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 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 under these conditions. Is it really required to carry out tightness test above 42kg/cm2g pr with nitrogen?

Thnx in adv.
Nirav

 

[ixchawla]

Dear Nirav,

I think you are talking about the leak test, correct me if I am wrong. For leak tightness, its a usual practice to test with a gas, say nitrogen with available pressure to find major leakages. Once the hydrocarbon gas is available at operating pressure, the test is repeated to find out any leak missed out in the first test. In your case, I don't think it is required to leak test with nitrogen at 100 kg/cm2g, as most of the leaks will be detected at 42 kg since gas has low viscosity and can escape easily.

Regards,

 

[quark]

Though I don't have experience with the system you told, I strongly suggest checking the system at higher pressure. Ideally, it would be the operating pressure or 10% more. What is the total volume of the system? Why can't you use Nitrogen gas cylinders? They are at 150 Kg/Cm[sup]2[/sup]g pressure generally.

If you check the pressure drop at the operating pressure, you can exactly quantify the leakage. You can also extrapolate the values at lower pressure but tesing at higher pressure is a good idea.

Regards,


Believe it or not : A Neutrino is so mass less(and electrically neutral) that, a conservative estimate states, it can pass through a 50 light year thick lead block.

 

[NiravK]

Thank both of you.

Yes, ixchawla. I'm talking about the leak test. In our other hydrotreater units also tht we supplied, the leak test was not carried out beyond compressor capacity.

The test by using cylinders is not feasible because of huge volume of the entire plant.

thnx again.

Nirav Kholiya
nirav-kholiya@enc.ltindia.com

http://www.lntenc.com

 

[FRChem]

From operating point of view, the hydrotreater (similar to any other high pressure system, e.g. hydrocracker)is pressured to acheivable recycle gas compressor discharge with Nitrogen, in your case 42 kg/cm2g range. However, during plant start up pressurizing is carried out slowly and gradually by the normal rich hydrogen process gas with stand by maintenance crew ready to deal with any flange/valve leak. This is assuming that all inspection testing such as X-ray/MPI/PT have been fulfilled as required.

Regards ,

 

[lubes]

I would add that you need to make sure you have heated up your system enough so that you are above the Minimum Pressurization Temperature for your system, before you start increasing the pressure. As our colleague above said, it is critical that you perform your pressurization in a stagewise manner. Do not go all the way up to 125 kg/cm2 without performing intermediate pressure checks, especially if you are dealing with hydrogen. Be aware that hydrogen gas has a lower Molecular Weight than nitrogen, therefore hydrogen leaks are more prone to happen than nitrogen leaks(H2 leaks are also easier to be detected, unfortunately H2 is pretty explosive stuff). Also, when pressurizing up with hydrogen, make sure your reactor bed temperatures are not so high that you reduce your HDT catalyst. This is a real risk and you dont want to kill your catalyst before you start. Get some operational guidelines (if you have not already done so) from the catalyst manufacturer to fine-tune your pressurization procedure.

 

[ixchawla]

Dear Nirav,

Fore safety, make sure that the pressure testing (say hydrotest) has been performed before putting such high pressure gas into the system.