Localized corrosion and stress corrosion cracking of stainless steels in halides other than chlorides solutions: a review

Fluorides, bromides, and iodides, despite being less common than chlorides, are present in various environments of industrial relevance. Stainless steels suffer pitting corrosion in solutions of all halides except fluorides, which can be understood considering that fluoride is the anion of a weak acid. The aggressiveness of the rest of the halides for pitting corrosion is on the order Cl- > Br- > I- for stainless steels with Mo content below 3 wt.%. Mo is not as effective in inhibiting Br- pitting corrosion as it is for inhibiting Cl- pitting corrosion. Most of those observations were rationalized based on the effect of anions on pit growth kinetics. Sensitized austenitic stainless steel suffers stress corrosion cracking (SCC) in solutions of all halides, albeit chlorides seem to be the most aggressive. Fluoride SCC is relevant for SCC under insulation of stainless steels, and standards and regulations developed to mitigate this problem consider this ion as aggressive as chloride. For the solubilized stainless steels, aggressiveness toward SCC is in the order Cl- > Br-. The SCC of solubilized stainless steels was not observed in solutions of F- and I-, and the possible reasons for this fact are discussed.Fil: Kappes, Mariano Alberto. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentin

Evaluation of the “nickel effect” in sulfide stress cracking of low alloy steels using thiosulfate as an alternative to H2S-containing environments

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The Role of Nickel in Low Alloy Steels exposed to H2S-containing environments. Part I: Trench Formation at the Open Circuit Potential

The nickel content in low alloy steels (LAS) for oil and gas exploration and production is limited to a maximum of 1 wt.% according to ANSI/NACE MR 0175/ISO 15156. This restriction is imposed to avoid sulfide stress cracking (SSC) in sour (H2S-containing) environments. In this work, the effect of Ni on SSC of LAS was studied independently of other alloying elements. For this purpose, quenched and tempered steels heat treated to a yield strength of 610 MPa with a Ni content below and above the 1 wt.% threshold were evaluated at the open circuit potential (OCP) in unstressed specimens, and in slow strain rate tests (SSRT) at room temperature. Thiosulfate was used as a surrogate of H2S, according to the Tsujikawa method. It is concluded that Ni contributes to the stabilization of the sulfide films that form on the steel´s surface at OCP. The rupture of this film due to tensile stress promotes the nucleation of elongated deep pits, referred to as trenches, which can act as sulfide stress crack initiators. Trenches were observed exclusively in stressed, Ni-containing specimens. Moreover, trenches´ morphology, dimensions, and distribution varied with the Ni content in the steels. For the steels studied in this work, the Ni effect on trenching persisted below the 1 wt.% threshold.Fil: Chalfoun, Dannisa Romina. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kappes, Mariano Alberto. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Perez, Teresa E.. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Otegui, José L.. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Iannuzzi, Mariano. Curtin University; Australi

Obtaininglow alloy steels with different Nicontents and similar microstructures and mechanical properties

Los aceros de baja aleación son ampliamente utilizados en la industria del gas y petróleo. La incorporación de Ni en estos aceros mejora la tenacidad a la fractura a bajas temperaturas y la templabilidad, con bajo impacto negativo en la soldabilidad. Sin embargo, la norma ISO 15156-2 restringe su uso hasta un máximo de 1 % en peso, exigiendo ensayos adicionales y costosos si se desean adoptar contenidos mayores de Ni. Este límite se basa en la hipótesis de que un exceso de Ni puede afectar negativamente la resistencia a la corrosión bajo tensión en medios con sulfhídrico (en inglés, Sulfide Stress Cracking (SSC)). Por otro lado, algunos investigadores han concluido que el fenómeno no depende del contenido de Ni, sino de la microestructura y dureza de la aleación, lo cual hace que el límite en composición del Ni planteado por la norma ISO 15156-2 sea controversial. El objetivo de este trabajo es desarrollar aleaciones y tratamientos térmicos que permitan obtener microestructura y dureza similares en aceros con distinto contenido de Ni (0-5% en peso), dejando así como variable principal el contenido de Ni. Estas muestras serán, en una etapa posterior del trabajo, utilizadas para estudiar la cinética de propagación de fisuras por SSC. Se realizaron mediciones de temperaturas de transformación de fases por calorimetría diferencial de barrido (DSC). La caracterización del material templado confirmó que las microestructuras finales obtenidas constituyenestructuras esencialmente martensíticas. Mediante tratamientos térmicos de revenido fue posible alcanzar valores de dureza menores que 22 HRC, tal como exige la norma ISO 15156-2 para maximizar la resistencia a SSC. La microestructura se evaluó mediante caracterización por microscopía óptica, electrónica de barrido (SEM) y dureza. A su vez, se caracterizaron las propiedades mecánicas de las aleaciones mediante ensayos de tracción.Low alloy steels are used in many applications in the oil and gas industry. The addition of Ni in these steels improves their low temperature fracture toughness and hardenability, with a low penalty on weldability. However, ISO 15156-2 standard restricts Ni content up to a 1 wt% limit, requiring additional and expensive tests if higher Ni steels are to be used. This limit is based on the hypothesis that higher contents of Ni may negatively affect Sulfide Stress Cracking (SSC) resistance in sour service applications. On the other hand, several investigators have concluded that SSC resistance depends on microstructure and hardness rather than Ni content. The 1 wt% Ni limit imposed by ISO 15156-2 is controversial, as recently pointed out by other authors. This work aims to develop alloys and heat treatments tailored to obtain the same microstructure and hardness in steels with different Ni contents (from 0 to 5 wt %), therefore leaving Ni content as the main variable. This will allow, in a future stage of the project, to study the effect of Ni on the SSC crack propagation kinetics. Transformation temperaturesof the alloys were measured with differential scanning calorimetry (DSC). Characterization of the as-quenched samples confirmed a fully martensite microstructure. Tempering of the samples allowed obtaining hardness values near 22 HRC. Microstructure was evaluated with optical and scanning electron microscope and hardness measurements. Tensile tests were performed to evaluate mechanical properties as a function of Ni content.Fil: Parodi, Santiago Ariel. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Kappes, Mariano Alberto. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Otegui. José Luis. YPF - Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Carranza, Ricardo Mario. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Aguirre, Alberto. YPF - Tecnología; Argentin

