Zhang, Yunan (Institute of Advanced Materials and Technology University of Science and Technology Beijing) | Xie, Yun (China First Heavy Industries) | Lu, Minxu (Institute of Advanced Materials and Technology University of Science and Technology Beijing) | Xu, Lining (Institute of Advanced Materials and Technology University of Science and Technology Beijing) | Chang, Wei (CNOOC Research Institute)
CO2 Top-of-Line Corrosion(TLC) is one of the most serious problems in wet gas subsea pipelines. Due to better localized corrosion resistance than carbon steel, the new generation of low Cr (2%~4%) alloy steels show superior resistance to CO2 corrosion. Experiments were carried out in a high temperature high pressure condensation autoclave simulating CO2 TLC environment. The composition and morphology of the corrosion scale are characterized by energy dispersive X-ray spectroscopy and scanning electron microscopy analyses. The results indicated that the 2% Cr and 3% Cr alloy steels exhibited slight localized corrosion, and the 4% Cr alloy steel exhibited uniform corrosion. With higher Cr content, the localized corrosion resistance of 4%Cr alloy steel was superior to 2%Cr and 3%Cr alloy steel.
Reservoir Souring is the unplanned production of increased concentrations of hydrogen sulfide (H2S) in wellstream fluids from production wells that are subjected to water-injection. The consequences of souring with respect to safety, corrosion and environmental risk can be significant. This is typically associated with the activity of a specialized group, the Sulfate-reducing bacteria (SRB). However, in recent years, various other micro-organisms are believed to be involved in souring, e.g. Sulfate reducing archaea (SRA).
In this study, fixed film up flow bioreactors (FFUBR) were utilized to assess the potential for H2S production or changes in such H2S production, when seawater is injected into a North Sea oil reservoir. The study has demonstrated how changes in fundamental parameters (e.g. bacterial nutrients, shut-in periods) can impact sulfide production and alter the microbial communities. The FFUBR’s were soured to create a ‘worst case’ scenario and different nutrient additions or remediation treatments were applied to represent either near injection wellbore or deep field conditions.
Typical oil field practice is to measure H2S in the gas phase. Partition modelling of H2S between water, oil and gas phase was applied to the measured sulfide data to give a real-world indication of the effect of H2S in gas when resuming production following a shut-in.
The following parameters were measured during the testing period: sulfide generation, volatile fatty acid organic carbon sources (VFA), iron, nitrate and nitrite concentrations. The microbiology of the system was evaluated both by traditional culture techniques and molecular methods, such as fluorescence in situ hybridization (FISH) analysis and other DNA-based analysis.
Results indicate that when sulfide generation had reached 1.5 mM, and the nutrient source was changed, almost complete cessation of sulfide generation resulted for a period of 7 days. Whereas, following shut-in period, sulfide generation recommenced after re-starting the flow and reached a concentration of 4.4 mM immediately and rose even higher to 5.0 mM over the first days of flow. However, sulfide concentrations returned to 2.0 mM again within 7 days after restart.
However, the changes in the microbial community were found to be somewhat selective to certain SRB families. The various effects of the different treatments and conditional changes are discussed further in this paper.
Ramachandran, Sunder (Baker Hughes Incorporated) | Lehrer, Scott (Baker Hughes Incorporated) | Jovancicevic, Vladimir (Baker Hughes Incorporated) | Magalhae, Alvaro A. (Centro de Pesquisa da Petrobras - CENPES)
Safe transport of sour gas involves the use of sulfide corrosion cracking resistant materials. Such materials can be expensive, so in some instances it may be more economical to use a hydrogen sulfide scavenger to remove hydrogen sulfide from the production fluid. Using a hydrogen sulfide scavenger can allow the use of less expensive materials. Conventional hydrogen sulfide scavengers such as triazines are not generally used downhole due to their high scaling tendency and low thermal stability. In many applications, conventional hydrogen sulfide scavengers exhibit slow kinetics resulting in the need to use a much higher amount than theoretical stoichiometry would dictate. A new test procedure was used to evaluate various candidate hydrogen sulfide scavengers and gain better understanding of the critical parameters that control the efficiency and kinetics of hydrogen sulfide scavengers in varied applications and conditions.
