Bimetal composite pipe welding method

The invention discloses a bimetal composite pipe welding method and belongs to the field of metal material welding. The method at least includes the steps of firstly, machining a pipe orifice before inner build up welding; secondly, build up welding the inner surface of a pipe; thirdly, smoothing after welding and performing groove preparation; fourthly, on-site fitting up and welding, wherein the welding adopts 100% CO2 protection arc welding. The method has the advantages that the covering layer and the base layer at the pipe end of the bimetal composite pipe adopt the pipe orifice inner build up welding technology which is high in quality and efficiency and low in dilution rate, the covering layer and the base layer at the pipe orifice are changed from traditional mechanical composition into molecular association, the stress concentration part caused by the self structure of the composite pipe is separated from the weak part of a butt joint weld joint fusion line, welding cracks and air holes are prevented, the corrosion resistance of a welding connector is increased, construction difficulty of on-site butt joint welding is lowered, and the method is high in construction efficiency, reliable in welding quality, low in cost and especially applicable to circumferential welding of the large-diameter bimetal composite pipe.