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Laser peening is a surface enhancement process that introduces compressive residual stress on materials by irradiating laser pulses under aqueous environment. The process utilizes the impulsive effect of high-pressure plasma generated by ablative interaction of each laser pulse. Around a decade ago, the authors invented a new process of laser peening without any surface preparation, while the conventional types required coating that prevented the surface from melting. Taking advantage of the new process without surface preparation, we have applied laser peening without coating (LPwC) to nuclear power plants (NPPs) as a preventive maintenance against stress corrosion cracking (SCC). Toshiba released the first LPwC system in 1999, which delivered laser pulses through waterproof pipes with mirrors. In 2002, fiber-delivery was attained and significantly extended the applicability. Now, the development of the third generation system has been just accomplished, which is extremely simple, reliable and easy-handled.Laser peening is a surface enhancement process that introduces compressive residual stress on materials by irradiating laser pulses under aqueous environment. The process utilizes the impulsive effect of high-pressure plasma generated by ablative interaction of each laser pulse. Around a decade ago, the authors invented a new process of laser peening without any surface preparation, while the conventional types required coating that prevented the surface from melting. Taking advantage of the new process without surface preparation, we have applied laser peening without coating (LPwC) to nuclear power plants (NPPs) as a preventive maintenance against stress corrosion cracking (SCC). Toshiba released the first LPwC system in 1999, which delivered laser pulses through waterproof pipes with mirrors. In 2002, fiber-delivery was attained and significantly extended the applicability. Now, the development of the third generation system has been just accomplished, which is extremely simple, reliable and easy-handled.

A technology to prevent the occurrence of Intergranular Stress Corrosion Cracking (IGSCC) by irradiating a high power Nd:YAG laser beam was developed. Laser Desensitization Treatment (LDT) process was realized by irradiating a laser beam onto the sensitized Heat Affected Zone (HAZ) surface of SUS304 stainless steel. LDT was formed by both a molten layer of approximately 0.2mm depth and a solution heat treated layer. The results of a Creviced Bent Beam (CBB) test showed that no cracks had appeared on the surface of LDT. After LDT was applied in the vicinity of welding joints on the inside surface of pipes, tensile residual stress was measured there. On the other hand, the tensile stress of outside surface of the pipes was decreased. From these results, LDT processing on the inside surface of a pipe can be expected to prevent the occurrence of IGSCC owing to the effect of both metallurgical improvement and decrease of the residual stress on the outside surface of the pipe. We developed the LDT processing system and successfully applied on the pipes of some actual nuclear power plants.A technology to prevent the occurrence of Intergranular Stress Corrosion Cracking (IGSCC) by irradiating a high power Nd:YAG laser beam was developed. Laser Desensitization Treatment (LDT) process was realized by irradiating a laser beam onto the sensitized Heat Affected Zone (HAZ) surface of SUS304 stainless steel. LDT was formed by both a molten layer of approximately 0.2mm depth and a solution heat treated layer. The results of a Creviced Bent Beam (CBB) test showed that no cracks had appeared on the surface of LDT. After LDT was applied in the vicinity of welding joints on the inside surface of pipes, tensile residual stress was measured there. On the other hand, the tensile stress of outside surface of the pipes was decreased. From these results, LDT processing on the inside surface of a pipe can be expected to prevent the occurrence of IGSCC owing to the effect of both metallurgical improvement and decrease of the residual stress on the outside surface of the pipe. We developed the LDT processing sy...