Opinion on tank neck threads please ?

"monty" <monty@scubadiving.com> wrote in message
news:69b0b639.0407230215.5c1a2cce@posting.google.c om...

Tapered thread in an AL scuba tank???

From looking at the picture, it looks like those are marks left by an
interrupted tap when the cutting was stopped, but what is strange is that
you generally never see a three flute tap of that size. More questions than
answers I am afraid.

Could also be from the male threaded part.

Why don't you try chasing the thread, and see what you get?

"Scott" <scottk@localaxes.com> wrote in message >
> Tapered thread in an AL scuba tank???

Yeah, quite common here - especially in medical oxygen cylinders.

> Why don't you try chasing the thread, and see what you get?

I have been told repeatedly by several people here that that is
"illegal" or "unacceptable".

No modifications of threads allowed whatsoever - not even for the
purposes of 'cleaning up' the threads ?

rgds
monty

In my experience, X-raying will cost more than a new tank.


"monty" <monty@scubadiving.com> wrote in message
news:69b0b639.0407230215.5c1a2cce@posting.google.c om...
> One of my 2 liter aluminium cylinders has just been condemned.
>
> They tell me that there are no Visual Plus probes for taper thread
> cylinders.
>
> Luxfer are unable to confirm which alloy it was made from and want me
> to ship the cylinder to them - Branded SM Gerzat, a subsidiary of
> theirs and made in '84.
>
> The strange thing is that there are 3 "cracks" exactly 120 degrees
> apart and that the "cracks" only appear on every second 'peak' or
> 'ridge' of the actual threads.
>
> Leading up to the "cracks" the material gets "dull" and almost looks
> smeared, and then it continues all bright and shiny on the other side
> of the "crack".
>
> I have taken it to several local inspection facilites and some
> engineering shops and the answers remain inconclusive.
>
> Some suggestions that it could be the 'tool start marks' from when the
> thread was cut in the cylinder neck ?
>
> There has been a suggestion that I should try to get it x-rayed ?
>
> Pictures are here :
>
> http://www.scubaculture.co.za/tank_neck_crack.html
>
> rgds
> monty

monty wrote:

> One of my 2 liter aluminium cylinders has just been condemned.
>
> They tell me that there are no Visual Plus probes for taper thread
> cylinders.
>
> Luxfer are unable to confirm which alloy it was made from and want me
> to ship the cylinder to them - Branded SM Gerzat, a subsidiary of
> theirs and made in '84.
>
> The strange thing is that there are 3 "cracks" exactly 120 degrees
> apart and that the "cracks" only appear on every second 'peak' or
> 'ridge' of the actual threads.
>
> Leading up to the "cracks" the material gets "dull" and almost looks
> smeared, and then it continues all bright and shiny on the other side
> of the "crack".
>
> I have taken it to several local inspection facilites and some
> engineering shops and the answers remain inconclusive.
>
> Some suggestions that it could be the 'tool start marks' from when the
> thread was cut in the cylinder neck ?
>
> There has been a suggestion that I should try to get it x-rayed ?
>
> Pictures are here :
>
> http://www.scubaculture.co.za/tank_neck_crack.html
>
> rgds
> monty


Why are you putting so much effort into an iffy 20 year old tank with
obvious damage on the tank neck threads?

1. If you have to worry about the tank, why continue to use it.
Replacements are not all that hard to come by.
2. Send it to Luxfer. If it's defective, you have a chance of getting help
with the cost of the new tank.
3. Scott's an expert compared to me, but if I saw something that looked like
a crack, surrounded by dull metal, I'd assume it was a load induced crack.
That's what the edges of cracks in aluminum I've seen look like.

