Simulated Deep-sea Environment Research Articles

Influence of cathodic polarization on stress corrosion cracking susceptibility of 35CrMo steel for high strength bolt in simulated deep-sea environment

The effect of cathodic polarization on stress corrosion cracking (SCC) of 35CrMo steel for high strength bolt in the simulated deep-sea environment has been studied. The results show that 35CrMo steel has a higher SCC sensitivity at open circuit potential in the simulated deep-sea environment than that in the shallow seawater. With potential negatively shifted to −750 mV, 35CrMo steel presents the lowest SCC sensitivity. And the SCC susceptibility is increased significantly with the further negative shift of potential because of the intensive hydrogen evolution. When the potential is below −950 mV, hydrogen embrittlement with hydrogen-enhanced-plasticity mediated decohesion should be the dominant SCC micro-mechanism.

Microscopic investigation on pitting corrosion of Ni-Cr-Mo-V high-strength steel weldment in simulated deep-sea environment

The pitting corrosion behavior and mechanism of Ni-Cr-Mo-V high-strength low-alloy steel weldment in simulated deep-sea environment were investigated by in-situ electrochemical measurements and microscopic observation techniques. The results show that pitting corrosion is the main degradation form of Ni-Cr-Mo-V steel in the deep sea, and its weldment exhibits more severe localized attack under the macro-galvanic effect at the welded joint. HAZ is more sensitive to pitting due to the inhomogeneity of microstructure and composition. Most pitting is associated with non-metallic inclusions. The Al-enriched inclusions makes greater contribution to pitting than Si-enriched and Ti-enriched inclusions. The hydrostatic pressure in the deep sea promotes pitting, which is induced either by the preferential dissolution of the soluble components of the inclusions or by the micro-crevices and internal stresses formed at inclusion/matrix interface.

Early corrosion behavior of 35CrMo steel for high-strength bolt in simulated shallow and deep sea environments

Early corrosion behavior of 35CrMo low-alloy steel for high-strength bolt in the simulated shallow seawater and deep-sea environment was studied using mass loss measurement, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Raman spectrometer, X-ray photoelectron spectrometer (XPS) and 3D microscope. The results show that the corrosion of 35CrMo steel initiates mainly at the steel matrix around the inclusions of CaO–MgO–Al2O3, (Ca, Mn)S and their mixed composite. The corrosion rate in the simulated deep-sea environment is lower than that in the shallow seawater, which is declined with immersion time. The corrosion products formed in the two environments are composed of γ-FeOOH, α-FeOOH, Fe3O4 and little Cr(III) oxide or/and hydroxide, but the rust layer produced in the deep-sea environment is thin and uniform. The steel has pits in a shallow dish shape and tends to develop uniform corrosion in the deep-sea environment.

Hydrogen Embrittlement Susceptibility of Ti-6Al-4V Alloys Fabricated by Electron Beam Melting in Simulated Deep-Sea Environment

The hydrogen embrittlement susceptibility of electron beam melted Ti-6Al-4V alloy (ET) was compared with that of conventional wrought alloy (WT). Hydrogen permeation, electrochemical, and slow strain rate tensile tests as well as surface observation were conducted under a simulated sea environment. The results show that the hydrogen embrittlement susceptibility of ET is lower than that of WT, which can be attributed to the intense texture of ET with a smaller specific surface area of grain boundary, preventing hydrogen permeation. Moreover, with increasing depth of the ocean, the hydrogen embrittlement susceptibility of both ET and WT TC4 alloys increases considerably. This reduced hydrogen embrittlement resistance can be attributed to the degradation of the passivation film, accelerating the permeation flux of hydrogen.

