Pin Hole Pipping Leak

[JungleJimTheSecond]

Hi

We currently have a chemical injection system operating at circa 50barg and there is a requirement to increse this to circa 100barg. What I am looking to understand is if there were to be a pin hole / small leak in this system would we expirience choked flow through the leak point?

I have used a simple orifice flow calculation to check what the potential leak rates might be for operating at an incerased pressure but can't seem to find any method for checking if any of these release scenarios will under a choked flow regieme and not relise the max flows predicted. For a gas system we would look at critical flow.

Any help would be appreciated

 

[IHQ22]

The way I would look at a pinhole leak is using the formulas available in Cameron Hydraulic Data under Flow Through Orifices and Nozzles which I think you did and use the results as the worst-case scenario.

 

[EdStainless]

Until the hole got very large it would be choked.
To be honest if this were a small leak the flow won't be different from what you have now.
Unless of course the higher pressure opened a new hole or made and existing one worse.

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P.E. Metallurgy

 

[ChEMatt]

Look up choked flow. Lemme see if I can find a link:

Choked Flow of Gases

Is that what you're looking for?

-Matt

 

[LittleInch]

A liquid choked flow is all about whether the liquid vapourises in the vena contracta.

When it does you're basically at critical flow. However this is not easy , as afar as I can tell, to determine.

Also certainly for control valves the increase in P1 ( upstream pressure) can impact the flow rate.

See things like this

https://www.emerson.com/documents/a...ng-choked-flow-in-fisher-valves-en-122950.pdf

I am struggling to know though why you're trying to do this? If you have a leak, shut the system down and fix the leak.

You will never be able to determine the size of the pin hole and in any event the hole tends to get bigger dur to erosion of the pipe so will increase over time.

Also I'm really not sure if pinhole leaks and orifice calculations are one and the same thing.



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[JungleJimTheSecond]

Hi All

Thanks for the information above

We do not currently have a leak and the question is related to the potential ability to ignite the chemical under a jet release scenario. Currently testing has been undertaken at 70barg and has concluded that the chemical can not be ignited, nor can it be ignited at ambient conditions.

Given that we are now increasing the injection pressure above the previous jet realease ignition testing, we need to review if the increased operating pressure could allow the jet to be ignited.

Original testing was through a 1.5mm orifice plate and if we can demonstrate that this was under choked flow conditions then we wouldn't require a retest at the higher pressure.

From what I can see I would need to know the critical pressure of the chemical (P[sub]C[/sub]) in order to calculate F[sub]F[/sub] which we don't have for this chemical. So the easiest option may be to retest at the higher pressure.

 

[LittleInch]

I think you're correct.

It would be good if you could do this and let us know the results once you've done it.

Posts remain open for about 6 months.

Not sure why if the jet couldn't be ignited before why it might at a higher flowrate / pressure, but if you need to test it to be sure then go ahaead.

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

 

[Compositepro]

If the liquid has a flashpoint, it will burn if turned into a mist or on a wick, and there is a source of ignition.

 

[Iomcube]

there are some gases which have a -ive JT coefficient. In our chloralkali industry small leak in H2 CS lines easily created fire which looked like tiny flares at night