APPLICATION OF OUTER SURFACE IRRADIATED LASER STRESS IMPROVEMENT PROCESS (L-SIP) TO PRESSURIZER AS RESIDUAL STRESS IMPROVEMENT METHOD FOR ALLOY 600 PWSCC MITIGATION

ABSTRACT Improvement of residual stress is effective in a countermeasure to deal with the stress corrosion cracks in pipe welds. A irradiated laser stress improvement process (L-SIP) will be introduced as a method to improve residual stress inside steel pipes. This work method is to improve inner surface residual stress from tensile stress to compressive stress by irradiating laser beam around the welds of steel pipe and utilizing the temperature differences between inner and outer surface. Recently this method is applied to PWR pressurizer surge nozzle on TRUGA unit 2. INTRODUCTION In the welds of steel pipes at nuclear power plant or thermal power plant, stress corrosion crack (SCC) is regarded as a damage mode. Stress corrosion crack is caused by tensile residual stress, materials and environment (including water quality and temperature, etc.). It is very difficult to improve the material and environment of pipes in operation plant. Therefore, the residual stress improvement work method is used as a simplified method. In order to improve residual stress, some ways of peening including shot peening are applied. In the welds of steel pipes, it is often impossible to apply them to inner surface of pipes where stress corrosion crack occurs due to the inaccessibility. To date, the use of laser beam as a maintenance technology for nuclear power plants have been studied (1)(2)(3)(4) , it is one of the applicable method from outside of the pipe. This study will report the first application to nuclear power plant in order to improve the inner residual stress of pressurizer surge nozzle

Heparin-Induced Hyperkalemia in an Extremely-Low-Birth-Weight Infant: A Case Report

ABSTRACT Heparin may cause hyperkalemia by blocking aldosterone biosynthesis in the adrenal gland. Dizygotic twin sisters were born by Cesarean section at 25 weeks ’ gestation. The younger sister developed acute hyperkalemi