Fatigue testing strategies for the X65 steel catenary riser with
small-scale specimens considering the effect of welding residual stress
Abstract
Wave-induced fatigue damage is inevitable for the deepwater steel
catenary riser (SCR). To accurately evaluate the fatigue performance of
the full-scale SCR using small-size specimens, five kinds of fatigue
testing strategies were explored, considering the effect of welding
residual stress. Further, the corresponding fatigue tests were conducted
regarding the welded joint specimens with the same weld profile, and the
relevant differences in fatigue testing results were comprehensively
analyzed. Through comparison with the full-scale resonant bending
fatigue testing results, the most equivalent strategy using small-scale
specimens was confirmed. The relevant results indicated that compared
with the fatigue lives of full-scale pipeline joint specimens, the
fatigue testing lives under the constant applied maximum stress of the
yield strength for base material or the constant applied mean stress of
the peak value of transverse welding residual stress strategy are
relatively lower. The fatigue life values obtained from the high-stress
ratio testing strategy are higher, especially in the low-stress range
region. Comparatively, the fatigue lives obtained under the 80 mm wide
specimen without the cutting process strategy were higher in the
high-stress range region. The variable applied mean stress strategy
using the 25 mm wide welded joint specimen was most suitable for
equivalence with full-scale fatigue testing results, and the difference
in the fatigue life testing results was only 9.7%. The difference
between the applied mean stress and the actual transverse welding
residual stress under various fatigue testing strategies is the key to
affecting the equivalence of fatigue testing results.