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Any compressed gas cylinder that gets refilled has to be requalified on a set schedule to prove it can still safely hold its rated pressure. Hedrick Fire Protection is a DOT-certified hydrostatic testing facility, operating under Retester Identification Number (RIN) H942, and we requalify a wide range of high-pressure cylinders for industrial, dive, sport, and medical use.
Hydrostatic testing, also called cylinder requalification, is the standard method for confirming a pressure vessel is safe for continued use. The cylinder is inspected inside and out, then filled with water and pressurized in a water jacket to five-thirds of its service pressure (so a 3,000 psi tank is tested at 5,000 psi). We measure how much the cylinder expands and how much of that expansion is permanent. A healthy cylinder returns to its original size, while one with corrosion, fatigue, or wall thinning expands too far or does not fully return, which is how a failing cylinder is identified before it is ever refilled.
The retest interval is set by the U.S. Department of Transportation under 49 CFR and depends on how the cylinder is built. Here is the general breakdown:
Intervals follow DOT 49 CFR and the cylinder's markings always govern. A cylinder cannot be refilled once its test date has lapsed, and any cylinder exposed to fire, high heat, or impact must be removed from service and retested before it is filled again.
Select a service below to see what it includes.
We hydrostatically test and requalify DOT specification high-pressure industrial gas cylinders across the 1800 to 6000 psi range. Each cylinder is inspected inside and out, pressure tested in a water jacket to five-thirds of its service pressure, and stamped with its new test date. Steel and aluminum cylinders are due every five years.
We test aluminum and fiber-wrapped (composite) paintball tanks from 1800 to 5000 psi. Aluminum tanks are requalified every five years, while fully wrapped composite tanks follow a shorter cycle depending on construction and carry a 15-year service life, after which they must be retired rather than retested.
We hydrostatically test scuba cylinders, and for steel tanks with internal corrosion we tumble the interior to remove rust and then apply a rust inhibitor. This restores a clean internal surface so the tank passes inspection and is safe to refill. Scuba cylinders require a hydro test every five years, and most dive shops also require a current annual visual inspection before they will fill a tank.
We requalify aluminum and steel oxygen cylinders, including the common 2015, 2216, and 2265 psi service pressures. Oxygen cylinders are handled and cleaned for oxygen service and tested on the standard five-year cycle so they stay safe and compliant.
Aluminum cylinders made from 6351-T6 alloy and used in scuba, SCBA, or oxygen service can develop sustained load cracking at the neck threads. At each five-year requalification, DOT requires these cylinders to receive an eddy current examination in addition to the visual inspection. The eddy current test uses electromagnetic induction to find cracks too small to see, and any cylinder with cracking into the threads is condemned.
Hydrostatic testing has to be performed by a facility registered with the DOT and holding a valid Retester Identification Number. Our RIN is H942. We inspect, test, document, and stamp every cylinder to 49 CFR requirements, and we tell you plainly when a cylinder passes, needs reconditioning, or has to be condemned. There is no guessing and no shortcuts on something built to hold thousands of pounds of pressure.
Under DOT 49 CFR, steel and aluminum cylinders are tested every five years, fully wrapped carbon fiber cylinders every five years, and hoop-wrapped, fiberglass, and Kevlar composite cylinders every three years. The cylinder's own markings are the final word, and a cylinder cannot be refilled once its test date has passed.
It is a water-jacket pressure test. The cylinder is filled with water and pressurized to five-thirds of its rated service pressure while we measure how far it expands and whether it returns to its original size. A cylinder that expands too far or does not fully recover has lost structural integrity and is failed.
Steel and aluminum cylinders have no fixed retirement date and can stay in service indefinitely as long as they keep passing their five-year tests. Composite cylinders (hoop-wrapped, fiberglass, Kevlar, and carbon fiber) carry a 15-year service life and must be retired at that point even if they would otherwise pass.
It is a non-destructive test that uses electromagnetic induction to detect cracks too small to see. DOT requires it at each five-year requalification for aluminum 6351-T6 cylinders used in scuba, SCBA, or oxygen service, because that alloy can develop cracking at the neck threads. It does not apply to CO2 or fire extinguisher cylinders.
Only a facility registered with the DOT and holding a valid Retester Identification Number (RIN) may requalify cylinders. Hedrick Fire Protection holds RIN H942, and our certified technicians test, document, and stamp each cylinder to 49 CFR requirements.
Common reasons include internal corrosion, excessive permanent expansion under test, cracks, neck-thread damage, and sustained load cracking on older aluminum. A cylinder that has been exposed to fire, high heat, or significant impact must be removed from service and retested before it can be refilled, and a failed cylinder is condemned so it can never be filled again.