DESIGN AND CATHODIC PROTECTION ANALYSIS OF SUBSEA PIPELINE IN JAVA SEA

• Main Author: Widihastuti, Prima
• Format: Final Project
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/63579
• Institution: Institut Teknologi Bandung

Significant technological developments in modern times have led to increased energy needs, one of them are oil and natural gas. The depleting sources of oil and natural gas have caused exploration activities for fossil energy reserves to shift towards offshore. The subsea pipeline system is the main alternative for effective and economical distribution of oil and natural gas, so a design plan that is in accordance with standards and meets the service life is required. Subsea pipelines need to be designed properly so that failure does not occur, starting from the installation to operation stage. The design of the subsea pipeline begins with determining the wall thickness of the steel pipe which refers to the DNV-OS-F101 standard. The subsea pipe steel walls are designed to withstand internal and external pressures 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 combined loading. The next design process is on-bottom stability analysis, which refers to the DNV-RP-F109 standard. Through this analysis, the subsea pipeline will be given a concrete weight coating if the weight of the pipeline steel itself is not sufficient to make the pipeline stable in the lateral and vertical directions. After that, an analysis of the subsea pipeline installation performed using the OFFPIPE and MOSES software to determine the configuration of the laybarge components so that the pipeline stress that occurred during installation was in accordance with industrial practical design criteria. Installation analysis performed under static and dynamic conditions at maximum and minimum water depth. Next, a free span analysis performed based on the DNV-RP-F105 standard. Free span occurs due to the uneven bathymetric contours of the seabed, so that there is a section of the pipe that is not supported. The maximum allowed free span length needs to be calculated so that the natural frequency due to the harmonic motion of the pipe is smaller than the natural frequency of the pipe material. Subsea pipelines are made of steel. One of the weaknesses of steel in subsea pipelines during operation is the problem of corrosion. The grains between the constituent materials of the pipe steel have potential differences so that a natural cathode and anode system are formed. The pipe operating environment is in the form of seawater which is an electrolyte. The presence of an anode and cathode that are electrically connected to the electrolyte causes corrosion of the subsea pipeline. Corrosion will affect the integrity of the subsea pipeline so it must be controlled. One of the corrosion control methods on subsea pipelines that can be done is cathodic protection with a sacrificial anode. Cathodic protection analysis was performed according to the standard DNV-RP-F103. Through this analysis, the number of anodes used, the distance between the anodes, and the total mass of anodes will be calculated. The subsea pipeline designed and analyzed in this Final Project is located in the Java Sea with a length of 19.75 km. The results obtained from the design of the pipe wall thickness are 12.7 mm and the required thickness of the concrete weight coating is 40 mm. Then, the configuration of the Timas DL-01 laybarge component was obtained in the form of a roller, tensioner, and stinger layout configuration as well as trim and hitch angles that met the industrial practical design criteria. Furthermore, the maximum allowed free span length is 18.9 m. Finally, the results of the cathodic protection analysis on subsea pipeline for a design life of 20 years, show that 68 units of bracelet type aluminum anode are needed, with the distance between the anodes is 24 pipe joint length or 292.8 m, and the total weight of the anodes is 2316.418 kg.