DESIGN AND CROSSING SUBSEA PIPELINE ANALYSIS USINGGROUT BAG AS SUPPORT OFF THE COAST OF WEST JAVA

• Main Author: Santoso, Dave
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/77215
• Institution: Institut Teknologi Bandung

In the process of planning underwater pipelines, there are often issues where a route of the underwater pipeline being constructed intersects with the route of an existing underwater pipeline from a previous project. To prevent direct contact between the existing and new pipelines, support structures are required. The design process of the underwater pipeline follows several design standards and is conducted with various combinations of loading conditions. The first stage of designing the underwater pipeline involves analyzing the pipe wall thickness using the DNV-ST-F101 design standard. In this design standard, the pipe wall is designed to withstand excessive internal pressure, pressure collapse due to external pressure, and propagation buckling. The calculated pipe wall thickness, adjusted with API 5L specifications, is determined to be 17.48 mm. The next analysis is the on-bottom stability analysis to determine the thickness of the concrete coating on the pipe to ensure vertical and lateral stability, following the DNV-RP-F109 standard. The required thickness of the concrete coating is 85 mm. The analysis continues with the analysis of free span length to determine the permissible free span length based on the DNV-RP-F105 standard. For this particular project, the permissible free span length is 21.9 m. During pipeline installation, other obstacles may be encountered, such as existing pipelines. To cross existing pipelines, support structures in the form of grout bags are needed. The stability of these support structures is analyzed in terms of ultimate bearing capacity, sliding, and overturning. The installation of support structures may also cause settlement, so it is necessary to check whether the height of the structure still meets design criteria after settlement occurs. The pipeline modeling is performed using AutoPipe to obtain the allowable stress values based on ASME B31.8 Chapter VIII. The modeling is conducted for both hydrotest and operational conditions. Iterations are performed to determine the height of the support structures and adjust the spacing between structures to meet the allowable stress and stability analysis based on the specified standards. The support structures are confirmed to be stable, and the stresses occurring in the pipeline do not exceed the allowable stress.