Visuals

[CIBDiving]

Luxfer recommends AGAINST using vis+ etc checks on the newer (read: not 6351) alloy tanks due to the possibility of false positives--which you seem to have just proven.

It's not Just that, the number of false positives of the 6351 alloy tanks sent back to luxfer for replacement was more than 80% of the Actual failures. It seems that tank monkies just can't read a VIP+ test machine. The manufactureing process for Al tanks leaves 'folds' in the grain of the neck that appear to be cracks to a VIP+, and can even look like cracks to the eye if they are exposed as the threads are cut into the bottle, but in fact are not a problem.

 

[PerroneFord]

Telling the difference between a fold and a crack is pretty simple on VisPlus3. The 3d graph you get that you can rotate on 3-axis is pretty handy for seeing how many threads are affected and how deep.

 

[mike_s]

BING BING BING We have A winner!!!!!

It's all a crock cooked up by the dive industry Years ago. The guy who started PSI was in the industry and wanted to make more money, since PADI had the quack certification catagory all sewed up he came up with the VIP.

The Only Legal requirement for a 'visual inspection' is when the bottle is hydroed.

That used to be the case..... Scuba cylinders did not have any legal requirements for visual inspection.

That changed on August 29th, 2006. But it only changed for Aluminum alloy 6351 tanks.

see http://dmses.dot.gov/docimages/pdf97/411928_web.pdf and do a search in the document for visual to find the ruling.

It doesn't affect any other tanks. There is no legal requirement for them to be visualed.


now... to stir this up a little, ask the people at your dive shop if they've every actually had an official certification class on how to visual tanks. I think you'll find that more than 50% of them (if not much more) will tell you NO.

 

[oxyhacker]

The 2006 HM220F rules you mention apply only to 6351 tanks as you point out, and do specifically mandate a visual inspection for neck cracks. But only at REQUALIFICATION TIME. That is to say, every 5 years when the tank is hydrotested. So this is nothing new since a visual has always been required, for all tanks, at requalification time - the DOT is just emphasizing that that visual should include a dedicated visual search for neck cracks rather than the requalifier relying on the eddy current test alone to find any cracks.

It's also interesting to note that the DOT has placed the responsibility for eddy current testing with the DOT-licensed hydro test stations, rather than letting dive shops and certified visual inspectors do it even though one suspects that at this point in time far more of them have eddy current testers than hydro shops do. This suggests that the DOT does not have a lot of faith in their competence or reliability in doing this sort of exam.

It will be interesting to see how the shops handle this - if the DOT says every five years is good enough for the bad alloy tanks, and places no eddy current requirements on the later aluminum tanks, then the rationale for dive shops to do eddy current testing, on 6061 tanks especially, becomes a lot weaker.

BTW, regarding claims that cracks have been found on 6061 tanks, they have been. But there is a huge difference in how older and newer tanks handle cracking. Newer tanks are designed to be "leak not break" safe, mainly by using alloys whose grain pattern will make them crack slowly and in crooked lines, so they will leak long before they get weakened enough to burst. The 6351 allow tanks had an unfortunate tendency to crack relatively quickly in straight lines which encouraged catastrophic failure. So even though cracks may be, though very rarely, found in 6061 tanks, they haven't been bursting, so eddy current testing remains of questionable value.

Now, re the original post, I think he ought to go back to the shop and tell the guy that, on the basis of the LDS's assertions, he has made a $50 bet with a buddy, and needs the shop guy to show him where it says so on the PSI website, so he can collect.

That used to be the case..... Scuba cylinders did not have any legal requirements for visual inspection.

That changed on August 29th, 2006. But it only changed for Aluminum alloy 6351 tanks.

see http://dmses.dot.gov/docimages/pdf97/411928_web.pdf and do a search in the document for visual to find the ruling.

It doesn't affect any other tanks. There is no legal requirement for them to be visualed.

 

[CIBDiving]

That used to be the case..... Scuba cylinders did not have any legal requirements for visual inspection.

That is not true, All cylinders (scuba or others) Must pass a visual inspection to qualify as hydroed. However that inspection is to be performed by the Hydro certifer NOT a scuba shop.

It will be interesting to see how the shops handle this - if the DOT says every five years is good enough for the bad alloy tanks, and places no eddy current requirements on the later aluminum tanks, then the rationale for dive shops to do eddy current testing, on 6061 tanks especially, becomes a lot weaker.

My quess is they wil do the same thing as most do now - they'll misinterpt the regulations to whatever they wish.

 

[Slipstrm]

It's not Just that, the number of false positives of the 6351 alloy tanks sent back to luxfer for replacement was more than 80% of the Actual failures. It seems that tank monkies just can't read a VIP+ test machine. The manufactureing process for Al tanks leaves 'folds' in the grain of the neck that appear to be cracks to a VIP+, and can even look like cracks to the eye if they are exposed as the threads are cut into the bottle, but in fact are not a problem.

