Annexure - B

BACKGROUND INFORMATION

ENGINEERING REVIEW

This consists of a review of all the appropriate drawings to determine all the areas which normally are, or potentially could be under vacuum. From this review the engineer develops a checklist of all the areas to be examined for leaks. Annexure - H is a sample checklist.

PERSONNEL REQUIRED

Sufficient personnel should be provided to allow the inspection of the areas data required by this procedure. Typically, the test crew will be composed of a Test Engineer (TE) and one or more Assistants. The Test Engineer will be responsible for making all assignments and ensuring that all personnel are competent to discharge their assignments. The assistants should be trained in their assignments and should be thoroughly familiar with the principles and operation of the instruments they are to operate. In addition, they should be instructed in the importance and objectives of the test and the contribution they are to make.

TEST CREW ORIENTATION

Using the checklist and the piping system flow diagrams, the engineer will familiarize the test crew with the systems under vacuum, the condensate cycle, and any other systems or cycle components in the vicinity but not under vacuum. After the review on paper, the same areas should be physically located on the unit (Operations personnel may be needed to assist in this).

REFERENCE DRAWINGS

It is helpful to have two sets of reference drawings identifying most if not all of the areas to be sprayed. With these drawings the person spraying the helium can communicate exactly where he will be spraying to the person at the leak detector. Also, the person at the leak detector can record the exact location of the leak, which is especially important when repairs cannot be made immediately. These drawings can be used in the future till there is no change in the system.

LEAK DETECTOR OPERATION

The Test Engineer should instruct the test crew on reading the leak rate display, including interpreting scientific notation and relating the indicated helium leak rate to air inleakage. The test crew should become familiar with calibrating and manually tuning the leak detector. The leak detector loses sensitivity over time, eventually

Annexure - B

becoming totally insensitive to helium. Upon loss of sensitivity the test person should initiate the machine’s automatic calibration sequence.

A whole unit air inleakage survey should start on the Turbine Deck at one end of the unit, continue around the turbine, including any other components on that deck applicable to the test and proceed in a similar manner with the next deck down. Regardless of the type of test gas, the test itself should run top to bottom, one deck at a time. Whether the test gas is lighter or heavier than air is not a significant factor in determining whether tests should progress from the top down or bottom up within a unit survey. Heat convection in combination with normal building ventilation flows, usually results in large, upward air mass flows that will more than compensate for any test gas composition considerations.

By beginning the test on the upper elevations, the probability of confusion caused by the tracer gas drifting to unknown leak locations is reduced. Typically, tracer gas released some distance under a large leak results in a signal response that is slow to occur (response time), slow to peak (slope), and slow to clear-out. (Please refer typical chart of Response time in Annexure - F)

Signal interpretation of indications for components in close proximity requires that consideration be given to the following prioritized items.

1.Signal magnitude

2.Signal response time

3.Rising slope of signal response

4.Clearing time of signal response

INTERPRETATION OF THE DATA SHOULD PROCEED AS FOLLOWS

1.After shots have been made and recorded for each of the possible paths, one indication may stand out above the others. Clearly, if one of the signals has a magnitude substantially greater than any of the others, it is the actual leak.

2.When two adjacent test areas show peaks of equal or near-equal magnitude, the one with the quicker response time is usually the leak location.