Ng, Sok Mooi (PETRONAS Carigali Sdn. Bhd.) | Khan, Riaz (PETRONAS Carigali Sdn. Bhd.) | Isnadi, Biramarta (PETRONAS Carigali Sdn. Bhd.) | Lee, Luong Ann (PETRONAS Carigali Sdn. Bhd.) | Saminal, Siti Nurshamshinazzatulbalqis (PETRONAS Carigali Sdn. Bhd.)
The objective of this paper is to share the holistic approach to managing aging fleet for offshore fixed steel structures. PETRONAS is currently operating a fleet of more than 200 fixed offshore structures in Malaysian water. More than half of it has exceeded the original design life. With enhanced oil recovery and other developing technologies, offshore platforms often than not are required to continue operating beyond its original design life.
A holistic approach for life extension of fixed offshore structures are being developed to ensure safe operations of the facilities. PETRONAS has started SIM journey since 2007. The approach of Data, Evaluation, Strategy and Programme in line with API RP 2SIM set the basis for managing the integrity of the offshore fleet. An integrated solution was developed to manage both topsides and substructures. The Structural Integrity Compliance System (SICS) which houses the integrity management of topsides deteriorations to prioritize resources through risk based anomalies management. Risk based underwater inspection also formed part of the solutions, addressing mainly extreme storm in the region. Other Major Accidental Hazards (MAHs) risk ranking included in SICS are vessel collision and seismic. Management of facilities with minimal redundancy such as guyed wire monopod is addressed through time based inspection. A regional hazard curve is also developed to ensure the facilities are meeting the acceptance criteria set forth by the industry.
Besides aging, other integrity triggers including shallow gas and subsidence required a different scheme in managing the integrity of the facilities, primarily addressed through a comprehensive monitoring programme.
There is no one size fit all recipe in managing the aged platforms for life extension. The data plays a crucial role in ensuring the right methodology is deployed in support of digitalization and data driven decision making. Implementation of the system is proven to be reliable in ensuring the offshore fixed structures are intact to support safe and continuous operations to the operator in a cost optimum manner. The data analytics help to enhance the predictive model to optimize the inspection and maintenance programme.
Strong ownership and commitment of the structural integrity engineers in ensuring the data integrity maintain the challenge in sustainability of the system and provide reliable source for data driven decision making to the operator.
Category: Operational Excellence (136 - Managing Aging Facilities)
This paper will discuss further on the recent decommissioning project of fields which has been completed on November 2017. These two platforms had been totally removed and became an artificial reef at Sarawak water in Malaysia. This paper will show the activities and best practices; the team had gone through from early stage until completion of the process based on the decommissioning phases. The decommissioning framework consists of five phases starting from Late Life Planning and Preparation; Regulatory, Compliance and Permitting; Facilities Hook-down and wells make safe; Removal and Remediation and lastly, Post Remediation. In baseline inspection, the underwater inspection had provided some information to the contractor on the scope and revealed some of the uncertainties about the decommissioning project. On an important note, an engineering study is critical to ensure safe operation. After our observation, we noted that actual operation is similar to the engineering's simulation where the team had to follow the engineering accordingly. Reefing engineering crucially needed to be performed to ensure the facilities been placed at the right location and position. During offshore execution removal of facilities, there were challenges we faced such as malfunction of the cutting/dredge equipment which led to a back up plan and innovative solution. We had to utilize other available equipments available onboard (Diamond wire cutter, abrasive waterjet internal cutter, dredger, soil plug removal, airlift, cutting torch etc.). Selection of cutting tools also needed to be considered to minimize the pinch effect of the facilities. Finally, Post decommissioning survey had been carried during the Post Remediation phase to assess the successful of the project. The post-decommissioning/reefing survey had been carried out and the result observed new marine growth and numbers of fishes at the reefed platform. It had been concluded that this decommissioning reefing project was successful. This paper should be an interest to those who will be exploring abandonment and decommissioning project which includes reefing as one of the decommissioning options. This paper will also show on decommissioning process through Engineering, Preparation, Removal and Disposal (EPRD) approach contract. The novelty in this paper is on the assurance that had been made by Company via baseline and post reefing survey to ensure environment aspect had been considered.
Müller, Nathalie (Fraunhofer-Institut für Windenergie und Energiesystemtechnik (IWES)) | Kraemer, Peter (University of Siegen) | Leduc, Dominique (Research Institute of Civil Engineering and Mechanics (GeM)) | Schoefs, Franck (Research Institute of Civil Engineering and Mechanics (GeM))
A fatigue test has been conducted on a large-scale offshore wind turbine grouted connection specimen at the Leibniz University of Hannover. For detecting damages in the grouted joint, a structural health monitoring (SHM) system based on fiber optic sensor-type fiber Bragg grating (FBG) has been implemented. By extracting the features of the FBG signal responses using the Wigner–Ville distribution (WVD) and one of its marginal properties, the energy spectral density (ESD), it is possible to detect the occurrence and the global severity of the damage. Some information about the local severity of the damage has also been obtained.
