Fact: Tanks do explode—but not often.
The usual suspects are aluminum tanks made by Luxfer, Walter Kidde, Norris Industries and Reynolds Aluminum before 1988 from an alloy called "6351." Of these manufacturers, only Luxfer continues to make scuba tanks, and has used a different alloy since then.
According to Department of Transportation records, 12 of these tanks in the United States, 17 worldwide, have exploded since 1986, almost all of them while being filled. For some proportion, consider that approximately 25.4 million tanks were made from the 6351 alloy.
Most of the explosions were due to what is called "sustained load cracking," apparently caused when lead in the 6351 alloy migrates, weakening the metal structure. Cracks begin to appear near the crown of the tank and spread slowly, usually over many years, up through the threads. As "sustained load" indicates, storing tanks under full pressure aggravates the problem.
Actually, small cracks are not that uncommon. Most cracks do not cause explosions and those that do should have been obvious to visual inspection for several years. The explosions that have occurred signal not only a problem with the aluminum alloy, but a more serious problem with the quality of many visual inspections.
In 1988, Luxfer switched to a "6061" alloy, which does not contain lead. (Catalina began making tanks in 1986 and has used 6061 from the beginning.) According to Bill High, founder of Professional Scuba Inspectors, Inc., the industry's only recognized training organization for tank inspectors, there have been almost no cracking problems in post-1988 tanks, nor in steel tanks.
High has had a few reports of "stress corrosion cracking" in Catalina 6061 tanks, "but this is very unusual," he says. None have exploded.
Pre-1988 aluminum tanks can be identified by their neck markings
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BTW- we have a steel tank at the shop the burst during a fill. It's not so much as an overfill/expansion issue as much as a need for VIP's to ensure there are no cracks or pits that can fatigue the metal. Overfilling only shortens the lifespan of the steel tank, but you will most likely die of old age before that will occur if you just bought your tank new.
As far as shops consistantly overfilling as standard procedure, incompetance of others is what makes us look so good when all we do is follow the safety guidelines so we reduce risk.
The usual suspects are aluminum tanks made by Luxfer, Walter Kidde, Norris Industries and Reynolds Aluminum before 1988 from an alloy called "6351." Of these manufacturers, only Luxfer continues to make scuba tanks, and has used a different alloy since then.
According to Department of Transportation records, 12 of these tanks in the United States, 17 worldwide, have exploded since 1986, almost all of them while being filled. For some proportion, consider that approximately 25.4 million tanks were made from the 6351 alloy.
Most of the explosions were due to what is called "sustained load cracking," apparently caused when lead in the 6351 alloy migrates, weakening the metal structure. Cracks begin to appear near the crown of the tank and spread slowly, usually over many years, up through the threads. As "sustained load" indicates, storing tanks under full pressure aggravates the problem.
Actually, small cracks are not that uncommon. Most cracks do not cause explosions and those that do should have been obvious to visual inspection for several years. The explosions that have occurred signal not only a problem with the aluminum alloy, but a more serious problem with the quality of many visual inspections.
In 1988, Luxfer switched to a "6061" alloy, which does not contain lead. (Catalina began making tanks in 1986 and has used 6061 from the beginning.) According to Bill High, founder of Professional Scuba Inspectors, Inc., the industry's only recognized training organization for tank inspectors, there have been almost no cracking problems in post-1988 tanks, nor in steel tanks.
High has had a few reports of "stress corrosion cracking" in Catalina 6061 tanks, "but this is very unusual," he says. None have exploded.
Pre-1988 aluminum tanks can be identified by their neck markings
-------------------------------------------------------------
BTW- we have a steel tank at the shop the burst during a fill. It's not so much as an overfill/expansion issue as much as a need for VIP's to ensure there are no cracks or pits that can fatigue the metal. Overfilling only shortens the lifespan of the steel tank, but you will most likely die of old age before that will occur if you just bought your tank new.
As far as shops consistantly overfilling as standard procedure, incompetance of others is what makes us look so good when all we do is follow the safety guidelines so we reduce risk.
