Diffusible hydrogen in underwater wet welding

The rapidly increasing development of the laying of high-strength steel underwater pipelines for the transportation of gas and oil requires adequate welding technology for maintenance and repair. As FCAW is suitable for automation and appropriate for application at greater depths it represents a welding process capable of replacing MMAW underwater wet welding. Moreover, the complexity of underwater wet welding on high strength steels up to grade X70 requires precise welding parameters and heat input control. This paper presents the basic issues of FCAW underwater wet welding. Measurement of diffusible hydrogen was made with the glycerine method for different welding parameters and levels of heat input for FCAW welding of API 5L X70 pipeline steel. In addition, hardness HV10 was also determined in order to define the effect of heat input on steel microstructure. This work was done as part of the scientific project Improvement of underwater welding and inspection which is being conducted at the Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb.