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The Study of Tandem Offloading Performance and Operability on The Cylindrical Hull FPSO Sevan Stabilized Platform with Variation in Mooring System Configuration Eko Budi Djatmiko; Jousie Rebecca; Murdjito Murdjito
International Journal of Offshore and Coastal Engineering (IJOCE) Vol 1, No 2 (2017)
Publisher : DRPM (Direktorat Riset dan Pengabdian kepada Masyarakat) ITS

This study has been carried out to evaluate the dynamic behavior of the Cylindrical FPSO Sevan Stabilized Platform (SSP) and the LNG Carrier (LNGC) during the process of tandem offloading. The study includes hydrodynamics modellings, computations, and simulations of both cases SSP and LNGC operated individually and in combination for offloading operations. The SSP is moored with two variations of mooring, namely taut and catenary. Environmental loads are waves with the incorporated winds and currents propagating 90o, 210o, and 330o relative to the SSP headings. Excitation of random waves up to Hs = 4.50 m instigates the relatively low SSP motions in standalone condition. In offloading condition, when LNGC is connected, the SSP motion could magnify as much as 2.0 up to 5.0 times higher than that in standalone condition, but still considered in an acceptable level. The motion quality of LNGC in offloading operation is comparable with the SSP. For various random wave headings with Hs = 4.50 m during offloading operation may generate maximum tensions between 1,600 kN up to 2,600 kN in the casse of catenary mooring, and between 4,700 kN up to 7,000 kN in the case of taut mooring. Even then, this largest tension preserves a safety factor of 2.05 which is well above the limit of 1.67 as required by the governing standards. Finally, the study conclude an operability of as much as 90% could be achieved on SSP and LNGC offloading operation in the Masela Block of the Abadi Gas Field.

Ultimate Strength of the Buoy Structure due to the Loads Arise from the Tanker and Mooring Lines Murdjito Murdjito; Handayanu Handayanu; Resy Agatya
International Journal of Offshore and Coastal Engineering Vol. 1 No. 1 (2017)
Publisher : Department of Ocean Engineering

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j2580-0914.v1i1.2893

A study was conducted to evaluate the ultimate strength of a 40 ton buoy induced by the dynamic loads arising from a 120,000 DWT Aframax tanker and mooring lines. The buoy is operated at Bangka Strait offshore oil terminal. The evaluation was commenced by analyzing the motion characteristics of the buoy and tanker due to environmental excitations, both in free floating conditions. This is continued by the simulation and time-domain analysis of connected buoy and tanker to observe the hawsers and mooring line tension intensities. The corresponding results show the largest tension occurs in the in-line configuration with the tanker in ballast condition, where hawsers tension reaches 1282.58 kN with a safety factor of 2.23 and mooring line tension 1974.18 kN with a safety factor of 3.20. The resulting tensions were further applied as input data for structural modeling using FEM to find out the stresses develop on the buoy structure. Results of this modeling reveal the maximum value of stress experienced by the buoy structure is approaching 184.28 MPa, which is below allowable stress of 200 MPa. Following this, the ultimate stress of 450 MPa will be violated by 143% incremental load above the maximum, namely 3,116.67 kN and 4,797.26 kN due to the hawsers and mooring line. This fact suggests that the structure is unlikely to experience ultimate failure if merely operated in the current operational site.

The Study of Tandem Offloading Performance and Operability on The Cylindrical Hull FPSO Sevan Stabilized Platform with Variation in Mooring System Configuration Eko Budi Djatmiko; Murdjito Murdjito; Jousie Rebecca
International Journal of Offshore and Coastal Engineering Vol. 1 No. 2 (2017)
Publisher : Department of Ocean Engineering

