NACE Solution Research Articles

CO2 Corrosion of X80 Steel under High Shear Flow Fields

Corrosion failure accidents owing to flow erosion and pipeline corrosion frequently occur during transportation. In this study, a high wall shear stress (WSS) experimental setup was established to conduct the online electrochemical corrosion test. The corrosion behavior of welded joints in NACE solution was studied by electrochemical experimental methods such as electrochemical impedance spectroscopy (EIS) and wire harness microelectrode (WBE). The results show that different areas of the welded joint show different corrosion phenomena in NACE solution. The weld metal (WM) has the significantly better corrosion resistance, while the base metal (BM) and heat-affected zone (HAZ) have worst corrosion resistance than WM. The current of the WM surface was cathodic current, while the current of the BM and HAZ surface were anode currents.

A Combination of Laboratory Testing, RCE, and Corrosion Loop for Inhibitor Selection

Corrosion inhibitors are evaluated in the oil industry with electrochemical tests of resistance to linear polarization with rotating cylinders following ASTM G170 and NACE 3T199 standards. With these tests, we can determine the corrosion rate (CR) and efficiency of corrosion inhibitors. In this work, a corrosion test protocol used by hydrocarbon-producing companies for the testing of corrosion inhibitors was used. This protocol consists of a 1045 carbon steel working electrode in a NACE solution composed of 9.62% NaCl, 0.45% CaCl2, 0.19% MgCl2, and 89.74% H2O, at a temperature of 65 °C and saturated with CO2. Each inhibitor tested was subjected to a series of 6000-4000-2000-4000-6000 rpm tests using rotating cylinder electrodes (RCEs). These electrochemical studies were carried out with the rotating cylinder to evaluate the ability of the inhibitor to prevent the corrosion of carbon steel in the presence of a centrifugal force. In our opinion, this test does not provide corrosion engineers with enough information to be used as a predictive tool, since what is obtained is the CR in a very short testing time. This document proposes the use of two more appropriate test methodologies, the rotating cylinder electrode (RCE) and the flow loop (FL), to evaluate the performance of the corrosion inhibitor. For the FL, the selected flow rate was 1.2 m/s, the same rate that fluids have in oil company pipelines installed in Neuquén, Argentina. Firstly, according to the company’s protocol, inhibitors are required to have an efficiency greater than or equal to 90% in RCE tests; therefore, inhibitors that meet these requirements were tested in the FL test. Unlike the RCE test, the FL test represents the experimental conditions of the laboratory that are closest to reality, for the evaluation of the performance of the inhibitors used in the pipelines of the oil and gas industry. FL tests have several problems involving corrosion, erosion, abrasion, biphasic fluids, the time it takes for the inhibitor to become effective, and the duration of its effectiveness.

Corrosion behavior and mechanism of X80 pipeline steel welded joints under high shear flow fields

The internal-pipeline local corrosion in the welded joint region has been a widely concerning issue, particularly under the synergistic effect of high shear stress and electrochemical corrosion, which can easily result in pipeline rupture. Classical electrochemical testing techniques and wire beam microelectrode (WBE) are used to investigate the local corrosion behavior of X80 steel welded joints in a CO2-saturated NACE solution at different flow rates (velocities of 3 m/s, 5 m/s and 7 m/s), and the corrosion product composition and characteristics are analyzed via scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and three-dimensional (3D) measuring laser microscopy. The results show that different welded joint zones exhibit different corrosion degrees. The heat-affected zone (HAZ) shows the worst corrosion resistance, whereas the base metal (BM) and weld metal (WM) show similar corrosion resistances. The HAZ is an anode that corrodes unsatisfactorily at high flow rates, and the enhanced wall shear stresses peel off part of the dense corrosion product film, promoting the development of local corrosion. Therefore, the HAZ zone is a weak link in the X80 steel welded joints. This study provides scientific guidelines for the corrosion protection of long-distance oil & gas pipelines.

