Analysis of internal corrosion in subsea oil pipeline

AbstractFailure of a subsea crude oil API 5L X52 steel pipeline which led to oil leakage has been reported to occur after 27 years in service. Some leaks were found to form at the bottom of the horizontal API 5L X52 steel pipeline near an elbow section which connected the pipeline to a riser. The present investigation aims to analyze the main cause of failure by conducting standard failure analysis methods including visual examination, chemical and mechanical characterizations, metallurgical examinations using optical microscopy in combination with scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analysis and corrosion test using a three-electrode potential technique. Results of this investigation suggest that the cause of failure is electrochemical corrosion combined with mechanical process known as flow-induced corrosion. The failure mechanism is discussed with specific attentions are paid to fluid flow rate and chloride-containing water phase

Optimal control of the heave motion of marine cable subsea-unit systems

One of the key problems associated with subsea operations involving tethered subsea units is the motions of support vessels on the ocean surface which can be transmitted to the subsea unit through the cable and increase the tension. In this paper, a theoretical approach for heave compensation is developed. After proper modelling of each element of the system, which includes the cable/subsea-unit, the onboard winch, control theory is applied to design an optimal control law. Numerical simulations are carried out, and it is found that the proposed active control scheme appears to be a promising solution to the problem of heave compensation

Pipeline Risk Assessment Using Dynamic Bayesian Network (DBN) for Internal Corrosion

Pipelines are the most efficient mode of transportation for various chemicals and are considered as safe, yet pipeline incidents remain occurring. Corrosion is one of the main reasons for incidents especially in subsea pipelines due to the harsh corrosive environment that prevails. Corrosion can be attributed to 36% amongst all the causes of subsea pipeline failure. Internal corrosion being an incoherent process, one can never forecast exact occurrences inside a pipeline resulting in highly unpredictable risk. Therefore, this paper focuses on risk assessment of internal corrosion in subsea pipelines. Corrosion is time-dependent phenomena, and conventional risk assessment tools have limited capabilities of quantifying risk in terms of time dependency. Hence, this paper presents a Dynamic Bayesian Network (DBN) model to assess and manage the risk of internal corrosion in subsea. DBN possesses certain advantages such as representation of temporal dependence between variable, ability to handle missing data, ability to deal with continuous data, time- based risk update, observation of the change of variables with time and better representation of cause and effect relationship. This model aims to find the cause of internal corrosion and predict the consequence in case of pipeline failure given the reliability of safety barrier in place at each time step. It also demonstrates the variation of corrosion promoting agents, corrosion rate and safety barriers with time

Analysis of Inspection Scheduling on Free Spanning Subsea Pipeline Using Risk Based Inspection (RBI) Method

The subsea pipeline system of PT. X located at north of West Java transports natural gas with 19 kilometers long and 16 inches standard pipe size. The rough seabed causes free span problem. The system will be threatened by a structural failure of fatigue due to Vortex Induced Vibration (VIV) and local buckling as the effects of free span. In this Final Project, a total of 136 free spans on subsea pipeline system due to the uneven seabed are analyzed. The screening will be done for spans with length and diameter ratio more than 30 to figure out the free span which pass the screening and know the risk level of the subsea pipeline due to free span. The result for fatigue screening due to VIV, spans with a length more than 25 meters did not pass the screening. Local buckling occurred at the longest free span with a length of 62 meters. The level of risk to structural failure caused fatigue due to VIV has the highest level in terms of business and the environment, namely in the medium category. The level of risk to local buckling failures for safety, environmental, and business terms was in low category

Determination of the Risk of Oil and Gas Offshore Pipelines in Indonesia: A Risk-Based Analysis Approach for Developing Inspection Strategy Policy

