Hull Steel Research Articles

Comparative analysis of hull steel corrosion in tropical marine atmosphere: Correlation between indoor simulations and outdoor exposures

Comparative analysis of hull steel corrosion in tropical marine atmosphere: Correlation between indoor simulations and outdoor exposures

Ship Hull Steel Plate Deformation Modeling Based on Gaussian Process Regression

The linear heating and formation of steel plates is one of the most critical technologies in shipbuilding. Excellent technology not only provides good hydrodynamics for the hull but also affects the whole hull construction cycle and cost. In the heating and formation of a steel plate, the material, size, and thickness of the steel plate; heating temperature; heating position; and many other factors affect the formation of a steel plate. It is a very difficult process to know the influence relationship between various factors. In this study, a steel plate model is established by the Gaussian regression method, which can predict the steel plate deformation according to the selected steel plate material, size and thickness, heating temperature, and heating position. The accuracy of the model was evaluated, and the Gaussian process regression model has a better accuracy compared to other machine learning algorithm models. Finally the model visualization; designing the UI; selecting the steel plate material, size, and thickness; and inputting the heating temperature, the deformation magnitude, and stress magnitude of the steel plate can be obtained. The model can provide guidance to field workers for the heating and formation of hull steel plates and achieve efficient and fast formation of target steel plates.

Impact toughness and fracture propagation mechanism of NiAl precipitation-strengthened HSLA steels

Impact toughness is essential for evaluating the mechanical properties of ship hull steels. This study focused on understanding the embrittlement mechanism of NiAl precipitation-strengthened HSLA steels by integrating advanced characterization and atomic-scale calculations. The factors causing the deterioration of the impact toughness of NiAl precipitation-strengthened steels, which have been contentious, were identified. The embrittlement mechanism and crack propagation mode were revealed using first-principles calculations and 3D impact fracture morphology, respectively. The results suggested that the numerous homogeneous NiAl nanoparticles within the bcc-Fe matrix reduced the impact toughness of the HSLA steels. As the precipitate interparticle spacing (L) decreased, the impact toughness decreased until it attained a critical value (∼27 nm). This is interpreted effectively by the calculations indicating that the shear modulus (75 GPa) and fracture energy (4.5 J/m2) of the NiAl phase, particularly the NiAlMn phase (46 GPa, 4 J/m2), are significantly lower than those of bcc-Fe (83 GPa, 5 J/m2). This induces the fracture of nanoparticles under rapid impact loading, which functions as numerous crack initiations before plastic deformation of the matrix. The small L achieved after peak-hardening aging can result in the interconnection of these crack sources and cause instantaneous cleavage fractures, similar to brittle materials.

Effect of Manganese on the Strength-Toughness Relationship of Low-Carbon Copper and Nickel-Containing Hull Steel.

The influence of varying the manganese (Mn) contents of high-strength copper-containing hull steel on its microstructural evolution and mechanical properties was investigated. With increasing Mn content from 2 to 5%, the tensile strength of the steel increased by ~100 MPa, while the elongation of steel remained at ~23.5%, indicating good plasticity. However, the 2Mn sample had 128 J higher low-temperature (-84 °C) impact work than the 5Mn sample. The microstructures of different Mn steels were composed of fresh martensite (FM), ferrite/tempered martensite (F/TM), and reversed austenite (RA). The increase in Mn content markedly increased the presence of RA and intensified the work hardening caused by the transformation-induced plasticity (TRIP) effect during the tensile process. However, as the phase transformation in different Mn steels occurred in the early stage of strain and did not extend throughout the entire plastic deformation process, increasing plasticity via phase transformation was difficult. In addition, although the volume fraction of RA increased significantly in 4Mn and 5Mn steels, the stability of RA significantly decreased. The presence of numerous metastable blocks and coarse lath-like RA contributed little to low-temperature impact work and was even detrimental to toughness. The substantial fresh martensite resulting from phase transformation facilitated microcrack generation, owing to rapid volume expansion and mutual impacts, thus reducing the work required for crack formation. Additionally, the abundance of deformation twins significantly reduced the work needed for crack propagation. These combined actions significantly reduced the low-temperature toughness of 4Mn and 5Mn steels.

