Various welding problems in the fabrication of high pressure boiler are divided into five groups and discussed as follows : Materials ; Author discusses how to weld heavy wall low alloy steel main steam pipes in the field and also introduces the difficulties encountered with the austenitic piping in the operation and the results of laboratory welding tests conducted with the austenitic piping from the literatures. Welding Machine ; Author discusses various types of welding machines which are applicable for the drums, pipes and tubes. Inspection of welded joints ; Author shows various methods of non-destructive inspection and their typical applications. Heat treatment ; Author made his own experiment to determine the holding time for post heating and the method to interrupt the heat cycle of heavy wall pipe welding. Root pass welding ; Author shows how to use EB insert ring, kellog's method and GE method for the root pass welding without backing ring.