About this Abstract |
Meeting |
2021 AWS Professional Program
|
Symposium
|
2021 AWS Professional Program
|
Presentation Title |
Dissimilar Pipeline/Super Duplex Steel Welds for Offshore Applications |
Author(s) |
Waris Khan, Rahul Chhibber, Nitin Saini, Yajing Wang, Leijun Li |
On-Site Speaker (Planned) |
Waris Khan |
Abstract Scope |
API grade line pipe steel is widely used in oil and gas transportation pipelines. Super duplex stainless steel due to its balanced ϒ/δ ratio, excellent combination of mechanical properties, high corrosion resistance, and economic viability over Ni-based alloys, becomes one of the most favorable materials for joining with pipeline steel. Gas tungsten arc welding is used to make two different dissimilar weld joints of API X70 pipeline steel and super duplex stainless steel Grade 2507 using austenitic 309L and super duplex 2594 fillers. The weld joints are fabricated using a heat input of around 0.51 kJ/mm in the shielding atmosphere of pure argon gas. The dissimilar weld joints are examined for microstructural evolution and mechanical performance. X-ray diffraction is used to verify the structural presence of austenite and ferrite in the weld zones. The dissimilar weld joints are tested for room temperature tensile strength and microhardness. Filler 309L solidifies in ferrite-austenite mode and results in a complex microstructure of skeletal ferrites in the austenite core. In comparison, super duplex 2594 filler solidifies in ferritic mode, which upon subsequent cooling below the solvus temperature, has the precipitation of multiple reformed austenite’s in the sequential order of grain boundary, Widmanstatten, and intergranular austenite in the solidified microstructure. Investigations of elemental distribution across the transition zone/weld boundary indicate a high gradient of chromium and nickel along with significant variation in molybdenum and silicon concentration on the X70/weld fusion interphase. The tensile strength of both the welds is superior to that of the X70 steel but lower than super duplex 2507 base metal. The fracture location of both the welds is observed slightly away from the weld zone towards the X70 steel. Thermo-Calc is used to predict the mole fraction of phases as a function of temperature for both the dissimilar weld joints. Scheil’s solidification calculations are also performed to obtain the solid phase fractions from the liquid with the TCFE6 database. |
Proceedings Inclusion? |
Definite: Other |