Liquid Thermal Expansion causing leaks 3

[slickstyles5]

Hello,

I have a pipeline of fuel which is currently leaking and I am suspecting that it is due to thermal expansion. I have a section that is closed between two ball valves and then then the ambient temperature increases and the pressure increases to the points where leaks are caused.

I'm assuming the easiest solution is a hydraulic accumulator. Are there any other alternatives?

ps. I need to keep the liquid in the line, so a pressure relief valve is not an option.

Thanks

Gabriel

 

[Jmoore1]

thermal expansion of the pipe will not increase pressure within the system, only increase stress on the material. And if your increase in temperature is due to ambient alone these stresses would be quite small.

Whats the process conditions, fluid etc.... this could be one of many different things.

 

[slickstyles5]

The system is a closed circuit, and if the ambient temperature increases, the fluid pressure within the closed circuit will also increase. The fluid is jet fuel and is not compressible.

 

[Jmoore1]

Ah I see...you could have regulator that vents to a small drum that would basically act as a pressure regulator for the system.

 

[ash9144]

Yes material closed between two valves can heat up and begin to leak at flanges or other connections. You could put in a relief valve or regulator with a small discharge that relieves back to the supply vessel. Or clear the line prior to blocking in.

 

[CastMetal]

Most likely impractical due to air entrainment and being active vs
passive but at least an alternative. Also assuming the fluid past
the second ball valve is discharged.


What about a third ball valve? Close the loop as usual then close a
third ball valve beyond the second then reopen the second ball
valve. Lower initial pressure lessens thermal effects.

 

[SNORGY]

Might be cheapest and possibly effective to expose the pipe (if sheathed or insulated) and paint it white.

Regards,

SNORGY.

 

[ione]

A typical jet fuel coefficient of thermal expansion is approx 0.00099 per Celsius degree. This means that a temperature increase of 30 °C will lead to a 3% volume expansion.

Now you can:
1) Prevent thermal expansion keeping the fuel temperature increase as low as possible

2) Consider an expansion tank that would accommodate the expanded volume

 

[BigInch]

Thank You ione. Yes,

Jmore1, thermal expansion of both the jet fuel and the pipe will result in a pressure increase, because the expansion modulus of the jet fuel is greater than the pipe's increase in volume for the same temperature difference and the jet fuel's bulk modulus is high, resulting in great pressure increases with only a very small amount of compression of the jet fuel.

galeblanc, all fluids are compressible. In fact everything is compressible. Ask a rock that is 20,000 feet below the Earth's surface, a piece of steel in a bridge pier, or what was 1 cubic foot of seawater at 0 MSL when it finally gets down to a depth of 5000 ft.

What is needed here is in fact a code required device known as a thermal relief valve that is needed whenever fluid in a closed off space (trapped between two valves, etc.) can become heated, when due to ambient temperatures, or emergency conditions, such as fire, arise.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[willhammett]

I agree with ione and biginch, either an expansion tank or modified "seal pot" type device(with vent back to supply). However, biginch, although fluids are compressible, I have to disagree with "all fluids" being compressible. Liquids are only compressible to the absolute slightest degree physically, yes(assuming ideally closed system). But in this application, its way more than negligible.

 

[BigInch]

willhammett, you were doing better than just fine until you decided to disagree about the all fluids being compressible thingy, then things turned totally pear-shaped. Ignoring the matter of degree of compressibility, or how compressible a fluid might be or not be, or if its compressibility actually makes a difference to your calculations or not, and if steel is compressible... right?, why would you think a fluid (any fluid) is not.

But OK, I'll bite. Which fluid do you think would be an example of your noncompressible theory? Be sure you know the value of its bulk modulus property before answering.

Is the bottom of the ocean open or closed? Open or closed doesn't matter, only thing that matters is if there is pressure or not and how many significant figures is important to you.

If water didn't compress, sound would not travel through it, but we all know that water manages to carry sound 6 times faster than air. How far away can you hear the engine coming when you put your ear on a steel railroad track.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[ione]

willhammett,

I agree there are cases where liquids can be considered not compressible, and this implies a certain degree of discretion, which is related to “engineering sensibility”.
Anyway I think this is not the case. I think it's worth the effort to take a glance at the FAQ below

http://www.eng-tips.com/faqs.cfm?fid=1339

 

[davefitz]

Whatever the piping code requires would be a starting point, and it might not require the use of a thermal relief valve- such items are required on "pressure vessels", but some piping codes do not treat pipelines as conservatively as do pressure vessel codes. But the original suggestion to install a compressible bladder is not a bad idea.

So either a thermal reilef valve discharging to a storage tank or use of a compressible bladder may be the way to go.

 

[hydtools]

Would not a vertical piece of capped pipe act as an expansion chamber. Like a water hammer absorber for lack of a better description.

Ted

 

[slickstyles5]

hydtools, yes that was another alternative that i considered but i will most likely opt for an accumulator with a precharge pressure slightly above the max operating pressure. in this case, in normal operation i guess the fluid won't go up the pipe? (sorry if its a stupid question)

biginch, a thermal relief valve is installed in series or you have to install a tee and then link it back to the tank? doesn't it act as a pressure relief valve? do you know of any manufacturers? i am looking at a pipe size of 1-1/2 in. with jet fuel in the lines.

ps. i did some calculations and it's pretty crazy that the pressure rises significantally with an increase in temp. just 2 deg F, will cause an increase of pressure of 180 psi, and 20 deg F will cause an increase of 3600 psi. i didn't think it was that big of a pressure increase. it's no wonder that everything leaks.

 

[BigInch]

Ladies I give you B31.3 p 301.4.2
Fluid Expansion Effects.

Provision shall be made in the design either to withstand or to relieve increased pressure caused by the heating of static fluid in a piping component. See also para. 322.6.3(b)(2).

A vertical piece of capped pipe, or any capped pipe, is capped or otherwise closed off, ie. isolated by being trapped between two closed valves, etc. and thereby also presumedly subject to fluid expansion and subsequent increased pressure and even if the capped portion of pipe was filled with vapor (saturated vapor in equilibrium with the fluid below) and the fluid expanded into the vapor space thereby only compressing the vapor, then the pressure would still reach that of the saturation pressure at whatever temp the system had at any given moment, which, if higher than the design pressure, must be relieved in accordance with the above clause.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[BigInch]

opps

622.6.3 b-

(2) For a liquid thermal expansion relief device
which protects only a blocked-in portion of a piping
system, the set pressure shall not exceed the lesser of
the system test pressure or 120% of design pressure.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[slickstyles5]

On a similar topic... The use of a single block & bleed valve only provides a way of isolating the system and incorporates a port to vent trapped pressure? Since this is jet fuel, it would have to be sent back upstream where an open circuit is present and the pressure can be relieved. I guess it comes to the same as installing a tee with a pressure relief valve that sends back upstream in case the pressure increases too high above design pressure.

What about a double block and bleed valve? Would it be useful in our case?

 

[BigInch]

Yes its common to vent the thermal reliefs across a block valve to a line that connects onward to a main pressure relief going directly to an oily water sump or some other approved point of disposal. But not across a double block and bleed as those are usually reserved for guaranteeing products do not become contaminated by one leaking across the valve into another product.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[ione]

Can't see the need of a block or double block and bleed valve. A thermal relief valve, which is basically a pressure relief valve, does the stuff you need. Check standards API 520 and API 521.