DESIGN AND RISK ASSESSMENT OF SUBSEA PIPELINE CAUSED BY DROPPED ANCHOR, DRAGGED ANCHOR, AND SINKING VESSEL IN MADURA STRAIT

• Main Author: Rayhan Rafsanjani, Muhammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/78263
• Institution: Institut Teknologi Bandung

The demands for oil and gas as energy resources and to fulfill industrial needs are increasing over time. This condition has driven the Indonesian government to plan exploration and exploitation activities for petroleum and gas until 2050. Subsea pipelines, as one of the oil and gas distribution systems, are designed based on feasibility and security standards. In this final project, a 33.64 km-long subsea pipeline is planned in the Madura Strait, involving a design process that includes wall thickness analysis based on DNVGL-STF101, on-bottom stability analysis based on DNVGL-RP-F109, installation analysis based on industry criteria and stress criteria in the DNVGL-ST-F101 standard, free span analysis based on DNVGL-RP-F105, and risk assessment based on DNVGL-RP-F107. Additionally, environmental data processing is conducted to obtain values for water depth, significant wave height, peak wave period, current velocity at 90% depth below the sea surface, tidal range, and storm surge. To ensure the environmental data used is more effective and representative, the subsea pipeline is divided into two zones based on environmental data similarity. In the wall thickness analysis, a subsea pipeline wall thickness of 14.3 mm is determined. In the on-bottom stability analysis, a concrete cover thickness of 40 mm is determined, with a trenching depth of 0.125 m and a trenching angle of 45° for zone 1, while no trenching is needed for zone 2. In the installation analysis, a lay barge configuration that meets stress criteria for both maximum and minimum water depths is determined. In the free span analysis, the allowable free span length is determined to be 11.95 m for zone 1 and 17.15 m for zone 2. In the risk assessment, the level of risk for subsea pipeline failure caused by dropped anchor, dragged anchor, and vessel sinking is determined to be within the acceptable and ALARP (As Low as Reasonably Practicable) range, with relatively low probabilities (ranks 1 to 3) and various consequences (ranks 1 to 4).