ДОСЛІДЖЕНЯ ПРОЦЕСІВ НАВОДНЮВАННЯ ВУГЛЕЦЕВИХ СТАЛЕЙ РІЗНОЇ СТРУКТУРИ У СІРКОВОДНЕВИХ СЕРЕДОВИЩАХ

The effect of applied static loads, structure, and carbon content in steels on their hydrogenation was investigated in the paper. The content of absorbed hydrogen was determined by the method of vacuum extraction at temperatures of 200, 400, 600 and 800 °С for 720 hours, after corrosion in the NACE solution. It was shown that the hydrogenation of 0.8% C steel in the number of structures: pearlite, sorbite, troostite and martensite increased. The ferrite-pearlite structure of 0.45% C steel was the most intensively hydrogenation (19.4 ppm), sorbitic, troostitic and martensitic - less by 30...50%. The main contribution to the absorbed hydrogen was made by diffusive-mobile hydrogen. Its share in the total amount of absorbed reached~65...74% for pearlitic, 50...54% sorbitic, 64...78% troostitic and ~67% martensitic U8 steel structure. For steel 45, it is ~61...72% for ferrite-pearlitic, ~74...79% sorbitic, ~61...75% troostitic, and ~52...85% martensitic. The absorbed hydrogen content of 0.8 % C steel with sorbitic, trostitic, and martensitic structures at temperatures of 400, 600, and 800 ºС increased, while that of steel 45, on the contrary, decreased. This indicated the greater strength of the hydrogen-metal bond in 0.8 % C steel. Therefore, the structure of steels affects the sorption of hydrogen more than the carbon content. Applied static loads  = 300 MPa increased the content of hydrogen absorbed by steels by ~9...15%. On 0.8% C steel, this manifests itself more significantly - СН/С0Н= 1.3...1.8. As the imbalance of the structure increased, the resistance of steels to corrosion cracking under static loads decreased. This was determined by the dispersity of the structure and the morphology of sulfide films, which are formed during the corrosion of steels in the NACE solution. Therefore, static loads most contributed to the hydrogenation of 0.8 % C steel with a troostite structure, and 0.45% C - troostite and martensitе.

Development of the NACE “MR-01-75” and NACE “TM-01-77” Standards, Part II: Accelerated Material Qualification Testing in Sour Environments at Near Atmospheric Pressure

This paper is Part II of a two-part series intended to narrate the history, some of which has been forgotten over time, leading up to the publication of the first Material Requirement (MR-01-75) standard prepared by NACE and its subsequent auxiliary standards. Previously, Part I described the field observations and discussed the metallurgical factors that were being investigated by the historical NACE T-1B and 1F committees to support the development of a sour service materials standard. In Part II, we focus on the rationale behind the use of accelerated laboratory test procedures designed to differentiate metallurgical behavior in sour environments. The original sulfide stress cracking test methodologies would later be codified as a Test Method in NACE TM-01-77 (1977). A review of the historical events culminating in NACE MR-01-75 and NACE TM-01-77 provides a technical basis for the historical use of NACE solution A (5 wt% NaCl + 0.5 wt% acetic acid) to evaluate metallurgical factors, and the origins of several common SSC NACE Test Methods still used today: Methods A (tensile), B (three-point bent beam), and C (C-ring). The accelerated laboratory test results, in combination with parallel field trials (performed in advance of the first NACE MR-01-75 publication), supported the ≤22 Rockwell C (22 HRC) hardness limit for carbon and low alloy steels in sour environments containing ≥0.05 psia H2S partial pressure. As the oil and gas industry continues to innovate and mature, it was imperative to maintain knowledge of the origins of the NACE MR-01-75 and TM-01-77 standards and their intended purposes.

CARBONIZATION OF CONCRETE AND CORROSION OF REINFORCEMENT OF REINFORCED CONCRETE STRUCTURES OF UNDERGROUND SEWERAGE SYSTEMS

The process of carbonization of concrete with different ratio of water to cement (W/C) was studied, and the influence of the environment on corrosion damage of reinforced concrete reinforcement was studied. The results of the study of carbonization of concrete on specially prepared model samples of concrete with a size of 250x250x250 mm with an exposure period in NACE solution for 500 days without external load are presented. Measurements of corrosion damage of reinforcing rods, which were placed inside concrete cubes, were performed. The method of estimating the amount of carbonization of concrete and corrosion of reinforcement is described in detail in known scientific papers. The obtained data testify to the active carbonization of concrete during the whole exposure period of the samples in NACE solution, however, concrete prepared at the ratio W/C = 0.5 and 0.6 is particularly significant in terms of carbonization intensity. Concrete with a ratio of W/C = 0.7 is less susceptible to damage. Moreover, a similar trend is observed for corrosion of fittings. This is due to the fact that the increase of the aqueous medium in the concrete mass facilitates diffusion processes of delivery to the reactive zone of chemically aggressive ingredients such as carbon dioxide, chloride ions, hydrogen, sulfur, sulfate ions, various types of bacteria and the like. The kinetics of concrete carbonization and corrosion of reinforcing bars in chemically aggressive NACE medium depending on the exposure period of the samples in the model solution was experimentally studied. It is established that with the increase of the water-cement ratio W/C from 0.5 to 0.7, the depth of carbonization and the layer thickness of corrosion products increase sharply. The flooding of the surface layers of the reinforcement and their strong embrittlement in the process of long-term operation of the reinforcement in the structure of reinforced concrete, which causes a decrease in crack resistance in general of reinforced concrete structures. The degradation of reinforcing steel during long-term operation in aggressive environments, which leads to premature corrosion damage to the reinforcement with subsequent destruction of the structure, was investigated experimentally with the involvement of high-precision metallographic equipment.

