Cracking of HSLA Steel Nioval 47 Caused by Exploitation Condition and Repair Welding

The metallurgical characteristics of high-strength low-alloyed (HSLA) steel and the effects that could lead to crack initiation, especially in the heat affected zone, have to be taken into account during defining welding technology.Primary aim of this study is dealing with the thermal effect caused by repair welding of HSLA Nioval 47, along with the damage analysis of a water supplying pipeline made of this steel and the circumferential welded joints.Analysis has shown the involvement of different damage mechanisms on reconstructed pipeline.Thermal cycle during repair welding with a focus on cooling time (t8/5) and with heat input (E) was thoroughly defined, along with recommended technological measures.After repair welding (using E 50 6 1 Ni B 42 electrode), microstructure analysis was performed on the surfaces at the most critical locations, i.e., the repaired circumferential welds A and B. In addition to martensite structure in the coarse-grain heat affected zone, crack initiated in the weld metal, ending at the fusion line, was detected, despite the adequately defined welding technology.One of the major remarks is related to the importance of available data needed for analysis and failure prevention during the exploitation period, guarantying reliability and safety of the pipeline.