Thermal Signature of Weld Defects Inside High Strength Steel Butt-Welded Joint Pipes

Design of complex infrastructures requires a multidisciplinary approach to prevent Natech accidents, which are secondary effects due to natural hazards. This approach follows two main directions: i) prevention of the loss of control over risk and ii) recovery from the loss of control over risk. These concepts may be applied to piping system installations, which are key elements of petrochemical and refinery plants. They are critical components that require special attention towards hazardous events because their rupture could cause leakage of the content resulting in possible explosions. Piping systems for oil and gas applications are generally an interconnection of carbon steel linear pipes, elbows, pipe fittings and auxiliary elements joined together using welding technology. The connection between the elements is a sensitive part that could trigger failure mechanisms in case of extreme loads. In fact, the manufacturing of the joints can take place under different condition e.g., technology adopted, manual or automatic welding process, manufacturing location, significantly affecting the final quality of the connection. It is important then to adopt proper diagnostic methods that allow to assess the development of imperfection inside the welded joints ensuring optimal quality acceptance levels. In this paper is described the possibility to adopt infrared cameras for this purpose. During preliminary experimental activity, were manufactured several pipe specimens using three different manual welding technologies. Each specimen consisted in two portions of X80 high strength steel pipe (diameter 12’’^3/4) connected through butt-welded joints having induced imperfections inside. The actual position and the magnitude of these imperfections were then determined using radiographic analyses. This information was subsequently combined with the measurements of the welding pool temperature, which is the temperature of the molten material along the joint and recorded during the manufacturing process using an infrared camera. This process allowed to obtain the thermal signature of each specific defect, which is the temperature of the molten material that is associated to the development of the imperfection.