Oil and gas fields can contain significant amounts of hydrogen sulphide and the behaviour of C-Mn pipeline steels exposed to sour environments (i.e. those containing water and hydrogen sulphide) continues to be one of the most active areas of research in the oil and gas industry. This project is aimed at improving the procedures used to assess the significance of flaws in offshore pipelines and risers operating in such environments. Experimental work has focused on examining the behaviour of C-Mn pipeline steel in a sour environment with respect to both static and fatigue crack growth behaviour, for which there is a paucity of data. In particular, the critical influence of crack depth on the crack growth rate has been studied, in order to ensure that test methods and assessment procedures used in industry are appropriately conservative. Under cyclic loading conditions, an environmental crack depth effect has been demonstrated, whereby, shallow flaws appear to grow faster than deeper flaws at the same (low) value of ΔK. The observed behaviour is believed to be dominated by bulk hydrogen charging, i.e. hydrogen charging by absorption from the external surfaces of the specimen rather than at the crack tip, and a lower concentration of hydrogen exists in the centre of the specimen than at the edges. The novel data generated have been applied to real-life pipeline defect assessments to demonstrate the influence of the observed crack growth rate, with a view to developing an improved assessment method. Example engineering critical assessments have been performed for circumferential surface-breaking girth weld flaws located on the internal surface of a typical steel catenary riser, operating in a sour environment and subject to vortex induced vibration fatigue loads. Companies operating in the oil and gas sector will derive benefit from this research programme through the application of new validated test methods and the development of improved in-service assessment procedures.

The aim of this research is to identify problematic microstructural features as hydrogen traps in linepipe steel that serve to increase the hydrogen embrittlement susceptibility. A comparison is made between the hydrogen trapping capacity and associated hydrogen embrittlement susceptibility of Ca-treated X60 grade steel skelp and X70 grade steel skelp: the latter typically being more susceptible to hydrogen-induced cracking in sour environments. Through-thickness variations in the steel skelp microstructure were characterized across multi-length scales using light optical microscopy (LOM) and scanning electron microscopy (SEM) equipped with X-ray energy dispersive spectroscopy (EDS). Key features under study include the composition, shape, and distribution of non-metallic inclusions, as well as differences in features present between the quarterline (¼ and ¾ depths) and centerline (½ depth) microstructures. The type, count, and average size of inclusions present in both steel skelp grades were analyzed using an automated SEM-EDS technique called ASPEX®. Major types of inclusions detected in both grades of steel skelp include those containing Ca, Al, Mn, Mg and Ti as major elements. Overall, the area fraction of inclusions detected in the X70 steel was larger than those detected in the X60 with the exception of Ti-containing inclusions, which had a larger area fraction within the X60 steel. Comparing the number of detected inclusions shows that there was overall slightly less Ca-containing inclusions and significantly less Ti-containing inclusions detected in the X70 steel but there was generally more Al-containing, Mg-containing, and Mn-containing inclusions than those detected in the X60 steel. Thermal desorption spectroscopy (TDS) measurements were made on samples prepared from the ¼, ½, and ¾ depths of X60 and X70 steel skelps after galvanostatic cathodic charging in an As2O3-containing solution using an applied current density of −10 mA/cm2. Hydrogen release was measured using a HYDROSEEL® probe while the sample was heated from 20°C to 650°C to detect temperature values at which hydrogen gas release peaks occurred, and thus provide information on types of reversible and/or irreversible traps present. The TDS results suggests that non-metallic inclusions indeed serve as irreversible traps along with grain boundaries and dislocations, which serve as reversible traps. Hydrogen permeation measurements were also made on samples prepared from the ¼, ½, and ¾ depths after galvanostatic cathodic charging in an As2O3-containing solution using an applied current density of −10 mA/cm2. Hydrogen gas release was measured using a HYDROSEEL® probe while the sample remained at room temperature (~20°C), providing information regarding the potency of reversible hydrogen traps when subjected to a flux of hydrogen. Only reversible traps can be detected at room temperatures due to their low binding energies. Higher temperatures are required to overcome the larger binding energies associated with irreversible traps. The hydrogen permeation results indicate no significant effect of through-thickness variations in the X60 steel, but the centreline depth of the X70 steel skelp trapped a larger quantity of hydrogen than either of the two quarterline depths, indicating the presence of a distinct problematic trap. The X70 steel skelp was also observed to trap more hydrogen than the X60 steel skelp. The observed hydrogen trapping capacity was linked to the hydrogen embrittlement susceptibility by comparing the uniaxial tensile behaviour of centreline samples with and without hydrogen charging applied as a pre-treatment step. Hydrogen charging was achieved by galvanostatic cathodic polarization at an applied current density of −10 mA/cm2 for 24 h in an NH4SCN-containing solution while simultaneously loading the samples to 85% of the yield strength using a proof ring tensile test cell. An increase in hydrogen embrittlement as a result of pre-charging was confirmed through tensile plots by comparing the area of reduction and failure strain of charged samples to uncharged samples. A decrease in both values was observed in the charged samples indicating a loss in ductility as a result of hydrogen charging. Fracture surfaces were imaged using SEM and inclusions of interest were analyzed for elemental composition using EDS. Inclusions observed along the fracture surfaces include oxysulfides of Ca and Al, oxides of Mg, Al-Ca-Si oxides, and Al2O3-containing inclusions which are likely to be heterogeneous Al-Ca-O inclusions. / Thesis / Master of Applied Science (MASc)

