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Pressure build up in a pipe system containing solvent

Pressure build up in a pipe system containing solvent

(OP)
Ok, having a bit of trouble here. there seems to be a gremlin in a system at work that is causing a pressure build up but we cannot find the cause.

in essence, the system is run off a huge vertical storage vessel, the solvent is pumped out via a pump at approximately 40psig. This then feeds two dispensing guns, 4 large mixers, 5 washers and a dispensing room with three outlets. The pump is only activated when a dispensing point is operational, and stops as soon as operations cease. The issue at hand is that there is a large pressure build up, intermittently, of up 150psig. Enough so that it can blow through a dispensing guns trigger operation.

Im looking for any help or ideas at what could cause such a build up within this kind of system and to this magnitude. Any ideas are welcome and happy to explain further details if you need more information.

thanks

Sean

RE: Pressure build up in a pipe system containing solvent

What is the pump discharge pressure, and the height of the storage vessel relative to the dispensing points when full?

What event/sensor or ?? causes the pump to run?

Are there flow check valves installed, and where are they.

I'm guessing it a positive displacement pump.

Are certain dispensing points more likely to cause the pressure build up?

Regardless, I'd be thinking about stuff like accumulators, pressure relief valves, and circuits to bleed/recirculate fluid from the pump discharge back to the main storage vessel.

6 down, 14 to go.

RE: Pressure build up in a pipe system containing solvent

Is the feed pressure that high? If so, sounds like a leak at the regulator, allowing for the pressure to build up to the main tank pressure.

If the main pressure isn't supposed to be that high, possibly something is allowing the compressor to run unattended, forcing the system pressure to rise.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Pressure build up in a pipe system containing solvent

You really haven't given us a lot to go on here. Initially sounds like thermal expansion or vapour creation but need system details, pump details, any valves, relief valves, sequence of operations. How does the pump start and stop? What is the flow min and max?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure build up in a pipe system containing solvent

Sounds like you have a positive displacement pump which is dead-heading against (hopefully) its relief valve before there is a chance to get the discharge open or the pump stopped. But to help you we need a lot more information about the system, otherwise we're merely guessing.

RE: Pressure build up in a pipe system containing solvent

(OP)
I shall try to attain all the information you're asking for, although you will have to excuse if some of this is new to me as I've only just started at my position here last week and been thrown a little in the deep end.

In regards to the tank, it is its self approximately 5 meters high and operates at atmospheric pressure. the exit to the tank is on the same level at the pump and all the dispensing points other than the 4 mixers which are at about 3 meters above ground.

The pump it automatically operated by sensors and switches, depending on the operation tool. Although this has already been tested and the pump shuts off immediately when operations cease.

I don't believe there are any flow check valves but would have to double check that one.

the pumps are centrifugal pumps that operate at approximately 3 bar and pump at a rate of 12000L/h.

I'll try to get any other information tomorrow (home time for me) and I appreciate the advice guys.

Current theory is possibly water hammer effect that gets "stuck" behind the only NTV which is directly after the pump but its a hard one to prove.

RE: Pressure build up in a pipe system containing solvent

Check all sources of heat rise. you will have an NRV somewhere in the system otherwise the pressure would just go backwards through the pump.

If this issue only arrives when you've got one dispenser running then it might be surge, but only a few degrees C will make a massive difference in pressure.

It could be something like a stretch of pipe is exposed to sunlight at certain times of the day and not others.

You'll need to try and get as amuch as you can from the pople who see it and try and find out what is going on when these pressure spikes appear.

Are they fast rise, slow rise?
How often does it happen?
Can it be replicated?
Try and formulate a set of trials to work out if its surge or temperature.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure build up in a pipe system containing solvent

Why not water hammer? Do the spikes occur when flow suddenly stops? Could some capacitance in the system absorb this?

RE: Pressure build up in a pipe system containing solvent

If you have a valve arrangement such that you have created a closed vessel (e.g. between a pump outlet check valve and closed valves at each of the subsystems that your pipe feeds) and the circumstances are such that the temperature is rising somewhere ... you are getting thermal expansion with nowhere for the fluid to escape.

