Reading Gas Cylinder Date Stamps and Markings

By Bill Byers / December 4, 2019
Gas Cylinder Date Stamp Title Image

Knowing how to find the testing date on your compressed gas cylinder is key.

And it doesn’t matter if you’re buying a used tank of compressed gas. Or you’re renting a tank of gas for your welding project.

Because you’ll want to check your gas cylinder tank is within its testing dates.

As you won’t be stuck with a defective tank.

And if you’re buying a tank, you want to know if you have to pay to get it tested.

Because you won’t get your cylinder filled without it showing a valid test date stamp.

How to Read Your Gas Cylinder Date Stamp Quick Overview

  • Look down the side of your gas cylinder.
  • You’re looking for two sets of numbers separated by a dash.
  • If the first set says 07. That means July.
  • If the second set of numbers after the dash says 16. This means 2016. Your gas cylinder was last tested in July 2016.
  • When your gas cylinder has more date stamps. The last set will tell you the date your gas cylinder was last tested.

DOT Marks on your Gas Cylinder

The fist set of numbers you see stamped on your gas cylinder may be the letters DOT followed by a set of numbers. The letters DOT stand for the Department of Transport.  This is the US department that sets the rules for the markings on high pressure gas cylinders.

For now ignore those figures. They are not your gas cylinder date stamps.

You’ll find out what those numbers mean later on in this article.

The next sets of figures are your gas cylinder date stamps.

Your Gas Cylinder Date

Gas Cylinder Test Date Stamp
Gas Cylinder Test Date Stamp

You’ll see in the picture above two yellow squares around the numbers stamped on the gas cylinder.

They’re the numbers you want to pay attention to. As they’ll you your gas bottle test date.

You’ll see that the first yellow square has an 01 in it.

This stands for the month. The gas bottle test on this cylinder was in January.

The second yellow square with 14 stands for the year. And for this cylinder it tells you that this gas cylinder’s last test was done in 2014. 

This particular compressed gas cylinder bottle was last tested in January 2014.

And if those are the only date stamps on this gas cylinder. Then this is the date the cylinder was made and first tested.

What’s My Gas Cylinder Expiration Date?

Now you know when your compressed gas tank was last tested.

If there are no other stamps beside the test date then this test is good for 5 years.

And the gas tank cylinder in this example would another test after Jan 2019. 

But you’ll see there are some other marks on this cylinder.

Gas Cylinder Plus and Star Markings
Gas Cylinder Plus and Star Markings

You’ll see that this compressed gas tank is stamped with a plus sign next to the gas cylinder date stamp.

What Does the Plus Sign Next to the Gas Bottle Test Date Mean?

This means that this cylinder was tested and rated for a 10% over fill. 

Useful if you’re trying to get as much cf (cubic feet) of compressed gas into your tank.

Because you’ll save money and trips for a gas refill. 

What Does the Star Stamp next to the Plus Sign on the Gas Cylinder Date Stamp Mean?

When you find a star stamp next to the plus sign right by the tank date stamp. This means you have 10 years before the next test is due on this cylinder.

Putting Together the Meaning of the Cylinder Date Stamps

If this was your tank of compressed gas. Then your cylinder was hydrostatically tested in January 2014. This gas tank was tested and is fine for a 10% overfill.

And the star means that your gas bottle doesn’t need retesting until January 2024.

Would you Like to See an Argon Tank Date Stamp Example?

Argon Gas Cylinder Example of Test Date Markings
Argon Gas Cylinder Example of Test Date Markings

On this Argon gas cylinder you’ll see a few test date stamps.

Don’t let that worry you.

The first stamp says 12 – 91. This means the first test on this Argon gas tank was December 1991. And this will be the year the gas cylinder was made.

The gas bottle test date has a plus and a star after the 12 – 91 date.

And that shows that in the test the bottle was good for a ten percent overfill. And the Argon tank didn’t need testing till Dec 2001.

The second set of Argon tank date stamps shows it was next tested in March 2003. The 03 – 03 tells you that.

And after the 03 – 03 test date stamp you’ll see a plus and a star and the letter UT.

So now you know that the March 2003 Argon gas cylinder date stamp was good for a 10% overfill. And that test was good to last until March 2013.

The last Argon tank test date stamp says 8 – 14.

And by now you’ll be in the swing of reading these tank test date stamps.

You’ll see this Argon tank was last tested in August 2014.

The plus and a star along side means this test is good till August 2024. And this is rated so you can have a 10% overfill.

Remember: No star alongside the date shown?

Means that your tank needs a test 5 years from the month and year tank test date stamped on the cylinder.

What Does the Letters UT Mean as Part of a Gas Cylinder Date Stamp?

Some tanks are ultrasonically tested.

And the letters UT means this Argon gas tank was ultrasonically tested. 

YouTube Video on High Pressure Cylinder Identification

You’ll find here a great YouTube video covering gas cylinder date stamps. The video starts 3 minutes in. Right at the point where he describes the gas cylinder marks and date stamps.  

High Pressure Cylinder Identification

Video Credit: Holston Gases:  Nathan Farquarson

How do I know if my gas cylinder is expired?

Picture of another example of test date markings

If your compressed welding gas tank has several date stamps like the one in this picture.

Look on down your gas cylinder for the last set of dates you can find.

Read the last cylinder date stamp. If you see no star after the date. then you know your cylinder needs a test five year’s after the last date.

If you see a star then your gas cylinder needs a test 10 years after the date stamp shown.

Has that date passed? Then your cylinder is going to need a new test.

Look at your compressed gas tank. Are there signs of obvious rust or damage?  If there is pass that gas tank by.

Gas tanks that have been kept well can go on for tens of years. So there’s no need for you to be put off by a tank that has some old test date stamps on it.

As long as the cylinder looks good and is currently within its test stamp date.

Reading the other Gas Cylinder Markings

Earlier in this article you’ll find a mention of the US Department of Transport

Gas Tank DOT No. And Serial No.
Gas Tank DOT No. And Serial No.

You’ll find other stamps on your gas tank.

The picture shows you an example. 

The yellow line underlines the first stamp mark. It’s a DOT mark. It has the letters DOT. The numbers beside it tells you the cylinder type. It’s a 3AA. The next set of numbers tell you the operating pressure of the compressed cylinder. These are the numbers 2400 in the picture.

The green line underlines the numbers in the next row. These are the serial numbers of this particular gas cylinder.

And on this particular gas cylinder the third line of letters and number is an owners stamp. HG1 means Holston Gas owns this tank.

Compressed Gas Cylinder Testing Frequency

The US Department of Transport lay down regulations. And these regulations set out the testing of DOT-3AA gas cylinders.

Your gas cylinder must be safety tested every 5 years. This testing can either be a hydrostatic test or an ultrasonic test.

The exception to this is where your gas tank has a star near the gas cylinder date stamp.  That star means your tank can have its test once every ten years.

And high pressure gas tanks well looked after generally have an unlimited life span.

Last Words

Thank you for reading my article “Reading Gas Cylinder Date Stamps and Markings”. Now you’ll be reading the date stamps on high pressure gas tanks like a pro.

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