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In this work, urea-formaldehyde resin was applied to enhance the corrosion protection properties of an epoxy coating. The urea-formaldehyde (UF) resin was synthesized through in situ polycondensation and the coatings were prepared by ball-milling grinding. The UF powder and coatings were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FTIR), sedimentation test, and electrochemical impedance spectroscopy (EIS). One major finding was that superior compatibility of UF resin with epoxy resin retained the high dispersion of UF in polymer matrix, leading to barely reunion during grinding. UF presented nano-scale size after grinding as shown by TEM measurements. In addition, there was not any flaw revealed from cross-sectional microstructural features of coatings. The UF resin has effectively prevented the corrosive medium from further permeating through diffusion channels to the interface between coating and steel substrate. Results further revealed that the UF resin could significantly reinforce the corrosion protection property of epoxy coatings on carbon steel substrate.
The corrosion of metallic materials poses a great threat to humans. Unfortunately, corrosion cannot be fully prevented, but only retarded and minimized. Many corrosion control strategies are currently available, such as the use of corrosion inhibitors, electrochemical cathodic protection, surface treatments, and coatings.1, 2, 3, 4 Among them, the use of protective coatings is attracting global attention because of their convenient construction and outstanding protection.5, 6, 7 Epoxy resin coatings are widely used because of their versatility, superior adhesion onto various substrates, high resistance to chemical solutions, intrinsic toughness, excellent electrical resistance, and durability at high and low temperatures.8, 9
However, the corrosion protection capability of neat epoxy resin coating is limited by the hydrolytic degradation after exposure to corrosive electrolyte. Corrosive media, such as oxygen, water, and chloride ions, reach the substrate/coating interface through diffusion channels.10 Adhesion is then lost, and the coating deteriorates.
The physical and electrolytic contact between the bottom plate of an aboveground storage tank and the underlying soil typically varies over the area of a tank bottom plates. External tank bottom plates are exposed to both electrolytic and vapor-phase corrosive environments. Cathodic Protection (CP) requires direct electrolytic contact between the tank floor and the underlying soil to effectively mitigate corrosion; hence it is ineffective in a vapor-phase environment.
There is a growing trend to supplement cathodic protection with Volatile Corrosion Inhibitors (VCI) beneath tank floors to specifically address vapor phase corrosion and enhance overall protection of tank bottom plates against soil-side corrosion. The objective of this experimental work is to expand on the study done by Pynn & Abed1 and investigate mutual compatibility and interactions of three different volatile corrosion inhibitors and cathodic protection when applied jointly on an oxygen concentration corrosion macro-cell setup.
The test results varied significantly between the three volatile corrosion inhibitors. One showed it had cathodic polarization effect and resulted in reduction of CP current requirement by 48%. Another had an anodic polarization effect and resulted in reduction of CP current requirement by 2%. Third had no polarization effect, and resulted in an increase of CP current requirement by 10%.
Effective control of soil-side corrosion on aboveground storage tank bottoms during the complete life cycle of the tank is critical both operationally and environmentally. Different foundation construction methods and corrosion protection techniques have been implemented over the last several decades in attempts to mitigate and control soil-side corrosion, including the use of asphalt pad, bituminous sand, cathodic protection and coating. Despite these measures, field experience and inspection activities indicate that soil-side tank floor corrosion persists in some cases.2-3
Underside surfaces of tank bottom plates are typically exposed to a combination of electrolytic and vapor-phase corrosive environments. While cathodic protection can be an effective corrosion mitigation technique where there is an electrolytic contact between the tank bottom surface and the underlying soil, it is ineffective in a vapor-phase environment. Air gaps or where there is intermittent moisture in the soil contacting the tank bottom surface are typical examples of vapor-phase environments under a tank floor. Published technical articles have discussed the practical limitations of the different protection methods, including cathodic protection systems, that are ineffective in providing protection in air gap areas or where cathodic current is shielded.2,4
Imidazoline derivatives have anti-corrosive effects on metals such as carbon steel and are widely used in acid-corroded pipelines for conveying oil and natural gas. In this paper, a novel imidazoline inhibitor was designed and synthesized. The corrosion inhibitor has excellent corrosion inhibition effect on in the environment of H2S / CO2. When the dosage is only 50mg / L, the corrosion inhibition efficiency can reach 94 %. SEM observation shows that fewer pits and corrosion product were found on the sample surface after adding the corrosion inhibitor. The adsorption performance of imidazoline derivatives on Fe (001) surface was calculated by molecular dynamics simulation. The molecular dynamics simulation showed that imidazoline derivatives had bigger adsorption on water than Fe (001), so that the corrosion inhibitor will first be adsorbed on the iron surface to play a role in the inhibition of corrosion, the frontier orbital adsorption sites of the corrosion inhibitor molecules are distributed around the phenyl group, thereby forming a more stable adsorption film on the metal surface.