Corrosion form transition of mooring chain in simulated deep-sea environments: Remarkable roles of dissolved oxygen and hydrostatic pressure

The corrosion form and mechanical properties deterioration of mooring chain steel in simulated deep-sea environments were investigated. With the increase of ocean depth, not only the pressure increases, but also the dissolved oxygen content decreases. These two factors affect corrosion evolution of mooring chain steel in simulated deep-sea environments, which was studied for the first time. Compared with uniform corrosion of mooring chain steel in shallow sea with sufficient oxygen, low dissolved oxygen leads to the corrosion dominated by pitting with pit covers. Meanwhile, hydrostatic pressure distinctly accelerates pitting initiation and propagation. The higher the hydrostatic pressure is, the more serious the pitting is. For failure mechanism of unstressed mooring chain steel serving in simulated deep-sea environments, both absorbed hydrogen and corrosion morphology can degrade the ductility of mooring chain steel, in which the leading factor depends on the service time. The severe pitting is the main factor and causes remarkable ductility loss of the steel after long-term immersion. But hydrogen plays an important role on elongation loss in early stage.

Effect of hydrostatic pressure on multilevel structure and bending progressive damage of 3D braided composites under simulated deep-sea environment

Compared to metal materials and laminated composites, three-dimensional (3D) braided composites are showing innovatively great potential in deep-sea pressure shell applications owing to their light-weight, excellent out-of-plane mechanical properties and near-net forming capacity. In this paper, three-dimensional six-directional (3D6D) braided composites with different epoxy resins are designed and fabricated. The samples are put in a deep-sea pressure simulator at 10 MPa pressure for 80 h and experimentally test via the three-point bending method. A multi-level evaluating approach, namely nano-scale, micro-scale, meso-scale and macro-scale, is proposed. The effect of the hydrostatic pressure on multilevel structure and progressive failure behaviours are analyzed. Results indicate that, although the moisture absorption does not lead to the generation of new chemical bonds on the nanoscale in the carbon/epoxy composites, the moisture absorption has significant effects on the bending mechanical properties and damage initiation of 3D6D braided composites. Moreover, after deep-sea hydrostatic pressure, the strength of 3D6D braided composites decrease by 15.64–30.93 %, and the damage volumes increase by 0.039–0.405 %. Furthermore, the final failure mechanism of 3D6D braided composites after deep-sea hydrostatic pressure are largely governed by the fiber-matrix debonding and matrix cracking.

Corrosion of high-strength steel in 3.5% NaCl solution under hydrostatic pressure: Initial corrosion with tensile stress coupling

The rust development on Ni-Cr-Mo-V high strength steel under hydrostatic pressure and tensile stress was investigated by microstructure characterization and electrochemical measurements. Deposition influenced by hydrostatic pressure and tensile stress shows two periods: the first stage of immersion, both hydrostatic pressure and tensile stress control the deposition of corrosion products, such as Cr3+; the later stage of immersion, only hydrostatic pressure contributes to the growth of rust, thus forming an inner rust layer with a large number of cracks; therefore, the worse protection of rust layer, which contains much β-FeOOH and Fe3O4, formed under the simulated deep-sea environment.

Synergistic Effects of Hydrostatic Pressure and Dissolved Oxygen on the SCC Behavior of Hydrogenated Ti6Al4V Alloy in Deep-Sea Environment

This work focused on the synergistic effect of hydrostatic pressure (HP) within the range of 0.1~50 MPa and a dissolved oxygen (DO) concentration within the range of 0.18~11.8 ppm on the stress corrosion cracking (SCC) behavior of hydrogenated Ti6Al4V alloy in a simulated deep-sea environment by electrochemical measurements and slow strain rate tensile (SSRT) tests. The potentiodynamic polarization and electrochemical impedance spectra results confirmed the corrosion resistance degradation with the HP increasing to 50 MPa. The fracture morphologies showed a mixed characteristic of brittle fracture on the surface layer and ductile fracture in the inner part. Higher HPs increased SCC susceptibility while a larger DO concentration decrease that of Ti6Al4V alloy.

Electrochemical corrosion behavior of high strength steel in simulated deep-sea environment under different hydrostatic pressure

The corrosion behavior of Ni-Cr-Mo-V high strength steel in the simulated deep-sea environment under different hydrostatic pressure and immersion time is investigated using electrochemical techniques, microscopic morphology observation and Raman spectrometer. During the first 10 days immersion, the corrosion rate presents wave-like changes. The corrosion rate under different hydrostatic pressure tends to be stable after 10 days immersion. The area with uneven composition will preferentially dissolve and form corrosion pits. The local corrosion takes the corrosion pit as the center, expands and fuses around, and finally forms uniform corrosion. High hydrostatic pressure promotes β-FeOOH transforming into other corrosion products. The anode of the steel tends to active dissolution and the cathode show oxygen diffusion control characteristics at the initial stage of corrosion. Under 20 MPa, step-shape passivation appears in the anode region. Due to the rapid reaction, the corrosion product film has poor protection performance and dissolves, which resulting in not obvious passivation phenomenon.

