i used to be a welding gas sub-dealer for a welding supply company. The cylinders should have a name around the top collar. Most welding gas companies only carry their own cylinders, if you switch companies, the new company may, or may not be able to accept the cylinder from the company to whom the cylinder belongs to.

In our area, cylinders 100 CF or smaller are all customer owned. The customer buys the cylinder and can get it filled at any gas supplier. Cylinders over 100 CF are all leased cylinders and have to go back to the company that owns them. Some companies require customer owned cylinders to be refilled rather then be exchanged, the reason being the cylinder recertification. Not all cylinder facility have the ability's to refill the cylinders on grounds, how the customer owned cylinders are handled will depend on the company policy. Usually leased cylinders have the recertification included in the lease costs, so those cylinders are exchanged. Customer that own the cylinders are often charged for the recertification costs.

Every welding gas cylinder needs to be recertified every 10 years. If you own that cylinder, the costs involved should be your expense, years ago that recertification fee was around $15, I have no doubt that cost has increased since then. If the cylinder can not be certified, the cylinder has to be replaced, also at your expense.

Some cylinders have been around a very long time. Often the cause of not passing certification is the cylinder valve itself. Those are not cheap to replace. each cylinder has a date stamp every time it has been recertified, look for the most recent date stamp. Some date stamps are in code, but any are not and may have a month and the last 2 digits of the year, or simply the year. Around here, the stamps are about 3/8" high number stamped into the cylinder on the bell shape or just above or below. I have a picture if I can get my computer to cooperate.