Effect of hydrogen at cryogenic temperatures on tensile properties of 316L stainless steel obtained by different manufacturing process

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O2 contamination in SSC / HIC test environments. Impact on test results and discussion on acceptable limits for high H 2 S content

International audienceIt is a well admitted fact that oxygen contamination shall be avoided during H 2 S cracking tests of low alloy steels. In the 2016 revisions of NACE TM0177 and NACE TM0284 documents, quantitative limits of O 2 contamination were included with thresholds at 10 and 50 ppb of dissolved oxygen depending on the considered mechanical properties of the tested grade. However, the scientific basis of these values are not well established and there is still a lack of experimental data to illustrate the potential impacts of an oxygen pollution. In addition, while the revised test methods explicitly address initial contamination of the test solution before H 2 S introduction, they do not consider a continuous oxygen supply during testing. Yet, continuous contamination is extremely difficult to be completely eliminated. In order to better understand the impact of O 2 contamination on H 2 S cracking, a 3-years Joint Industrial Project was launched at the end of 2015. The objectives were to evaluate if O 2 contamination can affect H 2 S cracking test results. A range of steel grades covering different types of O&G applications for High H 2 S content were used. SSC (uniaxial tensile tests as well as 4 point-bend) and HIC tests were conducted, with well controlled and continuous O 2 contamination. Three levels of O 2 partial pressures in the gas feed corresponding to 300 ppb, 50 ppb and less than 10 ppb dissolved O 2 were used. In parallel to the standard qualification tests, hydrogen permeation and weight-loss corrosion experiments were performed with the same test matrix, covering all regions of the SSC severity diagram. This paper aims at sharing the main results of this project for high H 2 S content

Co-existence of hydrogen embrittlement mechanisms of a X100 seamless pipeline revealed by fracture mechanics tests at 100bar H2 under different loading cycles

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Impact of Oxygen on Corrosion and Hydrogen Permeation of Pure iron in the Presence of H2S

International audienceThis paper examines the influence of oxygen traces on corrosion and hydrogen charging of steel in H 2 S containing environment. It is well known that H 2 S is the driving force for many types of steel failures such as hydrogen induced cracking (HIC), sulfide stress cracking (SSC), and stress-oriented hydrogen induced cracking (SOHIC). Since it is a huge concern for oil and gas industries, standard test methods have been developed and published as NACE technical methods (e.g. NACE TM0284 and NACE TM0177). Though it is recognized that oxygen pollution shall be avoided during H 2 S cracking tests, there is still a lack of experimental data to illustrate the potential impacts of a small oxygen pollution. The aim of the present study was to check if oxygen traces can modify corrosion mechanisms and hydrogen charging of steel in H 2 S medium. Experiments consisted in hydrogen permeation measurements through thin pure iron membrane. They were performed at corrosion potential in order to be in realistic environmental conditions. Corrosion rate was also evaluated through weight loss measurements. Analysis of test solutions was performed in order to identify reaction products between H 2 S and O 2

Corrosion and hydrogen permeation of low alloy steel in H2S-containing environments : the effect of test buffer solution chemistry

International audienceH 2 S-containing (sour) service environments present a considerable risk of hydrogen induced cracking (HIC) and sulfide stress cracking (SSC) to steel line pipe, pressure vessel and tubular components during upstream oil and gas production, through the ability of H 2 S to corrode and promote hydrogen entry into the material bulk via a cathodic reaction process. Materials selection for sour service is made via standard test methods such as NACE TM0284 and NACE TM0177. A commonly used test solution (NACE TM0177 solution A) comprises sodium chloride (5.0%) + acetic acid (0.5%), to work in a range between pH 2.8-4.0. When pH stability is essential over long testing periods, solutions that are buffered by acetic acid with sodium acetate are proposed. NACE TM0177 solution B (5.0% NaCl + 0.4% sodium acetate + 2.5% acetic acid) presents an initial pH of 3.4-3.6, specified not to exceed pH 4.0 over the testing duration. Newer, alternative solutions from the high-strength line pipe (HLP) research committee from the Iron and Steel Institute of Japan (ISIJ) propose higher acetic acid/acetate concentrations for enhanced buffering capacity. This may offer practical testing advantages, although material corrosion rates and hydrogen uptake are possibly affected. In this conference proceeding, we report on the corrosion and hydrogen uptake performance of a sour-grade X65 steel exposed to NACE Solutions A and B, and an HLP solution (at the same pH as NACE B solution, i.e. pH 3.5) under continuous H 2 S purging (0.1 MPa, T = 24°C) over 720 hours. Electrochemical methods measure electrochemical impedance at the entry face of, and hydrogen permeation across, the X65 membrane. Overall, the differences we note are linked to the different weak acid/conjugate base concentration. Keywords Hydrogen permeation, acetic acid, hydrogen sulfide, X65 steel

