DESIGN AND CATHODIC PROTECTION ANALYSIS OF SUBSEA PIPELINE IN MAKASSAR SRAIT

• Main Author: Arief Faishal, Muhammad
• Format: Final Project
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/57142
• Institution: Institut Teknologi Bandung

Indonesia is abundant in oil and gas. Their products are utilised in almost all sectors of life, leading to constant heralds of their exploration and exploitation. The trend of these activities has changed from onshore fields, (land/near the coast) to offshore fields, until the deep sea. To support both exploration and exploitation, facilities and infrastructure are needed. For primarily oil and gas exploration, the subsea pipeline system is one of the most crucial facilities. It is one of the most effective transportation systems to distribute fluids both massively and sustainably. However, fluids such as oil and gas in this subsea pipeline are environmental pollutants with the potential to harm human health. It is necessary to carry out various steps of design and analysis on subsea pipelines so that the system can withstand different loads and meet feasibility standards during its operation. The design process begins by determining the pipe wall thickness by the DNVGLST- F101 standard. The pipe wall must withstand internal and external pressure as seen from four failure criteria: bursting due to internal pressure containment, local buckling-system collapse due to external pressure, propagation buckling, and local buckling due to combined loading. Then is the analysis of on-bottom stability, calculated by the DNV-RP-F109 standard. Pipes must remain vertically and laterally stable. Insufficient weight of the steel pipe will lead to its instability. In this condition, a concrete coating is applied to increase the pipe's weight and achieve the minimum pipe weight required to obtain seabed stability. The next stage is the analysis of the subsea pipeline installation using OFFPIPE software. This lay barge component analysis configures the roller, tensioner, and stinger locations, as well as the angle of the trim barge and hitch/stinger rotation. These configurations ascertain that the pipe stress during installation follows industrial practical design criteria and the DNVGL-ST-F101 standard. Installation analysis is performed under static and dynamic conditions at maximum and minimum depths. The static analysis acknowledges physical factors such as pipe position during the installation process with lay barges. Meanwhile, the dynamic analysis acknowledges the movement of the lay barges due to hydrodynamic loads such as water waves. Ship movement data in RAO (Response Amplitude Operator) is obtained by modelling the barge and environmental loads on MOSES software. Both static and dynamic analysis results need to meet the stress design criteria. After that, a free span design and analysis of the subsea pipeline is carried out by the DNV-RP-F105 standard. Free span is the part of the pipe that is not supported on the seabed due to uneven sea bathymetry. The wave load experienced by the pipe segment in the free span will cause harmonic motion in the pipe. It is necessary to calculate the maximum free span of the pipe so that the natural frequency due to its harmonic motion is smaller than the natural frequency of the pipe material. Subsea pipelines are very susceptible to corrosion. The impurity of the materials that make up the steel pipe causes a potential difference between the grains, making the subsea pipe a natural cathode and anode system. The seawater operating environment is an electrolyte, causing the pipes to potentially corrode. Additional corrosion protection on the pipe is necessary and can be done using a cathodic protection system with the sacrificial anode method. The sacrificial anode used in subsea pipelines is usually a bracelet anode. An analysis is needed to determine the number of anodes used, the distance between the anodes, and the total mass of anodes. Calculations are carried out by the DNVGL-RP-F103 standard. In this final project, this design and analysis process is performed for a subsea pipeline in the Makassar Strait with a length of 301 km. The result is a wall thickness of 12.7 mm and a concrete layer thickness of 40 mm. Then the installation analysis was carried out with the Timas DL-01 lay barge with a trim angle configuration of 1.5º and hitch 0º. The highest value of stress in the pipe is 84.32%SMYS in dynamic analysis at maximum depth with an angle of incidence of 0º wave and residual stress of 688.95 kN. Furthermore, the allowed free span length is 11.73 m. Finally, the cathodic protection analysis was carried out with an anode bracelet made of aluminium. It obtained the required number of anodes that is 1041 pieces, with a total anode weight of 32.6 tons and an average anode distance of every 24 pipe joint lengths or 292.8 m.