Development of oxyrutile low alloy ferritic electrode for wet welding

Abstract

Offshore oil production with floating platforms and FPSO-type production vessels has grown continuously in the last decades. When in service, the structural elements of these vessels draw a maximum depth of about 20 m meters. Therefore, the need for in situ repairs is within depths of this order and wet welding should be considered as a solution since it has the advantages of simplicity, low cost, and accessibility. This work presents results from a research program whose main objectives were to develop consumables and welding techniques to produce underwater welded joints with structural quality with the shielded metal arc welding process. The experimental results were obtained from joints welded inside a hyperbaric simulator using a mechanized gravity feeding system at depths up to 20 m. The most important result was the development of a class AWS 70XX low alloy Ni-Mo ferritic stick electrode. Good weld metal properties such as elongation, toughness, porosity, and diffusible hydrogen were achieved. The results allowed the prediction of tensile strength, yielding strength, elongation, hardness, and toughness from the Ni, Mo, and Carbon contents. Depth had no significant influence on the mechanical properties and porosity up to 20 m. Field tests with diver-welders at depths of 5 m and 10 m have also been performed. The possibility of producing welded joints that meet the “Class A” requirements of the AWS D3.6M: 2017 code is discussed.

Keywords

• Underwater welding
• Wet welding
• SMAW
• Covered electrode
• Oxyrutile electrode
• Weld metal