Dive Cylinder Explodes - Sydney

[Peter69_56]

My LDS refuses to fill any of these tanks period. It's a blanket policy.
I've been given many of these tanks over the years by people who got out of diving and have no idea that they are 6351 alloy and wouldn't even know what that means. They just think they are being nice by giving me free gear. I thank them and the first thing I do is drain them then drill a big hole in the neck and they go straight to recycle. I used to pass on them but now I beg to get them just so I can disable them and dispose of the properly. There are too many good tanks out there to mess with those turds.

Lead alloy? WTF!!
I'm no metalurgist, but why would they do that??

Please dont just drill a hole in the neck, take a chisel to the thread area as well, or better still crush or saw them as you dont realise how many stupid people there are who can and do thread out the drill hole and put bolts in them and then grind them flush. A pneumatic gun ready to kill. I know you send them to recycle, but someone might do a deal or look after his mate and give him a few tanks to "fix".

Destroy the tank to a point where it can never be used, usually a cold chisel on the neck seat area and thread internally does it permanently.

The OZ standard says cutting in half or crushing is acceptable. If the owner does not agree with doing that then FAILED stamped on the neck and a failed report must be done. In OZ most test staions usually get you to fill in a statement to say if it fails they can destroy. If you dont sign, they wont test.

 

[BoltSnap]

I also spoke to a dive tech who had one explode on him while filling. He had it in a tank (out the back of the shop), and his comment was that he would have been hurt had the water tank (and steel containment wall) were not there.

I don't know but if this guy were a qualified person to give an authoritative opinion in this matter, he wouldn't have had a tank explode on him as far as I am concerned.

There are all sorts of "dive techs" out there and practically all of them are not even remotely qualified to give an authoritative opinion that would contradict what Bill High, Fred Calhoun, et al. have said and insisted on for all of these years.

 

[Wookie]

I also spoke to a dive tech who had one explode on him while filling. He had it in a tank (out the back of the shop), and his comment was that he would have been hurt had the water tank (and steel containment wall) were not there.

Now I am NOT an engineer or have experience in explosions and containment but thats my thinking and I guess the only way someone could change my mind is to do a test or show me the maths. Its not to say you dont know what you are talking about wookie, but I cant get my head past the logic above (sorry). You are an engineer, and I am just an amateur and where I dont have the skills I operate on what seems logical to me anyway (correct or not). If you can direct me to some studies or whatever, I am more than willing to change my "logic".

It's cherry picking, but the report from the 2001 steel cylinder explosion at the dive shop in Sebastian Inlet, FL. Partial report:

On Tuesday, November 13, 2001, at about 4:45 pm the co-owner of a Sebastian, Florida dive center was killed when an older steel scuba cylinder exploded during fill. The co-owner, age 72, died from massive chest and head trauma. Two other persons, the decedent's wife and a customer, were in the store but were not injured.
The cylinder appears to be an exterior vinyl-coated Voit brand cylinder that may have an undercoat of zinc. The interior may have an epoxy coat. This type of cylinder was sold in the late 1960's through the early 1970's. The cylinder's most recent observed hydro date was 1988 and latest visual inspection was 1999. Extensive pitting is observed in the photographs on the cylinder interior. The cylinder split open its full length but did not break into pieces.
The cylinder was being filled in a water-filled concrete tub having a thickness of about 8 inches with some evidence of rebar present. The explosion caused the tub to shatter, propelling large pieces into the victim and through the store concrete block wall into nearby Highway One. Portions of the building were heavily damaged as was the fill station area. Large air storage and oxgen cylinders were dislodged but did not rupture. Two other cylinders in the tub were damaged but did not rupture. Considerable damage occurred to various sir system piping and components.

Now, here's one in New Jersey that was in a tank in a sleeve to direct the force up. Mass Diving, Inc. - Learn to Dive The article doesn't mention if the water tank was full or not, assume it was, but look at the PVC sleeve. It's mostly intact. This would also prevent water intrusion because the tank wouldn't tip while filling.

I'm going to quit looking at incident reports now, it's late. But what I did find unnerving is that almost as many incident reports had cylinders exploding while static as they did while being filled. How's that grab ya?

