Development of heavy wall seamless line pipe X70 - X80 with low temperature toughness

SUMMARY: The continued shift of exploration and production to deep water fields will require the industry to develop alternative pipe solutions to cope with the challenging demands of these exploration regions. Because of the complexity of exploration conditions in deep water fields, e.g. high pressures, low temperature and sour reservoirs, higher grades and heavier wall thickness in combination with low temperature toughness and suitability for sour service are required. The Vallourec & Mannesmann Tubes's alloying concept for line pipe steels based on low carbon was extended to grades X70 and X80 with wall thicknesses up to 75mm. In this paper the latest results on industrial studies on high strength heavy-wall steels manufactured by seamless hot rolling and subsequent quench and temper treatment are presented. The work is a part of the development program for high performance heavy wall seamless pipes for special applications such as J-lay collars, buckle arrestors and risers. Mechanical properties, advanced metallographic examinations, results of the sour service resistance and weldability are reported.