Corrosion Maintenance Research Articles

A Corrosion Maintenance Model Using Continuous State Partially Observable Markov Decision Process for Oil and Gas Pipelines

This paper proposes a continuous state partially observable Markov decision process (POMDP) model for the corrosion maintenance of oil and gas pipelines. The maintenance operations include complex and extensive activities to detect the corrosion type, determine its severity, predict the deterioration rate, and plan future inspection (monitoring) schemes and maintenance policy. A POMDP model is formulated as a decision-making support tool to effectively handle partially observed corrosion defect levels. It formulates states as the pipeline’s degradation level using a probability distribution. Inline inspection (ILI) methods estimate the latest state of the pipeline, which also defines the initial state of the optimization process. The set of actions comprises corrosion mitigation operations. The errors associated with the ILI method are used to construct the observation function for the model. The sum of inspection, maintenance operations, and failure costs for a given state and action are formulated as rewards. Numerical experiments are made based on data collected from the literature. The results showed that different policies, whether derived from solvers (theoretical) or determined from practical experience, can be compared to identify the best maintenance alternative using the model. It was also observed that the choice of the solvers is important since they affect the discounted rewards and the run time to obtain them. The model approximates the parameters and uncertainty associated with the propagation of corrosion, proficiency of inspection methods, and implementation of maintenance policies. Overall, it can be applied to improve the maintenance decision-making process for the oil and gas pipeline as it incorporates the stochastic features of the operation.

Machine visual technology based steel corrosion evaluation and analysis of power transformation lines: A Zhejiang power grid case study

It can be seen that the corrosion failure of transmission and transformation equipment has increasingly restricted the safe operation of the Zhejiang power grid bottleneck problem. If effective anticorrosion measures are not taken promptly, transmission and transformation equipment serving in various sophisticated atmospheric environments will suffer serious corrosion damage in a relatively short period, which endangers the safe usage of transmission and transformation equipment and the security of grid operation. In this article, through the establishment of transmission and transformation steel components corrosion fracture mechanics model, a standard corrosion spectrum grading software based on DeepLabV3+ image segmentation technology is developed to determine the quantitative assessment method of corrosion damage and assess the corrosion status with safety degree of transmission and transformation equipment. According to the assessment results, the operation and maintenance units are guided to adopt differentiated corrosion maintenance and replacement strategies, so as to reduce corrosion safety hazards and reduce safety accidents and economic losses caused by corrosion, which is of great significance for the safe operation of power grids.

Bayesian Network Machine Learning Approach to Atmospheric Corrosion Modelling

The performance degradation of materials exposed to corrosive atmospheric environments is a serious problem. Corrosion maintenance strategies and cycles are informed largely by historical trends in corrosivity dependent on the location of interest. Assessments are often made with sparse experimental data and are generalized to certain materials and baseline conditions observed in the past. The development of a predictive model which can better inform maintenance strategies and cycles offers opportunities for time savings and cost avoidance. Such a model would need to predict corrosion damage accumulation as a function of material of interest, location of interest, and atmospheric conditions during the period of exposure of interest.Machine learning has recently gained attention as a way to model complex systems and processes. Atmospheric corrosion is certainly a complex process as there are many parameters that influence it which are uncontrolled and vary in difficult to predict ways. A machine learning algorithm would require data to learn from which might include environmental conditions such as temperature, relative humidity, UV light exposure, time of wetness, salt concentration, applied loads, and electrochemical data for substrates, inhibitors, and coatings. The ability of machine learning to determine models and relationships from large data sets is well demonstrated; however, a Bayesian model approach can be more suitable when data is limited, expensive or time consuming to obtain, and expert knowledge can be leveraged to construct the relationships. While certain meteorological variables are well categorized and easy to retrieve other variables like corrosion damage or salt deposition are sparsely reported if measured at all. For this reason, a Bayesian Network Model has been developed to better predict the corrosion damage accumulation of C1010 steel and three different aerospace coating systems applied over AA2024-T351.The network map was constructed from parameters (nodes) which are known to influence corrosion. Mathematical relationships were used to develop relationships between nodes or to calculate new nodes as available. Finite element analysis was used to refine the network map and provide supplemental inputs for features that are difficult to measure experimentally. The model was initially trained from historic corrosion data gathered from collaborators across the DoD. Contemporary experimental data was also gathered in a 19-site survey of field exposure sites across the world. This dataset provided further inputs for training and also data for validation and testing. The methodology behind model construction will be highlighted and model predictions will be compared against experimental results. To date, there has been good correlation between model predictions and experimental results for C1010 steel mass loss, which provides a basis to further extend the model to aerospace coating systems. Figure 1

