DESIGN AND UPHEAVAL BUCKLING ANALYSIS OF SUBSEA PIPELINE IN MAKASSAR STRAIT

• Main Author: Naufal Andika S, Muhammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/66806
• Institution: Institut Teknologi Bandung

The methods that commonly used in the transportation of oil and gas to onshore are by tankers and subsea pipeline. Subsea pipeline itself is considered more efficient because its use is more practical than ships and its transportation capacity is larger. The subsea pipeline that will be used needs to be designed so that it can function without any problems. In general, the subsea pipeline design process consists of pipe wall thickness planning, concrete coating calculation, feasibility analysis during installation, and determination of the free span length The design of the subsea pipeline begins with determining the pipe wall thickness based on the DNVGL-ST-F101 standard. The pipe walls are designed to withstand four failure criteria, which are bursting due to internal pressure containment, local buckling-system collapse due to external pressure, propagation buckling, and local buckling due to combined loading. The next design stage is on-bottom stability analysis based on the DNV-RP-F109 standard. From this analysis, the pipe will be given a concrete coating if the weight of the steel is not enough to make the pipe stable in the lateral and vertical directions on seabaed. The next step is an installation analysis using OFFPIPE dan MOSES program to determine the configuration of the roller, tensioner, and stinger on the ship used and the amount of trim and hitch angels. In this analysis, the magnitude of the pipe stress during installation must comply with practical criteria from the industry or the DNVGL-ST-F101 standard. After that, a free span analysis will be carried out 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 free span 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 pipeline sometimes needs to be buried on the seabed to avoid sizable waves and currents or other harmfull marine activity. However, buried pipe does not have the freedom to move, so it can be potentially exposed to compressive forces due to changes in temperature and internal pressure during operation. If there is a imperfection height in the pipe due to the uneven ground surface, then the compressive force can point vertically upwards. If the force is greater than the resistance of the soil and the weight of the pipe itself, there will be bending of the pipe out of soil, which is called upheaval buckling. Upheaval buckling analysis can be performed based on standards DNV-RP-F110 and DNV-RP-F114. The submarine pipeline designed and analyzed in this final project is located in the Makassar Strait with a length of 301 km. The result obtained from the design of the pipe wall thickness is 12.7 mm and the required concerete coating thickness is 40 mm. Then, the pipe installation is carried out with the Timas DL-01 barge which has a trim angle configuration of 1.5º and hitch 0o. Furthermore, the allowed free span length is 10.762 m. Then the results of the on-bottom stability analysis also stated that the pipes at stations 1, 2, 3, 4, and 8 need to be placed in a trench with a depth of 0.8 m, 1.05 m, 0.907 m, 1.043 m, and 0.8 m. Then, the critical span length due to imperfection height is obtained, where the pipe has the potential to experience upheaval buckling, respectively at the five stations are 51,832 m, 53,467 m, 118,279 m, 127,07 m, and 44,13 m.