Corrosion Pits Research Articles

Failure analysis of abnormal leakage in hydrogen cyanide reactor

Hydrogen cyanide (HCN) is a crucial building block for various industrial chemicals in organic synthesis. Due to its high toxicity to humans and the environment, meticulous care is required in the synthesis, use, and disposal of HCN and its derivatives. This study investigated the premature failure of the HCN reactor, a core component of the HCN production system. Despite a design life of 20 years, the reactor experienced abnormal leakage after only 4 years of operation. Comprehensive investigations revealed that corrosion pits caused by localized corrosion formed at the circumferential welding seam of the reactor shell. This problem was further aggravated by vortex scouring from the pressurized water medium. Additionally, residual stress at the welding seam contributed to decreased toughness. The analysis highlighted the intricate relationship between localized corrosion and vortex scouring as the primary mechanisms leading to perforation and leakage of the reactor shell. Based on these findings, effective countermeasures were proposed to prevent similar future failures, potentially enhancing the operational safety and reliability of the HCN production system.

Detecting and Estimating Local Corrosion Damages in Long-Service Aircraft Structures by the Eddy Current Method with Double-Differential Probes

ABSTRACT Monitoring corrosion in aircraft structures through nondestructive testing is crucial for maintaining long-term aircraft serviceability. Corrosion monitoring is particularly challenging when corrosion damage is situated on internal surfaces of multilayer aircraft structures. The eddy current method is one of the most promising techniques for detecting and measuring such subsurface corrosion damage without direct contact or disassembly. However, due to their low sensitivity traditional eddy current probes with coaxial coils are not well suited for detecting corrosion damages of the local type, such as pitting or corrosion pits, in multilayer aircraft structures. This study tested the use of low-frequency eddy current probes of the double-differential type, characterized by 8 and 10 mm operational diameters, in detecting and measuring hidden corrosion damages of this local type. Such corrosion damages were simulated by means of flat-bottomed drilled holes of differing diameters and depths (or different diameters and residual thicknesses of the inspected sheet in the damaged area). The signals from the eddy current probes were evaluated in the complex plane using a universal eddy current flaw detector. The correlations between the amplitude and phase of the eddy current signal and depth of location of the local corrosion damages were analyzed. Results indicate that it is possible to estimate the residual thickness of the skin in locally corroded areas by measuring the eddy current signal phase, independently of the local corrosion damage diameter (size), providing useful information for residual service life determination.

Effect of inhomogeneous microstructures on stress corrosion cracking sensitivity of 2050-T84 Al-Li alloy thick plate

Inhomogeneous microstructures in the thickness direction and stress corrosion cracking of 2050-T84 Al-Li alloy thick plate was investigated. The quarter layer of alloy thick plate exhibited the highest stress corrosion cracking sensitivity, which was related to AlCuMnFe IMPs, subgrains, orientation, T1 phase and dislocation density. In the quarter layer, the obstruction of subgrains to deformation bands resulted in significant stress concentration. Cracks originated from corrosion pits caused by AlCuMnFe IMPs around subgrains. The dealloying corrosion of T1 phase and the presence of Goss texture increased the brittleness of the alloy, further accelerating the stress corrosion cracking of the quarter layer.

Outstanding hot corrosion behavior of Pt modified CoNiCrAl medium-entropy alloy

Pt modified CoNiCrAl medium-entropy alloys were optimized to observe the hot corrosion performance. The results indicated that Pt solidly dissolved in the BCC phase, promoted the uphill diffusion of Al, compensated for the loss of Al caused by phase transformation, effectively repaired the oxide scale, and reduced cracks propagation and spalling of the oxide scale. Combined with DFT calculations, verifying that Pt increased the adsorption energy for S atoms, hindered the inward diffusion of S and suppressed internal sulfidation. 10Pt-MEA had a thinner internal oxidation and corrosion pit depth, which was related to the thickness of Al-depletion layer.