Management of Airframe In-Service Pitting Corrosion by Decoupling Fatigue and Environment

Corrosion-induced maintenance is a significant cost driver and availability degrader for aircraft structures. Although well-established analyses enable assessing the corrosion impact on structural integrity, this is not the case for fatigue nucleation and crack growth. This forces fleet managers to directly address detected corrosion to maintain flight safety. Corrosion damage occurs despite protection systems, which inevitably degrade. In particular, pitting corrosion is a common potential source of fatigue. Corrosion pits are discontinuities whose metrics can be used to predict the impact on the fatigue lives of structural components. However, a damage tolerance (DT) approach would be more useful and flexible. A potential hindrance to DT has been the assumption that corrosion-induced fatigue nucleation transitions to corrosion fatigue, about which little is known for service environments. Fortunately, several sources indicate that corrosion fatigue is rare for aircraft, and corrosion is largely confined to ground situations because aircraft generally fly at altitudes with low temperature and humidity Thus, it is reasonable to propose the decoupling of corrosion from the in-flight dynamic (fatigue) loading. This paper presents information to support this proposition, and provides an example of how a DT approach can allow deferring corrosion maintenance to a more opportune time.

High temperature corrosion memory in a waste fired boiler - Influence of sulfur.

The selection of fuel for a Combined Heat and Power (CHP) plant can vary over time. By choosing less expensive fuels, operation costs are reduced, however, cheaper fuels generally increase corrosion maintenance costs. The corrosiveness of different fuels has been studied extensively while how the current corrosion attack is influenced by corrosion history, i.e. previous deposit build-up and oxide scale formation, is less studied. This phenomenon may be referred to as a "corrosion memory" effect (Paz et al., 2017). The present work investigates the influence of addition of sulfur to the fuel on the corrosion memory through air-cooled probes in the Waste-to Energy lines at Måbjerg Energy Center (MEC) in Denmark. The results show a corrosion memory effect, i.e. as initially corrosive environment may increase the subsequent corrosion rate and vice versa.

A study on the condition based maintenance evaluation system of smart plant device using convolutional neural network

There are two main causes of plant accidents: poor maintenance management and human error. In this study, we implemented a smart plant maintenance system that can reduce human errors based on the conditional based maintenance (CBM) concept. Unlike smart plant technology, which focuses on existing technology, we interviewed actual engineers and implemented a system reflecting their needs. First, we implemented three methods for learning defective images using convolutional neural network (CNN) and found that blob detection processing improves learning accuracy. Second, the fitness for service API (FFS API) methodology used in the actual pitting corrosion maintenance evaluation method was used to implement the CBM system. Finally, we verified the reliability of this system by conducting validation through actual case study.

Development of Vinyl Ester and Reed Composite Material with Weight Fraction of 10% and Reinforcement at Different Orientations

Composite materials have been used to resolve industrial problems. Considerable attention from the industrial side started in the 1960s with the introduction of polymer-based composite materials. Their advantages such as low weight (density), resistance to corrosion, high strength and low maintenance cost made composite materials an attractive substitute to conventional materials. A new composite material was developed with 10% natural fiber at 0o, 90o and 0/90o orientations resulting in ample improvements in the mechanical properties as compared to previous studies. The sample at 0/90o orientation gives the best results with tensile, tensile strength, tensile elongation and Young's Modulus values of 2458.19N, 4594.5MPA, 4.7% and 23.0 respectively