Corrosion of the metal is a severe problem of industrial production and oil field transportation, which brings not only the waste of resources but also environmental pollution. To solve the corrosion problems, adding corrosion inhibitor is a convenient, economical and effective method. Imidazoline derivatives, a kind of environmental-friendly corrosion inhibitors, can effectively inhibit carbon steel corrosion in an acidic environment1-6. With the enhancement of people's awareness of environmental protection, the research on new type of corrosion inhibitor is developing towards the targets of high efficiency, multi-function and pollution-free. Imidazoline corrosion inhibitors are the hot topics of current research due to their high efficiency, low toxicity and good biodegradability.
The molecular structure of imidazoline inhibitor contains a hydrophilic group, five-membered heterocyclic ring, and a hydrophobic group. Each group has its role, such as hydrophilic group can increase water solubility, and hydrophobic group hinders the corrosive medium close to the metal surface. The change of imidazoline molecular structure can change the corrosion inhibition performance7. In this paper, an imidazoline inhibitor containing three phenyl groups was designed and analyzed. The frontier orbitals, molecular dynamics simulation, micro-corrosion morphology and corrosion inhibition performance of imidazoline inhibitor were analyzed by computer simulation, weight loss method, electrochemical method, and scanning electron microscope.
Tang, Dezhi (Petrochina Planning and Engineering Institute) | Du, Yanxia (Institute for Advanced Materials and Technology) | liu, Jie (Institute for Advanced Materials and Technology) | Lu, Minxu (Institute for Advanced Materials and Technology) | Chen, Shaosong (Beijing Safetech Pipeline Co., Ltd.)
Coupons have been widely used for cathodic protection evaluation of buried metallic pipelines. Under stray direct traction current condition, however, the application of coupon techniques faces some challenges due to IR drop errors caused by the inherent stray current which cannot be interrupted. In this work, factors affecting the measurements of coupon polarization potential in the existence of stray direct traction current were investigated through field experiments. The results showed that the measured coupon polarization potential was significantly influenced by multiple parameters, such as polarization retention period, “instant-off” potential sampling delay, coupon burial depth, coupon-to-CSE interval, and the proximity of groundbeds. Based on the experimental results, practical suggestions were proposed for improving the proper use of coupons under dynamic stray direct current interference.
It has been acknowledged1-7 that buried metallic pipelines would experience accelerated corrosion, especially pitting corrosion, in the presence of stray direct traction current. Moreover, the stray direct traction current would affect the performance of cathodic protection (CP) system and shifts the CP potential applied on pipelines to deviate from the design value8-9. The identification and evaluation of stray direct traction current interference was a research hotspot.
Nowadays, the most accepted method for identification and evaluation of stray direct traction current interference was to measure polarization potential of the interfered-pipeline by coupon technology10-13. However coupon technology faced some challenge due to the IR drop caused by the stray current which could not be controlled or interrupted during field test. Besides the measured coupon polarization potential would be affected by multiple parameters, such as polarization retention period, instant-off potential sampling delay, coupon burial depth, coupon-to-CSE interval, and the proximity of groundbeds. Unfortunately, very few literatures were available to provide practical suggestions for effective measurement of coupon polarization potential. In this work, factors that affected the measured coupon polarization potential under stray direct traction current interference were discussed and some practical suggestions were proposed.