The Materials Engineering Applying Exam Course at the Instituto Sabato: advantages of the usage of various learning strategies

El ingreso a Ingeniería en Materiales en el Instituto Sabato de la Universidad Nacional de General San Martín (UNSAM) y de la Comisión Nacional de Energía Atómica (CNEA) se apoya desde 2007 en un aula virtual de acompañamiento a los y las aspirantes. Con el objetivo de brindar las condiciones necesarias para generar y mantener en la persona que aspira a ingresar un compromiso con el estudio, hemos analizado alternativas de modalidades para el curso de ingreso. Consideramos que las oportunidades de aproximación y adhesión a las propuestas didácticas son mucho mayores si se presenta una diversidad de enfoques, adaptables a un mayor número de personas atraídas por diferentes tipos de propuestas. Con esto en mente es que hemos ido ampliando y diversificando las propuestas didácticas. Éstas abarcan desde módulos interactivos, con diferentes tipos de interacciones, hasta encuentros presenciales, foros virtuales, visitas, etc. En el año 2017 sumamos un nuevo recurso, un curso semipresencial de una semana seguido de un curso virtual con duración desde marzo hasta el día del examen en la primera semana de junio, con su propia aula virtual. Las ventajas de este enfoque son múltiples. Se forma una comunidad virtual de intercambio en los foros del curso, se forma una comunidad física en el curso presencial realizado en el Centro Atómico Constituyentes (CAC) (que deriva en la formación espontánea de un grupo de mensajería instantánea entre estudiantes e independiente del Instituto), y se da lugar también a un número mucho mayor de participantes que pueden mantenerse en contacto, interactuar a distancia y descargar diversos contenidos (el material trabajado en forma presencial en formato interactivo, ejercitación propuesta de Matemática, Física y Química, discusiones de los foros, etc.). Tras dos años de experiencia de esta nueva modalidad, presentamos un análisis de la participación y sus correlaciones con los resultados del examen de admisión a la carrera.The Materials Engineering Applying Exam Course at Instituto Sabato (Universidad Nacional de General San Martín, UNSAM, and Comisión Nacional de Energía Atómica, CNEA) is supported since 2007 in a virtual classroom. We have analyzed different options for the admission course in the aim of providing the best conditions for generating and maintaining a commitment with study in the person about to undertake the exam. We consider that the opportunities of interaction and adhesion to the didactic proposals increase if a diversity of approaches is offered, since they can be adapted to a great number of persons with different characteristics and living conditions. Bearing this objective in mind we have increased the didactic offer, comprising now interactive modules with different modalities, meetings, virtual forums, visits, among others. In 2017 we added a new resource, a blended learning course with its own virtual classroom consisting in a one week classroom-based course and a virtual course that spans from March till the exam in the first week of June. The advantages are many: a virtual community is formed within the course forums, a physical community is formed at the real classroom during the first week course that takes place at the Constituyentes Atomic Center. This physical community immediately gives rise to a messaging group that keeps in contact independently from the teachers and the Instituto Sabato. The virtual community can be integrated by a greater number of participants that maintain contact, interact and access to the learning material offered as interactive modules studied simultaneously at the physical and virtual classrooms. Exercises covering the three areas mathematics, physics and chemistry are offered all along the course. After two years of experiencing this new modality, we present here the analysis of participation and its correlation with the results of the Applying Exam.Fil: Alonso, Paula Regina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Bruyère, Vivianne I. E.. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Kappes, Mariano Alberto. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Roberti, Liliana. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Monti, Ana Maria. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentin

