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Abstract Hydrogen is crucial for decarbonization efforts due to its abundance, environmental friendliness, and versatility. To maximize its potential, an efficient transportation infrastructure is essential. While utilizing the natural gas pipeline network for transporting hydrogen is cost-effective, hydrogen embrittlement (HE) poses a significant challenge. When hydrogen enters the metal, it significantly compromises its fracture toughness. This study investigates the impact of high-pressure hydrogen on the mechanical properties of API 5L X65 carbon steel through a combined experimental and computational approach. To quantify the extent of HE, tensile tests were performed on identical specimens, one set pre-exposed to high-pressure hydrogen and another set kept in an inert environment for comparison. Finite element modelling, employing the Bai-Wierzbicki material model (BWMM), was used to simulate the material behaviour under large plastic deformations and correlate with experimental results. This synergistic approach integrates experimental data with simulations, creating a framework for predicting and preventing catastrophic failures.

The microstructure and mechanical properties were investigated in a 17.48-mm-thick electron beam-welded (EBW) API 5L X65 steel sheet. Electron beam welding has the advantage of joining thick steel parts in a single pass with a high energy conversion efficiency, low heat input and low warpage. The base metal has elongated bands of ferrite interspersed with pearlite colonies aligned along the rolling direction. After welding, a narrow and fine-grained heat affected zone (HAZ) consists of degenerate pearlite and martensite–austenite (M–A) islands. The microstructure of the fusion zone is coarser than the HAZ and more complex, consisting of lower bainite, Widmanstätten ferrite, acicular ferrite, grain boundary ferrite, and small islands of the M–A constituent. These microstructure changes are minimized when EBW is used and do not significantly affect the mechanical properties of the weld. Results of Charpy V-notch tests for weld beads parallel and perpendicular to the rolling direction met the requirements of the API 5L standard. EBW has proven to be a viable alternative for welding thick plates of advanced steels applied in pipeline construction and assembly. [ABSTRACT FROM AUTHOR]

Guanine was investigated as a potential green corrosion inhibitor to API 5L X65 carbon steel in HCl 0.1 mol.dm-3 solution, at pH = 2.0, under hydrodynamic conditions using electrochemical, weight loss and Raman spectroscopy experiments. Cyclic voltammetry and potentiodynamic polarization curves suggested that Guanine does not change the metal/solution interface appreciably and weight loss tests confirmed the low inhibition efficiency (IE) of Guanine in protecting the X65 steel in this corrosive medium. An IE = 22% was determined after 48 h of exposure, a value lower than that reported in the literature on the mild steel/Guanine/HCl system. Raman spectroscopy was employed to gain insight on the nature of the steel/Guanine interaction and the results pointed out to a weak physisorption of the molecule, thus explaining the very low IE values obtained.

A multifactorial study of erosion–corrosion (E–C) is carried out to quantify the effects of velocity, particle concentration, temperature, pH, dissolved oxygen, and copper ion content, with respect to the transport of tailings slurry through an API 5L X65 pipe. The experimental design is implemented using a rotating cylinder electrode and evaluating the resulting E–C damage by weight loss. An analysis of the statistical significance reveals that the variation in the wear rate is explained by three main effects (velocity, oxygen, and temperature) and two interactions (velocity/oxygen and particle/copper content). An empirical equation is formulated to produce contour maps of the main interactions. It is concluded that the primary damage mechanisms are the deposition of corrosion products consecutively disturbed by impinging particles and localized plastic deformation. [ABSTRACT FROM AUTHOR]

