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Cleaing Force Ratio - Pre commissioning

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Ebyate

Ebyate

Mechanical
Jul 27, 2016
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We are carrying out air blowing with Quick valve opening in the piping system. We fill the line to 5 bar and then open the valve. Now client is asking to show the CFR calculation to ascertain the force is adequate enough to clean the line.

While reviewing the CRF equation, it is flow rate applied versus the operating condition. As the service of the line is fuel gas and in the line list operating condition given is 0.3 bar with a density of 1.5kg/m3 and no mention of velocity nor flow rate. Could anyone advise on how to carry out calculation.
 
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You could make anything up as this is all rubbish.

Whoever came up with this ridiculous "calculation" needs to be put inside a large diameter pipe and be shot out of the end.

I've come across "explosive" cleaning only once and it didn't work. Sure it blows some dust out and looks impressive, but the velocity at the other end is virtually nil, so 50% of the dust or dirt stays in the pipe.

The way they did it on me was use a "bursting disc" - i.e. some cardboard - and sandwich it between a flange, pressure the pipe up until it went "BANG". First time it happended I jumped to the ground thinking something had blown up.

Maybe the client is having a laugh at your expense??

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Ok, I'll take that back - seems to be a "thing", but I still think it's not a good or safe way of cleaning pipes.

The ratio you refer to seems to be mentioned / calcualted on pages 9 & 10.

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What we do is typical to blow disk but here we use QOV (quick opening valve) and run the operation couple of time till no dirt is obtained. The only calculation they are looking for is to understand is the pressure applied is sufficient enough.

 
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Crf formula = M^2(blow)* Volume(blow) / M^2 (design) *Volume(design)

Diving the pressure would not be same as the flow in piping reduces with increase pressure.

It basically to compare the flow rate
 
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Isn’t the volume of the system fixed? So, Vblow = Vdesign.

Then M is proportional to P[sup]1/2[/sup] or M[sup]2[/sup] is proportional to P.

So Pblow / Pdesign.

Good Luck,
Latexman
 
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Latexman, they use what they call "specific volume" with units of ft3/lb. Which implies they are looking at the inverse of density and hence pressure comes into that term.

I can't really work out what they are measuring here to be honest.

This document is also 30 years old!

Ebyate - Any reason why you can't just pull a swabbing pig through the line, or a foam pig or something?

but look at the pressures they were using in table 2 - 800 psi down to 650 psi by pressuring up a large vessel (the steam drum) and then letting it go for several seconds.

So what they are doing is more akin to what I would call a blow through. What I think Ebyate is doing (more details?) is simply pressurising a section of pipe and then letting one end go pop?? That's not the same thing. So ebyate - what exactly are you doing?

Also without a working flow rate you won't get anywhere.

but I would stick a filter on the end of the pipe before whatever the fuel gas is supplying.

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We are doing typical to what you mentioned pressureize line and blow it off.

As it piping, we can't run a pig due to tee and short radius elbow. Generally all piping are typical air blown to remove dirt or particles in the line.

What can be inferred from the equation is that when the line is air blown higher than the normal flow rate, any particles even if left inside will not travel that could damage the internals of any equipment.

It is a general particle to air blow the line at 5 bar. It also needs to be shown by calculation that exit flow was much higher than the normal flow and by that it can be confirmed that 5 bar was adequate.
 
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Ebyate.

The difference with the document and the your description is that is was a blow through, i.e there was a large pressure vessel at one end and then they opened it up and blew the dust / dirt etc out. for 15 to 20 seconds.

What you have is a closed in pressure vessel (the pipe) and so all the dirt at the far end doesn't move because all the velocity is at the far end and last a few seconds at best.

Like I said, it looks impressive and everyone will swear it blows all the dirt and dust out - but it doesn't.

Toi do the best you need to it from both ends alternatively or just find a large pressure vessel and attach it at one end and then blow the dirt out in a more continuous fashion rathe than the explosion you get now.

either way, there is no calculation.

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The point is that it isn't the same because there is no big pressure vessel at one end, only a closed in pipe which they evacuate the air from one end very suddenly. So the dust and the dirt in the last ~third of the pipe gets blown out, but the rest remains. Whereas these steam blow / air blow things pump up the PV at one end and then flow the steam or air at higher than normal velocity for several seconds to literally blow through all the pipe at a steadily increasing velocity, but all the pipe see some level of sustained air flow.

This pump up the pipe with air to 5 bar and let one end go BANG thing is something completely different. Looks impressive and may be the best you can do, but it doesn't clean the whole pipe and hence you need to incorporate filter changes or commissioning filters to catch the rest of the sand / dirt / weld slag /weldolet cut out coupon / bolts / dead rat / water bottles/ plastic bags / welders gloves / fence posts (really) etc.

The last site I was a few years ago used this trick, but in the commissioning filters we thankfully installed before the turbines we got all of the above out of the supposedly "blown through" piping. The fence post turned up inside a large scrubber and could be heard banging around inside it until we blew it down and retrieved it and other debris.

We went through a few filters as well. A couple of them collapsed.

Most commissioning personnel will have seen something similar.

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LittleInch, I agree with you. But we are not decision makers here. They may even realise that 5 bar source pressure may not be enough for the blow-off by considering CFR values required in case the pipe length is not short enough.
In early days steam blow-off contractors used to provide at around 30 degree angled pipe at the end of the piping with provided adequate supports during blowing. I even have a video about it but I cannot leave it here. The angled pipe end open to atmosphere. However the blow side was emptied for debris for safe process. This can be done here too, but location should be adequate. Otherwise a debris collection and vent chamber is required as you mentioned. Additionaly, this process will take some time, and a silencer may also be required on the vent line.
 
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I think this is more like what he's talking about with a valve. note the opening is slow motion.
I think some of the apparent "dust" is actually water vapour dropping out of the air after sudden de-pressurisation / cooling.

Look, it's better than nothing, but it isn't scientific and it won't clean all your pipe.


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Also: If you get a response it's polite to respond to it.
 
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