Cycle monitoring method and apparatus

A fatigue cycle monitoring method for sensor monitoring a mechanical component in a nuclear power plant, said method comprising the steps of:

• (a) sampling a sensor signal from the sensor at a sampling rate;
• (b) checking integrity of the sensor signal;
• (c) comparing the sensor signal to first threshold range limit values;
• (d) storing sensor samples in a storage at a first storage rate if the sensor signal is within the first threshold range limit values;
• (e) storing sensor signal samples in the storage at a second storage rate higher than said first storage rate if the sensor signal is equal to or outside the first threshold range limit values;
• (f) continuing to store at the second storage rate until the sensor signal has been within the first threshold range limit values for a predetermined period;
• (g) comparing the stored sensor samples stored at the second rate to second threshold range limit values and storing a transient sensor sample in the storage when successive sensor signal samples are outside the second threshold range limit values;
• (h) comparing the stored sensor signal samples stored at the second storage rate and storing the maximum and minimum sensor signal samples in the storage when a maximum or minimum are detected, respectively;
• (i) computing component pressure stress from pressure transient sensor samples;
• (j) computing general thermal component stress;
• (k) computing transient thermal component stress by performing Duhamels integral on temperature transient sensor samples;
• (l) obtaining predetermined load stresses from the storage;
• (m) adding the component pressure stress, the general thermal component stress, the transient thermal component stress and the predetermined load stresses;
• (n) determining a stress intensity range from the added stresses;
• and
• (o) producing a component usage factor from the stress intensity range indicating the fatigue on the component with the component usage factor.

A cycle monitoring apparatus for a sensor monitoring a component, said apparatus comprising:

• sampling means for sampling a sensor signal producing sensor signal samples and detecting a transient in the sensor signal samples;
• compression means for compressing the sensor signal samples into a compressed transient after the transient is detected;
• and
• fatigue determination means for determining component fatigue from the compressed transient.