Lee

"monty" <monty@scubadiving.com> wrote in message
news:69b0b639.0407230215.5c1a2cce@posting.google.c om...
> One of my 2 liter aluminium cylinders has just been condemned.
>
> They tell me that there are no Visual Plus probes for taper thread
> cylinders.
>
> Luxfer are unable to confirm which alloy it was made from and want me
> to ship the cylinder to them - Branded SM Gerzat, a subsidiary of
> theirs and made in '84.
>
> The strange thing is that there are 3 "cracks" exactly 120 degrees
> apart and that the "cracks" only appear on every second 'peak' or
> 'ridge' of the actual threads.
>
> Leading up to the "cracks" the material gets "dull" and almost looks
> smeared, and then it continues all bright and shiny on the other side
> of the "crack".
>
> I have taken it to several local inspection facilites and some
> engineering shops and the answers remain inconclusive.
>
> Some suggestions that it could be the 'tool start marks' from when the
> thread was cut in the cylinder neck ?
>
> There has been a suggestion that I should try to get it x-rayed ?
>
> Pictures are here :
>
> http://www.scubaculture.co.za/tank_neck_crack.html
>
> rgds
> monty

Jon C <news@jonnythan.com> wrote :
> Why are you putting so much effort into an iffy 20 year old tank with
> obvious damage on the tank neck threads?

1. Because you cannot buy 2 liter cylinders here, they simply don't
get imported.

2. Buying stuff over the Internet isn't easy since we have "Exchange
Control" ( have to apply to the reserve bank for money to leave the
country - I live in South Africa )

3. Because I am sick and tired of dive shop staff telling me what I
can & can't do when they don't know what they are talking about.

rgds
monty

In article <69b0b639.0407250102.1df76851@posting.google.com >, monty
<monty@scubadiving.com> wrote:

€ 3. Because I am sick and tired of dive shop staff telling me what I
€ can & can't do when they don't know what they are talking about.

Then you should get along fine with them.

--
"We're going to rush the hijackers."
-Jeremy Glick, aboard United Airlines flight 93, September 11, 2001

Lee wrote:
> 2. Send it to Luxfer. If it's defective, you have a chance of
getting help
> with the cost of the new tank.
> 3. Scott's an expert compared to me, but if I saw something that
looked like
> a crack, surrounded by dull metal, I'd assume it was a load induced
crack.
> That's what the edges of cracks in aluminum I've seen look like.

I got a reply from Luxfer UK:
"These mark are not thread cracks but are a machining feature that
occurs when a fluted tap is used to cut the thread. These are common
when using this thread machining method. Reference is given to this in
BS EN 1802 : 2002, Periodic inspection and testing of seamless
aluminium alloy gas cylinders. The thread is a 6 degree 52' taper, 19.8
DIN 477 thread and is satisfactory to guages"

rgds
monty

One of my 2 liter aluminium cylinders has just been condemned.

They tell me that there are no Visual Plus probes for taper thread
cylinders.

Luxfer are unable to confirm which alloy it was made from and want me
to ship the cylinder to them - Branded SM Gerzat, a subsidiary of
theirs and made in '84.

The strange thing is that there are 3 "cracks" exactly 120 degrees
apart and that the "cracks" only appear on every second 'peak' or
'ridge' of the actual threads.

Leading up to the "cracks" the material gets "dull" and almost looks
smeared, and then it continues all bright and shiny on the other side
of the "crack".

I have taken it to several local inspection facilites and some
engineering shops and the answers remain inconclusive.

Some suggestions that it could be the 'tool start marks' from when the
thread was cut in the cylinder neck ?

There has been a suggestion that I should try to get it x-rayed ?

Pictures are here :

http://www.scubaculture.co.za/tank_neck_crack.html

rgds
monty

"Scott" <scottk@localaxes.com> wrote in message >
> Tapered thread in an AL scuba tank???

Yeah, quite common here - especially in medical oxygen cylinders.

> Why don't you try chasing the thread, and see what you get?

I have been told repeatedly by several people here that that is
"illegal" or "unacceptable".

No modifications of threads allowed whatsoever - not even for the
purposes of 'cleaning up' the threads ?

rgds
monty