We are about to carry out tightness

[NiravK]

We are about to carry out tightness test of a Diesel Hydrotreater reaction section for newly constructed plant. The op.pr. is 125 kg/cm2 range.

To carry out tightness test of this system with NITROGEN, Make-up gas and Recycle gas compressors can provide max upto 42 kg/cm2 g pressure because of constraint on discharge temp with higher disch. pr. The valves on compressor for nitrogen service are also not designed for higher pressure.

We are planning to carry out tightness test with Nitrogen upto 42 kg/cm2 g pr. and then inject Hydrogen to carry out tightness test upto about 100 kg/cm2 g pressure.
However, our client is asking us to carry out tightness test with NITROGEN only up to 100 kg/cm2 g pressure which is not possible with the compressor in the plant.

I would like to know if someone has an exp for carrying out tightness test with Nitrogen only under these conditions. Is it really required to carry out tightness test above 42kg/cm2g pr with nitrogen?

Thnx in adv.


Nirav Kholiya
nirav-kholiya@enc.ltindia.com

http://www.lntenc.com

 

[aybee]

I am glad I live a long way from this plant. This is a high pressure (in my opinion) to be carrying out a pnumatic test. I would avoid it if possible, and use Diesel or fuel oil ..I am presuming that this is a hydrotest you are doing and not a sensitive leak test. If its a sensitive leak test I would opt for a lower pressure using helium....maybe more costly but lots less dangerous

 

[NiravK]

Thanks for reply Aybee,
I am not talking about hydrotest. The hydrotest was done during mechanical works.
At present, we are talking about the 'leak test' of the system before commissioning. As you said, helium would be the better choice, but we don't have provision for that as the quantity of the gas required will be huge for the entire plant.

 

[bmoorthy]

I think using Hydrogen is not a great Idea. Secondly if you are checking the leak tightness of the whole system (All items in one stroke) you have a problem for gettig the required volume of inert Gas. Why don't you split your test scheme so that you are able to check in sequence and use the inert gas.

You are constraining yourself by using available resourse. You may hire a compressor to suit your pressure that is if the test is specified in your Purchase or contract document.

I suggest you make a detailed test procedure and get the same approved by local safety body and your consultant before venturing into such high pressure test.

Why don't you reason out with your process licensor and consultant and try offering Vacuum testing instead of High pressure test or other NDT leak testing methods.

How do you intend to check the leak?if there is a leak. Soap solution at each joint? At this pressure you're mentioning you're sure to miss any leak as the solution would jet off. Do you intend to check the raise or fall in pressure. If so then it is not leak test.

As per general engineering convention Leak test are generally low pressure test.

Any way i would be glad, if you let know as to what you did at the end.

Good Luck

 

[22082002]

Nirav,
After reaching 42 kg/cm2g pressure, you can inject Nitrogen from HP Nitrogen cylinders.... and I am sure you won't need many cylinders...

Before pressurising with Nitrogen, ensure that vacuum is held for atleast one hour(I am sure you're talking next step of this but...), there should not be any increase in pressure.

Once Hydrogen is put, it being smaller atom, it is possible that you will have leaks.. some can need even replacement of flange-gasket. Hot bolting(brass spanners,spark proof/pneamatic spark proof) is solution.

And be prepared for surprise leak when after no leaks were found (even during the course H2-pressure leak test and startup circulation) the moment you put oil in the reactor circuit. We had fire from CFE's at this point... !

All the best..
SAA

 

[bmoorthy]

So, it appears, it is an established norm to carry out such high pressure test by inducing H2. This is really new to me. There has to be some approved document based on some safety standard or local law, could some one give further information