New developments for corrosion protection of concrete structures in Australia

The corrosion protection, repair and maintenance of reinforced concrete structures located along the coast of Australia has been a challenging task for engineers and asset owners over the past thirty years. Most of these structures are bridges and wharves which are situated in marine environments and are subject to tidal exposure. These environmental conditions create challenges in planning repair work, especially if electrochemical systems such as cathodic protection are installed for corrosion protection of these assets. While impressed current cathodic protection (ICCP) is a proven technology which can provide long-term corrosion prevention solutions for marine structures, this technology has been viewed by many asset owners as overly complex and expensive. There is the perception that ICCP systems require costly permanent monitoring programs and have high maintenance costs. These perceptions have been supported by the frequent failure of power supply units, and in some cases, widespread defects associated with ICCP systems such as grout acidification in concrete elements situated in tidal zones. The perception about the complexity of ICCP technology has led to the selection of less effective galvanic-based systems for the protection of assets, and systems which require no monitoring and have low maintenance requirements. This paper will present information on the new developments which have emerged from long-term experience and research work related to the simplification in the design, installation and improved monitoring of ICCP systems.

Corrosion Detection and Analysis of the Underground Grounding Grid in a 220kv Transformer Substation

The first corrosion detection for the large grounding grid of a 220kV substation was performed based on electrical impedance tomography (EIT) technology. The impedance value of grounding grid branch which represented the corrosion state of metal was calculated using the current and voltage data acquired on-site through injecting a direct current from one down conductor and collecting voltage data from other down conductors. The results indicated that the impedance increase ratio of the No.143 grounding grid branch in test area D was higher than the warning value (>15 times), indicating a breakage has occurred on this grounding grid branch. The two-dimension corrosion image of the whole underground grounding grid was calculated and drawn accurately and visually using the corrosion diagnosis software. The corrosion rate of carbon steel was monitored in the serious corrosion area later, to realize the online corrosion monitoring of grounding grid metal. EIT technology realized the underground grounding grid statues visible exhibition, and could be used to detect the corrosion state, corrosion area and failure location of the underground grounding grid rapidly and effectively. This could reduce the blindness of corrosion detection for grounding grid and provide guidelines on the corrosion maintenance of underground grounding grid in large substation.

Reliability prediction for corroding natural gas pipelines

This paper aims to evaluate time-dependent reliability of a corroding onshore underground natural gas pipeline system over its lifetime. The reliability analysis is segment-based, as opposed to defect-based and the pipe segment is examined with respect to external metal loss corrosion. The non-homogeneous Poisson process (NHPP) and an empirical power law model are employed for generation of corrosion defects over time and for defect growth, respectively. The time-dependent probability of failure is evaluated by employing the limit state function for burst under internal pressure. Internal pressure is modelled using a Poisson square wave process-based method (PSWP). Thereinafter, the study uses the aforementioned analysis, in conjunction with a heuristic model, in order to investigate the influence of imperfect repairs on the reliability prediction of the pipeline system. The heuristic method is known as split system approach and it is used to describe the changes in reliability of the pipeline system over its lifetime with the consideration of multiple maintenance actions. A numerical example of the described methodology is presented based on a chosen maintenance policy. A parametric study is conducted to examine the impact of instantaneous generation rate of NHPP model, PSWP model and reliability control limit on the results of the numerical application. The proposed methodology aims to assist engineers in the decision making with regard to corrosion maintenance strategies.

