Boiler feed water pump shaft life assessment through residual stress measurement

In recent times frequent Boiler Feed Pump (BFP) shaft failures have been reported at various thermal power stations within India. Most of these were found to be due to reverse bend fatigue loading, with crack being initiated at the key way under the thrust pad. In BFP shaft material deterioration (damage) gets accumulated due to severe operating conditions. This can conveniently be monitored by the surface residual stress variation with time, using X-ray diffraction technique. In the present investigation residual stress measurements were performed periodically on flat specimens of BFP shaft steel which were subjected to reverse bend fatigue. The measurements were done at different locations in order to identify the exact region of maximum damage. A master curve between the residual stress ratio and the cycle ratio has been generated and its application to remaining fatigue life assessment of the component has been discussed.