trapped liquid

[Tycho]

Came across this picture online:
curvy.jpg

Apparently there has been trapped liquid that has expanded and stretched the pipe.

When I was an apprentice and we were working with R-22, one of the old hands explained a rule of thumb to me.

If you have trapped liquid, the pressure will increase by 5 bar for every degree Celsius the temperature increases.

So if we take -38 (0 bar) to +20, that is 58C difference and we reach a pressure of 290 bar.
It's a lot, but these are the same pipes the use in hydraulic systems running at 400 bar.

Does anyone have any better numbers?

Just imagine the forces needed to deform a pipe like that.

I've seen oil rectifiers on NH3 plants burst after the technician closed one to many valves, and turned on the heater, and those are made out of pipes with 8 mm wall thickness.

[NH3LVR]

I always wonder about that. I did a quick search and found a formula to calculate such things. http://www.eng-tips.com/faqs.cfm?fid=1339 The math is more than I wish to go through. But it amounts to a lot!

[RANGER1]

Post doubled up by mistake

[RANGER1]

IMG_1973.JPG

Tycho,
The pressures probably up there with this table below.

Whoever welded pipe in picture is top notch.

To me typical of this type/brand of valve, as you have to keep going back to seat valve until seat compresses enough to seal.
We had a similar issue, but it damaged valve shoe, as pipe did not expand (schedule 40 steel)

http://www.svasd.com/wp-content/uplo...ppedLiquid.pdf

https://www.engineeringtoolbox.com/s...res-d_463.html

[monkey spanners]

I've found 1/4" valve caps split and wondered if something similar had happened, full of trapped liquid and a temperature rise finds the weakest point.

Suppose its similar to damage that can be caused by ice formation in an enclosed space.

[Josip]

Hi all,

attached are photos from one plant in Costa Rica from year 2000 during start up of the plant ...











Those flexible joints we installed between buildings to protect ammonia leak
in case of earthquake .... good solution ... it is visible how it looks undamaged...

Unfortunately, we all miss one scenario what will happen if we (for some reason)
must isolate low temperature system when is working ...

we all know during time temperature and pressure will arise, but we have installed
bypass pressure safety valves (1/4") ...

... unfortunately PSV were installed on the wrong side of the
check valve (between pump and check valve and not between check valve and stop valve) ...
everyone of us overseen this design problem) due to hurry to start the plant on time.

and normally due to high pressure check valves were leak proof good for us,
but in this case not that much

Of course, I have to mention that start up was OK and to avoid any overnight problem
with unattended plant partially charged with ammonia, we isolate that part of the plant
with valves ... and went to restaurant to take a late dinner and to celebrate good job ...

... then in the middle of the dinner my mobile rung and man from other side told me there
were ammonia leak on the plant ... we all were frozen in the moment knowing some local workers used to sleep in the cellar (our compressors also were installed in that part) of the plant and there can be injured people ....

Fortunately, all finished with material damage only what we repaired soon (PSV replaced in the right position - after check valve on pump discharge pipe and we replaced damaged flexible joints)

So trapped liquid can be very very dangerous ...

This was good school for me ... to take care to install PSV in any possible position
where human error can happen ...


Best regards,
Josip

[al]

Nice post Josip, one hell of a lesson.

The attachment links aren't working though?

[Josip]

Hi al,

changed attached photos ... hope all be visible now ,,,


Best regards,
Josip

[RANGER1]

Operator error can also play a major part.
Many years ago (old person talking now) a new guy started with company I worked for, he was a ***** guy, not that it matters, but industrial has more valves, types than commercial stuff.
System R22, some copper, some steel pipework, hot gas defrost.
We had to pump down one air cooler(evaporator), valves in roof space.
He isolated a stop valve downstream of a non return valve on copper line.
Pipe hydrauliced & burst open, losing 1000kg R22.
No internet back then, I new what happened (because smart ), others thought faulty copper tube.
So faulty copper tube, replace, client happy, thanks for coming.

Another job, also R22 liquid overfeed, same situation as Josip, no relief on pumped liquid line, plant in commissioning stage, turn off come back tomorrow.
Arrived back on site next day, all ok, but pumped liquid line pressure gauge very high pressure, I think needle went around twice on high pressure gauge.
I quietly soiled myself, but at the same time thought I must have done some good steel to copper welds, as did not burst.
Forced open bypass valve, adrenaline pumping, all good.
From then on install relief valve on pump liquid line.
In this case a bit harder as in Russia, travel to site, start pumping down, wait for local pressure welder, turns up drunk, can't wake him up or get any sense out of him.
Many hours later, line welded in, happy days, sorry to bore you

[cricri]

Hi to all,
Sometimes trapped liquid kills.
I had two experiences with that.
One in La Guadeloupe, a maintenance engineer was going to clean a filter on an ammonia pumped liquid line. Closed the valves and using the drain valve ‘’drained it’’ an started to warm it up.
Then the threaded cap was blown out and the guy killed. We had to send there an experienced technician with a new filter to restart the warehouse plant locked by the autorities.
A second one in Brest on a reefer vessel. We had to send there two FSE and two pipper welders for repairs.
It was again a question of R22 filter fitted to a pumped liquid line. The ship was loaded of thousands tons of frozen chickens. After repairs I had to assist the prosecutor.
Two Polish crew members died and one was badly intoxicated when he tried to resue them.

What appened is. During the cleaning of the filter done many time a day due to water contamination of the system the two poorly trained guies closed the valves ans warmed up the filter. One of the valve spindle came accross the valve cone and when they started to remove the cover they suffocate and died in the ship bottom. The entire R22 charge was lost.

The repair had to be done under breathing apparatus with the support of firemens and their air bottles charging station. One day with breating mask was a long day for our 4 technicians!.


So take care of trapped liquid !

[Tycho]

Closest I've been, me as an apprentice along with an engineer were doing something on a plate freezer, don't remember what.

But for some reason we had closed the suction and overflow valve, leaving the liquid open and the refrigerant pump running.

After a while I noticed a tiny jet of liquid coming from a weld in the aluminum plate.

he was standing next to me so I tugged on his sleeve and casually pointed at the spray of R-22.

I've never really seen anyone turn that color of white that fast before or after.

The hand wheels were taken off the suction valve, and he grabbed a monkey wrench and hung from it, jumping up and down without moving the valve, in the end there were two of us hanging from it to get it moving.
The flow was towards the seat (correct way) and when we finally managed to get it half a turn open, the whole valve manifold was vibrating.

The needle on the pressure gauge had gone past the stopper and bent, showing 1 bar, and it didn't move at all as the pressure came down.

The leak on the plate was repaired with a punch and a hammer. I checked it on every service the next 10 years and it was all good

I'm glad I was too inexperienced to understand what was going on at the time