THE APPLICABILITY OF STRATEGY FOR RISK BASED MAINTENANCE TO A PENSTOCK

Abstract

The risk of brittle fracture of pumping up penstock was recognized in an early stage of design. To reduce the cost of penstock construction one tunnel was accepted. For that most stressed penstock section HSLA steel, 700 MPa yield stress, 47 mm thick, was selected. Two problems were induced regarding brittle fracture. Cold cracks in welding could be avoided applying undermatching approach. This required to specify welding procedure and to qualify it for used thickness. Designed thickness might produce plain strain condition. For detailed analysis of cracks effect and stress state it was accepted to produce two full-scale prototypes of penstock most stressed part. Obtained results by fracture mechanics methods have shown sufficient crack resistance of PM, WM and HAZ in welded joints. It was necessary to assure structural integrity of welded joints and penstock involving corresponding approach for maintenance and repair. Maintenance procedures are in continuous development, and most promising is probably risk based approach, developed in last years. In the paper the base requirements of this approach are considered, and the possibility and convenience to apply them for penstock is evaluated.