Air In Leakage

[marada93]

I noticed that while condenser vacuum is normal, my air in leakage detector is indicating 12-15 SCFM of in-leakage. This is roughly three times higher than normal.

All the routine checks for the source have turned up negative.

What I'd like to know is, whats the best way to look for air in-leakage? I've tried ultrasonic sensors. The results were ambiguous at best.

Thanks in advance

 

[pablo02]

We used to use refrigerant gases and an halogen leak detector (at the SJAE discharge)-- we no longer use that procedure... we also tried the ultrasonic method and quickly abandoned it...

We tried to use a couple of methods in tandem -- 1) used a small plastic squeeze bottle full of condensate and squirted valve packing, etc. to see if the condensate was sucked into the system.

2) used a helium leak detector (replacing the halogen leak detector) and then released minute quatities of helium near those areas prone to air-inleakage -- use of the helium had to be miserly in that it easily overloaded the detector and it took a while for the leak detector to return to "normal" it usually takes two people who are diligent and not in a rush...

 

[ilan7]

The only way we were able to find leaks at vacuum condenser is by shutting the system down, put the max. allowed gas (air)pressure and search with soap-water for bubbles.

The other way leaks were detected, is by the signals of dirt at the leaks area. Our steam is not clean but always have some traces of H2S or others, and where the air is leaking in the steam and gases are snikking out and after few days or weeks leaving footstep at the leaking area.

 

[Romefu12]

Marada33
There is an old fashioned way of detecting leaks in vacuum systems. Find you a smoker (the kind that bee keepers use) and use the bellows to pump small amounts of smoke around your seams, valve packing, pipe flanges etc. I have seen this method work successfully in many powerplants for finding various sizes of vacuum leaks.

Romefu12

 

[marada93]

Thanks to all for the usefull suggestions. We just finished a turbine major overhaul. Went down with 5 SCFM, and up to 15 SCFM when we got everything back together. You know how it goes sometimes...

 

[pablo02]

After a turbine overhaul is tough -- verify that the shells had been blued and you had good surface contact before torquing the studs... make sure the steam seals are working properly, check the lead diaphram to make sure it wasn't cracked or slightly cut by the knife edges, make sure the man-doors were properly sealed and tightened, verify the small ports for measuring rotor location were properly sealed, verify the vacuum breaker is sealing properly, etc.... there a long list..

typically, you should be able to ignore those items that weren't worked on... best of wishes...