Pressure testing gone bad

[Mark Hickey]

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

[Fred the Red Shirt]

Mark Hickey > wrote in message >...
> For those of you lucky / affluent enough to afford a pressurized
> aircraft, here is the way NOT to test yours:
>
> http://disastercity.com/kc135/
>

This is why whenever possible pressure testing should be
done with water, rather than air. Not an option in this
instance.

A former cow-orker of mine used to work for Cleveland Pneumatic
Tools which, in addition to aircraft landing gear, made these
big whatchamacallems, pressure chambers like deep sea divers
might sit in for a few hours to prevent the bends. Anyhow,
he saw one fail hydro testing one time. Said it looked like
a small tsunami as the water swept accross the shop. Had they
tested it with air it might have killed everyone in the room.

Back in another life when I was a contract engineer for a company
that made radiation monitoring equipment our QA technician was
hydrotesting a 'volume' for one of my jobs and I stopped
by to see how it was going, and also to be sure he didn't
have the radiation detector inside when he filled it with
water. He told me that he must have trapped an air bubble
in the volume because it took many strokes of the pump to get
the volume up to the correct pressure (225 psi
IIRC). I stepped back a couple of feet and explained to him
some of the differences between compressible fluids like air
and incompressible fluids like water. Then I pointed out that
1) if the volume he was testing failed the test badly it just
might explode, and 2) the air bubble reduced the sensitivity of
the test rendering the result invalid anyhow.

He was unimpressed and I went back up to my office. Later that
day another engineer told me what he saw happen next. The
technician had installed a short piece of tubing and a ball
valve to be used to drain the volume. The end of the valve
pointed straight out horizontally from the volume. So when
the time was up he went and got a bucket, held the bucket
under the end of the valve expecting to catch the water as
it dribbled out, and opened the valve. The water shot
accross the room hitting an oscilliscope on a wheeled cart
and knocked it over on its side.

I think he understood some of what I was trying to explain
after that.

--

FF

[- Barnyard BOb -]

(Fred the Red Shirt) wrote:

>A former cow-orker of mine used to work.....
++++++++++++++++++++++++++++++++++


Barny-ard BOb

[Big John]

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

On 20 Nov 2003 16:42:49 -0800, (Fred the Red
Shirt) wrote:

>Mark Hickey > wrote in message >...
>> For those of you lucky / affluent enough to afford a pressurized
>> aircraft, here is the way NOT to test yours:
>>
>> http://disastercity.com/kc135/
>>
>
>This is why whenever possible pressure testing should be
>done with water, rather than air. Not an option in this
>instance.
>
>A former cow-orker of mine used to work for Cleveland Pneumatic
>Tools which, in addition to aircraft landing gear, made these
>big whatchamacallems, pressure chambers like deep sea divers
>might sit in for a few hours to prevent the bends. Anyhow,
>he saw one fail hydro testing one time. Said it looked like
>a small tsunami as the water swept accross the shop. Had they
>tested it with air it might have killed everyone in the room.
>
>Back in another life when I was a contract engineer for a company
>that made radiation monitoring equipment our QA technician was
>hydrotesting a 'volume' for one of my jobs and I stopped
>by to see how it was going, and also to be sure he didn't
>have the radiation detector inside when he filled it with
>water. He told me that he must have trapped an air bubble
>in the volume because it took many strokes of the pump to get
>the volume up to the correct pressure (225 psi
> IIRC). I stepped back a couple of feet and explained to him
>some of the differences between compressible fluids like air
>and incompressible fluids like water. Then I pointed out that
>1) if the volume he was testing failed the test badly it just
>might explode, and 2) the air bubble reduced the sensitivity of
>the test rendering the result invalid anyhow.
>
>He was unimpressed and I went back up to my office. Later that
>day another engineer told me what he saw happen next. The
>technician had installed a short piece of tubing and a ball
>valve to be used to drain the volume. The end of the valve
>pointed straight out horizontally from the volume. So when
>the time was up he went and got a bucket, held the bucket
>under the end of the valve expecting to catch the water as
>it dribbled out, and opened the valve. The water shot
>accross the room hitting an oscilliscope on a wheeled cart
>and knocked it over on its side.
>
>I think he understood some of what I was trying to explain
>after that.

[Rich S.]

"Big John" > wrote in message
...
> 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)

It may be occasionally used for B-707's. Here's some pics of a test getting
underway. . .

http://www.harbornet.com/folks/shankland/test1.jpg

http://www.harbornet.com/folks/shankland/test2.jpg

http://www.harbornet.com/folks/shankland/test3.jpg

Rich S.

[B2431]

>From: "Rich S."
>
>It may be occasionally used for B-707's. Here's some pics of a test getting
>underway. . .
>
>http://www.harbornet.com/folks/shankland/test1.jpg
>
>http://www.harbornet.com/folks/shankland/test2.jpg
>
>http://www.harbornet.com/folks/shankland/test3.jpg
>
>Rich S.
>
What is the story behind those pictures?

Dan, U. S. Air Force, retired

[Ben Sego]

B2431 wrote:
>>From: "Rich S."
>>
>>It may be occasionally used for B-707's. Here's some pics of a test getting
>>underway. . .
>>
>>http://www.harbornet.com/folks/shankland/test1.jpg
>>
>>http://www.harbornet.com/folks/shankland/test2.jpg
>>
>>http://www.harbornet.com/folks/shankland/test3.jpg
>>
>>Rich S.
>>
>
> What is the story behind those pictures?
>
> Dan, U. S. Air Force, retired
Read here:

http://www.everzone.org/pics/707ditch.html

Ben "glad it wasn't me" Sego

[Rich S.]

"Ben Sego" > wrote in message
link.net...
> B2431 wrote:
> > What is the story behind those pictures?
> >
> > Dan, U. S. Air Force, retired
> Read here:
>
> http://www.everzone.org/pics/707ditch.html

Guess that answers the question. I didn't remember, actually - they have
just been sitting in my files for the last couple of years. Since the ones
on the web site that Ben linked are more comprehensive and have the
narrative, I'll go ahead and remove them from my server to save space.

Rich S.

[Fred the Red Shirt]

Big John > wrote in message >...
> 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
>

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.

--

FF

[Rich S.]

"Fred the Red Shirt" > wrote in message
om...

> 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.

[Big John]

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
om...
>
>> 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.
>

[Big John]

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.

[[email protected]]

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.

[GeorgeB]

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.

[Dave Hyde]

"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/Std/ASTCPax/img/Helo%20Dunker2.jpg

http://www.nomi.med.navy.mil/Text/Std/ASTCPax/img/SWET%20Trainer.jpg

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

Dave 'steel-toed boot in the teeth' Hyde

[David O]

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

[Model Flyer]

"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
>
>

[David O]

"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