Re: Welding oxygen

In article <3ecc7e6f$1@news.star.co.uk>,
Nigel Hewitt <news@REMOVETHISnigelhewitt.net> wrote:
>Uwe Hercksen wrote:
>
>> Don't trust any digital reading of a measurement unit to be correct
>> even for the least significant digit. Very often you will find a
>> sentence about a plus minus 1 digit error as well as other errors.
>
>Definitely. Also calibrating an O2 analyser by waving the
>sensor about and then dialing up 20.9 may be good enough
>to test a mix within the errors of decompression theory
>but it's hardly accurate. A better method is to set it
>at 100% on pure oxygen and read from there quickly before
>you are putting much reliance on the wild temperature
>compensation tricks in the sensor.
>
>Anything that comes from one of the big suppliers as
>'Oxygen' is probably better than 99% maybe even 99.9
>but for medical and diving grades you are paying for
>extra 9s on the end and the traceability to prove it.
>
>As an example: If the stuff in my welding bottles had
>1% CO2 in it it wouldn't effect the weld one iota as
>the torch produces masses of it but it would be very
>bad news to breath. I expect welding oxygen to be as
>pure as the diving grade but I can't prove it and I
>don't think AP could prove it either.

IF (big if) you produce el-cheapo oxygen by a fast
cryo process to eliminate a lot of nitrogen from the
air, then you will be left with excess amounts of
argon and CO2. If you just run the cryo process
directly in one step you will get around 95% O2, 4%
Ar and 1% CO2. This is perfectly OK to breathe at the
surface; but can wreck a dive. It is also perfectly
safe for welding.

Most processes are a lot better than this.

The other probable problem is contabination from other customers. 1
bar of contabination works up to 0.5% at 200 bar. If that is CO2 or CO
it is VERY BAD. This is why medical O2 is vacuumed a few times.

If the tanks are vacuumed and filled from a common source I don't see
much problems. But you must make sure. 100% sure.

Around here it is the tank rent that is the problem. To keep
the O2 tanks in good shape you MUST rent them, this sets
you back around GBP 140 for a year for a 50L tank. But then
they do the hydro, cleaning etc. without extra charges.

The fills themselves are cheaper. They even deliver at your
door near big cities at no extra charge. 10 M2 (a full 50L)
is around GBP 60, single user quantity. If you buy a lot
this price will come down substantially. With 25 tanks
per year and at least 2 tanks in rent the price is down to 45.

-- mrr

On Thu, 10 Jun 2004 18:30:04 GMT, Morten Reistad
<firstname@lastname.pr1v.n0> wrote:

>IF (big if) you produce el-cheapo oxygen by a fast
>cryo process to eliminate a lot of nitrogen from the
>air, then you will be left with excess amounts of
>argon and CO2. If you just run the cryo process
>directly in one step you will get around 95% O2, 4%
>Ar and 1% CO2. This is perfectly OK to breathe at the
>surface; but can wreck a dive. It is also perfectly
>safe for welding.
>
>Most processes are a lot better than this.

Air products lowest grade is >99.6%. Next is 99.995%

>Around here it is the tank rent that is the problem. To keep
>the O2 tanks in good shape you MUST rent them, this sets
>you back around GBP 140 for a year for a 50L tank. But then
>they do the hydro, cleaning etc. without extra charges.

It's about £5 per month here. And the shape doesn't seem to change
even when I don't rent them.... 5 year test and clean anyway.

>The fills themselves are cheaper. They even deliver at your
>door near big cities at no extra charge. 10 M2 (a full 50L)
>is around GBP 60, single user quantity. If you buy a lot
>this price will come down substantially. With 25 tanks
>per year and at least 2 tanks in rent the price is down to 45.

£14 for welding grade, £28 for the next grade, then + transaction
charge of £8 if you collect, £24 if they deliver. Any quantity.

Of course if you buy lots it gets even cheaper.

Pete S.

> >Around here it is the tank rent that is the problem. To keep
> >the O2 tanks in good shape you MUST rent them, this sets
> >you back around GBP 140 for a year for a 50L tank. But then
> >they do the hydro, cleaning etc. without extra charges.
>
> It's about £5 per month here. And the shape doesn't seem to change
> even when I don't rent them.... 5 year test and clean anyway.


Is that £5 per month for a rental of medical oxygen? Where is that from?
Does that come as a complete kit or do you need the masks etc as well?
I need to get an O2 kit and am trying to find the cheapest way of doing it.

Cheers, Pete F

Peter Filcek <p.r.a.filcek@durham.ac.uk> wrote:

> Is that £5 per month for a rental of medical oxygen? Where is that from?
> Does that come as a complete kit or do you need the masks etc as well?
> I need to get an O2 kit and am trying to find the cheapest way of doing it.

I pay 5 pounds a month for a cylinder. It seems to be any cylinder from AP.
Then 25 for a fill of Oxygen (J) and usually about 18 'transaction charge'
regardless how many cylinders I swop at once so we always try to do
several together.

I suspect the cheapest way is to own an O2 clean pony and buy the valve
and mask gear and get it filled especially if you are using the thing.
Don't think "I've never needed it so far so I'l never use it" because if you have
it you will reach for it as a precautionary measure.

nigelH