air droplets come out of AA1 drain in frame 6 gas turbine.
How can i decide whether it is condensate or AA cooler leakage?
Is Hydro test of cooler is the only option??

 

There should be a drain with a manual valve on it on the AA Pre-cooler shell. If you're getting lots of moisture out of that you can analyze it to see if it's just condensate (moisture from the CPD) or if it has any cooling water glycol in it (or whatever cooling water treatment is used at your plant).

If it's got cooling water treatment in it, it's a leak of one or more of the cooler tubes or tube nest.

If it's plain water that means the temperature regulating valve isn't adjusted properly. VTR2-1 should be set for 225 deg F (107 deg C)--which is just above the boiling point of water, which should prevent moisture from condensing in the AA Pre-cooler. Now, having said that, when the unit is stopped and cools, and then is re-started VTR2-1 has shut off nearly all the cooling water flow to the Pre-cooler--because it's trying to hold 225 deg F, but the ambient is less than that so it's trying to raise the temperature (but can't). So, when START is initiated it will take about 20-30 minutes for the Robertshaw temperature regulating valve to open to allow cooling water flow to the Pre-cooler to begin bringing the AA temperature down. Many times this results in an 'AA Inlet Temp High' alarm--which will clear as soon as the VTR2-1 can get cooling water flowing and bring the temperature down.

But, there should be NO condensate forming/condensing in the cooler because VTR2-1 should be set to keep the temperature above boiling during normal operation (soon after the unit reaches rated speed).

The dripping you see should be coming from the continuous low-point drain of the piping at the inlet to the Main AA compressor. That's to allow any condensate to be drained from the pipe, and it continually lets a small amount of CPD out--that, too, is unavoidable and necessary for the condensate to be drained out before it gets into the Main AA Compressor (where it can wreak havoc!).

Hope this helps!

 

this was really helpful from you.

 

Hi,

another approach is to check the vents of cooling water at generator inlet/outlet water pipes. it is a high point were most of air accumulate. when GT is running and there is a leak in AA cooler, the AA pressure will be much higher than cooling water pressure so air will penetrate through cooling water cycle trying to find high level passages. so if you have air coming out from the generator radiator vent and it continuously accumulate, then it will be a leak in AA cooler.

regards,

 

nldgeseeker makes an excellent point--if there is a tube- or tube nest leak in the AA Pre-cooler when the unit is running, the pressure of the air (CPD) in the cooler is higher than the pressure of the cooling water in the tube/tube nest which will prevent water/coolant from leaking into the cooler shell. Air will make its way into the cooling water system and, as nldgeseeker suggests, will make its way to high points in the piping. (Not all GE-design Frame 6B generators have water cooling; most are air-cooled.)

However, when the unit is shut down and the cooling water system is running and there is a tube- or tube nest leak then water/coolant will leak into the shell and can be moved along to low points in the piping when the unit is started--or make it's way into the Main AA Compressor (where it's not welcome!). Even if the cooling water system isn't pressurized if there is a leak water/coolant can make its way into the AA Pre-cooler shell when the unit is not running.

The AA Pre-cooler shell drain can be checked at any time, running or not, to check for condensate or water/coolant. But the biggest cause of moisture (condensation) in AA compressor piping is improper adjustment of VTR2-1.

By the way, the usual setpoint for the Main AA Compressor inlet high temperature alarm is 275 deg F (135 deg C), which is only 25 deg F below the maximum allowable Main AA Compressor inlet air temperature. When this alarm is annunciated when the unit is running it is important for operators to take appropriate action as quickly as possible to avoid damage to the Main AA Compressor. That means unloading the unit and verifying the temperature of the Main AA Compressor Inlet air (by looking at the temperature gauge which should be installed at the inlet to the compressor, and, if available, looking at the Main AA Compressor inlet air temperature T/C input to the Speedtronic turbine control panel), and checking the Cooling Water system and VTR2-1. Many of the Main AA Compressors used on GE-design heavy duty gas turbines (non-F-class machines) run at speeds of approximately 14,000 RPM and some even higher. When the inlet air temperature gets too high the expansion of the impeller can cause interference with the compressor casing, which results in severe damage.