This is what I saw from Luxfer....
February 4, 2004
Luxfer Gas Cylinders continues to require the use of eddy-current testing devices (such as Visual Plus and Visual Eddy) to detect sustained-load cracks (SLC) in Luxfer aluminum scuba cylinders manufactured from 6351 alloy. Luxfer also recommends the use of eddy-current testing on other types of Luxfer cylinders made from 6351 alloy. http://www.luxfercylinders.com
However, based upon extensive testing by both Luxfer and independent laboratories, Luxfer does not recommend using eddy-current devices to test cylinders manufactured from Luxfer’s proprietary 6061 alloy. The reasons are:
Cylinders made from Luxfer’s proprietary 6061 aluminum alloy are not susceptible to cracks, including SLC. This fact has been conclusively shown by the exemplary safety record of cylinders made from this alloy, which Luxfer introduced in 1988 when it discontinued use of 6351 alloy.
Eddy-current devices sometimes give “false positive” readings when used to test Luxfer’s 6061-alloy, and such readings can lead to erroneous cylinder condemnation. These erroneous readings fall into three main groups:
When threads are cut in the necks of new 6061-alloy cylinders, superficial tooling marks (sometimes called “tooling stops”) sometimes occur at the points where the thread-cutting tool starts and stops. On occasion these harmless marks are mistaken for cracks during eddy-current inspections, especially by inexperienced or inadequately trained inspectors.
As a normal result of the neck-forming process during manufacturing, a small number of 6061-alloy cylinders may exhibit extremely slight wall variations in the neck area. Consequently, when the neck is threaded, partial threads may occur in the lower cylinder neck. While these occasional partial threads are normal and not detrimental in any way to cylinder performance, they sometimes show up on eddy-current devices as signals that can be wrongly interpreted as cracks in the lower threads.
The threads of Luxfer 6061 cylinders sometimes exhibit superficial, harmless micro structural features that cannot be seen with the naked eye or even with a magnifying mirror. However, these features sometimes appear as low-level signals on eddy-current readouts, and inexperienced or insufficiently trained eddy-current operators can erroneously interpret these normal surface variations as cracks.
None of these minor, normal manufacturing variations is a product defect, and none leads to crack formation.
Luxfer continues to recommend regular visual inspection for its 6061-alloy cylinders in accordance with its published inspection guidelines. New developments in eddy-current technology now under way may lead to devices that can successfully test Luxfer 6061-alloy cylinders without “false positive” readings. Luxfer will test such devices on a case-by-case basis and issue timely recommendations concerning their use.
Luxfer is sometimes called upon to give “second opinions” about Luxfer 6061-alloy cylinders that have been erroneously condemned by inspectors who use eddy-current devices despite Luxfer’s recommendation against this practice. While Luxfer is willing to inspect such cylinders, we will charge $50 for each inspection, and all shipping costs must be paid by the person requesting the inspection.
If you have questions about this Luxfer inspection policy, please contact Luxfer Customer Service toll-free at 800-764-0366.

 

[oxyhacker]

That release is almost three years old. Each generation of eddy current machine gets better, and the latest ones seem to work on 6061 tanks (and are a lot more foolproof on the older ones).

However I think a large part of the reason the new ones do work on 6061 is that it was important, if the manufacturers were to sell any more of these machines (especially as the 6351 population is thinning out quickly as divers just get sick of the hassle and scrap them), they had to come up with a version which could be used on 6061 tanks - whether they need it or not! - just so the machines could earn their keep.

Sort of like the shop someone reported that was insisting on using their V+ machine on steel tanks, and charging for it, but, when challenged, admitted they knew it didn't work on steels, but "We have to pay for it somehow!".

 

[TomP]

That release is almost three years old. Each generation of eddy current machine gets better, and the latest ones seem to work on 6061 tanks (and are a lot more foolproof on the older ones).

However I think a large part of the reason the new ones do work on 6061 is that it was important, if the manufacturers were to sell any more of these machines (especially as the 6351 population is thinning out quickly as divers just get sick of the hassle and scrap them), they had to come up with a version which could be used on 6061 tanks - whether they need it or not! - just so the machines could earn their keep.

Sort of like the shop someone reported that was insisting on using their V+ machine on steel tanks, and charging for it, but, when challenged, admitted they knew it didn't work on steels, but "We have to pay for it somehow!".

Vance,
With all due respect, I'm not sure what relevance the age of the article is. Luxfer asserts in the article that eddy testing isn't necessary on 6061 cylinders because they aren't susceptible to cracks including SLC. Presuming that Luxfer's position hasn't changed - and you didn't indicate that it had - I'm more suprised that Dive Shops continue to invest in technology that seemingly has no practical purpose.

 

[rjack321]

I'm more suprised that Dive Shops continue to invest in technology that seemingly has no practical purpose.

Because, IMO, in many cases:
1) they feel a need to have the latest and greatest gadget
2) are looking for an edge on their VIP competition
3) don't realize that better training and experience is just as good for 6061 cylinders
4) don't know about Luxfer's recommendations or choose to ignore them for the sake of a, b, or c

 

[TomP]

Because, IMO, in many cases:
1) they feel a need to have the latest and greatest gadget
2) are looking for an edge on their VIP competition
3) don't realize that better training and experience is just as good for 6061 cylinders
4) don't know about Luxfer's recommendations or choose to ignore them for the sake of a, b, or c

All plausible but I'd like to think that the few LDS I use are professional enough to be above #1. Guess i'll find out when my next AL VIP comes due...