After installation of a subsea pipeline it is exposed to various risks during its operation life. One particular risk is damage caused by third-party interaction. The subject of this this paper is assessing the consequence of two possible events:
dropping an object on top of the pipeline, and
dragging the pipeline along by a dropped anchor.
The pipeline damage incurred by impact of the dropped object depends on various parameters and conditions. The relative contributions of mass and impact velocity of the dropped object, the pipeline content and the soil condition are evaluated by means of a sensitivity study. It is found that soft soils have the capacity to absorb a significant portion of the impact energy, leading to reduced pipeline damage. The effect of the pipeline being pulled laterally by a hooked anchor is assessed by means of a case study. It is aimed to quantify the influence of pipe burial depth on the consequence of such event. The pipeline can fail in different ways; therefore, different failure mechanisms are considered. It is found that deeper pipe burial would not necessarily reduce the expected pipeline damage should anchor impact occur. Instead, the governing mechanism might be changed.
Pipelines are subject to various risks after being installed on the seabed. One of these risks is third-party interaction. The following is required to quantify the risk corresponding to a certain event causing damage to the pipeline:
The likelihood of the event;
The consequence the event given that it occurs.
Assessing the likelihood typically requires a separate study next to assessing the potential consequence.
This paper focuses on providing a suitable estimate of the consequence of the following two possible third-party events:
Dropping an object on top of the pipeline;
Dragging of the pipeline by a hooked anchor.
Current practice treats the assessment of dropped objects impacting a pipeline with conservatism. In order to obtain more realistic results of expected damage it is important to duly account for the relevant parameters. This paper presents the relative contributions of several parameters, such as the combination of object mass and terminal velocity, influence of internal fluid and its pressure, and the influence of soil characteristics.