Microstructure and mechanical properties evolution of 310S and GH3536 in hydrogen metallurgy service

The evolution of microstructure and mechanical properties of 310S austenitic stainless steel and GH3536 nickel-based alloy in hydrogen metallurgy service condition is investigated by conducting heat treatment under high temperature and hydrogen atmosphere. As the annealing time increases at 750 °C, carbide precipitate phases of the σ and μ brittle phases appear in the materials. At 900 °C, the dissolution of carbides induces the dispersion of brittle phases, while the hydrogen content reaching its peak. These brittle phases are still present at defects like grain boundaries at 1050 °C, with the surface of precipitates showing corrosion pits. Materials exhibit increasing strength and hardness initially with temperature and annealing time, followed by a decrease. Meanwhile, fracture elongation shows a positive correlation with temperature but a negative correlation with time. After annealing at 1050 °C for 500 h, GH3536 retains its high-temperature softening behavior and elongation at fracture, demonstrating excellent plastic stability. Furthermore, the mechanism of high temperature and hydrogen affecting metals is expounded, providing reference for the selection and optimization of materials which service in high temperature and hydrogen.

Corrosion reason analysis and countermeasures of buried oil unloading pipeline in an oilfield

The material, corrosion morphology and characteristics, as well as the compositions of corrosion products of a 20# steel unloading pipeline were studied using on-site C-scan detection, laboratory corrosion morphology analysis, material metallographic analysis, chemical composition analysis and tensile testing. The uniform corrosion and pitting behavior of 20# steel were studied using a high temperature and high pressure autoclave under conditions of 50 °C and CO2 partial pressure of 0.05 MPa, 0.1 MPa, and 0.2 MPa, respectively. The microstructure and composition of the surface and cross-section corrosion product film were analyzed by SEM. The results show that the uniform corrosion rate of 20# steel increases with the increase of CO2 partial pressure. When the CO2 partial pressure reaches 0.2 MPa, there are a large number of corrosion pits on the surface of the sample, and the maximum local corrosion rate reaches 1.8719 mm/a. The corrosion product film has a multi-layer structure, with a surface layer of FeCO3 corrosion product films and an inner layer of (Ca, Mg)CO3 deposition layer. There are obvious corrosion pits at the interface between the corrosion product film and the substrate locally. The severe thinning of the on-site pipeline wall is mainly caused by CO2 corrosion. The defects of the corrosion product film and the deposition of scale layer accelerate local corrosion.

Accelerated corrosion tests of a contact pair austenitic stainless steel – titanium alloy

The results of accelerated corrosion tests of a pair of austenitic stainless steel — titanium alloy under conditions of elevated temperatures and high concentrations of corrosive agents are presented, conditions for the developing the mechanism of local corrosion being the same. The proposed approach included provoking the appearance of microstress concentrators by three-point loading of test samples with subsequent forced development of local types of corrosion through simultaneous exposure to an increased concentration of corrosive agents and temperatures at a fixed exposure in an autoclave. The results of modeling the corrosion process in a titanium alloy being in contact with stainless steel are assessed proceeding from the data obtained from metallographic studies of the state of surface layers of the metal and the morphology of corrosion products on prepared sections of the surface of templates cut from the samples under study. We considred a pair of steel 08Kh18N10T — titanium alloy VT-5. It is shown that the contact of samples under conditions of accelerated corrosion tests does not lead to a significant development of local types of corrosion of the titanium alloy. On the contrary, analysis of the state of the surface layers of the samples of stainless steel revealed the presence of deep corrosion pits, triggering the intergranular corrosion. In this case, corrosion of austenitic steel, both in the presence and in the absence of contact with titanium, proceeded in three stages: the initiation and fusion of pitting; formation of knife corrosion ulcers; propagation of intergranular cracks into the depth of steel. The proposed methodology of corrosion testing can be used to predict the possible nature of the development of metal corrosion under operating conditions that form local zones of static stresses in structural materials, and for prompt response to extend the design life of the equipment at thermal and nuclear power facilities.