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j2580-0914.v1i2.7054

This study has been carried out to evaluate the dynamic behavior of the Cylindrical FPSO Sevan Stabilized Platform (SSP) and the LNG Carrier (LNGC) during the process of tandem offloading. The study includes hydrodynamics modellings, computations, and simulations of both cases SSP and LNGC operated individually and in combination for offloading operations. The SSP is moored with two variations of mooring, namely taut and catenary. Environmental loads are waves with the incorporated winds and currents propagating 90o, 210o, and 330o relative to the SSP headings. Excitation of random waves up to Hs = 4.50 m instigates the relatively low SSP motions in standalone condition. In offloading condition, when LNGC is connected, the SSP motion could magnify as much as 2.0 up to 5.0 times higher than that in standalone condition, but still considered in an acceptable level. The motion quality of LNGC in offloading operation is comparable with the SSP. For various random wave headings with Hs = 4.50 m during offloading operation may generate maximum tensions between 1,600 kN up to 2,600 kN in the casse of catenary mooring, and between 4,700 kN up to 7,000 kN in the case of taut mooring. Even then, this largest tension preserves a safety factor of 2.05 which is well above the limit of 1.67 as required by the governing standards. Finally, the study conclude an operability of as much as 90% could be achieved on SSP and LNGC offloading operation in the Masela Block of the Abadi Gas Field.

The Study of Mooring Buoy Operability to Support Offloading Operation of Shuttle Tankers with Various Capacities Eko Budi Djatmiko; Murdjito Murdjito; Mochammad Afif Zahiru Fajar
International Journal of Offshore and Coastal Engineering Vol. 4 No. 1 (2020)
Publisher : Department of Ocean Engineering

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j2580-0914.v4i1.8704

This study was conducted to analyse of the operability of mooring buoy initially designed for offloading operation of 35,000 DWT shuttle tankers enhanced to serve the offloading operations of shuttle tankers with 50,000 DWT, 75,000 DWT, and 111,000 DWT capacities. Operability is reviewed in term of mooring line tensions induced by each new variation of tanker capacity under environmental conditions of 1-year, 10-year, and 100-year recurrence. The governing criteria is that the safety factor should meet the appropriate limit as stated in the API RP2SK. Tension on the mooring line increases in parallel with the increasing of tanker capacity. For the case of 35,000 DWT and 50,000 DWT shuttle tankers the operation can be performed in all environmental conditions. For the case of 75,000 DWT shuttle tanker with full load and 67% DWT capacity can fully operate in all environmental conditions, but with 47% DWT capacity could not be operated in the 100-year environmental condition with significant wave height 3.31 m for the direction of inline-L1, inline-L2, and between line-L1&L4. For the case of 111,000 DWT shuttle tanker at all capacity conditions can fully operate in the 1-year environmental condition with significant wave height up to 1.48 m.

Risk Analysis of Decommissioning Process: Case Studies of Lima-Compresor Platform Daniel Mohammad Rosyid; Murdjito Murdjito; Arif Windiargo
International Journal of Offshore and Coastal Engineering Vol. 4 No. 1 (2020)
Publisher : Department of Ocean Engineering

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j2580-0914.v4i1.8705

The process of petroleum exploration and exploitation is a crucial activity in the fulfillment of energy needs in the world. The process of petroleum exploration and exploitation is currently centred on shallow water regions in the continental shelf. In the process of petroleum exploration and exploitation in shallow waters, the structure of which is commonly used is the jacket structure. In Southeast Asia there are about 1300 platforms, of which 80% is over 20 years old. When the platform has reached its operational limit, according to the ministerial regulation of ESDM number 1 year 2011 The platform must be decommissioning in accordance with existing technical standards. In the process of demolition, there are certainly risks and hazards that can interfere with the process of decommissioning. It is necessary to do a risk analysis to map the risks that can occur while preparing the mitigation steps. In this study, risk analysis arel conducted by determining the activity that has a significant degree of hazard where it is concluded that activities that have a significant risk level are activities related to construction, lifting, maintenance, well service, and maintenance. From each activity that has a significant hazard level, there was a process of determining the cause of risk using the Fault Tree Analysis (FTA) method while determining the barrier that serves to prevent a risk occurring. The next is to determine the impact that can be inflicted from risk by using the Event Tree Analyis (ETA) method while determining the barrier that serves to prevent and reduce the impact that occurs when there is a peril. These two FTA and ETA diagrams are combined to create a Bowtie diagram to explain in detail the risk management performed at each stage of the decommisiioning process.