Load Rating Based Maintenance Approach for Corrosive Twin I-Girder Railway Bridges in India

In Indian Railways, about 75% of the bridges are exceeding 60 years’ life period and 80% of steel bridges population adopt simply supported twin I-girder structure. Corrosion has become one of the biggest challenge for maintenance of these old steel bridges. Currently the index called Condition Rating Number (CRN), utilized to assess the structural conditions and determine the maintenance strategy. CRN is a qualitative approach with individual bias in decision, therefore it is difficult to identify the prioritization of corrosion damages in same CRN category. In this study, a new approach based on load rating factor (LRF) for corrosion maintenance on typical twin I-girder bridges is proposed. Firstly, by considering frequently occurring corrosive location and the absolute maximum load effect, three categories of critical corrosive location and pattern are summarized. Secondly, LRF based on physical inspection is calculated using simplified theoretical approach and FEM approach. Various degree of corrosion is utilized to investigate the influence on the load capacity by incorporating the nonlinear phenomena such as buckling. It is found that the simplified approach is conservative enough to evaluate the structure practically within safety side. Finally, the practical decision flow regarding to the maintenance action is proposed, summarizing the relationship between the corrosion and the remaining load capacity by means of LRF. This approach is expected to provide not only an objective evaluation to load capacity of corrosive railway bridges, but also instructive information for the retrofit of structures with limited fund availability.

Methodology for Planning Tower Leg Foundations Corrosion Maintenance of Overhead Transmission Lines Based on GIS

In distribution and transmission electric power companies, many losses and risks are associated with corrosive processes that occur in buried structures, such as tower leg foundations of overhead transmission lines. Tower leg corrosion control at the foundation involves the collection and analysis of data generated by different inspection methods and practices for routine maintenance and repair. The aim of this paper is to demonstrate a methodology developed to identify locations and towers most susceptible to high rates of metal corrosion at the foundation of tower legs in order to facilitate better maintenance planning and evaluate the failure risks of these assets. To this end, using the Delphi methodology, variables that affect the corrosion phenomenon are correlated with geographic information and generate algebraic maps for advanced analysis. Despite the difficulty of searching and correlating georeferenced data, the results are interesting and promise possibilities for future applications.

Recyclability and Performance Stability of Corrosion Inhibition Improved Amine-Free Water-Soluble Cutting Coolant

The concern for environmental problems has been increasing rapidly in recent years. Water-soluble coolants are widely used in machining processes. To reduce management costs and the environmental load of water-soluble coolants, the authors studied a recycling system for water-soluble coolants. With this recycling system, water is extracted from a waste coolant by chemical or biochemical treatment; the recovered water is re-utilized as a diluent for a new coolant. Coolant recyclability depends on the coolant type. Most water-soluble coolants contain alkanolamines for corrosion inhibition and maintenance of putrefaction prevention. However, alkanolamines are difficult to eliminate from water-soluble coolants by chemical and physical waste treatment processes. Some amine-free, water-soluble coolants have been developed and are commercially available. The reduction of environmental load in the treatment of waste coolants is anticipated for amine-free coolants. We applied the recycling process to a commercially available amine-free, water-soluble coolant. The amine-free coolant showed good recyclability and lubricating performance. However, the corrosion inhibition performance of the coolant was inadequate for use in general machining. Recently, our cooperative company developed a prototype amine-free, water-soluble coolant with improved corrosion inhibition. In this study, we experimentally examined the recyclability and performance stability of this newly developed coolant. The experimental results showed that the new amine-free coolant has good corrosion inhibition equivalent to conventional amine-containing coolants. In addition, the recyclability, stability, and cooling and lubricating performance of the coolant are equal to conventional amine-free coolants. The amine-free, water-soluble coolant with improved corrosion inhibition has the advantage that it can be used in the recycling system for water-soluble coolants.

Uncertain (N, T) block replacement policy of aircraft structure subjected to corrosion damage

This paper focuses on an uncertain (N, T) block replacement policy with minimal repairs for the aircraft structure under corrosion damage. We consider a kind of structure component which is made by a new developed composite material, and its failure time is considered as an uncertain variable because of the absence of historical data. Given the chance constraint of corrosion maintenance allowance, an uncertain programming model for (N, T) block replacement model with minimal repairs which minimizes the expected cost rate is proposed based on uncertain theory, and the optimal time interval $$T^*$$Tź and the number $$N^*$$Nź of preventive repairs can be obtained by an improved branch and bound algorithm. Finally, a numerical example with parameter sensitivity analysis is illustrated to verify the proposed model and algorithm.

