| 摘要 |
PURPOSE:To prevent the wear of a steel pipe because of friction with fluid, by quenching the inner surface of the steel pipe such as a penstock which has been melted by arc heat so as to harden the inner surface of the steel pipe. CONSTITUTION:Inner surface, which needs to be hardened, of a pipe 1 made of carbon steel or low alloy steel, or inner surface of joined part of the pipes, is hardened in order to prevent the wear caused by the passage of fluid. For that purpose, an electrode 3 of a TIG welding set 2 is arranged at the inside of the pipe 1 with the electrode 3 directed to the inner surface. An electric arc is generated between the electrode 3 and the inner surface of the pipe 1 while revolving the pipe 1 at a low speed around the axis, and at the same time while spraying Ar gas through a nozzle 5 which surrounds the electrode 3 thereby melting locally the inner surface of the pipe. The melted portion is exposed to air and is cooled rapidly by the revolution of the pipe to form martensite structure and hardened. This pipe hardly wears by the passage of fluid, so that the life time of a penstock is extended. |