Corrosion of Pure iron and Hydrogen Permeation in the Presence of H 2 S with O 2 contamination

International audienceThis paper examines the influence of traces of oxygen on corrosion and hydrogen charging of steel in an H 2 S containing environment. It is well known that H 2 S promotes hydrogen entry into steels, that may result in many types of steel failures such as Hydrogen Induced Cracking (HIC), Sulfide Stress Cracking (SSC), and Stress-Oriented Hydrogen Induced Cracking (SOHIC). Since it is a huge concern for oil and gas industries, standard test methods have been developed and published as NACE technical methods (e.g. NACE TM0284 and NACE TM0177). Though it is recognized that oxygen pollution should be avoided during H 2 S cracking tests, there is still a lack of experimental data to illustrate the potential impacts of a small oxygen pollution. The aim of the present study is to check if oxygen traces can modify the mechanisms of corrosion and hydrogen charging of steel in H 2 S containing medium. Experiments consisted of hydrogen permeation measurements through a thin pure iron membrane. They were performed at free potential circuit in order to ensure more realistic environmental conditions. The corrosion rate was also evaluated and test solutions analyzed

Electrochemical study of oxygen impact on corrosion and hydrogen permeation of Armco iron in the presence of H 2 S

International audienceH 2 S corrosion of mild steel is a recurrent issue in the oil and gas industry. Many studies related to the corrosion and hydrogen permeation of steel in an H 2 S containing environment have been made during the past decades with the intent of improving the knowledge and the prevention of economic loss. Since H 2 S is also a hydrogen entry promoter, lots of studies are also dedicated to the understanding of H 2 S cracking. Although it is generally accepted to avoid oxygen contamination in such a medium, there is a lack of research concerning its effect on the corrosion and hydrogen charging of steel. In this study, the effect of oxygen on corrosion and hydrogen charging of steels in an H 2 S containing environment is studied using Electrochemical Impedance Spectroscopy (EIS). An equivalent electrical circuit has been built according to SEM observations, literature research and experimental results. Using this equivalent electrical circuit, experimental data was analyzed and the average corrosion rates were deduced and found to be in good agreement with corrosion rates obtained by weight loss measurements. Furthermore, the evolution of fitting parameters (double layer capacity, charge transfer resistance, diffusion impedance, etc.) was found to be in good agreement with the real physical meaning of such parameters in the given conditions. This research contributes to the explanation of the mechanism behind the high corrosion rate observed in an H 2 S environment polluted with traces of oxygen

EIS study of iron and steel corrosion in aqueous solutions at various concentrations of dissolved H2S : impact of oxygen contamination.

International audienceMildly acidic water containing dissolved H 2 S presents a strong risk in the cracking of low-carbon steels. Several studies on H 2 S cracking mechanisms have shown that the main driving force is linked to the ability of H 2 S to promote hydrogen entry into the bulk material. Standard test methods have been developed and published as NACE technical standards (e.g. NACE TM0284 and NACE TM0177) to aid materials selection in the oil and gas sector. Though it is recognized that oxygen pollution should be avoided during H 2 S cracking tests, there is a lack of experimental data to illustrate the effects of a small oxygen pollution. Dissolved oxygen concentrations greater than the recommended upper limit (50 parts per billion) can easily be obtained in the case of poor laboratory practices. This paper will focus on the interactions between oxygen and H 2 S on electrochemical behavior of unalloyed steel. A continuous O 2 injection at a level corresponding to 500 ppb is applied, together with H 2 S bubbling in our test solutions, for periods lasting the same order as SSC standard tests. Steel surface reaction phenomena/corrosion rates in H 2 S saturated solution, with or without oxygen pollution, are studied using electrochemical impedance spectroscopy. The evolution of corrosion rates obtained from impedance analysis was compared to two other independent methods: i/ weight loss measurements and, ii/ hydrogen permeation. Without O 2 pollution, a permeation efficiency of 100% was obtained, as expected. Permeation current density was thus found to match precisely with the corrosion current density determined by impedance analysis at different times. On the other hand, when a continuous O 2 pollution was added in the system, significantly higher corrosion rates were observed, associated with test solution acidification. At the same time, permeation efficiency was decreased by up to one order of magnitude

