trymixdiver
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hmmmm untrasonic testing would get expensive, SS tanks sound like a bad idea to me.
Andy
Andy
Stainless steel tanks
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And it is like finding a needle in a hay stack. For example I was testing some 6" pipe with a known pit on the bottom quad of the pipe. It took the tech 2 1/2 hours to find the pit. He even doubted that it was there. The pit was 0.054" deep on .188 wall, this doesn't sound like much but it is 28% wall loss.
scubafanatic
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....I remember reading a while back that the Russian (Soviet) military developed titanium scuba tanks......supposedly they were the size of a football! Those would be pretty cool!
Most steel tanks, like those maunfactured by PST and Faber, in particular are chrome molybdenum steel, not SS...
pescador775
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With deference to Fred, I believe the govt made the right decision on SS tanks. Adding another set of complex test criteria is a ripe field for contention and confusion. Who could you trust to certify the tanks and how many would invest in money losing ultrasonic test gear? How much wiggle room would be left to the tester? What about liability?
There really is no such thing as "stainless steel". There are two or three broad families of chrome/ iron ( so called 18-8 stainless) and carbon steel like alloys of which there are many, many variations with subtle differences in properties. As Fred stated, most of these work harden or have other weird properties such as stress corrosion which casts doubt on their suitability for commercially viable pressure vessels although stainless tubing and piping have been successful. Some of these 'steels' can be heat treated. The most well known of these is the 17-4 precipitation hardened steel used in spear shafts and tips. This stuff is really hard after heat treatment and has spring steel properties. It is very resistant to rusting. Other common varieties are heat treated carbon types (400 series) used in dive knives and have moderate rust resistant properties. These have the advantage of taking a sharp edge, something the 18-8 steels (chrome/nickel iron) can not do. The 18-8 type (especially 316 stainless) are the most rust resistant however.
There really is no such thing as "stainless steel". There are two or three broad families of chrome/ iron ( so called 18-8 stainless) and carbon steel like alloys of which there are many, many variations with subtle differences in properties. As Fred stated, most of these work harden or have other weird properties such as stress corrosion which casts doubt on their suitability for commercially viable pressure vessels although stainless tubing and piping have been successful. Some of these 'steels' can be heat treated. The most well known of these is the 17-4 precipitation hardened steel used in spear shafts and tips. This stuff is really hard after heat treatment and has spring steel properties. It is very resistant to rusting. Other common varieties are heat treated carbon types (400 series) used in dive knives and have moderate rust resistant properties. These have the advantage of taking a sharp edge, something the 18-8 steels (chrome/nickel iron) can not do. The 18-8 type (especially 316 stainless) are the most rust resistant however.
I recall in the 1980s Dacor coming out with a prototype SS Tank. Never made it to the market due to cost I am told.
tcatdiver
Guest
In the middle to late 70's I managed a dive shop in oxnard california and one day a salesman selling stainless steel scuba tanks came in . the tank was eighteen inches tall wieghed 25 lbs. held 90 cf. and fill to 5000 psi, it had a special valve made by sherwood, and it did have a DOT approval number. The tank cost to the shop was $350.00 and we would sell for $500.00.
The biggest problem that I saw with the tank was that nobody in the world at that time was setup to fill higher than 3000 psi. why sell that you can not completely fill, so we did not buy any. I have worked in military aircraft and the new SS alloys we have are quite flexible and can withstand pressure surges up to 6000 psi and beyond. Its a great idea that needs to be looked at again, if they made one now I would buy it immediately.
The biggest problem that I saw with the tank was that nobody in the world at that time was setup to fill higher than 3000 psi. why sell that you can not completely fill, so we did not buy any. I have worked in military aircraft and the new SS alloys we have are quite flexible and can withstand pressure surges up to 6000 psi and beyond. Its a great idea that needs to be looked at again, if they made one now I would buy it immediately.
tcatdiver
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sorry about that, in the reply that I just posted there is an error. it should read that the SS tank held 90 cubic inches, not cf.
Here you go. A little rust, and, I bet a little heat from inside the car, and what do you get? A remodeled car.
http://www.diveshop-pr.com/pages.dir/engl.dir/tankexplosion.html
The picture of the bottom of the tank appears to have a little bit of rust.
Amazing withj 3000 PSI can do isn't it?
nyresq
Contributor
any one who has tried to work with stainless steel will tell you about heating and bending. unlike standard chromemoly and high carbon steels, stainless does not heat in a uniform and even pattern. try heating a straight piece of stainless bar stock and watch when it cools, it will twist and distort several inches away from the heating point. I think someone filling a stainless tank would run a very high risk of heat damage from filling too fast.
Now I know your all sitting at your computers saying to your selves "noooooooooo, who would fill a tank too fast??" But I'm here to tell you, it does happen from time to time.... yes it really does... no really I'm serious, I've seen scuba-doobas fill tanks in a shop a little too fast (when I say a little, I mean hotfill to 3600 and cool down to 2800).
So if your LDS has some kid fill your $600 stainless tank too fast, guess what... stainless ain't gonna take it the way high carbon steel would. Do that a couple of times and a stainless tank would probably develop stress fractures in the body from uneven heating.
Incidently, the same thing can happen from hot filling tanks that are only half immerssed in a water tank while filling. The uneven heating caused by the bottom being cooled by the water while the top half heats up can do som interesting things to the body. Thats why if your going to bother putting them in a water bath while filling, put them all the way under. (this is also a good way to look for any leaks.
I seam to remember a shop telling me about some stainless or titanium tanks that were being sold in europe but the manufacture was having trouble meeting DOT specs. that was probably in the area of 1994. never heard any thing about it since.
Now I know your all sitting at your computers saying to your selves "noooooooooo, who would fill a tank too fast??" But I'm here to tell you, it does happen from time to time.... yes it really does... no really I'm serious, I've seen scuba-doobas fill tanks in a shop a little too fast (when I say a little, I mean hotfill to 3600 and cool down to 2800).
So if your LDS has some kid fill your $600 stainless tank too fast, guess what... stainless ain't gonna take it the way high carbon steel would. Do that a couple of times and a stainless tank would probably develop stress fractures in the body from uneven heating.
Incidently, the same thing can happen from hot filling tanks that are only half immerssed in a water tank while filling. The uneven heating caused by the bottom being cooled by the water while the top half heats up can do som interesting things to the body. Thats why if your going to bother putting them in a water bath while filling, put them all the way under. (this is also a good way to look for any leaks.
I seam to remember a shop telling me about some stainless or titanium tanks that were being sold in europe but the manufacture was having trouble meeting DOT specs. that was probably in the area of 1994. never heard any thing about it since.
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