A theoretical model for the oblique impact of fragments

A portion of the casing charge's fragments would strike the target plate and ricochet when it exploded close to or inside a steel structure, like a ship or manufacturing facility. Considering the high pressure, high temperature, and high strain rate during the impact, the kinematic characteristics of the ricochet fragment, such as ricochet velocities and ricochet angle, are challenging to describe using the existing methods. In this study, a novel theoretical model of ricochet fragment kinematics under oblique impact was proposed, and the corresponding initial assumptions and application conditions were presented. A series of oblique impact experiments was conducted to obtain the differences in kinematic characteristics under various impact velocities and impact angles. The parameters of the proposed theoretical model were determined. The accuracy of the theoretical model was verified by using 921A hull steel target plate. The average relative error and standard deviation of ricochet velocity were 7.4 % and 2.3 %, respectively, and the mean relative error and standard deviation of the ricochet angle are 11.2 % and 1.1 %, respectively. The results showed that the theoretical model can predict the ricochet velocity well, and the error of ricochet angle increased due to the different pile-up effect of different strength target plates, but it was still within the reasonable range. In addition, the effects of the impact velocity and angle on the ricochet velocity and angle were analyzed. When the impact angle was small, the ricochet angle and velocity were affected by both impact velocity and angle. When the impact angle increased to a certain Angle (>64.2°), the ricochet velocity only increased linearly with the impact velocity. The ricochet angle increased with the increase in the impact angle. When the impact velocity was less than 400 m/s, the ricochet angle increased with the increase in the impact velocity. When the velocity is greater than 400 m/s, the ricochet angle decreased with the increase in the impact velocity. When the impact angle was greater than 57° and the impact velocity was greater than 400 m/s, the ricochet angle was almost only related to the impact angle. The results indicate that the proposed model has good accuracy and can have high application value in terminal effects, safety engineering, and structural defense fields.

Investigating the corrosion performance of hull steel with different microstructure in a tropical marine atmosphere

The corrosion behavior of ship steel with different microstructure in a simulated tropical marine atmosphere was systematically investigated. Results show that homogeneous martensite structure obtained by water-quenching process was much more resistant to corrosion than that of ferrite-pearlite. Furthermore, the precipitation of carbide resulting from tempering process promoted the formation of corrosive microcells within the matrix and further intensified the corrosion. Rapid cooling rate led to the enrichment of chromium, which formed protective corrosion products such as FeCr2O4 and Cr(OH)3. This also facilitated the conversion of α-FeOOH and significantly enhanced the corrosion resistance.

Effect of Al Content on the Long-Term Corrosion Behavior of Arc-Sprayed ZnAl Alloy Coatings

The corrosion of steel structures in aggressive marine environments is a vital issue that induces significant degradation of their performance and lifespan. Herein, three arc-sprayed ZnAl coatings with varied Al contents of 0 wt.%, 15 wt.%, and 50 wt.% were deposited onto a hull steel substrate. The effect of Al content on the long-term corrosion protection performance of ZnAl coatings left in a chloride-containing solution for 840 h was systematically investigated. The evolutions of open-circuit potential, polarization curves, and electrochemical impedance spectroscopy of different ZnAl coatings during the long-term immersion test were examined. The morphologies and phase constitutions of the corrosion products were characterized. The results indicated that the corrosion rate of ZnAl coatings decreased as the Al content increased, and the ZnAl50 coating exhibited the most superior long-term corrosion protection performance. Moreover, for the three ZnAl coatings with an Al contents varying from 0 to 50%, their corrosion rate increased with immersion time in the initial 360 h due to the formation of the unstable and porous corrosion product ZnO; after 360 h immersion, their corrosion rate decreased with the prolonging of immersion time. This was revealed to be related to the formation of different corrosion products. ZnO and stable Al2O3 were the main corrosion products for the pure Zn coating and ZnAl15 coating, respectively. Al2O3 and powerful layered double hydroxide Zn6Al2(OH)16CO3·4H2O were found to be the dominant corrosion products of the ZnAl50 coating, which was responsible for its remarkable long-term corrosion protection performance.

Experimental studies of the influence of biaxial bending on the crack resistance of reactor pressure vessel steel

Background: to assess the residual life of nuclear reactor hulls in Ukraine, normative temperature dependences of the crack resistance of hull steels obtained on standard samples with a deep through crack under plane strain conditions are used. However, it is known that the thickness of the wall of the reactor body is subject to biaxial loading, which affects the value of the crack resistance characteristics. Therefore, in order to substantiate the possibility of lengthening beyond the design resource of VVER-1000 reactor hulls, an experimental study of the effect of biaxial load on the crack resistance characteristics of hull reactor steel 15X2NMFAA is relevant. Objective: development of an experimental technique and investigation of crack resistance under biaxial loading on small-sized samples in the the brittle-ductile transition temperature range of reactor steels. Methods: on the basis of numerical and engineering calculations, a specimen was developed, the corresponding additional equipment for its tests under biaxial loading on a uniaxial servo-hydraulic machine. The influence of biaxial bending on the fracture toughness of reactor steel 15X2NMFAA was experimentally investigated. Results: the results obtained on cruciform specimen are calculated according to the ASTM 1921 standard and plotted on the Master curve (temperature dependence of fracture toughness). The analysis showed that the data on crack resistance obtained on samples with "short" (a/W=0.1...0.2) linear and surface semi-elliptical cracks exceed the upper limit of the confidence interval of the Master curve, and biaxial loading of cruciform specimen reduces crack resistance compared to uniaxial loading.

