Welding of niobium microalloyed linepipe steels: 50 years of history and experience

This paper provides a brief overview of the history of the use of niobium in linepipe since its first application in 1959. The dramatic changes in pipe chemistry that have been enabled by the introduction of niobium are highlighted, in particular lower carbon and carbon equivalent levels at ever increasing pipe strengths, and the way in which these developments have progressively improved weldability are critically discussed. The important roles of advances in steelmaking, facilitating consistently lower carbon levels, and plate processing, such as TMCP, in recent decades are emphasized and the paper then proceeds to explain the way in which lower carbon allows the maximum benefit to be derived from increased levels of niobium. To emphasize the latter and to point the way towards the future, the success of the Chinese in adopting the latest metallurgical thinking through the application of vast tonnages of High Temperature Processed (HTP) steels containing carbon below 0.05% and niobium levels up to 0.11% is described. The HTP steel concept has provided the world with a dramatically improved, more economical route to the production of pipe strengths up to X80 and beyond and combined this advance with exceptional weldability over a wide range of welding processes and cooling rates. (AU) Copyright © 2013 Companhia Brasileira de Metalurgia e Mineração (CBMM) All Rights Reserved