 

[tbzep]

It was mentioned that containment units take up a lot of space. My FD uses a Mako BAM07H compressor. It is connected via a hp line to the Mako SCFS2HP 2 cylinder fill station that I use to fill SCBA and SCUBA cylinders safely. It can be placed anywhere within reach of the hose to the compressor to make better use of space. It is 67 3⁄4" tall x 32 3⁄4" wide x 26 1⁄2". A 3 cylinder unit is 10" wider. This is the SCBA version, but our AL80's will still fit. The SCUBA version is a couple inches taller and about 1.5" wider and deeper. The compressor can sit in another room if needed, allowing for better use of space and making the filling area quieter.

 

[Diving Dubai]

As far as eddy current testing training goes. I agree that becoming a QA technician and having the ability to perform different types of NDT takes a ton of time and a mountian of school to become certified. Being an eddy current technician, however, using one specific tool to check one specific part of one specific cylinder is a different animal. I can see a 2 hour course as being sufficient.

Having Just viewed a testing site. The Cylinder inspection course Pt 2 is over 2 days to include not only NDT but the factors affecting it.

Currently (as I understand) either the Automated or the manual Eddy Current (EFD) process is only used to flag up a defect, not to determine if a cylinder is suitable.


I'm happy to see in that course there is a segment on metallurgy. In NDT the material composition, it's state and other factors all affect the test. Eddy current is based upon material conductivity. The machines are set up using a reference standard (Often called incorrectly a calibration block) which is a material of the same alloy and that has been subjected to the same heat treatment processes as the component.

There are so many subtle variables that affect the test, only a skilled operator can properly evaluate the results.

I used to train operators (Note operators not technicians) in the use of an automatic aircraft wheel inspection. Basically the operator switched the machine on, loaded a wheel without a tyre onto a spindle and lowered the probe which was much like a record player arm. If the machine found an indication the operator would mark it with a was pencil and send it to us for further examination.

Generally the defect indication was caused by a paint imperfection of something else, possible only 1:100 wheels had an actual defect.

Even with a 2 day course it's only an introduction, saying someone is qualified and has the experience to fully make decisions using EFD after 2 days is like saying someone is a competent diver on completion of an OW course



Also interestingly

A quote directly from www.scubaengineer.com states:

"Further confusion exists in the scuba industry, in that the hydrostatic test is somehow believed to be the usual way a dodgy scuba tank is identified and removed from service. The paradox is that scuba tanks rarely fail hydrostatic test and It is the visual inspection where most scuba tanks are identified as having critical defects and are condemned or otherwise removed from service"

Below is a picture of further scuba cylinder failures, as you can see none are from the neck. No amount of thread gauging and visual inspection of that are going to identify these. And by the fact they have had a critical failure suggests that the defect was missed during inspection (or the tank has not been inspected)

 

[NAM001]

@Patoux01 @KWS

A couple of points that may relieve your concerns.

Firstly the working pressure of a scuba cylinder is referenced to a temp - so 200bar @ 20C (3000 PSI @ 70F as a round number) However Scuba cylinders are rated up to a maximum working temperature of 65C (150F). So as long as the pressure is relative to the temperature (i.e the pressure increases with temperature) all is okay)

Regarding fills, as you can imagine here in the Middle East, we get very high air temps and high humidity (well over 110F and 70% humidity. All the shops have air driers and air chillers to cool and dry the air before is enters the compressor (I believe the air chillers get the air down to 5C (41F).

Standard practice when I was filling was to simply fill the tank to the working pressure, take it off the whip and let it cool and then top off the pressure (rather than over filling). Our club had an air drier but no chiller.

Regarding cooling a cylinder. The tank walls are quite thick meaning it's a big heat sink. The external surface area isn't that big, to cool it effectively you'd need heat sink fins around the exterior. If you got the outside cold, and assumed the inside was hot from the compressed air, you would induce thermal stress. Better to allow the tank to change temperature gradually.

It may be already done, but I don't see why you can't reduce the air charge temp by putting an inter-cooler after the compressor to cool the air and make the charge more dense as used on vehicle engines

I did not think I had concerns. I agree with the first para.
The cooling tank was to cool the tank to room temp insteatd of filling an already hot tank and further increasing the temp from filling. Important in al tanks IMO.