Sperlingite, (H2O)K(Mn2+Fe3+)(Al2Ti)(PO4)4[O(OH)][(H2O)9(OH)]⋅4H2O, a new paulkerrite-group mineral, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany

Abstract Sperlingite, (H2O)K(Mn2+Fe3+)(Al2Ti)(PO4)4[O(OH)][(H2O)9(OH)]⋅4H2O, is a new monoclinic member of the paulkerrite group, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in corrosion pits of altered zwieselite, in association with columbite, hopeite, leucophosphite, mitridatite, scholzite, orange–brown zincoberaunite sprays and tiny green crystals of zincolibethenite. Sperlingite forms colourless prisms with pyramidal terminations, which are predominantly only 5 to 20 μm in size, rarely to 60 μm and frequently are multiply intergrown and are overgrown with smaller crystals. The crystals are flattened on {010} and slightly elongated along [100] with forms {010}, {001} and {111}. Twinning occurs by rotation about c. The calculated density is 2.40 g⋅cm–3. Optically, sperlingite crystals are biaxial (+), α = 1.600(est), β = 1.615(5), γ = 1.635(5) (white light) and 2V (calc.) = 82.7°. The optical orientation is X = b, Y = c and Z = a. Neither dispersion nor pleochroism were observed. The empirical formula from electron microprobe analyses and structure refinement is A 1[(H2O)0.96K0.04]Σ1.00 A 2(K0.52□0.48)Σ1.00 M 1(Mn2+0.60Mg0.33Zn0.29Fe3+0.77)Σ1.99 M 2+M3(Al1.05Ti4+1.33Fe3+0.62)Σ3.00(PO4)4 X [F0.19(OH)0.94O0.87]Σ2.00[(H2O)9.23(OH)0.77]Σ10.00⋅3.96H2O. Sperlingite has monoclinic symmetry with space group P21/c and unit-cell parameters a = 10.428(2) Å, b = 20.281(4) Å, c = 12.223(2) Å, β = 90.10(3)°, V = 2585.0(8) Å3 and Z = 4. The crystal structure was refined using synchrotron single-crystal data to wRobs = 0.058 for 5608 reflections with I > 3σ(I). Sperlingite is the first paulkerrite-group mineral to have co-dominant divalent and trivalent cations at the M1 sites; All other reported members have Mn2+ or Mg dominant at M1. Local charge balance for Fe3+ at M1 is achieved by H2O → OH– at H2O coordinated to M1.

Effect of impact-corrosion coupling damage on fatigue properties of 2198-T8 aluminum-lithium alloy

The peeling of aircraft surface paint due to foreign object impact can expose the aluminum–lithium alloy substrate to atmospheric corrosion, resulting in the fatigue performance being affected by the combined effect of impact damage and corrosion damage. In this work, the effects of impact damage and corrosion damage on the fatigue life of 2198-T8 aluminum–lithium alloy sheet were investigated. The strain field distribution of specimens with coupled impact and corrosion damage under cyclic loading was analyzed by Digital Image Correlation (DIC) technique, and the coupling relationship between impact and corrosion damage was analyzed based on the crack propagation path and fracture morphology. The results show that surface corrosion pits depth distribution of impact dents follows the same trend as residual stress distribution. For the coupling damage of the hemispherical punch, the coupled effect between impact damage and corrosion damage is most evident at low impact energy. At higher impact energies, the impact damage dominates the coupling damage. As the salt spray corrosion time increases, the fatigue life decrease rate gradually slows with increasing impact energy, and the impact damage has a greater effect on the fatigue life in the early corrosion stage. Compared to the salt spray corrosion environment at 35 °C, the fatigue life of the specimen at 25 °C increased by a maximum of 50.48 % as the impact energy increased from 10 J to 25 J.

