Abstract: The paper describes the experiments concerning butt-welding of the X- 65 Grade seamless steel line pipes with different fluxes and under different welding conditions. Results of the said experiments show that X- 65 Grade line pipes jointed with the special butt-welding technique can be used for acid oil/gas transport. In case of underground service pipeline jointed by means of welding with cellulose electrodes can be free of the heat treatment to the weld, and pre-welding heating of the joint will ensure impact toughness of the weld. For overhead pipeline, welding with basic-compound coated electrodes and pre-welding heating of the joint will reduce the joint thermal-stress.