The grouted connection consists of the high-performance grout-filled space between the two structural steel components of respectively the sleeve and the pile of offshore wind turbines (OWTs). For monopile OWTs, it is located around the water level between the transition piece and the pile, whereas for jacket and tripod OWTs, it is located just above the seabed, between substructure and foundation pile. While grouted joints for monopiles are exposed to bending moments, grouted joints for latticed substructures (tripods and jackets) are exposed to predominant axial loadings and low torsional moments (Schaumann and Böker, 2005; Schaumann, Lochte-Holtgreven et al., 2010). It is a critical structural part of OWTs. In 2009–2010, engineers reported grouted connection failures causing slight and progressive settlement of turbines. The problem affected approximately 600 of the 988 monopile wind turbines in the North Sea, requiring further investigations concerning the design of the grouted connection (Rajgor, 2012). Since then, two grouted connection designs reducing the axial forces in this area have been recommended by Det Norske Veritas (2014): using a conical grouted connection (first design) or a tubular connection with shear keys (second design).
Sun, Xiao-Qian (Zhong Neng Power-tech Development Co. Ltd.) | Cao, Shu-Gang (Zhong Neng Power-tech Development Co. Ltd.) | Chi, Yan (Zhong Neng Power-tech Development Co. Ltd.) | Zhu, Zhi-Cheng (Zhong Neng Power-tech Development Co. Ltd.)
This study investigated a vibration and tilt monitoring system for an offshore wind turbine constructed using a high-rise-pile- cap supporting foundation, which is the first offshore wind power project in South China with a batholith seabed. The analysis of data collected by the system during the 2016 typhoon Meranti showed that the typhoon significantly affected vibration and instantaneous tilt of the supporting system without any significant change to the first natural frequency. Additionally, it did not produce any permanent inclination, indicating that no serious structural failure occurred under the influence of the typhoon. However, during the typhoon, the vibration acceleration, vibration intensity, and the effective inclination of the high-rise-pile-cap supporting system using rock-socketed piles were smaller than those with driven frictional piles, indicating that the former is better than the latter in terms of resistance to vibration and tilt.
The construction of offshore wind power plants in China faces many challenges, including the raging typhoons in the East and South Seas. Each year, the Guangdong province experiences typhoons three times on average, accounting for 33% of the annual typhoons in China’s coastal areas. The proportions of typhoon episodes in Taiwan, the Hainan province, the Fujian province, and the Zhejiang province are 19%, 17%, 16%, and 10%, respectively (Wu and Li, 2012). The extreme vibration and abnormal inclination of the offshore wind turbine supporting system as a result of typhoons sometimes lead to structural failures and can even result in the collapse of the wind turbine structure into the ocean.
For site specific assessment of jack-up rigs, existing standards and practices require establishment of certain spud can fixity parameters. Among the required parameters are the maximum moment capacity and the maximum horizontal capacity. These parameters are established by use of site-specific soils data, spud can geometry and preload values. Logically the parameter formulations should provide for improvement in horizontal and moment capacity with increased penetration. Prior to the issue of ISO 19905-1 there was no such provision. However, work sponsored by the International Association of Drilling Contractors’ Jack-Up Committee (IADC) provided technical basis for inclusion of penetration-dependent foundation performance parameters to rectify this situation, particularly in the case of clay soils. The result was substantial increase in foundation parameter values for deep penetrations in clay. Subsequent hindcast studies using the new penetration-dependent parameters have reported very good agreement with actual field performance of instrumented rigs, and the IADC-recommended parameter formulations were subsequently adopted in ISO 19905-1 and in SNAME Bulletin 5-5.
The IADC recommendations were based, in part, of results of finite element analysis of spud-can/soil interaction. Those analyses modeled part of the spud can installation as well as the subsequent moment and horizontal loading. Both parts were done largely with both small strain and finite strain assumptions. More recent finite element work by on Zhang, Biennen and Cassidy (2013, 2014) used newer modeling techniques to substantiate more conservative recommendations.
The current revision draft of ISO 19905-1 prescribes the original IADC-based recommendations only for the case of uniform soil strength, and it prescribes recommendations based on Zhang, Biennen and Cassidy (2013, 2014) for the case of a strength profile increasing strictly linearly from negligible strength at the mudline. This situation leaves a gap in recommendations for more commonly encountered strength profiles intermediate to these two extremes.
The present paper reports results of new IADC-sponsored finite element analyses done with full Eulerian modeling for both the spud can installation and subsequent moment and horizontal loading. The new results support recommendations needed for the more commonly encountered strength profiles intermediate to the extreme cases now covered by the current revision draft of ISO 19905-1.