Corrosion behavior of X65 steel at different depths of pitting defects under local flow conditions

The electrochemical corrosion behavior and the development mechanism of the local corrosion of X65 steel under different defect depths were studied by using macroscopic electrochemical measurements and characterization techniques. A CO2-saturated NACE solution was used to study electrochemical corrosion characteristics in the single-phase flow-accelerated corrosion test loop system. Changes in the flow characteristic around the defects at different depths were characterized by COMSOL. The results indicated that samples with lower depth defects tend to deepen towards the radial direction both in the deep defects and shallow defects. Moreover, the upper and trailing edge of the defect has a tendency to deepen and expand the region of the defect under the influence of higher turbulent kinetic energy (TKE) and the shearing rate.

The Influence of Metallurgical Factors on Stress Corrosion Cracking of Various Steels in an Aggressive Chloride–Sulfide Environment

The influence of metallurgical factors on stress corrosion cracking of steels of different classes in an aggressive NACE solution at 25°C is analyzed. The dependences of the stress leading to the transition from active corrosion to the mechanism of hydrogen embrittlement (critical stress) on the yield stress and the coefficient of stress concentration are plotted. The relationship between the critical stress, conditional yield stress, and overstress values is revealed. It is concluded that the loss of corrosion resistance for unalloyed steels with a yield stress below 500 MPa is caused by an increase in the hydrogen concentration during deformation of the material in a corrosive environment.

Stress corrosion cracking behaviors of FV520B stainless steel used in a failed compressor impeller

Stress corrosion cracking (SCC) in compressor impellers made of FV520B stainless steel frequently occurred, and hence was investigated by slow strain rate tests (SSRTs) and fracture toughness tests, combined with finite element analysis (FEA) based on ABAQUS and ZENCRACK software. SSRTs revealed that the FV520B stainless steel had slight susceptibility to aqueous brine solution, which increased with increasing temperature, and fracture surface exhibited ductile feature with dimples similar to that in nitrogen; however, this material showed significant susceptibility to NACE solution A at various temperatures, and fracture surface consisted of initial quasi-cleavage region and subsequent dimple region; both tempered martensite matrix and localized δ ferrites were susceptible to SCC. Fracture toughness KIC (JIC) of this steel was 150MPam1/2 (102KJ/m2) in air, but threshold stress intensity factor (KISCC) dramatically reduced to 48MPam1/2 in NACE solution A, and Boltzman equation was modified to describe SCC propagation rate (da/dt-K) curves. Comparison with FEA results indicated that the fracture of SSRT specimen was initially affected by environmental factor and then mainly attributed to mechanical factor, whereas the whole fracture process of impeller was closely related to corrosive environment. This study was useful for SCC evaluation of materials and failure analysis of compressor impellers.

Development mechanism of internal local corrosion of X80 pipeline steel

The occurrence and development mechanism of internal local corrosion has always been a controversial topic, and especially under flow conditions. In this paper, an improved high shear force loop was experimentally used, and local flow field is induced by simulating corrosion defects on the surface of X80 pipeline steel specimens. The characteristics of corrosion products deposited on the surface of specimens in CO2-saturated NACE solution were investigated by means of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometry (EDS). The 3D micromorphology of the corrosion test surface after remove the corrosion scale used to measure the size of localized corrosion pit. Under the influence of local defects, the wall shear stress (WSS) and turbulent kinetic energy of local flow fields enhanced significantly, and pressure fluctuations in local flow field were induced. The results showed that the characteristics of surface corrosion products varied with flow velocity. The corrosion scales formed in various regions of specimens with defects exhibited different surface micro-morphologies and chemical compositions. Overall, these data offer new perspectives for better understanding the mechanisms behind local corrosion.

