Fatigue Performance of SMLS SCR Girth Welds: Comparison of Prefabrication-Type WPS

Abstract

The objective of the present research work is focused on evaluating the fatigue performance of different prefabrication welding procedures and determining the best compromise between manufacturing specifications, productivity and fatigue strength. Therefore, a large full scale fatigue campaign was launched at Tenaris to comply with this objective. SMLS SCR pipe (grade X65, outer diameter 10 3/4″, wall thickness 25.4 mm) was selected and manufactured according with the current most challenging offshore specifications and girth joints representative of prefabrication welding were manufactured in 1G position. Two different bevel geometries, two different welding techniques for the root pass and two different welding techniques for fill and cap passes were studied and compared. Finally, a post weld finishing technique has been implemented, aiming to improve the fatigue strength by removal of the weld root and cap reinforcements. Misalignment measurements, with stress concentration factor calculations, and post-tests fractographic investigations have been systematically performed on all the samples after testing. This activity was of paramount importance in determining the causes for fatigue initiation. The tests results demonstrated the important role played by the girth weld root internal geometry on the fatigue strength, the influence of the High-Low, the preferential fatigue initiation sites and the fatigue strength improvement by removal of weld reinforcements.