Fatigue Life Comparison of Modified and Conventional 3 Leg Jacket Offshore Structure Murdjito Murdjito; Muhammad Nabil Ghiffary; Rudi Walujo Prastianto
International Journal of Offshore and Coastal Engineering Vol. 4 No. 2 (2020)
Publisher : Department of Ocean Engineering

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j2580-0914.v4i2.9306

The jacket structure must be adapted to the conditions of the production field to support economic factors. So, the concept of a modular platform for minimal, low-cost facilities is adopted. However, the design differences will affect the performance of the jacket itself, in other words a modular jacket can withstand the same load as a conventional jacket model but has a different structural performance. Therefore, this research discusses the performance comparison, which includes the fatigue life and the natural period, between conventional and modular jacket structures, which in this study are referred to as modified jackets. Conventional jacket as a comparison structure takes the design basis of the modified structure, including the same structural profiles, and environmental loads. In this study, the two jackets will only be modeled on the jacket part and the superstructure will be modeled as a joint load on the three upper ends of the jacket legs. Fatigue life analysis in this study used the full spectral analysis method. By using SACS software, the natural period of modified jacket is 1.756 s and conventional jacket is 1.472 s. While the lowest fatigue life on modified jacket is 44.98 years and conventional jacket is 9125.79 years.

Lazy Wave Flexible Riser Dynamic Responses Analysis with Variation of SPM Offset from PLEM on Operation Condition Muhammad Naufal Hawari; Wisnu Wardhana; Murdjito Murdjito
International Journal of Offshore and Coastal Engineering Vol. 9 No. 1 (2025)
Publisher : Department of Ocean Engineering

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j225800914.v9i1.4503

The increasing use of flexible risers in oil and gas exploration projects is a big challenge for engineers to design better riser systems to improve further the efficiency and safety of exploration and production activities in offshore oil and gas fields. SPM is often used as an offloading facility connecting FSO or FPSO as recipients of oil and gas products from subsea templates or wells. Under operating conditions, SPM can move freely following the movement of environmental loads. Drifting or changes in position due to the load on the SPM can threaten the riser response, whereas the riser response can be different whether the SPM is moving or drifting in its stress or bending response. The results in this study also contain the effect of this phenomenon on their fatigue life. As a result, the difference in riser response due to the distance from SPM to PLEM is that the farther the distance from SPM from PLEM, the greater the stress response and bending radius it has. Fatigue life also follows the same results, where the farthest distance from the SPM configuration to PLEM has the lowest fatigue life compared to the closest distance from the SPM to PLEM configuration, with the highest fatigue life at 128.31 years and the lowest at 124.78 years.

Analysis of the Pretension Angle of Mooring Lines SPM and Its Effect on the Tension and Strength of Subsea Marine Hose Rabiatul Muthi’ah; Murdjito Murdjito; Eko Budi Djatmiko
International Journal of Offshore and Coastal Engineering Vol. 9 No. 1 (2025)
Publisher : Department of Ocean Engineering

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j225800914.v9i1.4506

The industry of oil and gas industry have developed along with advances in technology, so does the mooring system. Mooring system is a series that functions to keep the ship station or floating platform at all water depths. Currently, there are many types of moorings that can be used, one of which is Single Point Mooring (SPM). SPM itself consists of various types of mooring legs, as well as other supporting components such as subsea hose or riser. Subsea hose and mooring lines are closely related because in the application, the length of the mooring lines also determines the offset or limitation of motion of the SPM, while the subsea hose also has a maximum limit of pull caused by the movement of the SPM. In addition to the length of the mooring lines, another factor is the pretension angle. Therefore, in this study, an analysis was carried out by varying the pretension angle (45°, 50°, 55°, 60°) under extreme conditions and inline loading by reviewing the tensile forces on the mooring lines and risers. The larger the angle, the smaller the tensile force, so the offset would be larger, and vice versa. The results of this study indicate that the pretension angle applied must be appropriate so that the tensile force on the mooring lines that occurs can also be appropriate.

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