Design and Crossing Subsea Pipelines Analysis Using Grout Bag as Support in Java Sea
Vivi Ashwin Fatmawati 1) dan Rildova 2)
Program Studi Sarjana Teknik Kelautan
Fakultas Teknik Sipil dan Lingkungan, Institut Teknologi Bandung
Jalan Ganesha 10 Bandung 40132
viviashwinfatmawati@gmail.com 1) dan rildova@ocean.itb.ac.id 2)
Abstract: Selection of subsea pipeline routes, sometimes cannot avoid crossing with existing
pipelines to get effective and efficient route selection. So that the existing pipe and the new pipe
do not come into direct contact, it is necessary to provide a support structure. The subsea pipeline
design process follows several design standards and is carried out at various load combinations.2
The analysis begins with determining the pipe wall thickness using the DNVGL – ST – F101
standards with the fulfillment of four design criteria including internal pressure containment, local
buckling due to external overpressure, local buckling due to combined loading, and propagation
buckling. The pipe thickness value obtained after adjusting to API 5L is 14.3 mm. The next
analysis is on bottom stability to determine the thickness of the concrete layer on the pipe so that
the pipa has vertical dan lateral stability based on the DNVGL – RP – F109 standard. The thickness
of the concrete layer required is 40 mm. The analysis is continued with the analysis of the length
of the free span to determine the length of the allowed free span based on SNVGL – RP -F105. In
this final project, the allowed free span is 25.9 m. Next, for the stress analysis at the pipe crossing,
it begins with determining the minimum height of the support structure with vertical clearance
between the existing pipe and the new pipe is 0.3 m based on DNV – ST – F101. Then, the iteration
of the dimensions of the support structure is carried out to meet the structural stability requirement,
such as overturning stability, sliding stability, and bearing capacity analysis. In addition, settlement
analysis was also carried out due to the existence of a support structure. The height of the support
structure under operating conditions is the height of the structure after experiencing settlement. The
pipe modeling was carried out using CAESAR II to obtain the allowable stress values based on
ASME B31.4 Chapter IX. The modeling was carried out under hydrotest and operating conditions.
Iterations are done by increasing the number of support structures and adjusting the distance
between structures so that the resulting pipe profile curvature can meet the allowable stresses based
on these standards. The support structure used in this final project is a grout bag with total of four
pieces which results in the ratio of the maximum stress combination that occurs and is allowed to
be 0.991.
Keywords: free span, on-bottom stability analysis, pipe cross stresses, wall thickness.
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