Abstract
The subsea pipeline system of PT. X located at north of West Java transports natural gas with 19 kilometers long and 16 inches standard pipe size. The rough seabed causes free span problem. The system will be threatened by a structural failure of fatigue due to Vortex Induced Vibration (VIV) and local buckling as the effects of free span. In this Final Project, a total of 136 free spans on subsea pipeline system due to the uneven seabed are analyzed. The screening will be done for spans with length and diameter ratio more than 30 to figure out the free span which pass the screening and know the risk level of the subsea pipeline due to free span. The result for fatigue screening due to VIV, spans with a length more than 25 meters did not pass the screening. Local buckling occurred at the longest free span with a length of 62 meters. The level of risk to structural failure caused fatigue due to VIV has the highest level in terms of business and the environment, namely in the medium category. The level of risk to local buckling failures for safety, environmental, and business terms was in low category.
Highlights
Pipelines are the most effective means of transport in delivering oil, gas, water, and chemical chemicals [1]
Free Span analysis was used to determine the natural frequency of pipes in each of the free expansions that do not qualify for the L/D ratio screening
A span that has a ratio of L/D to more than 30 was considered causing a failure, fatigue due to Vortex Induced Vibration (VIV) and local buckling
Summary
Pipelines are the most effective means of transport in delivering oil, gas, water, and chemical chemicals [1]. The use of subsea pipelines can reduce transportation costs up to one fifth, and pipelines can deliver hydrocarbons in real time [2]. At the time of operation of the subsea pipe had problems resulting from the contour of rough seabed as it is on land, this causes the pipe to experience a free span. The free span of the subsea pipelines may pose a risk of buckling and fatigue caused by vibrations. While fatigue in the subsea pipeline structure can occur when the frequency of the vortex flow formed at the around of the pipe is close to the natural frequency of the pipeline itself, this vibration can result in fatigue damage that cannot be left on the structure [4]
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