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At 19:50 10.02.98 -0700, you wrote: >In 1996, the >cause for each of the 6 cylinder that exploded would have been discovered >by a properly trained technician well before the failure. >Divers who are concerned about the safety of their cylinder should insist >that the technicians who service their equipment have proof of training. >PSI, Inc. conducts more that 200 cylinder visual inspector training >workshops each year. >For persons at international locations where classes are not readily >available, training by correspondence can be arranged. I do hydro tests and visuals for a dive store in Norway. I've seen quite a few cylinders and with few exception those we condemn fail the visual rather than the hydro. Aluminum is tricky and treacherous. It doesn't corrode from condensation. If it sees salt water, however, the ensuing damage is obvious in no time. Those are the tanks we can stamp out and destroy without any further checking. According to regulations we're not allowed to expose aluminum to acid rinsing in an attempt to salvage it. Unless the entire inside surface comes out spotless after a hot water rinse, that cylinder goes. No sleep lost over corroded aluminum! The treacherous ones are old aluminum tanks that look OK. They have never seen salt water on the inside and present an flawless shiny surface. It may have been exposed to excessive heat, but this won't show. For a number of reasons, metal fatigue may change the strength of aluminum alloys, and the cylinder is still looking great. Theoretically, it will show as loss of elasticity during the hydro test, but I wouldn't bet my life on it. I'm pretty much looking for a reason to condemn any old alu tank I test! The Norwegian Navy throws away cylinders after 10 years of service these days. A few years ago a BC inflation cylinder spilled its guts while being stored in a locker. Nobody was injured. Needless to say, this cylinder was "in good standing" regarding hydro, but it failed anyway. It was, however, made of aluminum and it was older than 10 years. Steel is different. Fatigue is less of an issue -- when it's bad you can tell at a glance. Usually, the rust kills steel before it fails a hydro. Still, a badly rusted steel cylinder may still prove to be OK after an acid rinse. Superficial rusting may look messy, but what you really want to know is whether it has progressed to pitting. The point is, what you see is what you get. There's rarely any doubt whether a steel cylinder will pass or not. The only good-looking steel cylinder I've condemned since it failed hydro was produced in Germany in 1944. That was not exactly a good year for German industry since WWII had sapped the supplies of decent quality steel! Even so, it took almost 50 years to cause fatigue. Since metal fatigue is so hard to detect in aluminum cylinders, how about adopting the 10 year rule? The cost of condemning an old aluminum tank every 10 years is financially bearable. After all, the tank valves are half the price of a new cylinder. Besides, it's a lot more more expensive to replace hands. This being said, I prefer alu tanks as side-mounts due to their buoyancy characteristics. I'm in no way suggesting that alu is out. I'm just saying that old aluminum tanks are dispensable. regards Hans -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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