Effect of Plastic Deformation on the Structure and Magnetic Properties of Hull Steel

Effect of Plastic Deformation on the Structure and Magnetic Properties of Hull Steel

Multi-objective optimization of liquid hydrogen FPSO at the conceptual design stage

A conceptual design of a liquid hydrogen FPSO was developed in this research, and its hull dimensions were optimized under the environment at the Donghae gas field in South Korea. During the conceptual design stage, a process of production, storage, and offloading of liquid hydrogen was studied, and the topside and hull layouts for the liquid hydrogen FPSO were proposed. The capacities of each module were determined based on the operation scenario. The corresponding required areas and weight of each module were estimated from the literature review and the data from the ongoing project (KRISO, 2022). The optimized hull dimensions were presented by a Multi-Objective Evolutionary Algorithm (MOEA) with two objectives, minimization of the hull steel weight and the motion level considering the constraints related to geometry, stability, and hydrodynamic performances. The obtained Pareto set shows three classified solution types depending on the active constraints, which is able to propose a wide range of design alternatives for the liquid hydrogen FPSO with unique constraints compared to general ships.

Features of Behavior of Magnetic Properties during Elastic Deformation of 20GN Hull Steel in Various Initial Stress–Strain States

Features of Behavior of Magnetic Properties during Elastic Deformation of 20GN Hull Steel in Various Initial Stress–Strain States

Effects of Quenching and Tempering Heat Treatment Processing on the Microstructure and Properties of High-Strength Hull Steel

The construction of heavy polar icebreakers is usually done with special hull steels, which require comprehensive properties such as good low-temperature toughness, high strength, and superior fatigue resistance. Reasonable and satisfactory heat treatments should be investigated and applied to acquire the required high strength and superior low-temperature toughness, since this is deemed an effective approach to ameliorate the combined properties of high-strength hull steels. Regarding this, the present study specifically explores the effects of different laboratory-based quenching (850 to 930 °C) and tempering (580 to 660 °C) heat treatments on the final low-temperature toughness of the high-strength hull steels. The low-temperature toughness is eventually improved without significantly sacrificing the strength. The results show that a favourable combination of properties can be obtained in the specimens under 900 °C quenching and 660 °C tempering processes. Additionality, the specimens tempered at 620 °C present the highest hardness, owing to the higher percentage of tempered martensite. Detailed mechanisms of the enhanced properties of the typical specimens subjected to the corresponding quenching and tempering processing are analysed and explicated.

Corrosion behavior of WC–Co coating by plasma transferred arc on EH40 steel in low-temperature

Abstract To investigate the corrosion behavior of WC–Co composite coating, plasma transferred arc (PTA) welding was applied to prepare WC–Co coating on hull steel EH40 for achieving good metallurgical bonding. The phases of coatings were mainly composed of WC particles, solid solution γ-Co, Fe3Ni2, SiO2 and Mo2C. After electrochemical test, it can be concluded that Co-based coating with 45% WC content has better corrosion resistance in low temperature marine environment for obtaining denser oxide film. Through X-ray photo electron spectroscopy (XPS) analysis, the main corrosion products of immersion were Co(OH)2 and Co3O4. These corrosion products aggregate to form a stable corrosion product film, which plays some protective role for the coating. Hard particle WC is also partially oxidized to WO3. The pitting hole of 60% WC is the most serious. Pitting corrosion is easy to occur at the interface defects.

Effect of plastic deformation on the magnetic parameters and magnetostriction of the 20GN steel

The paper presents results of studying the effect of tensile deformation of the 20GN hull steel to various levels of plastic strain on the behavior of its magnetic characteristics, including linear magnetostriction. The deformation behavior of the magnetic characteristics indicates a change in the type of magnetic texture caused by large residual compressive stresses along the tensile axis. It is shown experimentally that the levels of plastic strain at which the behavior of the magnetic parameters changes are the same for all studied magnetic characteristics. The results can be used to develop methods of nondestructive testing of the strained state of structural components made of the 20GN steel, which suffer plastic deformation during operation.

