Abstract: A mobile truck 10 furnished with power source and travel drive mechanism is set in a cargo oil pipe 48 to run inside to inspect and monitor the state of the inner surface of a pipe wall by means of its built-in magnetic flaw-detecting instrument 12 and video camera 14, so that the image signals taken by the video camera 14 may be reproduced and inspected on a television receiver 30 in the monitoring stations located aboard the vessel while the inspection data signals from the magnetic flaw-detecting instrument 12 may be recorded in a recorder 20 at the same time.

Abstract: The invention relates to an apparatus to perform plasma welding, by providing a cooling water temperature detector at the inlet side of cooling water in the plasma welding torch, controlling the temperature at the inlet side of the cooling water running into the plasma welding torch at a set temperature of more than 4.degree. C. and less than 18.degree. C., starting a plasma arc when the temperature of the cooling water reaches a specified point after starting to pass the cooling water, and moving the base metals and the torch relatively upon lapse of a specified time allowed to form a keyhole after start of the plasma arc.

Abstract: The invention relates to a method and an apparatus to perform plasma welding, by providing a cooling water temperature detector at the inlet side of cooling water in the plasma welding torch, controlling the temperature at the inlet side of the cooling water running into the plasma welding torch at a set temperature of more than 4.degree. C. and less than 18.degree. C., starting a plasma arc when the temperature of the cooling water reaches a specified point after starting to pass the cooling water, and moving the base metals and the torch relatively upon lapse of a specified time allowed to form a keyhole after start of the plasma arc.