Abstract: J-lay is the best manner for sub-sea pipeline laying and offshore riser construction,in which only a welding station is applied to producing girth weld in horizontal position,and usually 4 ～ 6 pipes with the length of 12 m is firstly welded to increase operation efficiency. Automatic GMAW is commonly used at present J-Lay welding practice because temporary backing is difficult to be installed. The axial misalignment or "hi-lo"actually estimated from the corresponding surface mismatch must be controlled strictly in harsh deep water SCR application,so a series of factors are very important in pipe treatment such as dimensional specification,measurement,machining and sorting. Compared to great progress in welding technologies,BS7608 as the main fatigue design standard is limited or punitive especially on single-sided welds. In fact,a large number of sub-sea pipe girth welds test data demonstrate that Class E of BS7608 S-N curves might be considered to be suitable for singlesided butt welds made without backing in harsh deep water SCR application.