Caractérisation de revêtements PVD nanostructurés, à base de nitrures de métaux de transition, pour application mécanique - Aspects chimiques, mécaniques et tribologiques.

Une nouvelle génération de revêtements à structure nanométrique a été déposée par pulvérisation cathodique magnétron et par évaporation à arc sur un acier à outil de type M2, puis le comportement des pièces vis à vis de l\u27usure et de la corrosion (sèche et humide) a été évalué. Ces dépôts sont composés soit d\u27une structure multicouche TiN/CrN, caractérisée par une épaisseur de quelques nanomètres des strates (2D), soit d\u27une dispersion de nano-grains de TiN dans une matrice de nitrure de Bore amorphe (3D). L\u27ensemble des investigations entreprises démontrent la suprématie des revêtements 2D comparativement aux dépôts monocouches TiN ou CrN. L\u27amélioration des propriétés tribologiques par l\u27emploi d\u27une structure stratifiée est manifeste et expliquée par une répartition favorable des contraintes au sein des couches, gênant la propagation des fissures engendrées lors du frottement. Du point de vue des propriétés réfractaires, la très bonne résistance à l\u27oxydation a été attribuée à la présence de CrN, chromine formeur, au sein du dépôt. La couche d\u27oxyde de chrome dense qui se forme réduit considérablement la cinétique d\u27oxydation et augmente ainsi la durabilité des pièces revêtues. Enfin, les essais de corrosion aqueuse ont montré la nécessité de contrôler la nature de la dernière couche déposée, en contact avec le milieu agressif environnant. Pour le système TiN/CrN, une couche externe en nitrure de chrome est requise pour obtenir les meilleures propriétés. Ce résultat expérimental original est sous-tendu par le caractère passivable de CrN qui conduit à la formation d\u27un oxyde semiconducteur de type-p et ainsi à une modification des propriétés électroniques superficielles du revêtement 2D, ralentissant le processus de corrosion. Dans les conditions expérimentales sévères choisies, les dépôts nanocomposites TiBN, en dépit d\u27une dureté très élevée, n\u27améliorent pas les propriétés physico-chimiques ou tribologiques, comparativement à TiN monocouche

Improvement of the tribological behaviour of PVD nanostratified TiN/CrN coatings - An explanation

International audienceA hard TiN/CrN multilayered coating, consisting of alternating nanometer scale TiN and CrN layers (bilayer period of 40 nm), was deposited by arc evaporation process on M2 tool steel. Monolayered TiN and CrN are also deposited in the same conditions, and used as references. In order to get a better understanding of the tribological behaviour of coated parts, two types of experiments were performed. The dry-sliding wear resistance was evaluated with a ball-on-disk tribometer, while surface fatigue resistance was determined by a cyclic multi-impact test. The architecture of layers is measured by XRD and observed by TEM. The residual stress field was characterised using XRD and the sin2? method at a synchrotron radiation facility. All coatings present a columnar microstructure. TiN demonstrated better wear resistance than CrN and this characteristic is still increased two times by using the nanostratified coating. In the same way, the results of surface oligo-cyclic fatigue test confirm the high performance of the nanostructured coating with respect to the monolayered ones. The differences in mechanical properties of coatings evaluated through nanoindentation measurements do not lead to a direct correlation with the tribological results, and therefore cannot explain such differences. Moreover, a microscopic analysis of the samples after both tribological tests reveals two opposite cracking mechanisms. Monolayered TiN and CrN are subjected to a transversal crack propagation until the peeling of the coating, whereas the multilayered coating only undergoes cohesive cracks deviated in the TiN/CrN interface zones. Both opposite behaviours are the consequence of the distribution of stresses along the thickness of the fil