Влияние металлургических факторов на коррозионное растрескивание под напряжением различных сталей в агрессивной хлоридно-сульфидной среде

Проведен анализ влияния металлургических факторов на коррозионное растрескивание под напряжением сталей разного класса в агрессивном растворе NACE при 25oC. Получены зависимости напряжения перехода от активной коррозии к механизму водородного охрупчивания (критического напряжения) от величины предела текучести и коэффициента концентрации напряжений. Выявлена связь между критическим напряжением, условным пределом текучести и величиной перенапряжения. Сделан вывод о том, что потеря коррозионного сопротивления для нелегированных сталей с пределом текучести ниже 500 MPa обусловлена увеличением концентрации водорода в процессе деформации материала в коррозионной среде. Ключевые слова: коррозионное растрескивание под напряжением, водородное охрупчивание, предел текучести, коэффициент стойкости, сталь.

Development mechanism of local corrosion pit in X80 pipeline steel under flow conditions

In this paper, local corrosion pits were stimulated by arc defect pits (ADP) of different sizes. The corrosion of specimens was tested in high-speed flow CO2-saturated NACE solution. Electrochemical corrosion characteristics were monitored online. The characteristics of corrosion scale were then investigated by SEM and Raman spectroscopy. The results showed deepening and expansion of corrosion pits will occur at the same time under flow conditions for shallow pits. The development of corrosion pits at certain depth led to formation of complete corrosion scale, which inhibited further corrosion. As corrosion pits deepened, expansion process decreased and deepening rates accelerated. In-depth analysis suggested that corrosion rates were mainly affected by mass transfer rate and integrity of formed corrosion scale.

Influence of the Structure of Carbon Steels on the Corrosion, Hydrogenation, and Corrosion Cracking in Hydrogen-Sulfide Media

We study the influence of the structure of carbon steels on corrosion, hydrogenation, and corrosion cracking in NACE solution. The corrosion and hydrogenation rates of U8 steel increase with the range of particle sizes in the structure in the following order: pearlite, sorbite (high-temperature martensite), troostite (medium-temperature martensite), and martensite. In 45 steel, these rates are maximum for the ferrite-pearlite structure and minimum for sorbite. The 45 steel is less susceptible to hydrogen-sulfide corrosion cracking in a NACE solution than U8 steel, which reveals the dependence on the content of carbon and, hence, on the content of carbides. The 45 steel with sorbite structure and U8 steel with sorbite and troostite structures are characterized by the highest resistance to fracture in hydrogen-sulfide media. However, in view of the influence of hydrogenation, steels with sorbite structures prove to be most suitable for operation in hydrogen-sulfide-containing media.

Test Conditions for Pipeline Materials Selection with High Pressure Sour Gas

Acid gases, such as CO2, H2S, and/or sulfur in oil industry’s production fluids, can be responsible for both general and localized corrosion, acting with different mechanisms, which depend on chemical and physical properties of the produced fluids. Materials selection for handling such fluids is performed by combining experience with suggestions from standards and regulations. A good deal of knowledge is available to predict corrosion rates for CO2-containing hydrocarbons, but the effect of high H2S pressure is less understood, mainly due to the difficulty of performing laboratory tests in such challenging conditions. For instance, the so-called NACE solution to assess SSC (Sulfide Stress Cracking) susceptibility of steels is a water-based solution simulating production fluids in equilibrium with one bar bubbling H2S gas. This solution does not represent environments where high gas pressure is present. Moreover, it does not take into account the corrosive properties of sulfur and its compounds that may deposit in such conditions. Besides, properties of high pressure gases are intermediate between those of a gas and those of a liquid: high pressure gases have superior wetting properties and better penetration in small pores, with respect to liquids. These features could enhance and accelerate damage, and nowadays such conditions are likely to be present in many production fields. This paper is aimed to point out a few challenges in dealing with high pressure gases and to suggest that, for materials selection in sour service, a better correspondence of test conditions with the actual field conditions shall be pursued.

Corrosion cracking of carbon steels of different structure in the hydrogen sulfide environment under static load

Hydrogen sulfide corrosion is one of the main reasons of steels destruction in the oil and gas industry. Damages appear as a result of corrosion and hydrogen embrittlement, and corrosion cracking occurs when the load is applied. The influence of the steels structure on its stress corrosion cracking under the loads in hydrogen sulfide environment is insufficiently studied. The aim of the study is to determine the influence of the steels structure on its corrosion, hydrogenation and corrosion cracking in the NACE hydrogen sulfide solution.It was established that the corrosion rate and hydrogenation of steel У8 in the NACE solution grows when the structure dispersion increases from perlite to sorbite, troostite and martensite. The corrosion rate and hydrogenation of steel 45 are the greatest in pearlite-ferrite, while the smallest - in sorbite.The corrosion of steels У8 and 45 in the NACE solution is localized: the average size of the ulcers is 50 ... 80 μm on the steel У8 and 45 ... 65 μm on steel 45. The depth of ulcers is maximal on the steel У8 with the martensite structure (~ 260 μm) and on the steel 45 with the troostite structure (~ 210 μm).Static load (σ = 300 MPa) increases the hydrogenation of steels in the hydrogen sulfide environment. The concentration of hydrogen in steel У8 with troostite structure increases by ~ 1.8 times. The concentration of hydrogen in steel 45 with troostite and martensite structures increases by ~ 1.2...1.3 and by ~ 1.4...1.6 times, respectively.The steel У8 with martensite and perlite structures and steel 45 with troostite structure has the lowest resistance to corrosion cracking. Steels destruction depends on both hydrogen permeation and the corrosion localization, which leads to the increase of the microelectrochemical heterogeneity of the surfaces.

