Symposium on Risk analysis and Safety of Technical Systems (ECF22 conference, Serbia)
- José A.F.O. Correia
- A. Sedmak
- Vladimir Moskvichev
Corrosion effects on structural integrity and life of oil rig welded pipes are analysed by experimental, analytical, and numerical methods. Experiments were performed using standard tensile specimens and CT specimens for static loading, Charpy specimens for impact loading, and 3 Point Bending specimens for fatigue crack growth with amplitude loading. In each case new and old pipes were used to evaluate corrosion effects. Results indicated negligible corrosion effects in the case of tensile properties and impact toughness, and strong effects in the case of fracture toughness and especially fatigue crack growth rates, increasing the risk of static failure and reducing significantly structural life. Analytical expressions are used for oil rig pipe structural integrity and life assessment to quantify these effects. Recently introduced risk-based approach is applied to analyse oil rig drill pipe with a corrosion defect treated as a surface crack.
This paper presents an updated review of the external corrosion and failure mechanisms of buried natural gas and oil pipelines. Various forms of external corrosion and failure mechanisms such as hydrogen-induced cracking (HIC), hydrogen embrittlement (HE), corrosion fatigue (CF), stress corrosion cracking (SCC) and microbiologically influenced corrosion (MIC) for oil and gas pipelines are thoroughly reviewed. The factors influencing external corrosion and possible forms of environment-assisted cracking (EAC) of pipeline steels in the soil are also reviewed and analyzed in depth. In addition, the existing monitoring tools for the external corrosion assessment and the models for corrosion prevention and prediction, failure occurrence, and remaining life of oil and gas pipelines, are analyzed. Moreover, the articles on external corrosion management, reliability-based models, risk-based models, and integrity assessment including machine learning and fuzzy logic approaches, are also reviewed. The conclusions and recommendations for future research in the prevention and prediction of external corrosion are presented at the end.
Considering corrosion rate during the remaining life assessment of aging pipelines is fundamental to calculate the interval between two consecutive inspections. A total of 798 internal and external corrosion defects have been detected, using the Magnetic Flux Leakage intelligent inspection tool, over 48 km of a pipeline length located in the west region of Algeria. The statistical analysis has shown that there is a strong correlation between the corrosion defect length and the corrosion defect circumferential width, with a significant correlation coefficient equal to 82.87%. A probabilistic methodology is presented for the assessment of the remaining life of a corroded pipeline transporting gas, and a finite element method (FEM) was used to assess the pipeline failure pressure. The numerical FEM modeling results were compared with the commonly used codes-models for calculating limit pressure to establish a more realistic and accurate engineering model. The reliability analysis of an API 5L X60 steel made Algerian natural gas pipeline, in service for thirty years, and exposed to active corrosion attack, is presented. The sensitivity analysis of the basic random variables within the nonlinear limit state function was carried out to bring out the relative contribution of each variable affecting the remaining life of corroded pipelines. The reliability analysis is carried out by using Breitung's formula, based on the second-order reliability method (SORM). The reliability assessment of the corroded pipeline is based on the usage of the notched failure assessment diagram (NFAD), different codes for the calculation of the failure pressure, and the numerical results using the finite element analyses (FEA) software ANSYS.
