Det Norske Veritas - Germanischer Lloyd

Wellhead fatigue analysis
 N RP-0142

Annotation

Scope and applicability

The scope of this RP addresses the full lifecycle of any offshore well system. The assessment of wellhead fatigue damage under this RP is applicable during all stages or types of operations when riser systems interface to the well, including drilling, completion, production, workover, and P&A. Fatigue accumulation continues until the riser is ultimately disconnected from the wellhead.

This document provides a consolidated framework for fatigue assessment of subsea and surface well systems by considering the following:

— computation of both mean and cyclic loads experienced by the wellhead/casing system for each set of conditions

— relationship between cyclic loads and cyclic stresses, e.g., load-to-stress curves, stress amplification/ concentration factors, etc., for each location of interest

— damage model, e.g., S-N approach, initiation life method, fracture mechanics, etc., used to estimate fatigue damage at each location of interest.

Example locations of interest within the well system are listed in [4.1].

This document discusses several existing analysis methodologies and common assumptions typically used for the global model, local model(s), damage model, and fatigue calculations; however, a specific analysis methodology or set of assumptions is not prescribed. Moreover, different analysis approaches and differing levels of detail can be chosen, depending on the stage of the project, e.g., preliminary design, detailed design, hindcasting/forecasting, etc., and availability of required inputs.