RE: Pressure build up in a pipe system containing solvent

If the valve at the dispensing tool is closing even a millisecond before the pump stops, you could have an immediate spike in pressure. You're dealing with an incompressible fluid here, right? I would redesign the system so that the pump has fully stopped before the dispensing valve closes. Or let all the dispensing points feed from a common pressurized header, with an accumulator to provide some flexibility. Then the pump would only come on when the pressure in the header drops below a certain level.

I would also strongly recommend installing pressure relief valves throughout the system to prevent potential human injury.

RE: Pressure build up in a pipe system containing solvent

(OP)
All your advice guys is very helpful thus far. I shall be looking into each suggestion to see if it affects the system, although the company recently has a large data storage swap over so getting certain information is difficult, the joys of modern technology.

RE: Pressure build up in a pipe system containing solvent

(OP)
something else I should probably mention that just came to mind. The pressure build up seems intermittent, and build up seems to be slow, and not instantaneous after the line closes. Although this is hard to tell as the hand dispensing points where the problem is most visible isn't used that often, mostly the line is dispensed into closed mixers. While this would suggest some form of Thermal expansion, the pipe goes along the same pipe bridge, and through the same areas as about 8 other pipes, yet only this line has a pressure problem.

Again I know this isn't much to go on, but I'm new in this role and just looking for any spitball ideas that I can look at or test.

As always, I appreciate all your suggestions and advice.

RE: Pressure build up in a pipe system containing solvent

Does one pump feed all 8 pipes from an 8 legged manifold?
In order for just one line to develop high pressure, it suggests there is a check valve somewhere along each pipe, or at least THAT pipe.

If 100% positive prevention of back flow is not needed, a strategically place leak/bleed would prevent pressure build up.

19 down, just 1 to go.

RE: Pressure build up in a pipe system containing solvent

(OP)
Okay, here is a stripped back version of the line. For obvious reasons I cannot include any other information. This is just to give you an idea of the layout of the system. So, you have the two tanks which store the same fluid (used one at a time). From these the solvent is pumped through the two centrifuge pumps (also only running one at a time) to the areas needed. The line (approximately 2 inch steel pipe, with either 3 or 5 mm thickness) goes into a single large building (approximately 75-125 meters of piping in this system from one end to the other) which feeds the four stirrers, 5 washes, two gun dispensers and a dispensing room.

From what I can tell, which is why were having so much issue with it, is that there shouldn't be any way, other than the pumps, that pressure is input into the system. All the washers and stirrers aren't pressurized and the fluid is poured straight in, and all dispensing points are essentially open ended. All solenoids are run on a slow down procedure, which means when they detect that whatever they're filling is reaching the desired weight, they slowly close the valves. The pipe goes over the same bridge as several other pipes, so if there were thermal expansion in this pipe, it would also be in all the others. While there are no relief points, the centrifugal pumps should not be able to pump any more that 3 bar and about 3L/s. These have also been tested and they turn off as soon as all operational points cease using the fluid. The storage tanks are not pressurized either, so the max pressure at the bottom of the tanks when full is no more than 0.5 Bar.

At this point there is no silly suggestions, anything outside the box is welcome. Anything I can test or research is a positive step forward.

Thank you for all the suggestions so far, they have all be most appreciated

RE: Pressure build up in a pipe system containing solvent

Your pipe might be in the same pipe bridge, but you need to check out the vapour pressure versus temperature for this liquid - "solvent" could be virtually anything.

Exposed pipe in the sun can hit 60-70C and you might find that your liquid is boiling, but all depends on what it's physical properties are.

What are those vertical tube like things just downstream of the pumps? and on the lines in the solvent dispensing area? Why is only one connected in a through flow system?

you are only showing one PI upstream of the non return valves. Where are you measuring this 150 psi?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure build up in a pipe system containing solvent

(OP)
The Vertical Tube type things were just pipe identification codes, just removed the codes for this particular drawing. All the lines carry similar solvents across the bridge, but I could request the R&D department to run some tests on the fluid to see if that is the issue.

