Hydrotesting and Structured Packing

Firstly let me make it abundantly clear that I am not an "authority" on this extremely important subject.

Having said that, I can see no reason why it should not be acceptable to pressure test without removing the packing. I also can not see what effect this pressure would have on the packing.

What I would question is the reason for doing the pressure test. Pressure testing is normally carried out "after damage has been incurred or after repairs or modifications have been completed" (API 510)

The questions that I would have would be;

• what degradation mechanism has occurred that gives rise to the belief that a pressure test is necessary
• has a fitness for service evaluation been done as per API RP 579, or
• RBI as per API 580
• can the supporting structures withstand the load of a hydrostatic test

If none of these things have been checked (and they may well have been), then how do you know that it is safe to pressure test the vessel.

Pressure testing should not be used instead of all the other available inspection techniques.

Dear Guest,

Thank you very much for your reply and some very pertinent points you raised

• The vessel in question is at an offshore platform and as you rightly said,the supporting structures needs to be evaluated whether it can withstand hydrostatic load.
• No fitness for Service evaluation / Residual Balace life study has been undertaken so far
• The contactor handles sour gas ( H2S : 100 ppm CO2 :6% ) and needs to be internally inspected to satisfy facility recertification/ auditing requirement

Being a ASME U stamped vessel,i think we need to hydrotest once the vessel is opened up for inspection or else it cannot be re-stamped.

Thank you ,once again and best regards

<...need to hydrotest once the vessel is opened up for inspection or else it cannot be re-stamped...>

If the vessel is designed to be opened up and the inspection can be carried out without modification to it then there would be no need, in principle, to hydro-test it apart from looking for leaks at the surfaces that have been opened and re-sealed. If there is no need to hydro-test then there is little point in getting the vessel re-stamped.

yes ,why not

I was Guest # 1 - was not signed in.

RBI = Risk Based Inspection.

I agree with PW that you would probably not need to re-stamp, but take note of the quote from API 572 below and check the vessel code to see if pressure testing at intervals is required. (Again - I am not an expert, so please listen to an "authorised pressure vessel inspector" - at least now you can argue with him).

API 510 - extracts:

According to this, the material is a solid, so the effects of pressure on it should be negligible. The manufacturers can be contacted directly for further advice using the contact details within.

It is to be studied whether the water entrained in the packings will affect the process later after commissioining

I agree PWSlack and The Prof perfectly, where there is no need to hydrotest unless there is such a repair, alteration or rerating per the code which need a welding work directly to the pressure parts. And even you installed the packing, the vessel can be hydrostatically tested, unless the liquid of test or its traces have a pad effect on packing or any other chemical components inside the circuit under test, in this case you can apply a pneumatic test in lieu of hydrotest as per ASME code.

Thank you very much for all your comments to my query.

This happens to be my first posting on the site and your comments has given me something to work on.

Best regards

Dear sirs, I performed that kind of test in the past. I do not want to discuss neither the opportunity to do the test (I do not know) nor the coherence with Codes: only the technical point of view. 1 - It is possible and we do this 2 - With water and such a very large surface it is mandatory to examine the possible reaction of metal (you didn't specify the type) with water and with ions into the water (for example inox packing is sensible to pitting corrosion). 3 - Be careful and examine the possibility of damage of supporting grids in case of too fast depressurization and packing partly dirt. Sorry form my bad english Please tell us the end of the story...