On-site repair of heat exchange tubes with Nd：YAG laser

In the paper,the composition and equipment for on-site repair of damaged tubes by circular Nd：YAG laser deep penetration welding of inner sleeves are introduced.The inner sleeve is designed to be concave to reduce their axial constraints so that the residual stress of the welded part can be reduced and the tendency of stress corrosion can be decreased.Laser light is transmitted into the inner sleeve through an optical fiber,then reflected by a rotating mirror onto the inner wall;finally a circular weld of deep penetration is produced.The melted metal connects the inner sleeve with the outer tube,and prevents liquid seeping to the damaged part of the tube.Experimental results indicate that the grain growth of heat affected zone of parent metal caused by laser welding is small,the connection width is influenced by pulse power and that the tensile shear strength is influenced by pulse power and that the tensile shear strength is influenced by connection width.The tensile shear strength of the welded joint is about 62% of the tensile strength of Inconel 600 tube.