In this paper, the procedure for flaw acceptability assessment is examined through a case study of a semi-elliptical surface crack in an offshore monopile as it grows till it forms a through thickness crack. Using the procedure prescribed in an industrial standard (BS 7910), the fracture ratio, K_r is shown to increase monotonically with increasing crack depth. The load ratio, L_r, is initially insensitive to the crack depth. However, there is a rapid increase in L_r when the crack depth to thickness ratio exceeds 80%. L_r values obtained from detailed 3D FE limit analysis using elastic-perfectly-plastic material behaviour do not exhibit the asymptotic behaviour predicted by BS 7910 as the flaw transitions from deep crack to through-thickness crack. Furthermore, K_r predicted by BS 7910 is shown to be an over-estimation for the typical dimensions of offshore monopiles. The findings suggest that a structure with a deep flaw may be identified as unacceptable based on BS 7910 when it may still possess a non-trivial amount of structural residual life. This is a concern for monopiles where crack growth as a large flaw forms a significant part of the total life.

在本文中，通过对海上单桩堆中直至形成贯穿厚度的裂纹的半椭圆形表面裂纹的案例研究，检验了缺陷可接受性的评估程序。使用工业标准（BS 7910）中规定的步骤，断裂率K _r随着裂纹深度的增加而单调增加。载荷比L _r最初对裂纹深度不敏感。但是，当裂纹深度与厚度的比率超过80％时，L _r迅速增加。大号_[R从3D FE极限分析使用弹性-完全塑性材料行为获得的数值不会显示出BS 7910预测的渐进行为，因为裂纹从深裂纹过渡到了全厚度裂纹。此外，BS 7910预测的K _r被证明是对海上单桩典型尺寸的过高估计。研究结果表明，具有深层缺陷的结构根据BS 7910可能仍被认为是不可接受的，而该结构仍可能具有相当数量的结构剩余寿命。对于单桩来说，这是一个令人担忧的问题，因为裂纹是大缺陷构成了整个寿命的重要部分。