Design, Manufacture and UT Results on Blocks with Fatigue Cracks from L-0 Blades

摘要

The paper presents technical aspects of design and manufacture specific blocks with fatigue cracks from L-0 Blades – retired from service. The scope of this exercise was a multitude of projects running within OPG – IM&CS Division: Inspection Qualification for CANDU Piping (effect of root, suck back, counterbore in crack detection; detection and sizing capability for large thickness > 40 mm); PAUT crack sizing – outer surface techniques; PAUT crack sizing – specular large thickness > 120 mm – Nanticoke Boiler Feed Water Pump (Emergency Stop Valve and Governor Valve) and Main Steam Valves; PAUT crack sizing – L-0 steeple grooves (hook 2-5) – Darlington Nuclear GS. The challenge to optimize the block dimensions by preserving the crack profile and height was overcome by using an advanced 3-D drafting package with capability to incorporate and run actual data PAUT files in the 3-D specimen. The paper presents 3 categories of blocks [ bars with weld geometric defects, large thickness bars and pipe coupons and L-0 steeple test pieces-all with fatigue cracks], and PAUT results on multiple scanning combinations. This exercise came as a great success for Technical Justification-Inspection Qualification, for Capability Demonstration-L-waves large thickness and for technician training for in-situ PAUT inspection at Darlington Station in Feb.2010. Based on experimental data, PAUT parameters were optimized. Cracks as low as 5-mm are reliable sized at depth of 210 mm. Cracks as low as 3-mm are reliable sized at depth of 120 mm. Both conventional and PAUT are capable to detect and size fatigue cracks with h > 3 mm at depth of 40+mm.