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ITS » Undergraduate Theses » Teknik Kelautan
Posted by hassane at 25/11/2008 15:59:56  •  5619 Views


ANALISA TEGANGAN PADA PIPA BAWAH LAUT AKIBAT GERAKAN LAY-BARGE PADA SAAT LAYING DENGAN BERDASAR RANAH FREKUENSI

FREQUENCY DOMAIN STRESS ANALYSIS ON SUBSEA PIPELINE DUE TO INFLUENCE OF LAY-BARGE MOTION DURING INSTALLATION

Author :
Panambang, Mohammad A 




ABSTRAK

Subsea pipeline mengalami kondisi pembebanan paling ekstrim pada saat instalasi laying. Pada saat ini tegangan yang terjadi akibat gerakan lay-barge terutama bending relatif lebih besar sehingga diperlukan metode instalasi serta analisa tegangan yang tepat dan handal. Instalasi dengan metode S-Lay merupakan salah satu cara yang tepat dan sering digunakan untuk perairan yang dangkal sampai kedalaman menengah. Dalam penelitan ini lay-barge yang dipakai untuk model adalah Castoro II milik Saipem dengan dimensi utama 135 x 32.6 x 9 m L x B x H dengan maximum tensioner capacity 180 ton dan 12 konfigurasi mooring. Pipa yang dikaji mempunyai diameter 16 inch dan ketebalan 1 inch. Lay-barge tersebut dilengkapi dengan stinger yang berfungsi sebagai curvature control bentangan pipa di daerah overbend sehingga tegangan bending yang terjadi dapat dikurangi. Pemodelan dan simulasi pembebanan dilakukan dengan bantuan software MOSES Multi Operational Structural Engineering Simulator. RAO perubahan tegangan pada pipa diperoleh dengan mentransformasi gaya yang berkerja pada lay-barge akibat eksitasi beban gelombang angin dan arus dengan ditinjau pada tiap 5 arah pembebanan 0 derajat 45 derajat 90 derajat 135 derajat dan 180 derajat. Keganasan kondisi lingkungan direpresentasikan oleh kondisi ekstrem operasional 1-tahunan yang meliputi tinggi gelombang signifikan 3.4 m kecepatan arus permukaan 0.61 ms dan dengan kecepatan angin 10.7 ms. Hasil analisis menunjukkan terjadinya tegangan equivalent maksimum sebesar 331.6 MPa di daerah overbend. Mengacu pada hasil stress check dengan menggunakan ABS Code dapat disimpulkan pipeline masih berada pada daerah aman sebagaimana ditunjukkan oleh faktor pemakaian sebesar 0.9.


ABSTRACT

Subsea pipeline generally experiences the most extreme condition at the time of its installation. In this condition stresses develops due to the effect of lay-barge motion especially in the form of structural bending which is customarily greater than other load effects. Considering this fact a precise installation method and reliable stress analysis ought to be properly prepared. Pipeline installation with S-lay method to some degree is viewed as one of the best practice and is often used for activities in shallow up to intermediate water depth. In the current study lay-barge is modeled with a reference to Castoro II a vessel owned by Saipem having principal dimensions 135 x 32.6 x 9 m L x B x H. The vessel has a 180-tonne maximum tensioner capacity and 12 mooring configuration. The lay-barge is equipped with articulated stinger to control pipe spanning curvature and to prevent overstresses at overbend region. The pipeline under investigation is characterized by outside diameter of 16 inch and 1 inch wall thickness. Modeling and loading simulation are performed by Multi Operational Structural Engineering Simulator software MOSES. RAOs of the stresses on the pipeline are obtained by converting the forces acting on the lay-barge due to wave wind and current. These environmental loads are simulated to propagate in five directions namely 0 45 90 135 and 180 degree. The severity of the environmental loads is taken to be the 1-year operational extreme condition which is represented by the significant wave height of 3.4 m speed of surface current 0.61 ms and the wind speed 10.7 ms. Results of analysis shows the maximum equivalent stress is as high as 331.6 MPa at overbend region. In accordance to the stress check using the ABS Code it is found that the pipeline is within the safe region as indicated by the usage factor of 0.9.



KeywordsS-Lay ; Overbend ; Lay-Barge
 
Subject:  Pipa
Contributor
  1. Dr. Ir. Eko Budi Djatmiko, M.Sc
    Ir. Murdjito, M.Sc.Eng
Date Create: 25/11/2008
Type: Text
Format: pdf
Language: Indonesian
Identifier: ITS-Undergraduate-3100007030089
Collection ID: 3100007030089
Call Number: RSKe 621.867 2 Pan a


Source
Undergraduate Theses of Ocean Engineering Department, RSKe 621.867 2 Pan a, 2007

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Copyright @2007 by ITS Library. This publication is protected by copyright and permission should be obtained from the ITS Library prior to any prohibited reproduction, storage in a retrievel system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to ITS Library




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