Multiphase transportation of wet natural gas from production wells to treatment facilities exposes pipeline to corrosion risks. Among all types of corrosion attacks, pitting corrosion is the most common cause of failures in gas pipelines. Stochastic nature of pit initiation and growth cast uncertainty on CO2 pitting corrosion prediction. This paper discusses how precipitation of scales and corrosion products on the pipe surface along with other influencing factors contributed to the initiation of pits and finally failure of a wet gas pipeline in a sweet gas field, south of Iran. The technical analysis provided in this study is helpful for further understanding of pitting corrosion in wet gas pipelines.
Oil and gas extraction from reservoirs are to be continued as far as fossil fuels are the most dominate source of the world energy.1 Corrosion is a destructive and cost-bearing phenomenon for every industry dealing with metallic structures. Oil & gas production has been suffering from corrosion since the early history of the industry. Corrosion imposes significant cost of repair and replacement of infrastructures.2,3 Indeed, it forces unplanned shutdowns and causes catastrophic incidents that result in environmental contamination and human casualties. In 2013, NACE has estimated the total costs associated with all types of corrosion at $500.7 billion (3.1% of GDP) in the United States. Corrosion of onshore oil & gas transmission pipelines comprises $7 billion of this total.4 However, the costs associated with corrosion can be reduced significantly if appropriate corrosion mitigation programs are applied.5
Pipeline networks are the main body of all sectors of oil industry including exploration, production, treatment, and distribution. Multiphase pipelines of oil & gas gathering systems are more vulnerable to corrosion phenomena because of complicated water chemistry, presence of acid gas such as CO2 and H2S, multiphase flow, etc. Among all types of corrosion attacks, pitting corrosion is the cause of most failures, especially in wet gas pipelines. Therefore, maintaining pipeline integrity in oil & gas production and gathering systems is a real concern.4-7
In this work, a case study for the Life Cycle Costing (LCC) analysis to quantify and compare different corrosion mitigation methods based on their effectiveness and make an informed decision on the strategies to minimize the costs due to corrosion is presented. The LCC for corrosion constitutes the costs of corrosion monitoring and control, the equipment replacement costs, and the loss of production due to down time. In this work, the corrosion rates encountered in a gas gathering facility is assessed based on data provided in corrosion monitoring and inspection reports. The effects of employed corrosion control strategies on observed corrosion rate values are analyzed to develop a quantitative estimation of their effectiveness. A model is developed to calculate a resulting corrosion rate based on a selected combination of corrosion control methods. An economic analysis is then performed to include all elements for corrosion costs. The process is repeated for scenarios with better corrosion control and the optimal LCC strategy is proposed by comparison of various scenarios.
Oil and gas facilities such as booster stations, gathering centers and effluent water disposal plants employ multiple strategies to control corrosion. These include addition of chemicals such as corrosion and scale inhibitors for reducing uniform corrosion, and biocides to limit microbial effects on localized corrosion. Coating of tanks, cathodic protection and their maintenance over time is also part of corrosion control strategies. The tradeoff between the cost of these strategies over the reduction of corrosion rate of components is evaluated in this work. Bayesian models are employed to extract the uninhibited corrosion probability distributions based on environmental conditions. The effectiveness of corrosion control strategies is estimated using available data and expert knowledge. The resulting inhibited corrosion rates upon selection of desired corrosion control strategies are then computed using separate Bayesian models. Life cycle corrosion costs are obtained based on annual costs of corrosion control methods employed and the costs of replacement of the equipment in facilities due of corrosion related failure. The analysis provides a way of selecting most cost-effective corrosion control methods for minimizing corrosion and maximizing lifetime of the facilities. The LCC for corrosion constitutes the costs of corrosion monitoring and control, the equipment replacement costs, and the loss of production due to down time. Minimizing the replacements to zero might not be practical due to the highly corrosive conditions in some of the facilities. On the other hand, frequent replacements could result in very high costs especially accounting for loss of production during the facility stoppages for replacements. Reliance on only corrosion control through chemical additions or cathodic protection (CP) may also be expensive. Therefore, a trade-off between the selected corrosion control methods and planned replacement is evaluated for each facility for the optimal overall LCC. The benefits of corrosion control in terms of increased product revenue, etc. are not considered in this analysis.