A study of gouges and dents in the context of pipelines has been completed, using the non-destructive evaluation (NDE) techniques of magnetic flux leakage (MFL) and magnetic Barkhausen noise (MBN). The research is part of an ongoing effort by the Applied Magnetics Group (AMG) at Queen's University to improve the interpretation of the MFL signal, which is used extensively by industry for defect detection and evaluation. The gouges were found to have distinctive MFL signatures depending on their orientation relative to the magnetization axis. Features in the MFL signal were identified as superpositions of geometry-related effects and strain or work hardening of the surface material. A qualitative magnetic permeability distribution in the material near a gouge has been proposed. The distribution is expected to vary in magnitude and extent according to the defect severity. The MFL results of the dent studies, on samples made available by Gaz de France (GdF), largely agreed qualitatively with previous research of dents. However, the differences pointed to the need for study of more varied dent shapes; new signal features were observed that suggested tensile residual strain in the dent rim is more prominent than earlier studies and modeling have predicted. Additionally, upgrades made to the MFL scanning system used by the AMG and a novel approach for building computer models are detailed. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-09-24 17:13:12.775

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In recent years, the demand for alternatives to fossil fuels has risen dramatically, and ethanol fuel has become an important liquid fuel alternative globally. The most efficient mode of transportation of petroleum-based fuel is via pipelines, and due to the 300% increase in ethanol use in the U.S. in the past decade, a similar method of conveyance must be adopted for ethanol. Low-carbon, low-alloy pipeline steels like X52, X60, and X65 comprise the existing fuel transmission pipeline infrastructure. However, similar carbon steels, used in the ethanol processing and production industry, were found to exhibit stress corrosion cracking (SCC) in ethanol service. Prior work has shown that contaminants absorbed by the ethanol during distillation, processing or transport could be the possible determinants of SCC susceptibility; 200 proof ethanol alone was shown not to cause SCC in laboratory studies. To ensure the safety and integrity of the pipeline system, it was necessary to perform a mechanistic study of SCC of pipeline steel in fuel grade ethanol (FGE). The objective of this work was to determine the environmental factors relating to SCC of X65 steel in fuel grade ethanol (FGE) environments. To accomplish this, a systematic study was done to test effects of FGE feedstock and common contaminants and constituents such as water, chloride, dissolved oxygen, and organic acids on SCC behavior of an X65 pipeline steel. Slow strain rate tests (SSRT) were employed to evaluate and compare specific constituents' effects on crack density, morphology, and severity of SCC of X65 in FGE. SCC did not occur in commercial FGE environments, regardless of the ethanol feedstock. In both FGE and simulated fuel grade ethanol (SFGE), SCC of carbon steel was found to occur at low water contents (below 5 vol%) when chloride was present above a specific threshold quantity. Cl- threshold for SCC varied from 10ppm in FGE to approximately 1 ppm in SFGE. SCC of carbon steel was inhibited when oxygen was removed from solution via N2 purge or pHe was increased by addition of NaOH. During SSRT, in-situ¬ electrochemical measurements showed a significant role of film rupture in the SCC mechanism. Analysis of repassivation kinetics in mechanical scratch tests revealed a large initial anodic dissolution current spike in SCC-causing environments, followed by repassivation indicated by current transient decay. In the deaerated environments, repassivation did not occur, while in alkaline SFGE repassivation was significantly more rapid than in SCC-inducing SFGE. Composition and morphology of the passive film on X65 during static exposure tests was studied using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results showed stability of an air-formed native oxide under static immersion in neutral (pHe = 5.4) SFGE, and dissolution of the film when pHe was decreased to 4.3. XPS spectra indicated changes in film composition at high pHe (near 13) and in environments lacking sufficient water. In light of all results, a film-rupture anodic-dissolution mechanism is proposed in which local plastic strains facilitates local breakdown of the air-formed oxide film, causing iron to dissolve anodically. During crack propagation anodic dissolution occurs at the crack tip while crack walls repassivate preserving crack geometry and local stress concentration at the tip. It is also proposed that SCC can be mitigated by use of alkaline inhibitors that speed repassivation and promotes formation of a more protective Fe(OH)3 film.

