill station for its required pre-fill inspection |
| Original date is over 12 years old; no valid later mark | Do not request a normal refill; use an approved requalifier or cylinder exchange |
| Requalification interval has passed | Have it requalified by an approved facility or exchange it |
| Date or DOT specification cannot be read | Stop guessing and ask a propane professional to evaluate it |
| Leak, bulge, crack, fire damage, or serious corrosion | Keep ignition sources away and contact the supplier or fire department as conditions require |
What damage makes a propane cylinder unsafe to fill?
PHMSA says not to fill a cylinder with excessive rust, corrosion or pitting; dents, bulges, cuts or cracks; a missing or damaged foot ring, collar, or valve cover; or a leaking or defective valve or pressure-relief device. Evidence of fire or heat exposure also requires professional evaluation.
Pay special attention to the bottom where moisture collects. Surface dirt and harmless paint scuffs are not the same as deep rust or pitting, but a homeowner should not grind rust away to judge the remaining wall thickness. A qualified cylinder expert decides whether repair, requalification, condemnation, or replacement is appropriate.
The U.S. Department of Transportation’s PHMSA cylinder safety guide includes illustrated date marks and rejection conditions. It is the best quick reference to keep with this article.
Should you requalify or exchange an old grill cylinder?
Exchange is usually the simplest choice for one ordinary 20-pound grill cylinder; requalification makes more sense for a newer, well-kept cylinder you own and want to keep, or when a local approved facility offers convenient service.
- Exchange: Fast and widely available. The exchange company handles cylinder inspection and qualification, but the cylinder you receive may contain less than a full 20-pound refill.
- Requalify: Keeps your cylinder in service if it passes. Call first, because not every refill location is an approved requalifier and fees vary.
- Replace: Sensible when a cylinder is badly corroded, damaged, repeatedly leaks at the valve, or costs nearly as much to requalify as a sound replacement.
PHMSA maintains a locator for approved cylinder requalifiers. Only an authorized facility may apply a requalification mark. Never stamp a date yourself, swap a valve at home, or cover required markings with paint.
Can you exchange an out-of-date propane tank?
Many exchange programs accept out-of-date grill cylinders so the supplier can inspect, requalify, retire, or recycle them through its own process. Acceptance policies vary by company and location, and a severely damaged or actively leaking cylinder requires instructions from the supplier rather than an ordinary cage transaction.
Transport any accepted cylinder upright and secured in a ventilated part of the vehicle, go directly to the destination, and remove it promptly. Never leave a propane cylinder in a hot closed vehicle.
What should you do with a cylinder that cannot be used?
Contact a propane supplier, approved cylinder requalifier, exchange provider, or local household hazardous-waste program for instructions. Do not put a cylinder in household trash, curbside recycling, or scrap metal while it may contain propane.
Keep the valve closed and the cylinder upright outdoors, away from buildings, heat, and ignition, until the receiving facility tells you how to bring it in. Do not intentionally vent propane, puncture the cylinder, remove the valve, or try to burn off the remaining fuel.
How should you store a dated but usable cylinder?
Store it upright outdoors with the valve closed, protected from standing water and vehicle impact, and away from heat or ignition. Do not store portable cylinders in a house, basement, garage, shed, tent, or under a grill.
Date validity does not make indoor storage safe. The site’s grill winterization checklist explains why the grill body and its propane cylinder may need different storage locations.
Verdict: What should you do after reading the date?
Use the original manufacture date only until a valid later requalification mark takes over. Apply 12 years to the original mark, or five, ten, or twelve years to a requalification mark according to E, S, or no letter. Then inspect the cylinder’s condition. If the date is overdue, markings are unclear, or damage is present, do not ask a normal refill station to “try it anyway”—exchange the cylinder or take it to an approved requalifier.
Frequently Asked Questions
Does a propane tank expire at the beginning or end of the stamped year?
Neither. The month matters. A cylinder marked 06 21 reaches its original 12-year limit in June 2033, not January or December of that year.
What does E mean after a propane tank date?
E identifies an external visual requalification. Under current U.S. PHMSA guidance, that mark establishes a five-year interval from the stamped month and year.
What does S mean after a propane tank date?
S identifies a proof-pressure requalification. Current U.S. PHMSA guidance gives that mark a ten-year interval.
Is TW the expiration date?
No. TW means tare weight—the weight of the empty cylinder and its permanently attached valve. Use it to estimate propane remaining, not cylinder age.
Can a refill station refuse a tank that is still in date?
Yes. The filler must also inspect its condition. A leaking valve, severe rust, pitting, a bulge, crack, serious dent, fire damage, or damaged protective parts can disqualify it.
Can you requalify a propane cylinder yourself?
No. Requalification and the official marking must be performed by a U.S. DOT-approved facility using an authorized method.
Do the same date rules apply in Canada?
No. Canada uses its own Transport Canada requirements, commonly including a ten-year requalification period for portable cylinders. Follow the rules and markings for the country where the cylinder is filled.
About Frank W. Roberts
Frank W. Roberts is the author of Everything Grill Reviews. He has grilled since 1970 and brings more than 50 years of backyard cooking and cookoff experience to practical fuel handling and grill safety. This guide is based on current U.S. DOT/PHMSA material and does not replace a cylinder inspection by a qualified propane professional. Regulations and facility policies can change; the federal guidance was last verified November 13, 2026.