Hydrogen embrittlement (HE) in a specific sense meaning can be defined as the hydrogen-caused deterioration of the mechanical properties of most metallic materials and alloys. The coexistence of different HE mechanisms and their simultaneous effects in metallic materials, including steels, is still not well documented, while recognition of the dominant mechanism, one or more, is an extremely challenging and crucial problem. A special structural integrity model was proposed  for analysis, prevention, and prediction of HE based on the HELP + HEDE model  for HE in steels. The structural integrity model corresponds with the observed coexistence of HE mechanisms (HELP + HEDE model) in metals and transition from HELP dominance to HEDE dominance at a hydrogen concentration above the critical hydrogen concentration [2,3]. The further implementation of methods for evaluation, control, and prevention of hydrogen-assisted mechanical degradation processes and HE in metals requires that the variables relevant to the application be incorporated into the basic concept that define all necessary successive steps (5-step approach) for the industrial application . The global 5-step approach in assessment and prevention of hydrogen assisted mechanical degradation processes and hydrogen embrittlement in metals for the practical industrial application was proposed and consist of the following steps : (1) phenomenology analysis of hydrogen-related degradation (multiscale modeling and simulation of HE phenomena); (2) hydrogen sources and entry into metal/component; (3) structural integrity (SiM) model and (4) predictive maintenance (PdM) model which should provide the basis for future (5) reliable and accurate HE damage prediction of different industrial components.  M.B. Djukic, G.M. Bakic, V. Sijacki Zeravcic, A. Sedmak, B. Rajicic, Hydrogen embrittlement of industrial components: prediction, prevention, and models, Corrosion, 72 (2016), pp. 943-961.  M.B. Djukic, V. Sijacki Zeravcic, G.M. Bakic, A. Sedmak, B. Rajicic, Hydrogen damage of steels: A case study and hydrogen embrittlement model, Engineering Failure Analysis, 58 (2015), pp. 485-498.  M.B. Djukic, V. Sijacki Zeravcic, G.M. Bakic, A. Sedmak, B. Rajicic, The synergistic action and interplay of hydrogen embrittlement mechanisms in steels and iron: Localized plasticity and decohesion, Engineering Fracture Mechanics 216 (2019), p. 106528.
Hydrogen gas is a renewable energy source for electrical and transportation fuel for vehicular applications. However, the storage and transportation of hydrogen gas are challenging because of its very nature and impact on pipelines and storage tank/facility materials. This paper investigates the influence of hydrogen on the candidate fracture toughness (KQ) of low carbon steel immersed in acidic hydrogen environments for one year which has limited previous research. Steel specimens were coated from all sides except one surface to accurately quantify the influence of hydrogen diffusing from the environments into the specimens. Specimens were tested for crack tip opening displacement (CTOD) fracture toughness at six- and twelve-month intervals of immersion in acidic environments. Before KQ testing at various intervals, the hydrogen contents of the specimens were determined by an electrochemical approach. Based on test results, models for the degradation of KQ of steel were developed in accordance with the proposed hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) model (HELP + HEDE model) of hydrogen embrittlement. Furthermore, fractography of the specimens was performed to observe the synergistic action of HELP and HEDE mechanisms of hydrogen embrittlement (HE), and their subsequent effects on the microstructure and fracture resistance of steel. The significance of the research is highlighted by its practical application for assessing the durability of steel structures and infrastructure against hydrogen environment-assisted cracking (HEAC). Furthermore, this paper highlights the synergistic activity of the HELP and HEDE mechanisms of HE in steel and the importance of developing structures for storing hydrogen on a large scale.
The possibility of eliminating of electrically inactive areas from varistor body with maintaining varistor electrical parameters can be achieved by modifying Bi 2 O 3 in such a way that a Bi-rich layer which surrounds the grains of ZnO is as thin as possible and by minimizing of the amount of additives so as not to form electrically inactive areas in varistor. It has been proven that modification of Bi 2 O 3 with small quantities of other MeO results in significant changes in the varistor structure, thereby gaining the uniform distribution of the intergranular phase. The work contains the results on which Sb 2 O 3 were added in an amount of 15 mol%. After mixing with Bi 2 O 3 they were sintered and shivered. Modified Bi 2 O 3 was added to the varistor bulk in quantities of 1.0, 0.3, 0.2 and 0.1 mol% to study the varistor properties. The best results were obtained for the varistor doped with 0.3 mol% Bi 2 O 3 modified by Sb, which has the best compatibility with the mathematically model calculated by statistical methods describing 100% of conductive grain boundaries. The obtained results of the varistors microstructure modification led additionally to reduce amounts of additives for about 30% and thus to lower at about 10% of production costs.
Bearing in mind the multiple effects of hydrogen in steels, the specific mechanism of hydrogen embrittlement (HE) is active, depending on the experimental conditions and numerous factors which can be grouped as environmental, mechanical and material influences. A large number of contemporary studies and models about hydrogen environment assisted cracking and HE in steels are presented in the form of critical review in this paper. This critical review represent the necessary background for the development of a multiscale structural integrity model based on correlation between simultaneously active HE micro-mechanisms: the hydrogen-enhanced localized plasticity (HELP) and the hydrogen-enhanced decohesion (HEDE) - (HELP+HEDE) and macro-mechanical response of material, unevenly enriched with hydrogen during service of boiler tubes in thermal fossil fuel power plant. Several different experimental methods and techniques were used to determine the boiler tube failure mechanism and afterwards also the viable HE mechanisms in the investigated ferritic-pearlitic low carbon steel, grade 20 - St.20 (equivalent to AISI 1020). That represent a background for the development of a structural integrity model based on the correlation of material macro-mechanical properties to scanning electron microscopy fractography analysis of fracture surfaces of Charpy specimens, in the presence of confirmed and simultaneously active HE micro-mechanisms (HELP+HEDE) in steel. The aim of this paper is to show how to implement what we have learned from theoretical HE models into the field to provide industry with valuable data and practical structural integrity model.