Deterioration and imperfection of the ship structural components and its effects on the structural integrity: A review

Abstract The design of ship structural safety is crucial to ensure the ship’s survivability during the operation. Extensive research has been conducted on ship structural components, including box girders, stiffened panels, and plates, beyond the ideal conditions by considering the implication of manufacturing processes, vessel usage, and aging in the form of defects like cracks, corrosion, and imperfections, both locally and globally. Previous research has also explored various methodologies, conditions, and parameters to understand the impact of damages and imperfections on ship structure and strength. However, there is a significant need to bridge the gap in prior research to advance technology and ship structural strength analysis. A comprehensive benchmark study specifically focused on improving ship structural component needs, identifying differences and gaps among existing studies as challenging. This article thoroughly reviews ship structural components, such as box girders, stiffened panels, and plates, while examining the effects of structural defects like corrosion, cracks, and imperfections on ship structural integrity. It synthesizes the influence of various defect parameters, including crack length, angle, position, corrosion severity, pit corrosion, pit diameter, and pit models, using finite element modeling and experimental investigations, particularly emphasizing ship structural components. The comparative analysis of methods and parameters presented in this review will serve as a valuable reference for future investigations and studies related to ship structural strength and design. The article’s contribution is expected to enhance the understanding of ship structural strength, contributing to the sustainability and effectiveness of vessel design in the global maritime industry.

Dual strategy of improved crosslinking degree and incorporated inhibitory fillers for high corrosion resistance sol-gel coatings

In this work, high corrosion resistance sol-gel coatings were prepared by the dual strategy of improved crosslinking degree and incorporated inhibitory fillers. Firstly, a special attention was paid to the mechanism of 2MI improving the crosslinking degree of coatings. Furthermore, the inhibitory fillers 8HQ@Ce-MOF were incorporated to endow coatings with active corrosion protection. Results showed that the 1.3 μm thick coating incorporated with 2MI and 8HQ@Ce-MOF appeared no corrosion pits after neutral salt spray exposure for 21 days, which was ascribed to 2MI improving the crosslinking degree, corrosion inhibition of guest molecule 8HQ, and corrosion suppression of host nanocontainer Ce-MOF.

Dynamic Marine Atmospheric Corrosion Behavior of AZ91 Mg Alloy Sailing from Yellow Sea to Western Pacific Ocean.

In this work, the dynamic marine atmospheric corrosion behavior of AZ91 Mg alloy sailing from Yellow Sea to Western Pacific Ocean was studied. The corrosion rates were measured using the weight loss method. The microstructure, phase, and chemical composition of corroded samples were investigated by SEM, EDS, XRD, and XPS. The results show that the evolution of corrosion rates of AZ91 Mg alloy was divided into three stages: rapidly increasing during the first 3 months, then remaining stable for the next three months, and finally decreasing after 6 months. The annual corrosion rate of Mg alloy reached 32.50 μm/y after exposure for 12 months in a dynamic marine atmospheric environment, which was several times higher than that of the static field exposure tests. AZ91 magnesium alloy was mainly subjected to localized corrosion with more destructiveness to Mg parts, which is mainly due to the synergistic effect of high relative humidity, the high deposition rate of chloride ion, sulfur dioxide acidic gas produced by fuel combustion, and rapid temperature changes caused by the alternating changes in longitude and latitude during navigation. As the exposure time increased, the corrosion pits gradually increased and deepened. The maximum depth of the corrosion pit was 197 μm after 12 months of exposure, which is almost 6 times the average corrosion depth. This study provides scientific data support for the application of magnesium alloys in shipborne aircraft and electronic equipment. The results could provide guidance for the design of new magnesium alloys and development of anti-corrosion technologies.

Effect of corrosion pit on fatigue damage and failure in powder bed fusion AlSi10Mg

AbstractThis paper is concerned with environmental corrosion during service of load‐bearing aluminum alloys fabricated by additive manufacturing (AM) with a focus on damage evolution characterization and identification of dominated failure mechanisms of pre‐corroded selective laser melted aluminum alloy. An experimental strategy for analysis of the damage and failure process is presented, combining 3D surface measurement, 3D digital image correlation, and scanning electron microscopy, to provide a multi‐source experimental characterization of corrosion morphology, strain field evolution, and fracture morphology. Statistics and machine learning methods were employed to process the measured multi‐source experimental data, showing that local average roughness has a strong influence on macro‐crack initiation position. The analysis focuses on four primary types of fatigue micro‐crack initiation, namely, internal defect, diffuse corrosion, corrosion micro‐pit, and corrosion jut; internal defect and diffuse corrosion are unique features for powder bed fusion (PBF) AlSi10Mg. The micro‐crack initiation mechanisms for all four types are (i) local stress concentrations due to adjacent material micro‐structural defects, (ii) interaction of underlying alloy microstructure and corrosion‐induced stress/strain, and (iii) local stress/strain concentration at corrosion micro‐pit and jut, respectively.

