In-situ examination of turbine components (blade roots, rotor steeple grooves and disk-blade rim attachments) of low-pressure steam turbine, using phased array technology

A feasibility study test and 3 field trials were performed at Darlington NGS in 1996, 1999 and 2000 on ABB LP turbines. The scope of these trials was to commission in-situ automatic phased array systems capable to inspect blade roots and rotor steeples of L-0 and L-1 rows. GE disk-blade rim attachments were inspected at Bruce B nuclear station, in fall of 1999. The automated ultrasonic phased array technology is capable of high-speed rate and reliable detection and sizing. The capability demonstration was performed on mock-ups and reference blocks, using EDM notches. A custom built UT simulation software: Imagine 3D interfaces with SimScan to generates the spreadsheets/charts with target and probe coordinates and ultrasonic path and angles (refracted and skew) to hit the reference target. Examination of L-0 blade and rotor steeple grooves was performed with 2 phased array systems under networking. Data analysis was done in near-real time. Manual and automatic phased array were performed on L-1 blade roots (hook 1). Special linear array probes were designed by OPG and manufactured by lmasonic, to fit the specific geometry and to optimize the beam features for detection and sizing. Accuracy in sizing is ± 0.8 mm for height ± 1.8 mm for length. Location of indication is within ± 4 mm space envelope. Sizing based on Dynamic Depth Focusing (DDF) board is better for specular reflection of EDM notches on disk attachment. (author)