Hartley, On the question of "fitness for service" - a 15 year old
"good looking" cylinder could easily fail a hydrotest! The failure
probablility depends on factors such as (a) was it properly stress
relieved after it was made, (2) how often has it been cycled (filled,
refilled), (3) are there any inclusions in the metal, or any laps or
scratches on the interior, (3) are any small patches of corrosion
present on the inside, (4) were the neck threads cut properly. None of
these things will affect the cylinder's "looks" in any way, but they
will most certainly affect its ultimate life. The only way to find out
if there is stress corrosion cracking or fatigue cracking is to do a
hydrotest or an ultrasonic test (which is what I was doing for
customers).

As far as legalites go, the ex-ASTM president is still looking into the
question for me. However, I did a quick web search and turned up the
following relevant sites:

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgOrders.nsf/0/ed3ccb2b0c40bdad86256abf006f380c/$FILE/8000-40.pdf
This is FAA 8000.40D, "Maintenance of Pressure Vessels in Use as
Aircraft Equipment". Paragraph 6C is relevant one, and is as Gary Evans
stated above in his 2nd paragraph.

http://www.gawda.org/eSeries/Custome.../DOT/tab13.pdf
This is a summary of 49 CFR 173 that the Gases and Welding Distributors
Association offers to its members. Near the front, under Use and
Qualification of Cylinders, they say "49 CFR, §180 establishes the
requirements for the use and qualification of cylinders. A company may
not charge a cylinder that is out of test, leaks, has a bulge, has
defective valves or pressure relief devices, shows evidence of physical
abuse, fire or heat damage, or shows evidence of detrimental rusting or
corrosion."

Problem is, when I looked at 49 CFR 180 he
http://www.access.gpo.gov/nara/cfr/w...cfr180_99.html I
couldn't find anything that dealt with cylinders! If I could have, it
would have been the legal requirement we have been seeking!

Now, under Requirements for Filling and Shipping, they say 14 CFR
173.302 governs. That you can find he
http://frwebgate.access.gpo.gov/cgi-...99&TY PE=TEXT

I got totally lost in the formatting of this regulation, but near the
bottom, after the wall stress limitation table, the regulations says
"That an external and internal visual examination made at the time of
test or retest shows the cylinder to be free from excessive corrosion,
pitting, or dangerous defects.". This might also be part of a legal
requirement that you can't refill unless you test the cylinder, but to
me it seems an exercise in circular reference with 49 CFR 180

Maybe someone better versed in reading CFRs can give an opinion. To me,
it's as clear as mud!

-John



HL Falbaum wrote:

The legalities notwithstanding, is there a "real" safety problem with a
steel cylinder that is not retested ?

This is, after all, a life suppport system.

It seems clear that as long as the cyl is in the plane, it is probably legal
to fill it

How safe is it? What is the probability of a good looking 15 year old O2
cylinder failing a hydrotest?
If it fails is it by definition unsafe (technical but not significant
failure) --could this happen?