As a result, a new non-triazine based scavenger with high temperature stability and fast kinetics was recently developed for use in either oil or mixed production applications. This technology can either be used in direct injection applications top-sides or downhole injection via gas lift or umbilical. The improved kinetics of the new scavenger makes it especially useful for applications where the system residence time is low. The new scavenger has been tested for thermal stability and compatibility with metal, elastomers, plastics and other chemicals.
Increasing emphasis is being placed upon control of carrier pipe corrosion inside cased pipeline crossings from both an operator and regulatory perspective. Inline inspection associated with pipeline integrity management programs has identified external carrier pipe corrosion inside casings. Many factors contribute to this corrosion concern. Systems designed to proactively mitigate corrosion inside cased crossings were not readily available.
The desire for a proactive carrier pipe corrosion control system led a pipeline operator and a company expert in the manufacture and application of volatile corrosion inhibitor (VCI) chemistry to consider a new corrosion mitigation solution. This effort resulted in the development of a unique product designed to fill the annular space of a casing with a gelatinous product that proactively controls carrier pipe corrosion and prevents intrusion of water, etc. into the annular space. The gel filler has been applied inside cased crossings since late 2011. Electrical resistance (ER) probes have been installed through the casing vents and submerged in the filler to the carrier pipe surface. The probes are monitored remotely with automated technology. The corrosion rate data validates the effectiveness of the VCI filler. This new corrosion control solution produces an excellent opportunity to enhance the integrity of pipelines inside cased crossings.
Corrosion damage was observed in carbon steel heat exchangers tubes only after nine months of service. These exchangers cool down a recycle stream from the reactor, thus removing the heat in the reactor evolved due to dimerization reaction of Ethylene to Butene. The shell side medium is cooling water and the tube side is butane. Metallurgical structure and chemical composition of the heat exchanger pipe’s metal matrix were inspected by metallographic microscope and X-Ray Fluorescence Spectrometry (XRF) and carbon/sulfur (C/S) analyzer. Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) was used to study the damage morphology and the chemical compositions of the corrosion products. Biological analyses of cooling water were performed, as well. The analytical results suggest the main corrosion mechanism for the observed attack is microbiologically influenced corrosion (MIC).
Non destructive Testing (NDT) is commonly used to assess the extent of corrosion within plant, including vessels, piping and pipelines. In particular measuring instruments using ultrasound are used to find locations where loss of wall thickness has occurred and to determine the extent of the loss. Inherent in the measurement of wall thickness is the assumption that from a limited set of measurements it is possible to infer the condition of a vessel, heat exchanger tube bundle or section of piping. The determination of corrosion rate then requires a reassessment of the wall thickness at a later date. For old plants, the variability in corrosion damage both in a spatial sense and in depth of loss causes a difficulty in finding the worst case losses in wall thickness and in determining remaining life. It is also necessary to recognize that the measurement error depends on the skill applied by the inspector during the inspection. This paper discusses the use of probability of detection concepts for finding corrosion damage and illustrates it for a corroding vessel inspected over a 2 year period. It also describes the use of distributions of wall loss to characterize the condition of corroding vessels and pipelines. The incorporation of statistical principles into data analysis is required because of the inherent variability of corrosion damage.
