Det Norske Veritas - Germanischer Lloyd

DNVGL  Probabilistic methods for planning of inspection for fatigue cracks in offshore structures
 N DNVGL-RP-C210

Annotation

This RP is assumed to be used together with other DNV Offshore Standards (OS) or NORSOK N standards as listed in /1/ to /6/ or other recognised standards. It is assumed that this RP will be used together with DNVGL-RP-0005 Fatigue Design of Offshore Structures. This RP is intended to give sufficient guidance to the user on how to establish a sound basis for probabilistic in service inspection planning for fatigue cracks. This basis should as a minimum include advice on:

— Fatigue analysis methods for jacket structures, semisubmersibles and floating production vessels (FPSOs).

— Effect of methodology/refinement used in fatigue analysis with respect to calculated fatigue life.

— Basic distributions of parameters required for calculation of stochastic properties for load effects and capacity.

— Derivation of target reliability level in relation to consequence of a fatigue failure.

— Methodology for probabilistic analyses for planning inspection for fatigue cracks. Required theory to explain the methodology should be provided in order that users of the document can easier understand the use of the standard and significance of input parameters to the analysis.

The document may be used for planning inspection for fatigue cracks in new built and existing structures and also for analysis of lifetime extension of platforms.

Purpose

The purpose of this recommended practice (RP) is to provide guidelines for use of probabilistic methods for inspection planning of fatigue cracks in jacket structures, semisubmersibles and floating production vessels. This also includes guidelines for fatigue analysis of these structures as required for probabilistic analysis. The presented analysis methodology is rather general and it may be used also for inspection planning of other structures subjected to significant dynamic loading such as jackups.