Improved Ability to Resist Corrosion of Selective-Laser-Melted Stainless Steel Based on Microstructure and Passivation Film Characteristics

The local corrosion resistance of forging and selective laser melting (SLM) 304 steels was explored by intergranular corrosion analysis, double-loop electrochemical potentiodynamic reactivation, dynamic polarization experimentation, structural analysis, and passivation film characteristics analysis. The ability to resist sensitization of SLM 304 steel is greater than that of forging 304 steel at a temperature of 650 °C for 9 h. Moreover, the pit corrosion resistance of forging and SLM 304 steels is weakened by sensitization, while the pit corrosion resistance of SLM 304 steel is much greater than that of forging steel. Therefore, SLM technology can improve the ability to resist sensitization and pit corrosion of 304 steel. Analysis showed that the ability to resist corrosion of the passivation film of SLM 304 steel is greater than that of forging steel. In addition, corrosion pits are easier to generate at the interface of forging steel and SLM 304 steel. The grain boundary corrosion of SLM 304 steel intensified while the corrosion of the melt pool boundaries weakened after the sensitization treatment, resulting in a decrease in pit corrosion resistance. The coupling effect of these different structures and passivation films decides the pit and sensitization resistance of forging and SLM 304 steels. Clarifying the corrosion mechanism of forging and SLM steels is of great significance for scientific research and the widespread use of SLM technology.

Plastic behavior and shakedown limit of defected pressurized pipe under cyclic bending moment

Pipelines subjected to thermal or mechanical loads may fail due to plastic strain accumulation which leads to ratcheting. In this research, cyclic plastic behavior and shakedown limit are investigated experimentally and numerically for a defected pressurized pipe under cyclic bending moment. In the numerical model, the combined isotropic/kinematic hardening model based on the Chaboche model is adopted to represent the cyclic plastic flow of the material. The hardening parameters are determined experimentally and used in the finite element (FE) model. A four-point bending test rig is manufactured to test a pressurized API 5L steel pipe under cyclic bending. An elliptical defect is created by machining to depict corrosion pits in pipes. The plastic strains are measured experimentally and the results are used to tune the parameters of the FE model. The shakedown limit of the defected pipe is determined numerically by tracking the critical points behavior and the results are verified experimentally. Furthermore, the plastic work dissipated energy (PWD) is estimated within the defective structure to study the behavior of the pipe. By running this compatible model, it is found that the yield and the shakedown limits are lowered by mean values of 55% and 25% respectively due to the presence of metal loss defect occupying almost half of the pipe thickness.

Effect of Temperature and NaClO on the Corrosion Behavior of Copper in Synthetic Tap Water

The corrosion behavior of copper was investigated in synthetic tap water with and without sodium hypochlorite (NaClO) at different temperatures during immersion for 70 d by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical measurement techniques. The weight loss corrosion rate and pit depth of copper first increase and then decrease with the change in solution temperature from 25 to 80 °C. This is mainly related to the corrosion products formed on the copper surface. The main corrosion products change from Cu2O and Cu2(OH)2CO3 to CuO with the increase in solution temperature. The presence of 3 ppm NaClO slightly increases the weight loss corrosion rate and pit depth of copper under all temperatures except for 50 °C and reduces the temperature of the maximum corrosion rate from 50 to 40 °C. Free chlorine reduction accelerates the cathodic reaction of the corrosion process.

