DESIGN AND FATIGUE ANALYSIS ON SUBSEA PIPELINE FREE SPAN AT MADURA STRAIT

• Main Author: Sugiyana, Temmy
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/68044
• Institution: Institut Teknologi Bandung

Indonesia as one of the world's oil and gas producing countries has many exploration facilities, one of them is a subsea pipeline. The use of oil and natural gas meet more than 50% of national energy needs. Subsea pipelines are used to distribute oil and gas exploration products between facilities. The subsea pipeline design stage begins with the pipe wall thickness design based on the DNVGL-ST-F101 standard. The pipe wall thickness is designed based on internal overpressure criteria, external overpressure criteria, and propagation buckling failure criteria under installation, hydrotest, and operating conditions. The determination of the pipe thickness is adjusted to the availability of the pipe based on the API 5L Specification for Linepipe. The pipe wall thickness that meets all the criteria is 12.7 mm. Then the next design stage is the design of the concrete blanket thickness as the result of on-bottom stability analysis based on the DNVGL-RP-F109 standard. The on-bottom stability analysis describes the stability of the lateral and vertical directions of the pipe and the trenching requirements of the pipe. The thickness of the selected concrete coating is 70 mm with the need for trenching as deep as 0.1 m. Analysis of the subsea pipeline installation was carried out with the help of the OFFPIPE program. The subsea pipeline installation is carried out using the S-Lay method and a HAFAR NEPTUNE lay barge with a trim angle configuration of 1.5? and a hitch angle of -3?. The installation analysis is carried out in two water conditions and considered the response of the barge movement when exposed to waves from several angles of the direction of the waves. Laybarge configuration optimization is done by changing the roller coordinates, hitch angle and trim angle. Due to the uneven shape of the seabed and several other phenomena, it is possible for free spans to occur in the subsea pipeline. The free span analysis was carried out based on the DNVGL-RP-F105 standard by considering the VIV and direct wave loading on the pipe. The allowable free span length is 16 m based on screening fatigue criteria and 23 m based on ultimate limir state criteria. The calculation of the fatigue life of the submarine pipeline is carried out using the DNV FatFree program with a fatigue life criterion of 50 years.