Method for manufacturing joint of carbon steel pipes suitable for expansion and expanding method

摘要

Carbon steel pipes are joined to each other in a non-oxidizing atmosphere by using an insert constituted by a Ni-base alloy or a Fe-base alloy having a melting point which is lower than 1200 DEG C and a thickness of 80mm or smaller under conditions that the surface roughness Rmax of the joined surfaces of the carbon steel pipes is 20 mu m or smaller, the joining temperature is not lower then 1250 DEG C nor higher then 1330 DEG C, duration at the joining temperature is 30 seconds or longer and the pressure is not lower than 2 Mpa nor higher than 4 MPa. The expanding operation is performed such that the maximum difference in level of the joined portion is not larger than 25% of the carbon steel pipe and the expansion ratio is 25% or lower.