The Lightship Mass Calculation Model Of A Merchant Ship By Empirical Methods

Estimating the lightship mass is an important factor in the early stage of ship design given its impact on shipbuilding costs. The mass of the hull and equipment, as well as its distribution, affects the hull strength, deadweight, and stability of the ship. Furthermore, a good estimate of the lightship mass in the preliminary phase is very important for defining the construction costs as accurately as possible. As the time available to the designer in the conceptual or preliminary phase of ship design is often limited, the methods used to determine the lightship mass must be reliable, fast, and effective. The paper presents and analyzes methods for estimating the lightship mass that are based on empirical data of built ships. Several empirical methods were combined and calibrated to establish the least-squares method which combination gives the value of the lightship mass closest to the one given in the collected database for three types of merchant ships: tankers, bulk carriers, and container ships. The paper presents the results of the calculations of the masses of hull steel, outfitting, machinery, and superstructure. It can be concluded that the presented model for all three types of merchant ships gives satisfactory results.

Insight into effect of alloy elements on corrosion extension of defective coating/AH32 steel system in short-term immersion

The service life of vessels is closely dependent on the corrosion resistance of coated hull steel systems due to the harsh marine environment. In this work, the three-dimensional corrosion extension law of a defective epoxy coating/AH32 steel system in the initial stage was investigated by using micro-Raman spectrum, electron probe microscopic analysis, and X-ray photoelectron spectroscopy. Q235 steel was utilized as a contrast sample. The chemical composition of the AH32 steel was 0.183C, 0.199Si, 1.33Mn, 0.0896Cr, 0.007Mo, 0.0078Al, 0.005Cu, 0.0428P, 0.0258S, and Fe and that of Q235 steel was 0.0692C, 0.0981Si, 0.163Mn, 0.0219Cr, 0.001Mo, 0.0176Al, 0.008Cu, 0.0318P, 0.0318S, and Fe. Results showed that when the electrolyte solution reached the coating/metal interface through the defect, the corrosion of the AH32 steel substrate preferentially developed in the lateral direction. By contrast, the corrosion extension of the Q235 steel showed increased severity in the depth direction. This difference could be attributed to the protectiveness of the corrosion products that had formed at the defect. The oxidation of the Mn element in AH32 accelerated the formation of the protective rust layer of α-FeOOH, which retarded the further vertical penetration of the electrolyte solution into the steel. Therefore, corrosion initially occurred at the under-film area near the defect.

Study of corrosion behaviour of Al2O3-13 % TiO2 and Cr2O3 coated ship hull steel in 3.5% NaCl solution

Corrosion degradation of ship hull plates is an important aspect responsible for failure of ships in marine environment. Surface coatings are being used to protect the metallic materials from corrosion. In this work, Al2O3-13 % TiO2 coating and Cr2O3 coating were deposited on ship hull building material using D-gun flame spray method. The corrosion behaviour of coatings and substrate was investigated using cyclic polarization test. The microstructure and phase composition of coatings were analysed by scanning electron microscopy (SEM) and electron dispersive spectrum (EDS). The corrosion rate was evaluated from the corrosion parameters extracted from graphs. The uncoated and coated substrates were compared on the basis of corrosion parameters.

Immersion studies of Al2O3 – 13% TiO2 and Cr2O3 coatings on ship hull plate in simulated seawater environment in laboratory

In the present work the corrosion behaviour of Al2O3 – 13% TiO2 and Cr2O3 coatings in an artificial seawater environment is investigated by immersion test and weight measurement methods. The coatings are deposited on ship hull steel by D-Gun flame spray method. The microstructure and phase composition of coatings are studied by scanning electron microscopy (SEM) and electron dispersive spectrum (EDS). The corrosion resistance of coatings is compared on the basis of weight measurement and visualization technique. The change in microstructure and elemental phase composition is also observed by the corroded micrographs.

Effect of Flow Rates on erosion corrosion behavior of hull steel in real seawater

Effect of Flow Rates on erosion corrosion behavior of hull steel in real seawater

Multi-objective parametric optimization of FPSO hull dimensions

In order to achieve a good and competitive FPSO design, the building cost and the motion performances are the two most critical and conflicting KPIs to be considered. In this study, the author's previous work (Lee, et al., 2021) on the optimization of an FPSO's hull dimensions with 1800 MBBLs storage capacity at Brazil field was extended using a multi-objective parametric optimization with the hull steel weight and the operability which are closely related to the building cost and the operational cost during the lifetime, respectively. For the purpose of more realistic and practical FPSO design, the constraints related to crew comfort and the safe helicopter take-off and landing operation were newly added. Also, the green water on deck was calculated accurately to check the suitability of the designed freeboard height using a newly developed real-time calculation module for the relative wave elevations. With aids of this updated optimization formulation, we presented multiple optimal FPSO dimensions expressed as a Pareto set which aids FPSO designers to conveniently select the practical and competitive dimensions. The excellence of the developed approach was verified by comparing the optimization results with those of FPSOs dimensioned for operation at West Africa and Brazil field.