Pipe elbows (bends) are considered critical pressurized components in the piping systems and pipelines due to their stress intensification and the effect of bend curvature. They are prone and hence more exposed to different corrosion failure modes than straight pipes. Late detection of such elbow damages can lead to different dangerous and emergency situations which cause environmental disasters, pollution, substantial consumer losses and a serious threat to human life. A comprehensive safety and reliability assessment of pipe elbows, including usage of prediction models, can provide significant increases in the service life of pipelines. It is well known that the limit pressure is an important parameter to assess the piping integrity. In this paper, the integrity assessment of damaged pipeline elbows made of API 5L X52 steel was done within the framework of numerical modeling using the finite element method (FEM) and finite element analysis (FEA). The evaluation of numerically FEM modeled limit pressure in the corroded elbow containing a rectangular parallelepiped-shaped corrosion defect with rounded corners at the intrados section was done and compared to different codes for calculating limit pressure. Moreover, the area with the corrosion defects with different relative defect depth to wall thickness ratios was FEM modeled at the intrados section of the pipe elbow where the highest hoop stress exists. The results showed that the codes for straight pipes could not be applied for the pipe elbows due to the significantly higher error in the obtained limit pressure value compared with numerically FEM obtained results. However, the results for modified codes, adapted for the pipe elbow case using the Goodall formula for calculation of the hoop stress in pipe elbows with defects are pretty consistent with the numerical FEA results. The notch failure assessment diagram (NFAD) was also used for the straight pipe and pipe bends with different corrosion defect depth ratios, while the obtained critical defect depth ratios further highlighted the criticality of pipe elbows as an essential pipeline component.
The aim of this Hydrogen embrittlement Special Symposium in Engineering Fracture Mechanics journal was to bring together top scientists and researchers in the field of hydrogen embrittlement in order to present the latest achievements, the current state of the art, and the future research framework in understanding hydrogen embrittlement phenomena. Hydrogen embrittlement continues to be a critical degradation mode of structural metals and is becoming increasingly important as society works toward a hydrogen economy as part of the solution to sustainability and climate change. The effects of hydrogen in metals are numerous, as hydrogen segregates to defects, affects metal plasticity, and of course, causes a premature fracture. Research is thus investigating all of these topics, and their dependencies on specific metal types and alloys. Understanding of these phenomena in any alloy system may provide strategies for mitigating the effects of hydrogen or guide usage of components, while a more holistic understanding of the fundamental physics, mechanics, and materials science may provide strategies for the development of new alloys that resist hydrogen embrittlement.
