3.1 Leak Detection in Condenser

There are several methods for locating air leakage in steam turbine/ condenser.

A.     Online leak detection	B.     Offline leak detection
1.      Helium leak detection	a.       Flood test
2.      Freon leak detection
3.      Ultrasonic leak detection
4.      Infrared images

 

Helium Leak Detection:

This method uses helium, the lightest inert gas, as a tracer element. It is sprayed in the vicinity of the potential in leakage path and is drawn into the system through the leak and is measured by a detector paired with mass spectrometry at the turbine exhaust.

Advantage	Disadvantage
It is by far the best test method for locating leak today.	Helium may not be the best gas for locating leaks greater than 3.4 Nm3/hr, because of it high sensitivity.
As a tracer gas, Helium is quite attractive, because it is inert, non flammable, non toxic.	Large leaks tend to overpower current leak detectors even at maximum metering scale. This fact makes it difficult to evaluate large leaks quantitatively.
Helium mass spectrometry is highly sensitive.
The gas being very light, it penetrates small leaks and diffuse readily.

Helium leak detector:

Freon Leak Detection:

It is similar to Helium leak detection with the only exception that it draws on Freon instead of helium, as a tracer gas.

Advantage	Disadvantage
Less specialised skill is required than helium leak detection technique.	Freon is quite heavier than helium, therefore it takes considerably length of time to dissipate from the region around the leak and for detector to clear.
Large leaks can be screened and individual leaks pin pointed.
Easy maintenance of detector.

 

Ultrasonic leak detection:

It detects sounds above 15 kHz associated with a leak. This sound signal is then amplified and converted to audible frequencies of 100 to 4000 Hz. As a gas or liquid escapes from one high pressure system to lower pressure side the molecule become agitated. The turbulence produce sound pressure variation of vacancies all along the spectrum from 20 Hz 100 Hz.

 

Advantage	Disadvantage
The cost of high end ultrasonic detector required for condenser leak detection is less than the helium leak detection system.	It is almost entirely an operator skill oriented process.
This method is very fast.	Leakage sound will be affected by background sound of the plant.

Infrared images:

Recent revolution in infrared camera have become popular with power plant industry for hotspot detection. Infrared camera have been used successfully to capture the thermal image of any object. Thermal image of condenser surface can be easily capture and comparative analysis of condenser thermal image can detect the air in leak point. The surface temperature pattern obtained from the thermal image of condenser is used to identify air ingress into the condenser.

Advantage	Disadvantage
This method is non contacting and easy image capturing using infrared camera in   which data is in digital form.	Accuracy of image depends upon the resolution of infrared camera and application of advanced image processing tool.
This method is fast.

 Thermal Imager: 

Thermal image of Condenser:

Conclusion:

We have focused on different method of condenser air in leak test and its importance. Different type of gases tracer test are popular in condenser leakage test. Helium leak detection are the ideal solution for leak detection and leak tightness testing under vacuum. the test gas helium is safe and a small light molecule which is suitable for detecting micro leeks. The detection range of helium in vacuum test lies between 10^-2 and 10^-13 Pa.m³/sec.

Helium leak detection is extremely accurate, quantitative and repeatable. Fast cycle time are a further advantage.