VALVE TESTING

[GAL02]

Dear all, Good morning!
Regarding the subject matter I have check valve 12" & 6" 2500 Class (Swing type)
on Sy.Gas Compressor discharge line.
According to the API 598 allowable passing (Leak) rate is 0.25 M3/Hr.
As we test 6" valve it was on the threshold of allowable leak rate but continuous passing.
In view of above is it acceptable to take it in line? (Resolving matter of compressor reverse rotation)
Pl. advice.

Thanking you!

 

[Danlap]

Dear GAL02,

There are two approach:
a) Seeing this condition from valve perspective only
- If this 6" Check valve is new or refurbished as new, and you're using API 598 as your governing standard. Then it is not acceptable.
- If this is a used valve, and leakage rate is at the threshold. And nobody have any idea or solution to make it within the tolerance, then used the ALARP analysis. IMHO, it is acceptable and quite normal for Swing Check valve to have bigger leakage rate

b) Seeing this condition from your system point of view.
- From logic point view, your system should consist Compressor - 6"/12" Check valve - 12"/6" check valve - and Block valve. CMIIW
- Check valve is back flow preventer, and does not recommended to be used as Block valve
- There is a volume between Compressor and your Check valve which allows enough time for your Operator to either Close the Block valve or other means to prevent the pressure built up to reverse turn the Compressor.

The back flow (with pressure) should encounter the 12" Check valve (with acceptable leakage rate) and then the 6" Check valve (with descent leakage rate) and then volume to fill. Before the pressure built up able to reverse flow the "High pressure" compressor.
It is an unlikely scenario, unless the Operator doesn't do anything by means of closing the block valve or drain the pressure built up

Regards,
MR

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

 

[GAL02]

Dear Mr. Danlap, Good afternoon !
As you said these valves (New)are in yard for last 30 years and we want to test it before we use it on system.
6" valve having metallic seat & leak is at @0.25 m3/hr. but continuously not holding the pressure at any moment.

Your concept of Comp - Check Valve (12 x 6) - (6 x 12)check Vale - Block Valve are point of concern for Operation & Licenser.

Pl. find herewith P&ID for the system for any corrective measures.

With regards

 

[Danlap]

Hi GAL02,

The P&ID is not clear,
Not judging, however in my view its not fair to burden (the potential) back flow by means of 1 Check valve only between the vessel and Compressor.
Nonetheless, some people who design this 30+ years ago may have a good reason / confidence that it is unlikely to happen. I see many branches in/out the vessel, so there is a good chance it would borne by the 6" itself at full pressure.
30 years Swing check valve with that leak rate is already amuse me. Suggest to repair/lapping it, and if not possible (due to seat/disc deformation beyond repair OR not enough time) I am almost sure that it would not cause problem to the compressor. But then again, I am not a process/rotating person with detail exposure to your component.

Regards,
MR

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

 

[GAL02]

Dear Mr. Danlap, hi!
Licensers design can't be change but by MOC we can push the matter ahead.
We are looking forward to repair these valves, hopefully it will give better results then.

Thanking you.

With regards