Corrosion induced failure of buried ferrous pipelines causes significant economic losses to the world. Many of the existing buried water pipelines are made of ductile iron in most of the developed countries. Literature shows that the research on the corrosion-induced degradation assessments of ductile iron pipelines is limited and mostly deals with the physical deterioration i.e., loss of wall thickness determined by short-term research. This paper addresses this gap and presents a comparatively long-term study on the corrosion and its subsequent effect on the composition and nanomechanical properties of buried ductile iron pipelines in the accelerated corrosive environment. For experimentation, ductile iron specimens were immersed in the acidic simulated soil solution for 365 days. Physical deterioration assessment over the time was carried out in terms of corrosion rates measured at intervals of 180 and 365 days. A significant change in the percentage composition of key elements and phases were quantified. Furthermore, the mechanical properties of the grains were found to be considerably reduced after 365 days of immersion in the acidic environment by the nanoindentation technique. The results revealed an alarming increase of structural degradation at nano scale for some of the grains due to chloride induced localized corrosion. The significance of the current research is its in-depth analysis of the corrosion-induced degradation of ductile iron pipes which enhances the knowledge related to the failure of these pipelines
We are reporting in this study the hydrogen permeation in the lattice structure of a steel pipeline designed for natural gas transportation by investigating the influence of blending gaseous hydrogen into natural gas flow and resulted internal pressure values on the structural integrity of cracked pipes. The presence of cracks may provoke pipeline failure and hydrogen leakage. The auto-ignition of hydrogen leaks, although been small, leads to a flame difficult to be seen. The latter makes such a phenomenon extremely dangerous as explosions became very likely to happen. In this paper, a reliable method is presented that can be used to predict the acceptable defect in order to reduce risks caused by pipe failure due to hydrogen embrittlement. The presented model takes into account the synergistic effects of transient gas flow conditions in pipelines and hydrogen embrittlement of steel material due to pressurized hydrogen gas permeation. It is found that blending hydrogen gas into natural gas pipelines increases the internal load on the pipeline walls due to overpressure values that may be reached in a transient gas flow regime. Also, the interaction between transient hydrogen gas flow and embrittlement of API 5L X52 steel pipeline was investigated using Failure Assessment Diagram (FAD) and the results have shown that transient flow enhances pipeline failure due to hydrogen permeation. It was shown that hydrogen embrittlement of steel pipelines in contact with the hydrogen environment, together with the transient gas flow and significantly increased transient pressure values, also increases the probability of failure of a cracked pipeline. Such a situation threatens the integrity of high stress pipelines, especially under the real working conditions of hydrogen gas transportation.
The paper presents the results of comparative strength tests on reinforced concrete beams with two different types of reinforcement. The test beams had glass-fibre-reinforced-polymer reinforcing bars with transversal stirrups, while the control beams used conventional streel reinforcement. Both groups were prepared with appropriate geometric parameters and dimensions to enable meaningful comparison. The research was based on the standards, technical approvals, recommendations and strength data of manufacturers. The four-point bending strength test was performed after 28 days to determine the stiffness and bending load capacity of the beams. The class of concrete prepared on cubic cubes was also determined to confirm the design assumptions. The obtained measurements were used to assess the suitability of individual material combinations for practical applications.
This paper aims to investigate the effect of hydrogen-induced mechanical degradation of low carbon steel at macro-, micro- and nano-levels in the hydrogen-rich acidic environments. From the test results of specimens, a relationship in hydrogen concentration and corrosion propagation was observed that led to the significant reductions of bulk elastic modulus after 28 days of exposure to the hydrogen-rich acidic environments. Through microstructural analysis, the deformation of larger grains, cracks, and blisters caused by hydrogen penetration was found as the possible cause for this reduction. Moreover, by performing nanoindentation on the areas of interest of various specimens at planned time periods, the influence of hydrogen on the nano-elastic and nano-hardness properties of grains was determined. The 3D surface profiles of the nano-elastic modulus and nano-hardness of various specimens are presented in this paper.
In this study, two erosion protection MMC coatings with WC particles were deposited by the plasma transferred arc (PTA) welding. One of the coatings with tungsten carbide WC in the NiBSi matrix (WC/NiBSi), and the second coating WC in NiCrBSi matrix (WC/NiCrBSi) was deposited by the flame spray process on the same substrate material S235JR steel. Experiments were performed using a gas blast sand erosion test facility with high-velocity erodent particles impact (approximately 100 m/s) at different particle impact angles (20°-45°), with an objective to study erosion wear characteristics and mass loss of two MMC coatings. Microstructural characterization of MMC coatings was done by scanning electron microscope equipped with energy-dispersive X-ray spec-troscopy, whereas X-ray diffraction analysis was used for identification of present phases. The hardness of coatings was determined by Vickers hardness measurements. WC/ NiBSi obtained by the PTA process shows superior hardness and erosion properties.
