Results and Discussion
DNV fatigue assessment results
Fatigue screening was conducted in accordance with DN-RP-F105 rules. Three potential fatigue scenarios were assessed, and the results are as follows:
- No cross-line VIV fatigue assessment was required
- No in-line VIV assessment was required
- In-line VIV and wave loading were required
Due to an unknown wave direction for spanning orientation, the worst case was assumed. Wave loading was estimated, and it was found that the wave loading was insignificant and very unlikely to cause significant fatigue damage for 20 years. As the dynamic response from environmental loads was insignificant, VIV was unlikely to occur.
API 579 and ASME B31.8 static loading assessment results.
The localised equivalent strain due to the dent was 13.3% against an ASME B31.8 allowable of 6%. In the API 579 level 3 assessment, the load case passed the plastic collapse and collapse from buckling assessment. However, acceptance for protection against local failure assessment was not proven. The maximum principal stress and plastic strain are shown in Figures 1 and 2.