In this paper, the electrochemical behavior of the third-generation Al-Li alloy 2098 was investigated with a fundamental approach, where experimental results were theoretically analyzed in terms of the Point Defect Model (PDM). For this purpose, the AA2098-T851 was tested in NaHCO3 solution under a CO2 atmosphere to investigate the kinetics of formation and breakdown of the protective passive film. Experiments were performed at potentials where both metal dissolution and the hydrogen evolution reaction (HER) occur. Electrochemical impedance spectroscopy (EIS) was conducted at potentials obtained by stepping the potential in the anodic direction with the impedance being measured after holding the potential constant after each step for a sufficient time for steady-state to be achieved. The data were interpreted in terms of the Mixed Potential Model (MPM) that describes the passive dissolution of the metal as described by the PDM and uses the Butler-Volmer (B-V) equations to describe the kinetics of the cathodic reaction of hydrogen evolution. Optimization of the MPM on the EIS data showed that the principal point defects in the barrier layer are Al interstitials. Therefore, the diffusivity of these point defects plays a major role in the formation of the passive layer, particularly the outer layer. The barrier layer is formed exclusively via the generation of oxygen vacancies at the metal/barrier layer interface. On the other hand, the passive current density is dominated by the migration of metal interstitials and the hydrolysis of the metal interstitials ejected from the barrier layer at the barrier layer/solution interface. This leads to the formation of the non-defective outer layer. Furthermore, the cathodic Tafel constant (βc) was obtained by considering quantum mechanical tunneling of the charge carriers produced by HER across the barrier layer on the metal surface, which revealed that the cathodic partial reaction was consistent with the slow discharge of water for the HER.
Ghanbari, Elmira (University of California) | Kovalov, Danyil (University of California) | Saatchi, Alireza (University of California) | Kursten, Bruno (R&D Waste Packages Unit) | Macdonald, Digby D. (University of California)
An important factor in determining the breakdown of the barrier layer of the passive film on carbon steel in halide-containing solutions is the anion size. In this study, the influence of the size of aggressive anions on the passivity breakdown of UNS K02700 grade carbon steel exposed to saturated Ca(OH)2 solutions with the addition of different halides was investigated by using the potentiodynamic polarization (PDP) experiments. The PDP results were interpreted by using a mechanistic description based on the Point Defect Model (PDM). The experimental results revealed a linear dependence of the critical breakdown potential (Ec) on the logarithm of the activity of the breakdown-inducing halide (F-, Cl-, Br-, and I-), as predicted by the PDM. Furthermore, the PDM successfully accounted for the order with which the halides induce passivity breakdown, F- < Cl- > Br- > I-, in terms of competitive Gibbs free energy of anion dehydration and expansion of surface oxygen vacancies, into which the halide must absorb as the initial event in the breakdown process.
UNS K027001 grade carbon steel is currently the reference material for the fabrication of the overpack in the supercontainer design that is developed for the geological disposal of the High-Level Nuclear Waste (HLNW) in Belgium.1 Damage to the supercontainer is envisioned to possibly occur by localized corrosion resulting from the presence of aggressive species in the annulus between the carbon steel overpack and the stainless steel envelope, which is filled with a cementitious material similar to Portland cement. The aggressive species may lead to passivity breakdown of carbon steel and to the development of pits. Therefore, the reliability and the corrosion performance of these metallic containers are of great importance in assuring the public safety. However, only using the empirical approach for studying the corrosion damage and passivity breakdown of the metallic parts of the barrier layer, cannot satisfy the need for predicting the corrosion performance over many millennia.
Al-Rasheed, Naser (Kuwait Gulf Oil Company) | Kamshad, Tariq (Kuwait Gulf Oil Company) | Sabesan, Manickavasagan (KGOC/SAC Joint Operations) | Al-Ghamdi, A/Rahman (Saudi Arabian Chevron Inc) | Siriki, Ravi Shankar (KGOC/SAC Joint Operations) | Farah, Mohamed M. (Weatherford Kuwait for Petroleum Services)
Oil and gas facilities can be subjected to faster deterioration during period of shutdown than those in operation; hence replacement of damaged equipment or piping can be very costly. Among the myriads of short-term preservation methods available, chemical treatment preservation program represents one of the most effective method to minimize the risk of continuous deterioration, hence safeguard the overall integrity of the facility.