As for the point at which the pressure is displayed, the Gauge is located at the dispensing gun in the production room. The Gauge hasnt been added to the drawing yet as it was only added fairly recently. But thank you for pointing that out, something I can do fairly quickly today.

RE: Pressure build up in a pipe system containing solvent

Hmmm,

Only thing I can suggest more is for YOU to physically check the entire run of pipes from tank through to each dispensing point using your drawing just to make sure no one has added a tapping point or connected something to any of your blanked off valves. don't trust anyone else with this.

Also figure out how much of your pipework in volume is exposed to any form of solar heating. It might only be 20% of the entire volume, but could easily raise pressure by 7 bar if you get s ay a 20C rise in temperature. Solvents and hydrocarbons in general are notorious for thermal expansion / pressure rise issues.

Find out what it's volumetric temperature expansion co-efficient is. Some typicals for solvents are 0.0015 m3/m3/C. Water by example is 0.0002, so 8 times worse than water.

Try and get a history of these pressure rises to see when they occur and what was happening before and during it.

otherwise just fit a pressure relief line back to the tank or fit a pressure accumulator d/s the pumps NRV set at some suitable pressure which doesn't impact on the D/S equipment.

It could be your system is just new and the non return valves are seating better than any other system where there are few more leak paths.

Keep us informed.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure build up in a pipe system containing solvent

You have not said anything about ambient conditions, solar exposure, nearby heat sources and when (day or night) these high pressures occur. As alluded above, a heat source could be the culprit.

RE: Pressure build up in a pipe system containing solvent

(OP)
Well, we had an "interesting" incident the other day. On of the large machines has some solvent dispensed into it. after which the pressure at the gauge reads an increase of just over 1 bar a minute. within 15 minutes it reaches 20bar. As the pressure is building, I go to check on the pump. As I expected, its off. At the point, when the pressure is 20bar, the dispensing gun is used to relieve pressure briefly, immediately after the build up ceases. We had a second incident using the same machine in the afternoon, as soon as it was done pressure built up (yet the pump was off, and its a centrifugal pump with a maximum output of 10 bar I might add). This time the gun was was used to relieve pressure at 10bar. Yet like last time the pressure stopped building afterwards. Now the machine that "triggered" the events is just an open top mixer, it has no pressure at all and the solvent is simply poured into it.

At this point I have given up trying to find the cause because this system simply shouldn't physically be able to build up 20bar in 15 minutes then just stop. So I've moved onto designing a modification to the system to allow it to be used safely.

RE: Pressure build up in a pipe system containing solvent

It really is time we knew what this solvent is.

Is the solvent stored somewhere that's much cooler than the rest of the factory?

A.

RE: Pressure build up in a pipe system containing solvent

Is there any potential for a bit of backflow from the dispenser and you're getting some sort of reaction occurring inside the pipe which is then limited by the small amount of material either forced back into the mixer pipe or somehow "sucked" into it?

Have a close look at the end of the dispenser - is it below liquid level? Can it get reacting fluid back flowing into the pipe??

Still better to solve this at source, but a pressure relief back to the tank would be a good idea in any case.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure build up in a pipe system containing solvent

(OP)
Zeus, its a in in house blend of several solvents. While it is rather potent, if it was a solvent reaction or thermal one then the build up would be a constant effect. But it only happened after this specific machine was activated.

LittleInch, the dispensing pipe into the mixer is at the top of the vessel, and the feeding pipe even higher. There isn't any way that some other material could work its way back into the pipe by that route. Also it wouldn't explain why the pressure build up suddenly stops when the hand gun is used briefly.

RE: Pressure build up in a pipe system containing solvent

Well it suggest there is something different with this machine or location.

If you only suck in a small amount of material then it will only generate a certain amount of gas which is then relieved as soon as you operate the gun and then there is no more material to create any gas.

