Francis Hydraulic Turbine Guide-vane shear pin is a mechanical sacrificial component designed to break when the mechanical overload arises to prevent severe damage of guide-vane, which is an expensive component in the turbine assembly of hydro-power station. The pin is expected to serve for a minimum period of 10 years under normal working condition before failure occurs as obtained in most hydro-electric power stations globally. The shear pins in Shiroro hydro-electric power generation station located in Niger state of Nigeria were found to be frequently failing within a year of operation before reaching its predetermined load. This research investigated the possible causes of the frequent failure of the shear pins with a view to proffer solution. Analyses of the existing shear pin with respect to material specifications, micro-structural analysis using spectrophotometer where both visual and scanning electrode microscopy (SEM) was done in addition to mechanical tests to ascertain conformity with standards. The results showed that the shear pin material conforms to the ASTM 420, which is the standard for production of the shear pin. The SEM results shows that the failure of the shear pins was due to low cyclic fatigue growth attributed to the effect of intermittent and unsteady operations of the turbine. The visual examination revealed no defect on the phases of the material indicating that the fractured failure was not due to any form of inconsistency resulting from segregation or related effects. The mechanical test revealed yield strength of 600 N/mm2, ultimate tensile strength of 750 N/mm2 and hardness of 29 HRC which agreed with standard specifications for the shear pin. The results indicated that the frequent failure of shear pins could be as a result of other sources other than material specifications.

Shear Pin

Hydro-Electric Power

Hydraulic Turbine

Guide-Vane

Micro-Structure

Scanning Electrode Microscopy

Mechanical Tests

Cyclic Fatigue

Segregation