This paper details the unique challenges encountered within the Al-Wafra oilfield when implementing chemical treatment method under the stagnant and highly corrosive conditions, as a result of unscheduled shutdown. These conditions alongside the entrapped sludge and accumulation of fluids at low spots is expected to lead to the dominance of under-deposit (UDC) and microbial induced corrosion (MIC), hence any chemical program should be designed to effectively mitigate these damage mechanisms. Consequently, the methodology developed involved initially flushing the facilities with less saline water to remove deposits and sediments, and subsequently treating the entire facility with a mixture of corrosion inhibitor, oxygen scavenger and biocide in brackish water. This is expected to significantly reduce the corrosion rates in comparison to uninhibited system. A range of corrosion monitoring techniques alongside fluid chemistry analysis was implemented for the field monitoring to ascertain the overall efficacy of the program as per key performance indicators (KPI).
The Joint Operation (JO) Al-Wafra Oilfield is located in the west central part of the Kuwait-Saudi Arabia Neutral Zone. The Al-Wafra oilfield reserves were first discovered and wells drilled in 1954. The Al-Wafra field produces two types of crude oil, Ratawi (light oil, 24 API) and Eocene (heavy oil, 18 API), with average water cut 80-85% from multiple production wells. During operation, the production wells produce the oil emulsion through coated flowlines to sub-centres (SC) where the sour oil, water and gas is separated. Joint Operation has two gathering fields; Eocene and Ratawi. Eocene has 2 phase separation, whilst Ratawi has 3 phase separation. The sour gas flows to the Main Power Generation Plant, whilst the oil is produced to the Main Gathering Centre (MGC) and the produced waters are routed to the Pressure Maintenance Plant (PMP) for treatment and eventual re-injection for secondary recovery.
A range of parameters must be considered carefully when modelling AC corrosion. Prediction of induced AC voltage profiles along pipelines due to shared right-of-way with high-voltage power lines has been practiced for decades. Modelling of the cathodic protection level on a pipeline resulting from types, position, and current output from CP sources, pipeline dimensions, coating conditions, soil conditions, isolation, etc., has also been implemented during several years. Computer aided prediction of corrosion rates caused by induced AC as a function of AC and DC current densities, coating fault geometry and thickness, soil resistivity, etc. has been attempted only in recent years. The complexity of the AC corrosion process calls for careful and critical evaluation of the computed results, and their practical applicability.
The present paper presents and discusses the various components contained in an electrical equivalent circuit describing the AC corrosion process from a computer modelling perspective. The effect of the coating defect size and geometry on spread resistance and resulting AC current density, the effect of the kinetics of electrochemical reactions relevant for the corrosion process, the effect of diffusion and diffusion coefficients for active chemical species, as well as the impact of the capacitive effect of the electrochemical double layer as a short circuit of the electrochemical processes, soil chemistry, texture and soil resistivity are all aspects that influences the AC corrosion process and therefore the reliability of a computer model. These aspects will be discussed together with the sensibility of a model and the risk of generating inaccurate results due to missing or erroneous inputs. In addition, different model approaches will be discussed and sustained through examples.
The utilization of mathematical modelling in cathodic protection design as well as interference problem solving has proved to be of great value.1,2 The success of the modelling approach relies on correct initial assumptions of the processes occurring in the specific scenario, the use of correct parameters and magnitudes, and a proper mathematical modelling tool. The modelling cannot be a standalone tool as the results must be validated against real observations and measurements on the system under investigation. Mathematical modelling has also been attempted in relation to AC corrosion, which is a complex scenario in terms of the chemistry and physics involved.3 Nevertheless, a successful model would be beneficial in terms of the understanding of AC corrosion, risk assessment and mitigation. Due to the high level of complexity of the problem, a careful analysis of the basis for the modelling is a clear pre-requisite, and a meaningful way of validating the model results should be defined.