Effects of Ternary Shielding Gas on Weld Characteristics of All-Position Welding for Pipelines

Abstract

As an efficient welding method, Gas Metal Arc Welding (GMAW) has the advantages of low thermal energy input and stable mechanical properties of ring weld joints. GMAW has now become the main welding method for large-diameter oil and gas pipelines. Narrow gap welding is widely needed in pipeline manufacturing, yet lack of fusion on side walls is often produced in this process when conventional binary shielding gas (Ar–CO2) is used. Here, we use a ternary shielding gas (Ar–CO2–O2) to improve the weld formation of all-position narrow gap welding of pipelines. The weld formation and weld penetration depth of the pipe welding at 0 o’clock (flat welding), 3 o’clock (vertical welding), 6 o’clock (overhead welding) are investigated. Macroscopic metallographic analysis on the melt width are carried out, and feasibility of the ternary shielding gas is illustrated. Comparing to the binary shielding gas, the ternary shielding gas leads to better weld formation, weld width and weld penetration. Especially, the weld penetration depth can increase by 20%, which helps to reduce the lack of fusion.