Study on JCO Double face-three layered-four wire Hi-speed SAW Process for Heavy-wall Nb-containing Micro-alloyed Steel

The weld seam metal and JCO forming process of the BNS anti-H₂S steel pipe are designed,and the welding method and heat input for the pipe are determined.The BNS steel plate and BNS pipe furnish conditions are analyzed,and the H₂S resistance of the BNS pipe is evaluated.Based on relevant analysis,it is identified that the NBS steel possesses fine SCC/HIC resistance,and that its hardness obviously influences its H₂S resistance,and the higher the steel strength grade,the poorer the SSC resistance will be.Moreover,hardness and hydrogen embrittlement sensitivity of the weld seam metal is increased along with the increase of Nb content in the micro-alloyed steel.However when the Nb content is below 0.03%,the negative effect disappears.Reducing the MnS inclusion in the steel or totally turning such inclusion into spheroid inclusion will be helpful for resistance against HIC.Finally,when weld seam metal of the BNS steel pipe possesses large amount of fine acicular ferrite,its H₂S resistance will be the best.