Effect of hydrostatic pressure on galvanic corrosion of low-alloy steel in simulated deep-sea environments

ABSTRACT In order to study the effect of high hydrostatic pressure on the corrosion of low-alloy steels in deep-sea environments. The electrochemical corrosion behavior of single-metal system and triple-metal coupled system of 907A steel, 921A steel and 1# steel under different hydrostatic pressures were studied by electrochemical, weight loss and morphology observation methods. The results show that the high hydrostatic pressure promotes the corrosion of low-alloy steel by changing the composition and morphology of corrosion products. In addition, there was also severe galvanic corrosion between the couples with a low potential difference (< 60 mV),907A steel was used as the anode of the three-metal coupled system, and 921A steel and 1# steel as the cathode. The galvanic coupling effect accelerates the pitting corrosion of 907A steel as an anode metal. When using multi-metal couplers with low potential differences, they should be protected by both coating protection and cathodic protection.

Correction to: Insight into the Corrosion Resistance Deterioration and Corrosion Film Transformation of Ti6321 Weldment in a Simulated Deep Sea Environment

Correction to: Insight into the Corrosion Resistance Deterioration and Corrosion Film Transformation of Ti6321 Weldment in a Simulated Deep Sea Environment

Investigation on compressive and impact performance of GO-modified hollow glass beads/epoxy resin composites in simulated deep-sea environment

In order to enhance the performance of lightweight and high-strength composites in the deep-sea environment, epoxy resin (EP) was used as the matrix and hollow glass beads (HGB) was used as the reinforcing phase to reduce the density of composite. Graphene oxide (GO) was employed to modify HGB for improving the interfacial adhesion between HGB and EP. In this work, the effect of GO on the mechanical properties of HGB/EP composites in simulated deep-sea environment was investigated. The results show that compared with HGB/EP composite, the compressive and impact strength of GO@HGB/EP composite after high-pressure seawater treatment is increased by 26.6% and 29.7%, respectively. And the compressive and impact strength after low-temperature seawater treatment is increased by 23.1% and 51.3%, respectively. The improvement of mechanical properties of HGB/EP composites makes its application in deep-sea environment more promising.

The role of hydrostatic pressure on the metal corrosion in simulated deep-sea environments — a review

This paper reviewed the corrosion behavior of metals in simulated deep-water environments and briefly discussed the effect of hydrostatic pressure on the different corrosion types for the active and the passive alloys. A consensus on the corrosion mechanism is that hydrostatic pressure accelerates the dissolution kinetics, changes the chemical compositions of the product layer or passive films, and promotes the adsorption of Cl− on the metal surface. In addition, a newly-developed mechanism that hydrostatic pressure facilitates the dissolution process by thinning the electric double layer was reviewed, the synergistic effect of hydrostatic pressure and tensile stress on the stress corrosion cracking was discussed, and the modified coating with chemical bonding interface to prolong the service life in this environment was introduced.

Insight into the Corrosion Resistance Deterioration and Corrosion Film Transformation of Ti6321 Weldment in a Simulated Deep Sea Environment

Insight into the Corrosion Resistance Deterioration and Corrosion Film Transformation of Ti6321 Weldment in a Simulated Deep Sea Environment

Electrochemical Evaluation of Stress Corrosion Cracking Susceptibility of Ti-6Al-3Nb-2Zr-1Mo Alloy Welded Joint in Simulated Deep-Sea Environment.

