Damage assessment and refurbishment of steam turbine blade/rotor attachment holes

This paper presents a case study dealing with the assessment of cracking observed at steam turbine blade attachment holes, and subsequent use of an innovative repair solution based on a friction processing technique, friction hydro-pillar processing (FHPP). This was performed with a bespoke welding platform developed specifically for repair of radially cracked or incorrectly drilled blade attachment holes in LP turbine rotors. The paper initially outlines a fracture mechanics analysis of observed in-service cracking aimed at assessing critical defect sizes to support repair or replacement scenarios. It then briefly discusses development of the FHPP process before focusing on characterisation of the residual stresses resulting from the welding process and their amelioration by heat treatment; a necessary part of the procedure approval for turbine refurbishment.