| dc.description.abstract | The world’s energy resources on land are getting depleted, and mush attention is given to the
development of offshore fields. Over the past years, new reserves located offshore have been
regularly discovered. Once the hydrocarbons have been extracted, it is necessary then to
transport them to the storage places, refineries or gas processing plants, and to deliver to the
consumers. There are several ways of hydrocarbon transportation. One of the most cost-effective
and popular means of oil and gas transportation is pipelines.
Construction and operation of subsea pipelines are known to be very hazardous and risky
processes. In order to ensure reliable and safe operation of submarine lines, it is essential to
design them according to the international standards and codes. However, observance of rules
sometimes does not guarantee safe pipeline operation. Some undesirable events can occur from
time to rime. One of such events is dragging anchor incident, which poses great threat to the
subsea lines. The consequences of this incident may be huge, involving environmental pollution,
asset losses and even fatality. The mitigation of these outcomes becomes problematic, expensive
and impossible. That is why it is recommended to carry out relevant investigations before the
mitigation measures are planned and implemented.
This work is mainly focused on the anchor damage assessment of subsea pipelines. The
comprehensive discussion on a PARLOC 2001 database is done in order to determine major
pipeline incidents, their causes and consequences. The questions regarding pipe-anchor
interaction scenario have been studied a lot. It has been found that the extent of pipeline damage
is heavily dependent on its unique properties. In addition, not only the pipeline data, but also a
combination of vessel characteristics and anchoring equipment parameters has been very useful
for the analyses.
Based on the results of AIS ship traffic data processing, main pipe damage criteria checks have
been performed. The findings indicate that not all the anchors have potential of hooking and
approaching the pipeline resting on the seafloor. Key parameters here are anchor class (size),
chain length, ship speed and water depth. Moreover, the geometrical configuration of all the
anchors has been taken into account as well. Not only a theoretical approach, but a model scale
test has been carried out in order to understand the variation of anchor towing depth with
different ship velocities. The comparison of analytical solution results with the experimental
results is also included in this thesis.
Anchor pulling consequences are established in accordance with the global scale analyses
performed in the FE program SIMLA for a certain number of sensitivity cases for both small
(16-inch) and large (40-inch) diameter pipelines. The pipelines responses have been determined,
and their cross-sectional capacities have been checked. In addition, pipelines failure frequencies
have been estimated.
This work shows how critical it is to have detailed ship and equipment class data for doing
pipeline integrity assessment. In accordance with the results obtained, the dragging anchor
interference assessment methodology is developed. | nb_NO |