Your 3rd para about fill cool and then top off instead of over filling. You are not over filling. this is a misnomer in the community. you can fill a 3k tank to 3100 and not be gulty of having a over filled tank. The standard is working pressure is the psi that is as marked @ a given temperature. 3100 is the correct pressure for a tank at 90F and 3200 is the correct psi for a tank at 110F.

Cooling the air with an inter cooler reduces eth heating a bit but more importantly it allows more moisture to be removed before getting to the filter desicant. Filters last longer and remove more contaminants. I think I mentioned m y planes to run the hot compressor gas through a coilin ice water prior to getting to the mechanical moisture condencer to enhance the pressure dewpoint effects on the final output.

 

[Peter69_56]

I don't know but if this guy were a qualified person to give an authoritative opinion in this matter, he wouldn't have had a tank explode on him as far as I am concerned.

There are all sorts of "dive techs" out there and practically all of them are not even remotely qualified to give an authoritative opinion that would contradict what Bill High, Fred Calhoun, et al. have said and insisted on for all of these years.

The only comment I can say is he was certified in OZ for tank testing and works in a NSW dive shop. What I stated was a summary of what he told me as he failed my $20 tank I took a risk buying from ebay. Naturally it failed, but I was still just starting up as a diver then and have learned if its cheap its for a reason. As to his authority on the subject we discuss I cannot comment other than to say he works in the field. As for the names you mention, they mean nothing to me or who they are, but from your comments I suspect they are experts in the subject we discuss? Clearly I am not, however scubaboard is about talking about things and allowing all levels of people to discuss so we all broaden our knowledge and understanding?

I will however make this comment regarding authority/certification etc. I would hope you are not implying that as a person has (say) an engineering degree thus their word is gospel. In all fields there are those who are good to exceptional in their field, and I can certainly certify that there are some extremely bad ones as well, and often they make the most noise. I work in the electricity/steam industry and we have certainly had our fair share of duds in engineering. So when I ask for supporting proof or substance and they can provide it, it not only supports their argument but shows they have their (for a better word I cannot write here) poo together. I appreciate that wookie has done exactly that (although I have not read the info yet).

 

[Peter69_56]

I have posted previously about my experience/exposure to badly looked after tanks while in Thailand doing my Dive Technicians course (and I would state I am not an experienced Tech or tester, I mainly took the course because I wanted to expand my knowledge). Many tanks have not been washed or opened in 10 years and are filled on the dive deck as people walk past. They get finally tested when the owners go broke and change ownership.One tank shown to me by my instructor was brought in and the owner was complaining of an air leak, when asked where the air leak was, he showed the tester, a hole in the side wall, corrosion from inside the tank and air was leaking out.

My instructor was a rocket scientist and is extremely knowledgeable on many things diving along with being able to calculate deco algorithms from first principles (as well as rockets). I am personally glad to have had the chance to gain some knowledge from him, over the normal, here is the book, read it and pass the exam style training.

I also remember my instructor writing a paper on the exact subject KWS brought up relating to tank fills/overfills and the temperature relationship.

 

[Peter69_56]

Another thing most dive shops do not do is to chain off the whip so if there is a hose failure, the whip will not "whip" about and hurt/kill people within its range. The Thai boats I talk about have a whip probably 6-8m long and fittings of steel all corroded. I have yet to see a dive shop in OZ that chains their whip, in particular those who fill in the customer area.

When we dived with Tech Thailand they banned everyone from the dive deck while filling, good to see.

Something else to think about.

 

[Peter69_56]

It's cherry picking, but the report from the 2001 steel cylinder explosion at the dive shop in Sebastian Inlet, FL. Partial report:


Now, here's one in New Jersey that was in a tank in a sleeve to direct the force up. Mass Diving, Inc. - Learn to Dive The article doesn't mention if the water tank was full or not, assume it was, but look at the PVC sleeve. It's mostly intact. This would also prevent water intrusion because the tank wouldn't tip while filling.

I'm going to quit looking at incident reports now, it's late. But what I did find unnerving is that almost as many incident reports had cylinders exploding while static as they did while being filled. How's that grab ya?

Wookie, thanks for the info. I am very surprised that the 8" reinforced concrete tank came apart, but I take your meaning of hydraulic pressure.

In the second example I guess the main reason that the SS tank did not fail was the significant reinforcement via the internally welded bars. So is it the combination of water and reinforced SS, or would just a reinforced SS tank be more effective.