An application at the forefront of the accelerating digitalization of offshore exploration and production (E&P) is remote condition monitoring (CM) of platform equipment, especially with a unique data-sampling technique called time stamping. CM tracks the performance data of equipment, watching for deviations from baseline performance benchmarks. Any unexpected variances from those established baselines may indicate a developing fault in systems found typically on offshore platforms. Technicians can then be dispatched to further investigate or service the equipment, targeting root causes of the variances—an approach called condition-based maintenance (CBM). The CBM approach has shown that it can improve reliability, availability, and asset use.
Icebergs can pose risks to platforms in arctic and subarctic regions. These risks require careful consideration during design, and as well during operations. Platforms must be designed to withstand potential impacts from icebergs, or to disconnect and move offsite to avoid impacts. ISO 19906 allows use of ice management to mitigate iceberg and sea-ice actions. In the case of icebergs, management may include detection, monitoring, towing, disconnection and evacuation. Threat assessment is also a critical input to the iceberg management decision-making process. For example, given one or more detected icebergs and available information on the iceberg and environment characteristics, what is the probability of exceeding platform design ice actions? Based on the threat assessment, better decisions can be made regarding which iceberg to manage, whether more information should be acquired, and whether shut-down or evacuation is needed.
This paper describes a new tool developed to estimate the distribution of iceberg impact actions from an encroaching iceberg given concurrent metocean conditions, conditional on impact. The tool can be used in a number of ways depending on the information available to the user. It can be used to assess the threat from a single iceberg or can be used to compare actions from multiple icebergs in the region, or for the same iceberg but with changing weather conditions. The iceberg load assessment tool is demonstrated for several example cases on the Grand Banks, showing the benefit of improved iceberg characterization obtained through rapid iceberg profiling.
Different kinds of offshore structures are designed and built to resist the scenarios of the arctic environment. This paper focuses on different ice load scenarios and the challenges for fixed offshore structures. Model test methods will be presented to assess the suitability of the design for the corresponding environmental scenarios. Measurement possibilities will be explained monitoring the design challenges as ice resistance, vibrations and encroachment of ice.
The feasibility of different ice model test setups will be described and the main observations will be presented. The findings of the general phenomena of the resistance and encroachment will be discussed to assist the design process of offshore structures.
The IMO's International Code for Ships Operating in Polar Waters (Polar Code) entered in to force on 1 January 2017 and provides, for the first time, an international regulatory framework for ships operating in Polar waters. In addition to technical regulations, the Polar Code requires that the Polar Ship Certificate should reference a methodology to assess operational capabilities and limitations in ice: essentially setting operational limitations for the specific ship navigating in Polar waters. The Polar Operational Limit Assessment Risk Indexing System (POLARIS) has been developed as an acceptable methodology for providing guidance on the operational limitations in ice of ships assigned different ice classes and has been directly referenced by the IMO in the Polar Code. The system was developed as a collaborative effort, drawing on operational and regulatory experience from industry and national administrations with experience in setting navigational limitations for ice covered waters. This paper presents the technical background behind the system and supporting information on its practical use both as a voyage planning tool and as real-time guidance on assessing ice regimes ahead of the ship. Validation of the system in the context of other existing regulatory requirements is discussed. The limitations of the system are explored and commentary and proposals are provided on recommended future enhancements.
The support structure of offshore wind turbines is working in harsh ocean environments, where uncertainties exist and affect the performance of the whole system. This work presents an efficient methodology for the Reliability Based Design Optimization (RBDO) of the support structure of offshore wind turbines considering uncertainties. Reliability analysis is a feasible option in the absence of field measurement data. Monte Carlo simulations are robust and used as reliability analysis benchmark, but they are very computationally demanding for offshore wind turbine cases. Efficient Fractional Moment reliability analysis method was proposed. The results show that the proposed methodology can obtain a reliable design with better dynamic performance and less weight. Compared with the deterministic optimization, the presented dynamic RBDO of offshore wind turbines is more practical, and this methodology can be applied in the design of other similar offshore structures.
The support structure of offshore wind turbines is working in harsh ocean environments, reliability analysis is a feasible option in absence of field measurement data (Yang et al., 2017). To ensure that the proposed offshore wind turbine design is cost effective, it is necessary to check whether the decided support structures provides optimal life cycle cost.
For a reliable design, it is essential to consider various uncertainties in the dynamic analysis of offshore wind turbine (Xiao and Yang, 2014; Zhang et al., 2017). Due to the random nature of environmental parameters, wave, wind and currents must be modelled as stochastic process (Zhang and Yang, 2014). Hence, there is a need of stochastic dynamic analysis on one hand and the need of developing performance assessment, maintenance and optimization of the offshore wind turbine system with uncertainties. We try to answer the following questions: a) Can we formulate an efficient and accurate method for reliability analysis to replace Monte Carlo simulations which are robust but too time consuming; b) How to overcome computational challenges associated with reliability-based optimization methodology of offshore wind turbine system?