Le Piégeage et le Stockage du dioxyde de Carbone (PSC) est reconnu comme ayant un rôle important dans la lutte contre le changement climatique et la réduction d’émissions de dioxyde de carbone (CO2). Ce processus consiste à capturer le CO2 des sources anthropiques, et le transporter vers des sites de stockage appropriés. Le transport de telles quantités de CO2 entraîne de nouveaux défis pour les concepteurs et les opérateurs des gazoducs. Parmi ces défis, nous citons : le comportement de phase du CO2, la température atteinte lors de la décompression, la présence des différentes impuretés et la pression de service très élevée. Malgré l’enjeu important, et contrairement au gazoduc de transport de gaz naturel et de pétrole, peu d’études ont été consacrées à la sûreté et la rentabilité des gazoducs de transport du CO2. À l’égard de ces défis industriels, cette étude a été menée pour identifier et comprendre les mécanismes de rupture des gazoducs, à haute pression, transportant du CO2 supercritique. Ce travail a engagé la mise au point d’une nouvelle approche qui anticipe l’éclatement du gazoduc. Pour répondre à cette problématique, nous avons utilisé en premier lieu une approche théorique basée sur les fondamentaux de la Mécanique de la Rupture. En second lieu, et en conjonction avec la méthode des éléments finis, nous avons développé un outil numérique robuste. L’ultime objectif de ces travaux de recherche est d’enrichir les codes de dimensionnement des gazoducs, souvent restreints au transport de gaz naturel et au matériau à faible ténacité. De plus, cette thèse apporte une large base de données d’essais de ténacité à basse température liés à des séries d’analyses par éléments finis sous le code de calcul Abaqus 12.6. La finalité de notre recherche réside dans la proposition d’une méthodologie complète d’évaluation des risques d’éclatement des gazoducs en fonction du matériau et de la nature du fluide transporté / Capture, transport, and storage of Carbon dioxide are well-known applications for their key role in the field of climate change and reduction of CO2 emissions. This process involves the use of some particular technologies, not only to collect and concentrate the CO2 emitted by the anthropogenic sources but also to transport it to a suitable storage location. The transport of such a big quantity of CO2 creates new challenges for designers and pipeline operators. For instance, CO2 phase behavior, the temperature reached during the decompression phase, the presence of various impurities as well as the high operating pressure. Contrary to natural gas and oil transportation structures, a very few studies have raised the issue of the integrity of CO2 pipeline. In order to meet the industry needs particularly in this CO2 integrity application, the present research was conducted to identify and to better comprehend pipeline failure mechanisms at high pressures. This work includes the development of a new numerical approach about running ductile fracture arrest for high pressure gas pipeline. To address this issue, we have initially used a theoretical approach based on the fundamental knowledge of Fracture Mechanics. Based on the crack-tip opening angle (CTOA) fracture criterion and the finite element method along with the node release technique, a new two-curve method (TCM) was proposed for the prediction of gas pipelines’ crack arrestability. The results of this newly developed method were discussed and compared to those obtained by using other methods commonly employed in the Fracture mechanics, for instance, Battelle-TCM, HLP and HLP-Sumitomo method