 Indonesia has a target of producing 1 million BOPD of oil and 12 BSCFD of natural gas in 2030. The strategy for achieving the production target in 2030 is transformation from resources to production, accelerating chemical EOR, massive connectivity for finding large wells, and optimizing field production. In optimizing existing field production, one of the supporting factors is production facilities, so production facilities with good integrity are needed to minimize upplanned shutdowns. One of the oil and gas installations that pose a high risk is the installation of oil and gas pipelines. The existing pipeline installation in the Java Sea, from North Cirebon to the Seribu Islands, has an area of 8300 km2 and is operated by PT XYZ. Therefore, it requires complete and accurate inspection data to find out. This research method uses a modification of the Kent Mulhbauer scoring index. The risk level of the three subsea pipelines at Company XYZ, namely 4 in Gas Line Mike Mike, 8 in Gas Line Echo pipeline, and 8 in Gas Line Mike Mike pipeline, is found to be in the very highrisk category. The inspection strategy carried out for the third pipe with a very high risk category is visual inspection (ROV), freespan assessment, cathodic protection check (CP), UT thickness inspection on the riser and elbow (topside and subsea), and UT thickness inspection on the bottom pipe sea using the NACE ICDA method for thickness taking points and inspection periods once every 4 years or based on risk-based inspection (RBI). The cost and effort of examining the strategy will be assessed directly with the level of the risk category. Because of this, so that the inspection of the strategy can be optimal, effective, and efficient, it is divided into 3 (three) risk categories, namely low, medium, and high/very high, where the selection of strategy inspection is appropriate with the level of risk. The results of this study are expected to be a reference in making a policy or regulation to carry out regular inspections of underwater pipelines by using the risk analysis method to determine the inspection strategy

Application of Layers of Protection Analysis (LOPA) for subsea production systems - A risk based model for determination of integrity levels in a global perspective

Depletion of onshore and shallow water reserves, in combination with new subsea technology, has made the petroleum industry advance into deeper water. However, new technology also brings new risks. Since most widely accepted standards and regulations are not directly aimed for subsea systems, new methods have to be developed. By developing a LOPA-model, which can be used specifically for subsea context, this thesis intends to be a part of filling that gap. The models main objective is to evaluate subsea production system risk and to determine the appropriate safety Integrity level (SIL) for all present independent protection layers. The method is semi-quantitative in nature, which means that the model output is based on a combination of generic statistical data, expert judgement and logical reasoning. According to the model validation, the result seems to be credible due to what is economically and technically feasible. For example, when a single satellite well subsea system was evaluated it ended up with SIL3 requirements for the “isolation of well function” and lower SIL requirements for other less critical safety functions

On-Bottom Stability Study of Non-Metallic Pipeline Due To Hydrodynamic Loadings

In order to prolong the service life, the integrity and stability of the submarine pipeline always been a concern of the oil and gas industry. However, conventional steel subsea are subjected to corrosion in sour service and even sweet service. Inspection of the subsea pipeline are frequently scheduled to ensure the integrity of the pipeline which is very costly. The non-metallic pipeline are introduced to be replacement of the steel pipeline. The non-metallic properties is known to have highly resistance to corrosion yet it also has lighter weight which lead to on-bottom stability problem. Hence, this project aim to determine the minimum weight of chain per unit length for the subsea non-metallic pipeline to be stabilized. The on-bottom stability study will based of DNV recommended practice with the use of finite element analysis package. This project also will include a finite element analysis of the submarine pipeline by using ABAQUS. The water velocity and acceleration are generated from the sea surface wave and current given the sea state in the South China Sea. The weight of chain is determine from the optimization of the simulation. The simulation’s result by using one year return waves and currents show 32.32kg/m of chain can stabilize the non-metallic pipeline with 0.7654 m lateral displacemen

Towards a framework for environmental risk assessment of CCS: subsea engineering systems