Study of the Rate of Corrosion and Its Mechanisms in Aluminum Alloy after the Intense Torsional Plastic Deformation

The research results concerning the rate and mechanism of corrosion in aluminum alloy 6201 of the Al–Mg–Si system in a NACE solution are presented. The alloy was studied in three states: after standard treatment T6 (quenching + aging) and after the intense torsional plastic deformation (ITPD) at the temperatures of 130°C (dav = 280 nm) and 180°C (dav = 440 nm). It was shown that the corrosion resistance of alloy after ITPD is lower than in the case of state T6. The corrosion rate of alloy after ITPD at 130°C is higher than that at 180°C. The change in the surface roughness was analyzed.

Investigation into the corrosion rate and features of the samples made of nanostructured aluminum alloy in the H2S-containing medium

The corrosion rate was determined and corrosion damage features of the samples made of AK4-1 aluminum alloy were investigated in the NACE solution containing hydrogen sulfide (H2S). The alloy was investigated in the ultra-fine-grain state compared with the coarse-grain state formed after standard treatment T6 (quenching + ageing). The alloy was nanostructured by equichannel angular pressing (ECAP). It is shown that the alloy corrosion rate after ECAP is higher than after T6 treatment by a factor of 1.9. Herewith, the total corrosion takes place in alloy after ECAP, while pitting corrosion is also observed after T6 treatment in addition to the total corrosion. The corrosion effect strongly affects surface-roughness parameters of the samples made of AK4-1 alloy after ECAP compared with the samples after T6 treatment.

Static Crack Resistance of 20 and 30KhMA Steels in a Nace Solution

We study the crack resistance of 20 and 30KhМА steels in a NACE hydrogen-sulfide solution under static and repeated static stresses and found their threshold stress intensity factors. A conclusion is made that these steels almost satisfy the criteria of their applicability in hydrogen-sulfide media accepted in the engineering practice.

Numerical and electrochemical analyses on carbon dioxide corrosion of X80 pipeline steel under different water film thicknesses in NACE solution

Gas-liquid flow in a wet gas pipeline with low liquid loading was studied by computational fluid dynamics (CFD) simulation. Eulerian wall film model was used to calculate the formation and development of water film on the wall of large diameter pipe. Based on the water film thickness obtained by CFD, carbon dioxide corrosion of X80 pipeline steel under water film of NACE solution was investigated using a wire beam electrode (WBE). It was found that secondary flow promoted water film fluctuations. The distribution of water film became wider as the elbow angle was increased. The total anodic current density decreased slightly and then became stabilized ultimately as water film thickness was increased from 648 μm to 2500 μm. The distributions of large cathodic regions and small anodic regions were formed. Maximal anodic current density was observed at 350 μm. When the water film thickness was less than 350 μm, FeCO3 was easily formed and anodic current density decreased. The distributions of large anodic regions and small cathodic regions were found. The side walls of the elbow and the impact walls of the vertical pipe downstream of the elbow faced a high risk of mesa attack due to different water film thicknesses.

Protective Properties of Aluminum-Based Coatings in Hydrogen-Sulfide Media

We study the corrosion and corrosion-mechanical properties of 20 steel with electric-arc sprayed aluminum coatings in chloride- and hydrogen-sulfide-containing media. The elevated corrosion resistance of the coatings is observed in all testing media. It is shown that hydrogen sulfide has practically no effect on the corrosion rate of the coating. The high resistance to hydrogen-sulfide corrosion cracking (HSCC) of 20 steel with aluminum and combined (thermally sprayed aluminum + polyurethane Hardtop flexy) coatings is established. Under the conditions of slow tension of the specimens with aluminum coatings in NACE solutions, the stresses corresponding to the onset of damage of the coating (with its subsequent final failure) are determined.