DESIGN AND FATIGUE ANALYSIS USING DETERMINISTIC METHODS ON FREE SPANS OF SUBSEA PIPELINES IN THE MADURA STRAIT

• Main Author: Gading Salsabiyla, Taaba
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/61788
• Institution: Institut Teknologi Bandung

Indonesia is abundant in oil and gas. Along with the increasing demand for gas and oil, exploration and exploitation of these resources must continue to be promoted. Supporting facilities are needed to accommodate oil and gas resources, one of the common facilities is a subsea pipeline system, It is one of the most effective transportation systems can distribute fluids from one place to another massively and sustainably. Subsea pipelines need to be designed properly so that failures do not occur which can cause contamination of the surrounding ecosystem. The design process begins with determining the pipe wall thickness which refers to the DNVGL ST-F101 standard. The pipe walls are designed to withstand internal and external pressure which are analyzed based on four criteria, namely bursting due to internal pressure content, local buckling in the form of system collapse due to external pressure, propagation buckling, and local buckling due to a combination of loading.The next design process is the on-bottom stability analysis by the DNVGL RP-F109 standard. This analysis aims to obtain the value of the thickness of the concrete layer as ballast so that the pipe can be vertically and laterally stable on the seabed. Then is the free span analysis of the subsea pipeline refers to the DNVGL RP-F105 and DNVGL RP-C203. Free span is the part of the pipe that is not supported on the seabed due to uneven seabed bathymetry. The wave load experienced by the pipe segment in the free span will cause harmonic motion in the pipe. The free span is checked for static criteria due to self-load. The spans that meet the stature criteria are then checked against the fatigue screening criteria. If the span does not meet the fatigue screening criteria, it is necessary to carry out a fatigue analysis. All free spans are checked against the ultimate limit state criteria so that they do not exceed the material strength limit. In this final project, the design and analysis stages are carried out for a subsea pipeline in the Madura Strait with a length of 20 km. The result is a wall thickness of 19.1 mm and a concrete layer thickness of 50 mm. Then, the results of the static free span analysis showed that there were several spans that did not meet the criteria so that they required modification of the length of the span, there are free spans numbered 165, 167, 169, and 172. Meanwhile, spans that passed the static criteria but required fatigue analysis were span number 171. From the results of the fatigue calculation, it is found that the free span number 171 can withstand a service life of 45 years and is not sufficient for the design life (50 years), but when compared to the expected service life of 20 years, it is sufficient, so there is no need to modify the length of the free span.