Beavers, J.A. (DNV (U.S.A.), Inc.) | Brossia, C.S. (DNV (U.S.A.), Inc.) | Gui, F. (DNV (U.S.A.), Inc.) | Scott, C. (DNV (U.S.A.), Inc.) | Cong, H. (DNV (U.S.A.), Inc.) | Sridhar, N. (DNV (U.S.A.), Inc.) | Wiersma, B.J. (Savannah River National Laboratory) | Frankel, G.S. (The Ohio State University) | Boomer, Kayle (Washington Group)
Stress corrosion cracking (SCC) is a potential threat to the integrity of the double shell tanks at the Hanford site, which store legacy waste from the nuclear weapons program. The SCC behavior of carbon steels similar in composition to the tank steels was investigated in a series of environments designed to simulate the chemistry of these wastes. Both slow strain rate tests using tensile specimens and constant load tests using compact tension specimens were performed. Based on the tests conducted, nitrite was found to be a strong SCC inhibitor. The cracking behavior also was a strong function of potential, and, in the majority of simulants, anodic polarization was required to promote SCC. These findings have driven the development of a field program at Hanford to measure corrosion potentials of the waste tanks and compare the results with the results of the laboratory SCC testing. The information obtained to date has shown that the tanks being monitored are operating at potentials out of the cracking ranges.
Within an oil & gas station, normally different kinds of electrically connected metal structures are cathodically protected as a whole to protect them from corrosion, which is called regional cathodic protection in China. The metal structures protected in a station include buried oil or gas pipelines, sewage pipelines, vent pipelines, tank bottoms, equipment foundations and grounding systems, etc. These metal structures with poor coating or even without coating, such as tank bottom, grounding system, will consume large quantity of protective current and cause problems of interference and shielding, which brings challenges for the design of regional cathodic protection. In this work, several key technologies were studied on regional cathodic protection, such as the determination and reduction of current requirement, the disposal of shielding and interference problems.
A thin layer of semi-conductive material was developed and combined with MMO coated titanium tape anodes for reinforced concrete structures. This system was developed to overcome the problems experienced with existing cathodic protection systems. These problems include poor CP current distribution caused by near-short circuits and shallow concrete cover, acid generation at the anode-concrete interface and dryness of the anode-concrete interface for structures which are not exposed to direct moisture such as tunnels or deck soffit and substructures. In addition, by eliminating complex CP anode engineering and installation, the CP system becomes more users friendly and cost effective for many structure owners and contractors.
This paper discusses the problems with existing CP systems and describes an innovative state-of-the art impressed current CP system. Data obtained from the laboratory and the field trials will be presented.
Romero, Nathalie (Universidad del Zulia Ciudad Universitaria) | de Rincón, Oladis Troconis (Universidad del Zulia Ciudad Universitaria) | Millano, Valentina (Universidad del Zulia Ciudad Universitaria) | Polo, Everlyn (Universidad del Zulia Ciudad Universitaria) | Espina, María (Universidad del Zulia Ciudad Universitaria) | Linares, Douglas (Universidad del Zulia Ciudad Universitaria) | Salas, Orlando (Universidad del Zulia Ciudad Universitaria)
Nowadays, most of the anodizing for aluminum worldwide and locally is done in a sulfuric acid based system which requires high energy consumption, besides the cost of waste disposal. Therefore, the aim of the present work was to investigate formulation of new electrolytes, based on mixtures of different acids and natural environmentally friendly substances, which could improve the manufacture and corrosion resistance of aluminum in highly aggressive marine environments. Different acid based electrolyte mixtures were initially evaluated (sulfuric, oxalic, boric, phosphoric and citric acids) with and without additives of natural substances (Caesalpinia coriaria fruit, commercial tannin, aloe vera, mango tree’s leaves and neem’s fruit), in a pilot scale production of anodized with a 5 µm minimum thickness. They were evaluated in 3.5 wt% NaCl, using electrochemical techniques i.e. Linear Polarization Resistance (LPR), Anodic Potentiodynamic Polarization (APP) and Electrochemical Impedance Spectroscopy (EIS), in order to make an initial selection of those with higher corrosion resistance, lower energy consumption in manufacture and more environmentally friendly electrolytes. The selected products were then subjected to accelerated atmospheric testing as per ISO (1) 11474. The results of the investigation are presented in this paper.