Hydrogen embrittlement is a common, dangerous, and poorly understood cause of failure in many metal alloys. In practice, it is observed that different types of damage to industrial components have been tied to the presence and localization of hydrogen in metals. Many efforts have been made at understanding the effects of hydrogen on materials, resulting in an abundance of theoretical models and papers. However, a fully developed and practically-applicable predictive physical model still does not exist industrially for predicting and preventing hydrogen embrittlement. The connection of microstructure-based behaviors of materials and effects on the macroscopic measurable characteristics (stress levels, hardness, strength, and impact toughness) is of the utmost importance to achieve a unified model for hydrogen embrittlement. This paper gives an overview of the application of a model for structural integrity analysis of boiler tubes made of plain carbon steel exposed during operation to a local corrosion process and multiple hydrogen assisted degradation processes: hydrogen embrittlement and high-temperature hydrogen attack. The model is based on the correlation of mechanical properties to scanning electron microscopy fractography analysis of fracture surfaces in the presence of simultaneously active hydrogen embrittlement micro-mechanisms. The proposed model is practical for use as a predictive maintenance in power plants, as it is based on the use of standard macro-mechanical tests. Copyright © 2016 NACE International. All rights reserved.
The EU-NoE aims to strengthen scientific and technological excellence by developing an integrated and interdisciplinary understanding of materials technology, and co-evolution with science, industry and society, and also by addressing the fragmentation of the European research in this area. Its main objective is to enable an open and productive dialogue and free online collaboration tools in accordance with the growing R&D networking demands between all disciplines which study materials science from any scientific or technological perspective and which in turn are being transformed by continuous advances within the European Union and worldwide.
In offshore structures, the consecutive environmental and operational loading lead to an ever-changing stress state in the topside structure as well as in the substructure, which for offshore jacket-type platforms (called of fixed offshore structures) commonly used, result in fatigue damage accumulation. A wide variety of codes and recommended practices provide approaches in order to estimate the fatigue damage in design phase and remaining life in existing structures. In this research work, fatigue damage accumulation analyses applied to an offshore jacket-type platform using hot-spot stress and notch strain approaches are presented. These analyses are performed using wave information from the scatter diagram collected in North Sea. The wave loads used in this analysis were obtained using the Stokes 5th order wave theory and Morrison formula. The jacket-type offshore structure under consideration has a total height of 140.3 meters, a geometry at mud line of 60×80 meters and composed by tubular elements.
Characterization of metal degradation after prolonged service is necessary for evaluating component exhaustion and its remaining service capability. Martensitic steel X20CrMoV 12.1 has been extensively used as a material for tubing systems and pipelines in thermal power plants. This paper compares data provided by two imaging techniques. Following tests were performed: impact testing at different temperatures and characterization of fracture surfaces of Charpy specimens by scanning electron microscope and 3D digital optical microscope. In this study three new geometrical characteristics were established, as a measure of the ductility change of material.
Comparative analysis of a repaired and a new crane wheel, was performed in Steelworks Smederevo, including an economic analysis and technological procedures. The repair procedure for a crane wheel is presented, along with the selection of filler materials, as well as testing of mechanical properties performed on samples taken from hard faced welds. The advantages of repair techniques compared to the manufacturing of a new wheel are shown, but also the flaws that may affect the worklife and integrity of wear-damaged elements and components.
In this paper we presented and discussed the capabilities of Serbian Network of Excellence (NoE) in materials characterization that aims to strengthen scientific and technological excellence by developing an integrated and interdisciplinary scientific understanding of materials characterization of engineering materials and their co-evolution with science, materials science, industry and society. Proposed research framework in hydrogen embrittlement refers to the challenges and most obvious problems of how to link models, phenomenology and morphology of different materials failures of industrial components at different scales and how to successful translate the insights gained into outcomes of practical value to the engineering community
Hydrogen evolution and permeation occur during electroplating, corrosion, and cathodic protection. Hydrogen accumulates in areas of high stress and may reach a critical concentration, potentially causing fractures and catastrophic damage. This chapter describes hydrogen permeation and hydrogen-induced damage in metals and alloys. It also discusses hydrogen evolution kinetics, theoretical diffusion solutions, and basic hydrogen permeation models. Models are used as a diagnostic tool to determine the effectiveness of various metals and alloys as hydrogen permeation inhibitors. It then explains experimental atomic hydrogen permeation transient determination and hydrogen absorption rate constants and diffusivity evaluation into metals using case studies. Hydrogen embrittlement, hydrogen-induced cracking, hydrogen blistering, and hydrogen stress cracking are also discussed to show the relationship to hydrogen permeation and hydrogen-induced cracking mechanisms. Finally, various techniques used to prevent and control hydrogen damage of metals and alloys are described.