Exothermic Additions in a Tubular Covered Electrode and Oxidizing Reactions Influence on Underwater Wet Welding

During Underwater Wet Welding (UWW), the water that surrounds the arc decomposes liberating large amount of hydrogen and oxygen. As a consequence of the presence of these gases in the arc atmosphere and weld pool, porosity in the weld metal occurs. In the past years, many research programs had been carried out with the objective to reduce or eliminate porosity in wet welds. A simple way to accomplish this goal is using chemical elements or ingredients to promote or avoid certain chemical reactions in the weld pool. In conventional stick (shielded metal arc - SMA) electrodes, it is possible to add alloying elements or other ingredients through the external covering. A tubular covered electrode (TCE) (a hybrid process between SMA and flux cored arc - FCA welding) allows the addition of reactive elements in the hollow rod, separate from the other ingredients used in the flux covering. This way, it is possible to use exothermic elements, placed inside the tube, to control the oxidation reactions, but limiting these reactions to the arc plasma and in the weld pool. Exothermic additions in welding consumables can promote desirable oxidation reactions, change the metal transfer mode, reduce the cooling rate, and decrease the electrical dependence of the welding process. Theoretically, the application of flux cored shielded metal arc (FC-SMA) welding with exothermic additions will permit better control the weld metal composition and reduce the porosity in wet welds. This paper describes underwater wet welding with tubular covered electrodes that contain exothermic additions such as (CaC2) and aluminum (A1), and the influence of these ingredients on weld metal composition and porosity.

Metal-Cored Welding GMAW Consumables Development for Girth Welding of X-100 Pipe

Metal-cored wire electrodes with different compositions were used to make girth weld joints at a heat input of 0.7–0.8 kJ/mm. Design of experiments methodology was used to create a response surface primarily in carbon (C), manganese (Mn) and nickel (Ni) space in steel containing molybdenum (Mo), titanium (Ti), and boron (B) additions. This allowed the modeling of all-weld-metal yield strength, tensile strength and Charpy impact toughness as a function of weld metal composition. Results indicated that weld metal yield and tensile strengths have a linear dependence on the %C, %Mn and %Ni content of the weld. The Charpy impact toughness behavior at −20° C was more complex, initially showing a dependence on %C and %Ni in small scale trials, and subsequently showing a dependence on the %oxygen (O) and %Mn content in full scale production trials. These results can be combined for graphical optimization of the response surface to identify regions in weld metal composition that contain the desired weld metal yield, tensile and Charpy impact toughness for design of metal-cored wire electrodes for the welding of X-100 pipe. These results and their implications for design of girth welds in X-100 pipe are presented in this study.