Non-destructive Evaluation of Close Die Forged Main Body of Primary System Valves

The main body of primary system valves discussed in this paper is made of stabilized austenitic stainless steel and are of intricate shapes & sizes. These bodies are produced through close die forging route and are manufactured first time in Indian forging shops. Finished forgings produced through three stage close die forging process are subjected to comprehensive quality assurance plan at each stage of manufacturing. The stages of manufacturing are raw material processing, close die forging, heat treatment, material testing, machining, hydro test & dimensional measurements. Non-destructive examinations (NDE) required at various stages of manufacturing are mentioned in this paper. Main NDE examination is ultrasonic examination and is generally performed on close die forging in two stages i.e. one in solid condition & other in hollow condition (after drilling central holes) to satisfy code requirements. The examination at former stage is straight beam examination of solid product whereas at later stage it is angle beam examination of a hollow product. The quality of the forgings is ultrasonically evaluated with stringent acceptance requirements for straight & angle beam scanning. Reference reflectors are flat bottom holes (3 mm or less) and V notches (3% of finished thickness). This paper describe the procedure that envisages both stage ultrasonic examinations performed after heat treatment of forged blocks & ensures ultrasonic quality requirements of forged blocks as well as finished body. Some of the challenges are, ultrasonic examination of stainless steel forgings with higher sensitivity, maximum coverage of metal volume with intricate shape, combining of ultrasonic examination stages to improve productivity. The main task is to establish, demonstrate and train vendor manpower to conduct ultrasonic examination in line with specification requirements. Major advantage of the procedure was performance of two stage ultrasonic examination (i.e. solid & hollow product) in single stage, which is completed before shipment from forging shop. It eliminates one machine setup resulting in reduced machining time without compromising the quality & avoids conflicts with vendors.