Experimental and Modeling Study of the Effect of Corrosion Pitting on Fatigue Failure Locations in Aircraft Components

It is well established that corrosion pits reduce the fatigue life and structural integrity of aluminum alloy aircraft components. A great deal of research has been conducted in this area in the last 20 years. This problem is not unique to aluminum alloys or aircraft however. Similar problems have been observed in the steel components of other engineered structures such as steel pipelines and steam turbine blades. However the effect of pitting corrosion on the probable location of fatigue failures has been overlooked. This is problematic as corrosion pits have caused fatigue failures in locations and components where they were unexpected, such as the trailing edge flap lug of the F/A 18 fighter aircraft. DSTO have called this problem ‘Corrosion Criticality’. This paper reports the development of Monte-Carlo models of how pitting corrosion affects the location of fatigue failures in two fatigue specimen geometries that have different stress concentration factors (kt). These specimens are a low-kt fatigue life specimen and a high-kt fatigue life specimen with three holes arranged along its centerline. The modeling results for the low-kt specimen are then compared with experimental results for that specimen. The low-kt model produces good estimates of fatigue life and of the probability of fatigue failure at any given location in the specimen’s gauge section. The process that will be followed to develop the high-kt model is outlined. The paper includes a discussion of using the Corrosion Criticality models to reduce the cost of corrosion maintenance by (i) identifying areas in which corrosion inspections are critical and (ii) identify aircraft components for which pitting corrosion will not be a threat to airworthiness during the life of an aircraft.

Comparison of Retrofits for Three Strut-Arm Tainter Gates Using a Longevity Corrosion Maintenance Factor

This paper presents a methodology to compare various Tainter gate strut-arm retrofit techniques based on the longevity corrosion maintenance (LCM) factor. The rating system is designed to encourage agencies to select retrofits that will better upgrade existing conditions to meet current design standards for hydraulic steel structures and achieve a long design life. An overview of past Tainter gate failures, governing strut-arm load cases, past strut-arm retrofit strategies, current design standards for hydraulic steel structures, and the consequences of welding or bolting to existing structures has been considered in this study as evidence to support the proposed Tainter gate retrofit comparison methodology. An example problem illustrates how to determine the LCM factor and assign a LCM grade for three retrofit scenarios.

Why North American markets have shifted to spoolable pipe versus traditional pipeline materials and its implications for Australian operators

During the past 12 years, spoolable pipe has become a widespread preference for in-field gathering and injection applications compared to welded steel and stick fibreglass pipelines. It is now broadly used in oil and gas fields throughout North America, with more than 300 end users, including every major operator. To date, more than 25,000 km of spoolable pipe has been installed in North America for more than 450 operators. Fast installation, lower costs, safer installation, immunity to corrosion and low maintenance in service are the drivers for this rapid success. The technology is well on its way to displacing steel or stick glass-fibre reinforced epoxy (GRE) pipe as the technology of choice for lines up to nominal 6-inch in diameter. Compared to a single 8- or 10-inch line, companies are finding having multiple spoolable pipes in the same ditch to be more economical. Field results have demonstrated spoolable pipe’s immunity to corrosion and have also shown how using spoolable pipes can save 25% or more in costs when compared to overall installed costs for welded steel or stick fibreglass pipelines by significantly reducing onsite construction expense, installation time and onsite manpower requirements, including skilled welding personnel.

Reliability analysis of screwed connections in high-speed trains, considering fatigue, corrosion, and imperfect maintenance operations

The reliability of railway equipment is of central interest in the choice of design and maintenance strategies. In high-speed trains, known as TGV, the assembly of mechanical parts is performed by the use of prestressed screws. In order to ensure safe operation of the railway network, the French company SNCF has undertaken a reliability-based analysis of the life cycle of screwed connections. This study aims at establishing a consistent reliability-based methodology for the assessment of equipments subjected to fatigue, corrosion, and imperfect maintenance operations, in order to improve their inspection on the basis of cost and reliability balancing. This methodology incorporates the life cycle of the equipment, including the deterioration modes, the imperfect maintenance operations and the uncertainties in geometry, loading, and material properties. The results of the study show that despite the high resistance regarding the applied load, the connection is still very sensitive to parameter variations: friction, tightening and prestressing. Although the large safety margin in fatigue design, the robustness of screwed connections should be sought when operation and maintenance conditions are considered.

