Method and apparatus for determining rotor life expended

A method for determining the life expended for a turbomachine rotor based upon cyclic heating and cooling of the rotor comprising the steps of:

• measuring the temperature adjacent the rotor surface;
• calculating a positive stress half-cycle and a negative stress half-cycle depending upon whether the rotor is heating or cooling;
• storing a maximum positive stress and a maximum negative stress to determine the occurrence of a cycle;
• combining the maximum positive stress and the maximum negative stress for each cycle to determine a stress range for the cycle;
• comparing the stress range for each cycle with a calculated curve representing stress range versus life expended to determine the rotor life expended for each cycle;
• and,
• accumulating the cyclic life expended for each cycle to determine the total life expended for the rotor.

An apparatus for determining the expended life of a turbomchine part comprising:

• means for measuring at least the approximate temperature of the turbomachine part;
• means for calculating stress in the turbomachine part from the measured temperature, said calculated stress being positive or negative depending upon whether a heating half-cycle or a cooling half-cycle is taking place;
• means for determining the occurrence of a cycle;
• means for storing a maximum negative stress and a maximum positive stress for each cycle;
• means for calculating a stress range for each cycle by summing the maximum positive stress and the maximum negative stress absolute;
• means for comparing the stress range for each cycle with a curve representing a calculated stress range versus life expended to determine the life expended for each cycle;
• and,
• means for accumulating the life expended for each cycle to determine a total life expended for the turbomachine part.