Dive Cylinder Explodes - Sydney

[redacted]

Filling in water is a great way to introduce water into the tank.

 

[Peter69_56]

There s so much talk about whether these tanks are good or bad. Most of the tanks are good except those made in a vary narrow window time. Because of that the odds are in your favor of noting happening. The bad part is that those that do VIP's are very poor at what they do and the chances of a bad tank being ok"d to use is very high. personally Im all in favor of total removal of those tanks in the effected window from service. That however will only work is all tanks can get looked at for birth date.

I dont recall but is Australia one that hydros every year or every 2 years.

Every year

 

[Peter69_56]

Duplication

 

[Peter69_56]

Filling in water is a great way to introduce water into the tank.

I disagree totally. Filling in water is fine as long as you be careful. Its a non issue. Testing in water will fill the tank with water but thats a non issue. I cant believe that you say filling in water introduces water into the tank. If you ensure that the neck is above water whats the issue. No ingress of water into the tank, if it blows the water contains the explosion over doing it in open air?

If you fill with no water, I cannot believe its safer and also less prone to contamination? Conect the fill hose and introduce it into the water tank, how does that introduce water into the tank?

 

[NAM001]

I disagree totally. Filling in water is fine as long as you be careful. Its a non issue. Testing in water will fill the tank with water but thats a non issue. I cant believe that you say filling in water introduces water into the tank. If you ensure that the neck is above water whats the issue. No ingress of water into the tank, if it blows the water contains the explosion over doing it in open air?

If you fill with no water, I cannot believe its safer and also less prone to contamination? Conect the fill hose and introduce it into the water tank, how does that introduce water into the tank?

Pete you could not have said it better. PSI will argue with you to death about this, but i am with you. Once again this is a one rule fits all thing. yes you have a higher chance of getting water in the tank. but if you do it dry and you put a wet hose (from condensation) to the tank you get the same thing. PSI will argue that it is an attempt to cool the tank from too high of fill rate. I have never seen anyone fill 600 psi a min or less. And even if you do fill at 500 psi a min i want a full tank that is 70ish F and not 90 ish. when full. Any tank, even steel white ones, are hot from the sun when you start to fill. So what good is a 100 F + tank getting a fill to 130 or more hitting the water and haveing a 90% fill. I am surprised on how much heat is disipated even with a slow fill on steel tanks. I wrap a wet towel on the tank and it has to be rewet several times to keep it wet. Or weather here is in the mid to high 90's with high humidity to boot. A tank from the car or from the sun is easily 120 and then a fill,,, and it is hot for sure. At 5 psi per degree above 70 and a full tank at 130F is already going to end up 300+ psi short when you hit spring water unless you can cool it or let it sit over night and then top off. Now what shop can keep customers when it takes hours to get a full fill. And of course there are those that say no over filling such as 3300 fill on the tank above. 3300 is not an over fill on a 3k tank. Why don't so many understand that the working pressure is at 70 degrees. Every one has their fears and many organizations exploit those fears. Sad to say PSI like so many others is one of them.

 

[Wookie]

Yes filling them in a water tank helps if they fail. Testing is done in a chamber but the tanks are pressurised with water and if they fail its water that releases and not a big deal compared to air test. While filling if done in a water tank it reduces the impact, but most dive shops chose to fill in the shop on the ground, thus exposing the whole shop to a bomb.

Poppycock.

Filling in a water bath does nothing to enhance the fill. There are three main theories about filling in a waterbath that are easily debunked.

1. Filling in a waterbath keeps the tank cool. Actually, it may increase the temperature gradient across the wall of the tank, resulting in an even worse metallurgical situation. The tank heats from the inside out, from the adiabatic heating as the gas is compressed upon entering the cylinder. So heating the cylinder from the inside while simultaneously cooling it from the outside will result in expansion of the inside of the cylinder while retarding the expansion of the outside of the cylinder and causing unneeded stress across the cylinder wall. In reality, the effect is so negligible as to not cause a problem. The only way to keep a tank full to get a full fill is to fill it slowly, at Luxfer's recommended 50 PSI/min.

2. Filling in a waterbath mitigates the risk of a tank explosion. In reality, you would have to fill the cylinder at the bottom of a swimming pool to have enough water on the cylinder to ensure that no shrapnel exits the pool. The failure mode of cylinders is almost always in the neck and shoulders. There are hundreds of pictures of blown up cylinders around the internet and they all start in the neck and shoulder, and may split down the side shell, but the shrapnel comes from the neck and shoulder. Now, filling in a cement tank may direct some of the force up, or may turn the cement chunks into shrapnel with the force of the explosion.

3. There is no danger of filling in a waterbath, just keep the neck and shoulder dry. cylinders float when empty. Valves are the heaviest part, so when placed in a waterbath, they tend to tip over and float neck down. I can't tell you how many times I've walked past a fill station in the Caribbean and seen random tanks floating in the fill bin valve down while being filled. And if the cylinders are packed in thick enough to not tip over, and the neck and shoulder are dry, well, you just negated number 2 above.

The only way to avoid the hazards of a cylinder explosion are to fill away from people (I've seen this in many many dive shops) or use a containment fill station. Filling in a waterbath out in front of the dive shop may be convenient as hell, but in the unlikely event a cylinder does rupture, the customers are the folks who take the brunt of the mishap.

As far as introducing water. The little bit between the face of the valve and the face of the fill adapter is enough to coat the inside of the entire cylinder to a depth of 4 microns. 4 microns, you say? So what? If it's salt water, the salt that's left behind immediately starts attacking the interstitial defects in the tank wall. In a steel tank, the tank will start to rust before the water dries off due to the dry air.

There is no valid reason to fill in a water bath.

 

[tarponchik]

The tank heats from the inside out, from the adiabatic release of energy as the gas expands upon entering the cylinder.

As the gas expands, it does the opposite, cools down (Joule-Thompson's effect). This is how your refrigerator and AC work. The cylinder heats up because the gas contracts under pressure.

 

[Wookie]

As the gas expands, it does the opposite, cools down (Joule-Thompson's effect). This is how your refrigerator and AC work. The cylinder heats up because the gas contracts under pressure.

You are correct. My bad. Called adiabatic heating as the air is compressed. Same effect, wrong concept.

 

[tarponchik]

Yep. Otherwise, you are an expert in this. But just speaking from my amateur perspective, I'd one more point, though. Shrapnel is not the only thing that can hurt when a tank explodes, there is also the shock wave, like with any explosion. And even 1 ft of water should reduce its energy significantly.

 

[wetb4igetinthewater]

O2 cleaning is to rid the tank of hydrocarbons. If you don't have them in there to begin with there is nothing to clean. Granted you get them from every fill from a system that does not explode when under the same pressure. You also purge the tank of hydro carbons as you breath the gas. IMO O2 cleaning is a general procedure that covers all O2 systems. A one solution fits all. piping right angle bends expansions and restrictions. most of which you do not have in a scuba tank and valve to the degree you have in a real O2 system. Also as long as you control your fill rate you don't have any problem. Yes a sparkley cleaning may be what saves you when you do an O2 fill 0-3000psi in 30 seconds on a tank with a oil puddle in it. I respect the hazards of such systems. That respect comes from knowledge and not fear.

The problem is that in this particular cylinder's case, there were hydrocarbons, and with the oxygen was put it, it was starting to eat at the walls of the tank, fortunately not to the degree that the tank had to be condemned. I don't have the expertise to know exactly when ignition is going to occur, I just follow the industry safety guidelines.