Pressure testing gone bad

Rich

Said much better than I did. Tells it how it is.

Big John

On Fri, 21 Nov 2003 15:28:31 -0800, "Rich S."
wrote:

"Fred the Red Shirt" wrote in message
. com...

IIUC Scuba tanks are routinely filled while submerged in water for
cooling purposes. In the examples I gave the vessels were pressure
tested while FILLED with water so that there was no compressed air
inside.

In the scuba example the water ouside the pressure vessel provides
(some I suppose) protection from the explosion should it fail.

In the earlier examples, filling the pressure vessel with water
prevents an explosion should the vessel fail.

Just to be clear.

Scuba tanks are filled with air while immersed for cooling and protection.
They are also hydrostatically tested every five years, during which they are
filled with water to mitigate expansion if they fail.

Rich S.

a@aa

Had forgotten the comets (either age or 'booze berries). Tnx.

Big John


21 Nov 2003 13:51:50 -0800, wrote:

In article , Big John says...

Fred

One more.

Scuba tanks have to be pressure tested every few years. This is done
in a tank of water in case they fail.

So under water testing is a common thing (except for KC-135's BG)

Big John

It's been done. Remember the Comets that blew up back in the 50's? This is the
way they figured out the failure mode...

"The Ministry of Civil Aviation decided upon a unique test to find out. They
built a tank large enough to hold one of the grounded Comets. The wings
protruded from water-tight slots in the sides of the tank. Then the tank and
cabin were flooded with water. The water pressure inside the cabin would be
raised to eight and a quarter pounds per square inch to simulate the pressure
encountered by a Comet at 35,000 feet. It would be held there for three minutes
and then lowered while the wings were moved up and down by hydraulic jacks. The
hydraulic jacks would simulate the flexing that naturally occurs in aircraft
wings during flight. This process continued non-stop, 24 hours a day. This
torture test continued until the cabin in the tank had been subjected to the
stresses equivalent to 9,000 hours of actual flying. Suddenly, the pressure
dropped. The water was drained and the fuselage examined. The investigators were
horrified to find a split in the fuselage. It began with a small fracture in the
corner of an escape hatch window and extended for eight feet. Metal fatigue! Had
the Comet not been under water, the cabin would have exploded like a bomb.

On Fri, 21 Nov 2003 17:49:15 -0600, Big John
wrote:

:Rich
:
:Said much better than I did. Tells it how it is.
:
:Big John

The water submersion while filling is for cooling, since the heat
could, in theory, weaken the tank if it got hot enough. If a tank
lets go the water won't do much to damp the explosion, I saw pictures
of a scuba shop after one failed (someone powder coated an aluminum
tank and destroyed the temper). Not much was left of the entire shop,
or of the owner.

IIRC, hydrostatic testing of a tank takes it to 5/3 of it's rated
pressure, and it can't expand more than 2% to pass.

On Sat, 22 Nov 2003 03:07:40 GMT, wrote:


The water submersion while filling is for cooling, since the heat
could, in theory, weaken the tank if it got hot enough.

I believe it is more an issue of time to reach equilibrium pressure;
the hot air, when cooled, drops in pressure. I _DOUBT_ that the
temperature would get high enough to be of any effect on the aluminum
heat treatment, but may be wrong.

If a tank
lets go the water won't do much to damp the explosion, I saw pictures
of a scuba shop after one failed (someone powder coated an aluminum
tank and destroyed the temper). Not much was left of the entire shop,
or of the owner.

Yeah, I remember those pictures and warnings ... what, some 25 or 30
years ago now? I believe that significant weakness occurs in the
alloys used above about 300F.

IIRC, hydrostatic testing of a tank takes it to 5/3 of it's rated
pressure, and it can't expand more than 2% to pass.

I BELIEVE it is the difference in expansion and recovery ... must
recover 90% of the fluid used to expand the vessel (and compress the
water)

One fills the tank with de-aerated water, measures the water volume
required to attain the 5/3 pressure (verifying a stable reading, no
leaks, etc), decompresses, the fluid recovered in decompression must
be 90%-100% of that used to compress.

"Rich S." wrote:

So under water testing is a common thing (except for KC-135's BG)

It may be occasionally used for B-707's.

They use a smaller version on engineers :-)

http://www.nomi.med.navy.mil/Text/St...%20Dunker2.jpg

http://www.nomi.med.navy.mil/Text/St...%20Trainer.jpg

It's kind of fun as long as you don't inhale.

Dave 'steel-toed boot in the teeth' Hyde

Mark Hickey wrote:

For those of you lucky / affluent enough to afford a pressurized
aircraft, here is the way NOT to test yours:

http://disastercity.com/kc135/

Mark Hickey


Those pictures remind me of this one, a pressure failure of a
different kind.

http://tinyurl.com/w8od


David O -- http://www.AirplaneZone.com

"David O" wrote in message
...
Mark Hickey wrote:

For those of you lucky / affluent enough to afford a pressurized
aircraft, here is the way NOT to test yours:

http://disastercity.com/kc135/

Mark Hickey


Those pictures remind me of this one, a pressure failure of a
different kind.

http://tinyurl.com/w8od

That's the one that started this thread.
--
---
Cheers,
Jonathan Lowe.
/
don't bother me with insignificiant nonsence such as spelling,
I don't care if it spelt properly
/
Sometimes I fly and sometimes I just dream about it.
:-)



David O -- http://www.AirplaneZone.com

"Model Flyer" wrote:

"David O" wrote in message

Those pictures remind me of this one, a pressure failure of a
different kind.

http://tinyurl.com/w8od


That's the one that started this thread.

No, the one that started this thread was this
http://disastercity.com/kc135/, a series of pictures of a KC-135 whose
fuselage ruptured during a cabin pressurization test.

The link I posted, http://tinyurl.com/w8od, is to a picture of a
C-141B Starlifter whose wing ruptured during fueling.

David O -- http://www.AirplaneZone.com