In the energy market, there is an increasing demand for oil & gas transmission pipelines with larger wall thicknesses and from higher strength linepipe steels. Addition of niobium (Nb) to the steel chemistry in combination with thermo-mechanical controlled processing allow increasing the thickness of the linepipe steels on coil while maintaining good strength and toughness. However, pipeline construction companies often indicate their concerns about the weldability of high Nb containing linepipe steels and in addition, Nb levels are restricted in some of the steel specifications for linepipe applications.
In this study, field weldability of industrially produced helical pipes made from 23.7 mm thick, high Nb containing X70 linepipe steel was evaluated. Welding procedure development was realized for narrow-groove mechanized gas metal arc welding (GMAW). Characterization of the girth welds produced revealed the suitability of the material for typical field welding procedures for onshore pipe laying. The details and the results of the investigations are presented and discussed in the paper.