1980 Volume 66 Issue 12 Pages 1689-1695
The development of a 9% nickel steel pipe suitable to the transpotation of the liquefied natural gas has been studied to both laboratory and mill scale.
(1) As-rolled 9% nickel steel plates were formed to the pipes by UOE process. The pipes were welded by using the 9% nickel steel wire with SAW or MIG welding equipment, and quenched and tempered by continuous heating pipe QT installation. As a result the developed pipes had good qualities and properties in both pipe body and weld portion, and satisfied A333 Gr. 8 in the Standard of ASTM.
(2) The microstructures in the weld portion of the 9% nickel steel pipes produced by pipe-QT process were consisted of the tempered martensite and partial retained austenite structures as same as in the pipe body, and the maximum hardness in the weld portion was only Hv. 264.
The toughess of both pipe body and weld portion, and the macrostructure of welded joint were of good properties.
(3) The optimum condition for the rapid heating cycle in a short time is to quench at 790°C and temper at 620°C for 4 min.