Titanium alloys have high specific strength and excellent corrosion resistance and have been applied in deep-sea engineering fields. However, stress corrosion cracking may become one of the biggest threats to the service safety of a high-strength titanium alloy, as well as its weldment. In this work, stress corrosion cracking of a gas-tungsten-arc-welded Ti-6Al-3Nb-2Zr-1Mo (Ti6321) alloy influenced by the applied potentials in simulated deep-sea and shallow-sea environments was investigated by combining slow strain rate testing with electrochemical measurements. The results showed that the service environment and applied potential have a substantial effect on the stress corrosion cracking behavior of the Ti6321 welded joint. The Ti6321 welded joint exhibited higher stress corrosion susceptibility in a simulated deep-sea environment and at a strong polarization level owing to the diminishing protection of the passive film under passivation inhibition and the enhancement of the hydrogen effect. The fracture of a Ti6321 welded joint in the weld material could be attributed to the softening effect of the thick secondary α within the coarse-grained martensite. The electrochemical evaluation model of stress corrosion cracking susceptibility of a Ti6321 welded joint in a simulated marine environment was established by adding the criterion in the passivation region based on the literature model, and four potential regions corresponding to different stress corrosion cracking mechanisms were classified and discussed. Our study provides useful guidance for the deep-sea engineering applications of Ti6321 alloys and a rapid assessment method of stress corrosion risk.

Controllable defect engineering to enhance the corrosion resistance of Cr/GLC multilayered coating for deep-sea applications

A cleaning intervention is introduced to control the growth defect of Cr/GLC multi-layered coating to avoid premature failure in the deep-sea environment. The results demonstrated that the introduction of the cleaning intervention significantly decreased the penetrating defect density as expected, together without deteriorating the superior mechanical and tribocorrosion properties. The localised corrosion resistance was improved dramatically in the simulated deep-sea environment. It was illustrated that controllable defect engineering can be an effective strategy for improving the anti-tribocorrosion performance of GLC coatings for harsh deep-sea applications.

Stress Corrosion Crack Propagation of 40cr Steel Used for High Strength Fastener in Simulated Deep-Sea Environment

Stress Corrosion Crack Propagation of 40cr Steel Used for High Strength Fastener in Simulated Deep-Sea Environment

Effect of hydrogen charging on SCC of 2205 duplex stainless steel with varying microstructures in simulated deep-sea environment

The effect of hydrogen on stress corrosion cracking (SCC) of 2205 duplex stainless steel (DSS) with different microstructure in simulated deep-sea environments was studied through microstructure characterization, electrochemical measurements, hydrogen determination and slow strain rate tensile (SSRT) tests. Hydrogen degrades corrosion and SCC resistance by penetrating into matrix, weakening passive film and accelerating anodic dissolution (AD). Therefore, SCC is controlled by hydrogen embrittlement (HE) and hydrogen-facilitated anodic dissolution (HFAD). Microstructure has a great impact on SCC, and quenched DSSs are more SCC susceptible due to coarser grains, unbalanced partition of two constitutional phases, brittle precipitates and higher defect density.

Influence of Hydrostatic Pressure on the Pitting Corrosion Behavior of API X80 Steel

The effect of hydrostatic pressure on the metastable and stable pitting corrosion of API X80 steel was investigated in a simulated deep-sea environment. Cumulative probability distribution analysis of metastable pitting events revealed that hydrostatic pressure promoted the occurrence of metastable pitting corrosion and the transformation of metastable pitting corrosion to stable pitting corrosion. According to the results of scanning Kelvin probe force microscopy tests, pitting corrosion of the test steel originated at the interface between inclusions and the substrate. Combined with finite element analysis, the mechanism by which hydrostatic pressure promoted the occurrence and propagation of stable pitting corrosion of test steel in the simulated deep-sea environment was explained.

Synergistic effects of fluid flow and hydrostatic pressure on the degradation of epoxy coating in the simulated deep-sea environment

The anticorrosion performance of epoxy varnish coating/steel systems under a simulated deep-sea fluid-pressure (FP) environment was studied using physical performance tests, electrochemical measurements and finite element modeling. The results show that fluid flow provides an initial kinetic energy to water, and the hydrostatic pressure difference reduces the energy barrier for water absorption, leading to premature corrosion of the coated steel under FP condition. Detachment of polymer pieces from the coating surface and large areas of blistering are found to occur under the synergistic effects of fluid and pressure, which can be attributed to the release of internal stress at coating defects.