Blending hydrogen in existing natural gas pipelines: Integrity consequences from a fitness for service perspective

Blending hydrogen in existing natural gas pipelines compromises steel integrity because it increases fatigue crack growth, promotes subcritical cracking and decreases fracture toughness. In this regard, several laboratories reported that the fracture toughness measured in a hydrogen containing gaseous atmosphere, KIH, can be 50% or less than KIC, the fracture toughness measured in air. From a pipeline integrity perspective, fracture mechanics predicts that injecting hydrogen in a natural gas pipeline decreases the failure pressure and the size of the critical flaw at a given pressure level. For a pipeline with a given flaw size, as shown in this work, the effect of Hydrogen Embrittlement (HE) in the predicted failure pressure is largest when a failure occurs by a brittle fracture. The HE effect on failure pressure diminishes with a decreasing crack size or increasing fracture toughness. The safety margin after a successful hydrostatic test is reduced and therefore the time between hydrotests should be decreased. In this work, all those effects were quantified using a crack assessment methodology (level 2, API 579-ASME FFS) considering literature values for KIH and KIC reported for an API 5L X52 pipeline steel. To characterize different scenarios, various crack sizes were assumed, including a small crack with a size close to the detection limit of current in-line inspection techniques and a larger crack that represents the largest crack size that could survive a hydrotest to 100% of the steel Specified Minimum Yield Strength (SMYS). The implications of a smaller failure pressure and smaller critical crack size on pipeline integrity are discussed in this paper

Hydrogen Embrittlement of Magnesium and Magnesium Alloys: A Review

Magnesium and magnesium alloys are susceptible to stress corrosion cracking in various environments, including distilled water. There is compelling evidence to conclude that SCC is assisted, at least in part, by hydrogen embrittlement. This paper reviews the thermodynamics of the Mg-H system and the kinetics of hydrogen transport. Aspects of magnesium corrosion relevant to hydrogen absorption are also discussed. Crack growth mechanisms based on delayed hydride cracking, hydrogen adsorption dislocation emission, hydrogen enhanced decohesion, and hydrogen enhanced localized plasticity have been proposed and evidence for each of them is reviewed herein

Hydrogen solubility, diffusivity, and trapping in quenched and tempered Ni-containing steels

Hydrogen permeation experiments were performed in quenched and tempered (Q&T) low alloy steels with varying Ni contents exposed to 1 bar H2 at 30, 50 and 70 °C. From the analysis of build-up and decay transients, it is concluded that the permeation coefficient, the apparent diffusion coefficient (Dapp) and the concentration of hydrogen in interstitial sites on the charging surface (C0) decreases as the Ni concentration increases from 0 to 5 wt.%. The total concentration of hydrogen on the charging surface (C0,r), which includes interstitial and reversibly trapped hydrogen, is about an order of magnitude larger than C0. The hydrogen binding energy (Eb) and trap density (Nr) were calculated from the Dapp vs. temperature dependence, under the hypothesis of low trap occupancy. C0,r, Eb and Nr do not show a clear correlation with Ni content, indicating that trapping is controlled by a microstructural feature other than Ni atoms in solid solution.Fil: Chalfoun, Dannisa Romina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina. YPF - Tecnología; ArgentinaFil: Kappes, Mariano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Bruzzoni, Pablo. Comisión Nacional de Energía Atómica; ArgentinaFil: Iannuzzi, Mariano. Curtin University; Australi

Hydrogen uptake and diffusivity in steel armor wires with different chemical composition, carbide distribution, grain size, and degree of deformation

In this study, six flexible pipe steel armor wires used in oil and gas transportation are characterized, and their hydrogen diffusion coefficients and hydrogen uptakes are measured using an electrochemical hydrogen permeation technique. The wires have ferritic–pearlitic microstructures with round, lamellar, or partially lamellar carbides and the shape and orientation of the grains indicate that the microstructures were plastically deformed to different degrees. It was assumed that hydrogen was transported through the ferrite, so the presence of cementite in the steel armor wires leads to longer hydrogen diffusion paths through the ferrite, which was quantified with a tortuosity factor. After compensating for tortuosity, the normalized steady-state flux shows a tendency to increase as the grain size decreases. The effective diffusion coefficients increase with a decrease of the ferrite–cementite interface area, suggesting trapping on the ferrite–cementite interfaces. The uptake of diffusible hydrogen was lowest for the least plastically deformed materials and about twice as high for the more plastically deformed materials.Fil: Skilbred, Ellen S.. Norwegian University of Science and Technology; NoruegaFil: Kappes, Mariano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Iannuzzi, Mariano. Norwegian University of Science and Technology; Noruega. Curtin University; AustraliaFil: Johnsen, Roy. Norwegian University of Science and Technology; Norueg