Analysis of Mechanical Stress Improvement Process (MSIP) on the welding between Reactor Vessel Inlet/Outlet and Reactor Coolant System (RCS) Piping

Due to welding process and different material characteristics, welding areas at the inner diameter (ID) of the Pipe experiences tensile stress. Over certain period of operation, this areas encounter circumferential and longitudinal cracks due to Primary Water Stress Corrosion Crack (PWSCC). To reduce the crack in this areas, one of the method is to apply the Mechanical Stress Improvement Process (MSIP). This paper will study the effects that optimize the method of MSIP. For the individual graph of 3 inch width thickness, we can make the conclusions Higher applied pressure 'P' at the same distance 'a' will induced higher compressive stress in weld. The optimal distance 'a' is 1.5 inch away from the weld. At distance 'a' equals 2.5 inch, the compressive stress induced to weld is much smaller than other position. For the 3 graphs for different width 'b' of the Clamps, we can make the conclusions For a higher applied pressure 'P', the tensile stress in weld will be converted to a higher compressive stress. For any distance 'a' of the Clamp, after the MSIP, the tensile stress in weld will be reduced greatly. For Clamp with larger width 'b', the conversion from tensile to compressive stress is more uniform in the welding area related to surrounding area. For Clamp with larger width 'b', compressive force induced in weld is higher for the same pressure applied