Computer-aided oxygen transport model of mass and energy simulation for corrosion of reinforced steel

The paper includes automated modeling and experimental verification of corrosion in reinforced concrete construction under the effect of varying oxygen concentration. Various construction corrosion cells with different concrete compositions under four different environmental conditions (air dry, submerged, 95% R.H and alternate wetting–drying) have been investigated under controlled laboratory conditions. Using the results (half-cell potential and gravimetric corrosion mass loss) of these laboratory tests and an automated computer-aided simulation model based on mass and energy transfer through the porous construction media for the corrosion process, it was possible to predict, maintain and manage the influence of oxygen concentration on the corrosion rate of the reinforcement in concrete construction under various defined conditions satisfactorily. The variation in oxygen concentration available for corrosion reaction has been taken into account simulating the actual construction field conditions such as by varying concrete cover depth, relative humidity, water–cement ratio, etc. The modeling task has been incorporated by the use of an automated computer based construction durability model ‘DuCOM’ developed by our construction research group at The University of Tokyo as a finite element computational approach for the effect of oxygen on corrosion in relation to W/C, concrete cover, chloride concentration and various environmental humidity construction conditions. This paper is of interest to a broad readership for those interested in automation in reinforced concrete construction involving durability design & engineering related to corrosion of steel in concrete, corrosion resistant construction technology, corrosion maintenance & management. The scope of this paper encompasses various stages of the corrosion in construction life cycle from initial planning and design, through construction of steel reinforced concrete facility, its operation and maintenance, to the estimation of demolishing due to limiting oxygen controlled corrosion damage. This paper contains novel investigations involving computer-aided durability design, corrosion modeling under varying oxygen, classification and standardization of corrosion product data. The paper incorporates mass and energy process simulation models and graphics for the effect of oxygen on corrosion and its automated inspection as well as management. This comprehensive automated modeling and experimental investigation involving variety of materials and environmental variables will help in profound understanding, maintenance and management of oxygen controlled corrosion reaction in RC construction and will provide significant future research prospects in the field of oxygen limiting automated corrosion modeling of RC construction.

Evaluation of corrosion cost in some selected food and agro‐processing industries in Nigeria

PurposeBecause of the peculiar nature of food and agro‐processing industries, the industries cannot tolerate corrosion deposits in their production lines. Hence, there is the need to account for corrosion control before and during the production operations. This is more so in Nigeria where there is little or no proper accountability of corrosion cost in all production system.Design/methodology/approachThe industries investigated were grouped into: meat and meat product, dairy and milk, beverages and brewery, confectionery and agro‐processing centres. Questionnaires and interview pro forma were used to collect information from ten major factories/outlets in each category. The study involved the use of life cycle costing to assess corrosion management alternatives and to determine the annualized value of each option.FindingsAmong the corrosion prevention methods identified in the industries, greasing gave the least cost contribution (15.9 percent) to the total cost of corrosion prevention followed by painting (17.97 percent) and cleaning (66.14 percent) in that order, while the contribution of each corrosion maintenance method to the total cost of corrosion maintenance was, respectively, 13.08, 7.23, 20.73 and 58.96 percent for annual maintenance, repair, rehabilitation and wages of workers.Originality/valueThis study reveals some of the control measures commonly adopted for minimizing corrosion damage in some selected food and agro‐processing industries in Nigeria. It also investigated the cost implication of each measure and how it affects the present value of processing machineries in each industry. The results of the study have created a state of awareness of corrosion problems to stakeholders, which would encourage preventive actions.