This study investigates the effects of ER308L butter layer on the microstructure and mechanical properties of API 5L X65/dissimilar joint. High strength low alloy API 5L X65 and AISI 304 steel grades are widely used in a wide range of industrial applications, and more specifically in the oil and gas sector. Dissimilar welds between API 5L X65 pipeline and austenitic stainless steel joints have long been used in the oil/gas and petrochemical sectors. Using buttering layer to improve properties of these types of dissimilar joints has lately received significant attentions. In the present work, the ER308L butter layer was applied on the API 5L X65 side through gas tungsten arc welding, followed by a stress-relief heat treatment at 600 °C. Buttered API 5L X65 samples were welded to AISI 304 samples through gas tungsten arc welding in 5 passes. Microstructures of joints were evaluated by scanning electron microscope (SEM) and optical microscope (OM). Mechanical properties were also assessed by tensile, impact, and Vickers micro-hardness tests. Fractography and phase identifications were carried out using SEM and energy dispersive spectroscopy (EDS). Results showed that a martensite layer on the fusion zone with a thickness of about 30 μm was observed at the interface of API 5L X65/butter layer. It appears that compositional changes played a significant role in the formation of martensitic structures and type-II grain boundaries. Results also showed that the fracture positions in both heat treated and as-welded samples were in the heat affected zone (HAZ) of API 5L X65. The implications of buttering and post-buttering stress-relief heat treatment for the microstructure and mechanical properties are comprehensively discussed. • A martensitic layer was observed at the interface of the API 5L X65 steel and the buttering layer. • Stress relieving post-buttering heat treatment at 600 °C resulted in hardness reduction of martensitic layer. • At the API steel side, grain size has changed from rolled/deformed microstructure to equi-axed recrystallized grain structure. • Reduction in microhardness has been observed around the HAZ region of API 5L X65 steel. [ABSTRACT FROM AUTHOR]

High-strength low-alloy steel girth weld specimens were subjected to fatigue tests in saline environments saturated with different carbon dioxide partial pressures. As expected, results show that increases in gas concentration initially affect fatigue life adversely, but when higher partial pressures are associated with low stresses, a reduction in the negative impact of environmental conditions is seen. This may be related to a competition between corrosion rates and mechanisms of crack initiation and propagation. Data is presented with the aim of contributing toward the establishment of a database of results in literature which may lead to better understanding of the phenomena involved through association of these with ongoing research. [ABSTRACT FROM AUTHOR]

Erosion-corrosion (E-C) of carbon steel API 5L X65 by mineral quartz and alumina slurry is studied to understand the mechanism of corrosion-accelerated material's degradation. A rotating cylinder electrode is employed to simulate the E-C damage and for electrochemical characterization, observed at different flow velocities and contents of dissolved oxygen (DO). Microstructural inspection using SEM and EBSD reveals the extension of the work-hardened layer and other features of the sub-surface. The effect of nominal flow velocity is shown to be associated with an increment in average particles' impact angle and frequency of impacts at the faster flow. The increase in DO availability is shown to promote localized-type corrosion different from pitting, demonstrating the mechanism of erosion-enhanced corrosion. • Microstructural effects of velocity and DO on erosion-corrosion damage are studied. • Sub-surface of X65 after E-C exposure is inspected by EBSD and KAM analysis. • Damage by slurry flow is attributed to impact energy, frequency and effective angle. • DO promotes localized-type corrosion by the mechanism of erosion-enhanced corrosion. [ABSTRACT FROM AUTHOR]

Pitting corrosion in microalloyed steel and its welded joints occur in fabricated structures, such as pipelines for oil and gas transport, which are exposed to corrosive environments. Although the formation of the pits consumes only a relatively small mass of material, the role of the pits as defect sites for crack initiation and continuing corrosion can be substantial. Furthermore, in natural and industrial environments where microorganisms are widely distributed, pitting corrosion is aggravated by the release of many reactive microbial metabolites. This is a report of a 28-day study aimed at the microbiologically influenced corrosion of joint welds by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) exposed to laminar and turbulent flows. The characterization of the planktonic microbial community indicated that laminar flow created an anoxic environment promoting the dominance of anaerobic microorganisms, in particular sulfate reducing bacteria (SRB). Both types of welded joints showed similar pit densities in the base metal (BM), heat-affected zone (HAZ) and weld metal (WM), nevertheless the pit depth was higher in the HAZ than the BM and WM. On the other hand, turbulent flow retained dissolved oxygen content, ensuring the presence of aerobic microorganisms, but there was no inhibition of SRB growth. Although the pit depth was low in both types of welded joints, the pit density was exacerbated in only one HAZ of each welded joint due to WM reinforcement height, while the other HAZ showed low pit density. This study demonstrates that turbulent flow can reduce the biocorrosion of non-welded areas but can aggravate welded joints biocorrosion. Image 1 • Biocorrosion of joints welded by gas tungsten arc welding and shielded metal arc welding were investigated. • The type of fluid flow regiment influenced the planktonic microbial community. • Planktonic sulfate reducing bacteria number was not affected by turbulent flow. • Pitting corrosion was more severe in the heat-affected zone, regardless of the welding process and flow regime. • Turbulent flow promoted a differentiated distribution of pits in the welded joints. [ABSTRACT FROM AUTHOR]