Ultra Heavy Wall Linepipe X65: Material Performances for Severe Applications

Tenaris together with Centro Sviluppo Materiali launched a Joint Industrial Project aimed at developing heavy wall linepipes and evaluating their suitability for very severe applications possibly involving high service pressures and temperatures, large strains applied to the line, aggressive sour environment. The full project programme includes development of a the new generation of heavy wall products, laboratory scale evaluation of the material response when subjected to severe mechanical and environmental loading, evaluation of full component, pipe and girth weld, behaviour by means of full scale testing. Another technical publication in this conference (OMAE2009-79153) reports the activities of development of the new generation of heavy wall seamless pipes. In the present paper indeed, main outcomes of laboratory testing activities of the above programme on pipe material (grade X65, outer diameter 10 3/4^″, wall thickness 46 mm) are reported as far as pipe body material properties are concerned. A fitted for purpose special testing programme, including mechanical and SSC laboratory scale testing, has been executed. Full thickness longitudinal specimens were extracted from the pipe body to apply severe strain cycling (1% and 2% maximum strain for various numbers of cycles, up to 200 cycles). Material showed a very encouraging behaviour, exhibiting an important reserve of strength even after application of severe strain cycling. Both mechanical, tensile compressive and toughness, properties and stress corrosion properties resulted to be suitable for the envisaged applications. Furthermore the pipe material showed suitable mechanical and stress-corrosion properties even after the severe cycling as well as after severe cycling and subsequent ageing. The influence of different straining conditions was also investigated, showing no significant difference in material properties after strain–ageing, due to different straining histories.