INVESTIGATION OF FAILED ACTUATOR PISTON RODS

Actuator pistons had failed after very short service life by intergran ular cracking in a circumferential weld. Analysis of the welds and sub sequent heat treatments showed that the austenitic filler material use d to weld the carbon steel resulted in carbide precipitation during ni triding. Combined with high residual stresses, these carbides promoted intergranular fracture at normal operational loads. It is shown how t he changes that had been made to the initial design and processing of the actuators were not entirely compatible with each other and reduced the ''metallurgical safety factor''. Recommendations for improvements were successfully implemented. (C) 1998 Elsevier Science Ltd. All rig hts reserved.