The safety of pipelines and subsea structures are key elements in subsea field developments. As part of the safety engineering, protection from dropped objects and third party impact actions is required. This article addresses this aspect.
Dropped object from a platform or a vessel is one of the design scenarios. The fall-pattern of the object is essential for the impact velocity and corresponding energy, model of the path and the effects of hydrodynamic behavior is outlined.
In lieu of accurate information, the design code use energy band for energy estimates and may give extremely conservative impact energy. The falling objects structural flexibility and properties are discussed and evaluated regarding the energy dissipation and possible damage of the pipeline.
The pipeline combined response from global deflection and denting regarding impacts are investigated. Analysis and testing methods applied in pipeline design are presented. Focus is placed on the overall interaction between the impacting object, the deformed pipeline and energy dissipation by coating and soil.
Typically, pipeline damage from design codes provides conservative cross sectional damage estimates. This is confirmed from both simplified and detailed FE analyses, as well as fullscale impact experiments performed by REINERTSEN AS.
One of the main objectives promoted by the authors is the importance of both impact velocity and mass during impact, and not only the kinetic energy of the impact. The kinetic energy from a dropped object is unlikely to be fully dissipated as cross sectional deformation of the pipeline.
Global deformations will be triggered, which implies that the dissipated energy going into local denting is reduced to a fractional value. The effect is more pronounced for small diameter pipelines than for pipelines with large diameter. This paper discusses the impact mechanics and seeks to estimate the fractional value by using simplified element analysis.