It's not easy to guess remotely, but it's all I can think off.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure build up in a pipe system containing solvent

I once encountered a steam system that kept losing steam and condensing even though the pressure and temperature both remained in the range in which we should have had steam. We discovered that one of the tire presses fed by this system had an internal leak (faulty check valve) that was allowing high pressure inert gas (nitrogen) to leak into the steam lines. So the steam wasn't at the gage temperature and pressure. It was at its own partial pressure, and accordingly condensed. Do you have some other higher pressure source of another gas connected to that one machine? If so, you might have an internal leak from one source to another.

RE: Pressure build up in a pipe system containing solvent

(OP)
Okay, so I got tired of all the second hand data and set up a test myself. Two of the 4T mixers would be filled with 1.8T of solvent and the results and data recorded. What I found was that the normally operating machine stopped quietly, as designed. When the other machine stopped, it sounded like a truck had been driven into it. This would suggest that a rather severe Water Hammer would be the issue.

The real question on my mind now is; Why does the pressure build up so slowly after such an immediate event? After the water hammer, I recorded the pressure of the system every 5 minutes for 20 minutes:

0 minutes - 3 Bar
5 minutes - 8 Bar (+5)
10 minutes - 11.5 Bar (+3.5)
15 minutes - 14 Bar (+2.5)
20 minutes - 16.5 Bar (+2.5)

So what do you guys think could cause the pressure to build up so slowly over 20 minutes, rather that instantaneously?

RE: Pressure build up in a pipe system containing solvent

Water hammer isn't going to do that.

There's something else going on that you haven't figured out yet.

What happens if you leave a valve open somewhere? Obviously the pressure won't go up (which leads into the prior suggestions that you've got thermal build-up in a closed system), but how much comes out of that valve and over what time period?

RE: Pressure build up in a pipe system containing solvent

Is the temperature of the solvent increasing during flow?
What happens to the pressure when the operations cease during plant closure?

RE: Pressure build up in a pipe system containing solvent

you've got me stumped at the moment.

It still looks thermal related to me, but maybe there is somewhere a device which is taking out the high pressure then slowly pumping it back in?

I still think you're going to need to physically check the entire pipe run versus your P & ID / schematic to see if anything else is connected to this system that isn't on your drawing.

There is something weird going on here.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure build up in a pipe system containing solvent

Is this solvent reactive with air/oxygen? Is it possible that air is gurgling up the line as the solvent dumps into the mixer, and the air bubble then slowly reacts with the solvent (releasing a gas phase) to build pressure after the valve closes?

RE: Pressure build up in a pipe system containing solvent

Look at the system with a thermal camera or at least a non-contact thermometer. I will bet that somewhere along the way that a line runs next to a heat source. Maybe it's a radiator or just under a sunny window. But the slow climb seems heat soak related.

RE: Pressure build up in a pipe system containing solvent

(OP)
BTrueBlood, the solvent is Butyl Cellosolve Acetate, which I'm pretty sure isn't particularly reactive with air, but its definitely an idea to see what it does react with.

3DDave, Its worth a try, but again the issue is that as soon as the pressure build up is relieved once through the dispenser, the pressure stops rising. A pressure increase from the sun, or some other constant thermal input, would resume after the pressure is relieved.

Furthermore we had another build up last week, completely different machine was used. Over the course of 100 minutes, it went up to 40 bar at a constant gain. When the valve was cracked open the pressure relief, from 40 bar down to 6, dispensed just over 7kg of solvent. Now (if we have a high estimate of 100m pipe with an average of 2 inch dia) that means there was a low approximation of 4% more fluid than there should be (closer to 5% with a slightly more accurate approximation). Which for a line that has an in-compressible fluid in it, is quite high. Furthermore the 40bar reading is simply the limit of the gauge that's on the line at the moment. When we relieved the pressure, in order to prevent damage to the gauge, it was still climbing at about 1 bar every 5 minutes.

I have a few more tests planned out for now, but this issue is just getting more and more peculiar by each passing week.

RE: Pressure build up in a pipe system containing solvent

At that sort of volume it implies some sort of gas production.

The reason it might stop once you relieve it is that once the gas expands and forces some fluid out of the pipe then more gas production has a gas volume to expand into where the pressure rises much slower. Aslo if it is a small section where you're getting heat then maybe it's all evaporated.

