Abstract: The thinned zone of oil and gas pipelines by corrosion or mechanical damage and the installing for side transibutery stream pipelines require commoly the field welding practice. This will result in a large economic losses unless the welding is conducted without interruption of the flow of oil and gas. However, welding on pipelines with flowing oil and gas may cause hydrogen cracking in HAZ located at the fast cooling.In order to prevent from hydrogen cracking and obtain a sound welded joints, the effects of welding residual stress, hydrogen content, welding cooling rate and welding procedures on hydrogen cracking induced in carrier line during welding were studied in this paper. Some beneficial results had been obtained in the experiment, and the direction of futher study was settled.