Expander-compressors pressurized oil system, Gas leak test required ?

[Matchess]

Hi all,
I design a pressuriez oil system for an expander-compressors (acc. to API614 firth edition annex G & API617 Part4)
The operating pressure of the oil tank is > 60 barg with flammable gas.

The design pressure of the seal gas oil system and compressor/expander/bearing casing is > 90 barg

Following the performance test is it mandatory/recommended to do a Gas leak test at 90 barg (with N2 for exemple) on the Whole system (oil, seal gas, and casing line and tank) ? or is it only required for bearing and expander casing.
The API617 is not clear for PRESSURIIZED oil System ?

"API 614 Part 4-Expander-compressors
6.3.4 Assembled Machine Gas leakage Test
6.3.4.1 After the mechanical running test is completed, each completely assembled machine casing
intended for toxic or f1ammable gas service shall be tested for gas leakage. The assembled casing shaH
be pressurized to the lowest of the expander or compressor casing MAWP, held at this pressure for a
minimum of 30 minutes and subjected to a soap bubble test to check for gas leaks. The test shall be
considered satisfactory when no casing or casing joint leaks are observed.
NOTE These tests are intended to verify the integrity of the casing joints."

Regards

 

[machineryguy007]

My understanding is that gas leak test is applicable for gas section i.e only for expander .

In mean while, I have another question on API 617 annex. 4G - Lubrication and Sealing Systems.
The Gas recovery line from Oil tank vent to the compressor suction size does not specifies the limit on the allowable contents.
Does anyone aware of any guidelines on allowable oil content depending upon services such as flammable, hydrogen gas expanders etc.?
Oil tank does has some kind of mist eliminator, but is it enough for critical application where compressor gas purity is important?. Do we need to consider additional filtration ?

Thanks in advance.

 

[georgeverghese]

IMO, if your expander is running low temps, it is a bad idea to send this oil tank vent back to compressor suction - it will be high in fine oil mist which will contaminate the gas stream and may poison any intermediate treating chemicals ( like mole sieves or alkanolamines / TEG etc). Better to dump this vent stream to LP fuel gas or similar.

 

[machineryguy007]

Yes, it is cold service H2 expander service, hence there is concern.
I am looking for some industry guideline/practise.
Basically API is silent on this point,so i am thinking what could be the scheme for installed expanders(oil type) with simillar application where contamination of compressor gas is not acceptable or acceptable with some very defined low level of oil.
any experience on such industry application may help to guide.

 

[georgeverghese]

Have my doubts if there is an engineering guideline on this - to me this is a simple precautionary process design measure that a process engineer would take to avoid operating problems.