Nowadays, we are observing a continuous rise in trends of greenhouse gasses’ concentration in the atmosphere, especially of carbon dioxide, and this is, in great part, attributable to human activities. The first detrimental effects on climate have already been observed and ever more long-term changes in weather patterns should be expected if no concrete action to contrast these trends is put in practice. The scientific community is thus suggesting innovative and practical solutions for both mitigating climate change and adapting to its impacts: carbon capture and storage (CCS) is one such option. CCS involves capturing carbon dioxide (CO2) from power plants, industrial activities and any other sources of CO2 and storing it in a geological formation. The appeal of this technique resides in the fact that CCS is able to combine the use of fossil fuels, on which our society still relies a lot, with the environmental exigency to cut carbon dioxide’s emissions. However, despite the interesting mitigation option offered by CCS, there is the impelling need, as for any other human activity, to assess and manage risk; this work is intended to do so. The focus is, more precisely, on marine environmental risk posed by CO2 leakages, as how this risk should be addressed still represents a largely debated topic. Specific risks can be associated to each of the stages of a CCS system (capture, transport and storage). The focus of this work is on the subsea engineering system, thus, offshore pipelines (transport) and injection / plugged and abandoned wells (part of the storage). The aim of this work is to start approaching the development of a complete and standardized practical procedure to perform a quantified environmental risk assessment for CCS, with reference to the specific activities mentioned above. Such an effort would be of extreme relevance not only for companies willing to implement CCS, as a methodological guidance, but also, by uniformizing the ERA procedure, to begin changing people’s perception about CCS, that happens to be often discredited due to the evident lack of systematized methods to assess the impacts on the marine environment. The backbone structure of the framework developed sees the integration of ERA’s main steps, which are the problem formulation, exposure assessment, effect assessment and risk characterization, and those belonging to the well-known quantified risk assessment (QRA). This, in practice, meant giving relevance to the identification of possible hazards, before the fate of CO2 in seawater could be described (exposure assessment), and estimating the frequencies of the leakage scenarios, in order to finally describe risk as a combination of magnitude of the consequences and their frequency. The framework developed by this work is, however, at a preliminary stage, as not every single aspect has been dealt with in the required detail, thus, several alternative options are presented to be used depending on the situation. Further specific studies should address their accuracy and efficiency and solve the knowledge gaps emerged, in order to establish and validate a final and complete procedure. Regardless of the knowledge gaps and uncertainties, that surely need to be addressed, this preliminary framework can already find some relevance in on field applications, as a non-stringent guidance to perform CCS ERA, and, anyways, it constitutes the foundation of the final framework

An investigation on the effect of widespread internal corrosion defects on the collapse pressure of subsea pipelines

Acknowledgements This research is funded by Chevron through its Anchor Partnership with the UK National Decommissioning Centre (NDC). We also acknowledge funding and in-kind support from the Net Zero Technology Centre and the University of Aberdeen through their partnership with the UK National Decommissioning Centre. The authors are grateful for helpful discussions with Dr Alethea Madgett of NDC.Peer reviewedPublisher PD

Numerical Investigation of Dynamic Pipe-Soil Interaction on Electrokinetic-Treated Soft Clay Soil

© 2019 American Society of Civil Engineers. Researchers have underscored the importance for a pipeline to safeguard against adverse effects resulting from its displacement in the vertical, axial, and lateral directions because of the low shear strength of the soil. The seabed may sometimes consist of soft or very soft clay soil with high water content and low shear strength. Dissipation of the water content from the soil void increases its effective stress, with a resultant increase in the soil shear strength. The electrokinetic (EK) concept has been applied to increase soil bearing capacity with barely any study conducted on its possible application on pipe-soil interaction. The need to explore more options merits further research. The EK process for the pipe-soil interaction consists of two main stages: the electroosmotic consolidation process and dynamic analyses of the pipe-soil interaction. The present study numerically investigated the impact of EK-treated soil on pipe-soil interaction over the non-EK process. The results of dynamic pipe-soil interaction on EK-treated soil when compared with non-EK-treated soil indicate a significant increase in the force required to displace a pipeline