Offshore tubular members are manufactured in a very wide thicknesses and diameters. The design curves considered for the fatigue design of such structures are assessed based on testing small scale laboratory specimens. A correction factor is applied to account for differences in thickness and weld geometry. However crack growth behaviour in tubular elements is complex and it is not totally clear if this can accurately be represented by testing small-scale coupons. Large scale fatigue tests aim to characterize the fatigue behaviour in a more realistic manner. However conducting such tests is very expensive. Hence, a medium scale strip type specimen with dimensions between small scale standardized specimens and a full pipe is designed. It has the same curvature and thickness as the pipe from which it is extracted and a quasi semi-elliptical notch is introduced. It is hypothesized that can account for most of the scale effects. Furthermore it can be tested in conventional test rigs at rather high frequencies.
With the objective of quantifying the scale effects between standardized ESE(T) specimens and medium size coupons, a series of crack growth based tests on a high strength offshore steel are carried out. By comparing the corresponding da/dn-ΔK curves it will be possible to evaluate possible scale effects.