Resonant Fatigue Tests on Polished Drill Pipe Specimens

In this study, the fatigue strength of polished drill pipe specimens was investigated and compared with previous test results of corroded and not-corroded pipes. The resonant fatigue test rig, which was designed and implemented by the University of Pisa, is initially presented by providing a detailed description of the set-up of the machine, the calibration of the strain gauges, the control system, and the correct identification of the vibrational node locations. A polishing rig was also designed and put into operation to remove the corrosion pits from the outer surface of almost the entire length of the drill pipe specimens. After the fatigue tests with the resonant rig, and the observation of the fatigue fracture of the specimens, a few samples were extracted from different zones (corroded and not corroded) of the failed drill pipe specimens. This allowed for investigations to be carried out using a scanning electronic microscope. The obtained results were analyzed using the Murakami model, and a discussion is presented about the effect of the corrosion pits on the fatigue strength.

Experimental study on rock-breaking characteristics of advanced premixed abrasive water jet

ABSTRACT To investigate the rock-breaking characteristics of the advanced premixed abrasive water jet, experiments of abrasive water jet eroding granite were carried out. The micro-failure morphology of erosion pits was observed and analyzed by CT (Computerized Tomography) and SEM (Scanning Electron Microscope). The results show that the difference in erosion effect caused by different rock breaking pressures is due to the difference in impact kinetic energy. The higher the jet pressure, the higher the impact kinetic energy of abrasive particles, and the erosion effect is enhanced. The difference in erosion effect caused by abrasive types is that the harder abrasives produce greater cutting force on the rock and consume less fracture surface energy. The CT scanning results show that the conical crack at the bottom is caused by the stamping action of abrasive particles and expands rapidly under the action of a water wedge, the action of reflective particles makes the erosion holes appear spindle-shaped. The results of SEM show that the sidewalls of the erosion pit are dominated by the cutting and fatigue-crushing effects of reflected abrasives. The bottom of the erosion pit is mainly driven by the punching action of the incident abrasive.

Selective Initiation of Corrosion Pits in Stainless Steel Using Scanning Electrochemical Cell Microscopy.

Scanning electrochemical cell microscopy is a useful technique for determining variations in corrosion behavior across a surface. However, the numerous options for experimental parameters and little understanding of their effect on the corroding system render comparisons of results between studies difficult. Herein, we explore changes in corrosion behavior of two martensitic stainless steels, a cast CA6NM and a wrought S41500, as a result of the chosen experimental parameters, including scan rate, approach potential, surface oil immersion, and tip aperture diameter. The study demonstrates that these experimental parameters can be controlled to probe oxide passivation kinetics and single pitting events by changing the surface state and cathodic currents. We measured the pitting and repassivation kinetics of a single pit and determined the compositional change of the Al2O3 inclusion site initiation point. Hundreds of data points were measured within 17 h of experimental time on the stainless steel samples, allowing statistical averages of corrosion and pitting values. This work will open new avenues for fine-tuning various corrosion aspects at the microscale, thereby contributing to a deeper understanding of the corrosion processes and mechanisms of diverse materials.

Effect of alternating interval of laser power on the element distribution, mechanical, and corrosion performance of electrochemical deposited multilayer Fe–Ni coatings

A new multilayer (ML) Fe–Ni coating was developed by frequently alternating the laser power (5 and 20 W) during electrochemical deposition. Owing to the thermal effect of the laser, the elemental content in each layer changed continuously. As the intervals for adjusting the laser parameters became shorter, the formation of ML Fe–Ni coatings became increasingly challenging due to the laser's thermal effect. This study suggests that a constant laser action exceeding 480 s improves the uniformity of the alternating elemental content distribution in the new coating without visible interlayer boundaries. Moreover, the elemental composition of each layer was affected by various laser parameters during the Fe–Ni reduction process. For a stable ML structure (480 s interval), the range of variation in Fe content reaches approximately 16.6 wt% (from approximately 32.6 to 49.2 wt%). Compared with the overall coating, the bonding force increased by approximately 24.5 %, the microhardness increased by approximately 17.3 % (load of 200 g), the wear rate decreased by approximately 21.6 % (load of 5 N), and the corrosion rate decreased by approximately 53.5 % (3.5 wt% NaCl). The improved wear resistance was attributed to the inhibition of crack extension and spalling. In addition, the ML structure was conducive to inhibiting the propagation of corrosion pits. This study provides guidance for analyzing the structural and performance characteristics of ML coatings formed via laser electrochemical deposition.