I still think you need to run / view the entire line to see if you're getting hot spots (anything over 75C will make it boil) or some strange connection not on the piping diagram.

When you get to this condition, is it possible to start the pump and flush the line through a dispenser to see if any gas appears?

Anyway thanks for the update - too many threads just stop without any further information

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure build up in a pipe system containing solvent

(OP)
Well, we are getting some thermal cameras in for the electrical engineers so could use that when they arrive to look at the line. Although according to the data sheet on BCA, the boiling point 1atm is 184-195 Celsius. So it is unlikely to boil, and 99% of the pipework is visible from the ground so it would be obvious if it went past a heat source that could put that much energy into the line.

Whenever the pressure builds up, we relieve it through the dispenser. As far as we can tell there is not gas getting out.

RE: Pressure build up in a pipe system containing solvent

It doesn't take much. A bud I worked with was with a big aircraft company and he said a bunch of them had a great idea - use self-sealing disconnects to the vertical stab so that the tail could fold (not sure which plane; may have been a military bomber??) without draining, refilling, and bleeding the air out.

So they did all the design work and went through all the budgeting and so forth and got a test item set up. All worked great with none of the draining, refilling, and bleeding they had to do before the self-sealers were used.

Then came the great news. Their test plane had ruptured a hydraulic line in the tail. Without a place to vent expanded fluid, the warmth of the sunshine was enough to exceed the ability of the lines to contain the fluid.

A short time after, when the hurt had worn off enough to talk about it, an old guy sitting nearby overheard the conversation. He said, "Yup, same thing happened 40 years ago when we tried it."

Which gives me an idea. Is the supply tank typically cooler than the rest of the factory? It may just be the cold fluid from the tank warming on the way into the distribution lines. I can imagine a bunch of interactions based on how much insulation there is, how much thermal mass there is, thermal conductivity, and time dependency. It may be that the solution is to warm the tank to close or slightly above the room temperature.

RE: Pressure build up in a pipe system containing solvent

Good thinking. I like that idea. It is difficult to get to the volume being seen but I don't know what the expansion coefficient is of this stuff?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure build up in a pipe system containing solvent

(OP)
It is a good idea, And I shall endeavor to have a look and see what kind of effect it may have.

The solvent is kept in external tanks, so if we say for argument that the temperature outside is 4C, the solvent line is about 60% outside with the tank, the other 40% is inside the factory which is kept at a cool 19C. I personally cant see 15C temperature difference making a 40 Bar increase. None the less, I will attempt to run some calculations to see what I can find.

RE: Pressure build up in a pipe system containing solvent

"the solvent is Butyl Cellosolve Acetate, which I'm pretty sure isn't particularly reactive with air"

Depends on how you define reactive, but it does react:

see https://en.wikipedia.org/wiki/2-Butoxyethanol_acet...
and similar entry for 2-butoxyethanol.

Both will react with oxidizers, and air (containing oxygen) is one such; in the atmosphere, the reaction is catalyzed by pollution (sources of OH and similar radical species). Granted, it is likely to be a slow reaction if at room temperature, since the stuff will not burst into flame with contact with air. Might be worth a small scale lab test: half fill a tube with solvent (the other half being air), then cap it and measure any pressure rise.

Slow reaction in air (vapor phase presumably) yields formates of various types, and some aldehydes (propanal being one, which also has a fairly high vapor pressure), which should be identifiable by a decent lab chemist; if you have such on staff, give them a catch sample from the pressure relief and let them analyze it for those contaminants. From a quick look on google using "oxidation of butoxyethanol" as search term.

I do agree that the bp of this solvent is quite high, and it's unlikely that heat alone is creating a vapor bubble...but if some reaction creates lighter species, and more of them, from single molecules of solvent...well, you get my drift.

RE: Pressure build up in a pipe system containing solvent

Coefficient of thermal expansion of this stuff is 0.0009 per C according to Dow. That's about 4 times water at 20C. Easily enough to get the pressure but not the volume you found.

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