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- Dec 18, 2022
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Yea, as I noted the smaller diameters are far better for pressure, the 1.5 meter Spheroid didn't survive the pneumatic pressure test but that was after it was cycled once to 6750PSI. The cylinders you are talking about are likely not over 8" in diameter, the smaller diameters and around 24" long, are not as susceptible to the same stresses. The reason they are 5 year test is likely because they are DOT cylinders and that is the requirement regardless of the material.The fire service has CF air cylinders for self contained breathing apparatus with operating pressure of 4500psi, and 5500psi units are starting to be offered. 5 year testing cycle, with a maximum service life of 15 years. Those are pressure cylinders (containing pressure) though not made to resist external pressures.
I've seen several people now (people into submersible design, not random internet people) who have commented on the unsuitability of CF for deep sea use. There was a CF deep sea vessel that went far deeper than Titanic but it was a more traditional sphere design and essentially disposable. It was designed as a one time use vessel from the start, as they believed the dive would result in damage rendering it unsafe for a second dive.
From these comments I get the feeling CF is like a rope, a rope is useful for pulling or lifting an item, but pretty useless for pushing. The CF strands are apparently very strong vs internal pressure (puling), but offer little strength against external pressures, the epoxy carrier providing most of the strength in that case.
On prior dives passengers reported hearing the resin matrix cracking. It seems each dive weakened the structure, and the last dive was the one dive to many in a submersible that was already made to just barely take the pressure.
Keep in mind shape has a great deal to do with it as well, for external pressure a sphere is much better, even presser on the outside. Cameron once said when he was diving on the Titanic that they dove with the light bars spread in case a light bulb imploded because the change in pressure at those depths on a single point along the hull could cause the sphere to lose integrity and implode. When a deep water drilling rig has its riser down to depth, 5 to 10,000 feet, they have to be careful to insure it is always full lest it collapses and it is healthy seamless alloy pipe.
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