Marine Steel Structures Research Articles

Thermal analysis of marine structural steel EH36 subject to non-spreading cryogenic spills. Part II: finite element analysis

ABSTRACT In Part I of this paper, six liquid nitrogen (LN2) pool boiling tests were carried out to locally cool down six different EH36 steel plates to cryogenic temperatures. Leindenfrost and Critical Heat Flux (CHF) points of LN2 boiling curve were estimated. These estimations together with the recorded temperature histories are used in this part for the development of a heat flux curve for EH36 steel-LN2 pool boiling through Finite Element Thermal Analysis (FETA) of the problem investigated experimentally in Part I. Thermal conductivity and heat capacity of EH36 are defined by two unprecedented temperature functions based upon experimental studies in cryogenic temperatures. A user subroutine written in FORTRAN defines the air convection coefficient as a function of surface-air temperature difference, which changes with time and location. Results of this study contribute to the Accidental Limit State (ALS) design of marine and offshore structures for liquified gas spill scenarios.

Thermal analysis of marine structural steel EH36 subject to non-spreading cryogenic spills. Part I: experimental study

ABSTRACT Liquefied Natural Gas (LNG) spills may cause steel to embrittle, leading to the brittle fracture of marine structures due to the cryogenic temperatures. For the integrity assessment of marine steel structures in the event of an LNG spill, first and foremost, an accurate heat transfer analysis is required. This study presents an experimental set-up that allows for thermal-structural analysis of steel structures subject to non-spreading cryogenic spills. A local, non-spreading cryogenic spill was replicated by building a liquid nitrogen (LN2) pool at the central zone of an EH36 steel plate under tensile loading. Six pool boiling tests were conducted on six different specimens. Temperature histories recorded by nine thermocouples are presented and discussed as well as the effect of surface roughness on cooling rates and boiling regimes. Numerical simulations of the experiments, discussed in Part II of this study, resulted in a heat flux curve for EH36 steel-LN2 pool boiling.

Uniaxial behaviour and corrosion-welding-based constitutive model of marine structural steel

To address the coupled damage from corrosion and welding on the performance of marine structures in a rationally macroscopic way, an experimental attempt is conducted and to propose a generalized corrosion-welding-based material model for various corrosion and welding scenarios. The tested D36 steel specimens have welding seams with three angles and six corrosion degrees generated by the accelerated electrochemical corrosion method. The uniaxial behaviour of the specimens is studied from the aspects of failure process, stress vs. strain curves and strain distributions. All the performance parameters, as well as elastic segment, yield plateau and nonlinear strain hardening segment, can be affected by both corrosion degree and welding angle. Welding can cause increased yield strength and ultimate strength, but at the cost of yield plateau and toughness. Both welding and corrosion can affect the strain development in two directions. The proposed corrosion-welding-based model that consists of a linear segment and a nonlinear strain-hardening segment with the calibrated parameters by the test data can desirably describe the coupled damage. It is believed to be able to extend the fiber model for the structure-level performance assessment of corroded-welded steel jacket offshore platforms.

A dimensional metrology-based approach for corrosion measurement of ship grade steels exposed to various marine environmental conditions

ABSTRACT Corrosion-induced degradation in marine steel structures is highly dependent on the surrounding environmental conditions and sea water compositions that varies significantly around global sea water bodies. This research investigates the corrosion behaviour of ship-grade steels exposed under different sea water compositions and environmental conditions typical of the Arabian Sea. More, environmental conditions spanning those anticipated for the shipping structures operating in the highly saline and warmest regions in the Arabian Sea have been simulated in laboratory-based experiments by using heated and aerated artificial sea water. Following their exposures, the corrosion performance of coupons has been investigated using the standard weight loss and a new dimensional metrology-based approach. Besides, the corrosion products formed on the steel surfaces have been characterised using various analytical techniques. Considerably higher corrosion losses and maximum corrosion depths were observed in the nutrient-rich polluted sea waters than those recorded in the natural sea waters, as well as in the simulated artificial sea water conditions.

Corrosion fatigue crack growth mechanisms in welded joints of marine steel structures

This paper presents a model of fatigue crack growth in a welded joint and a two-dimensional model of anodic dissolution based on Donahue model and anodic dissolution mechanism, respectively. In addition, a model for predicting the corrosion fatigue crack growth rate in welded joints of steel marine structures is established and crack growth mechanisms are analyzed. The results show that during early stages of crack growth, corrosion fatigue crack growth rate in welded joints is mainly controlled by corrosion action, whereas cyclic loading becomes more influential during the later stage of crack propagation. Loading frequency and effective stress ratio can affect rupture period of protective film at the corrosion fatigue crack tip and the length of corrosion crack increment, respectively, which changes the influence of corrosion action on crack growth rate. However, the impact of stress amplitude on crack growth rate is only significant when crack propagation is caused by cyclic loading. Welding residual stress not only improves the effective stress ratio of cyclic loading, but also promotes crack closure and increases corrosion fatigue crack growth rate in welded joints. Compared to corrosion action, welding residual stress has a more significant influence on crack growth caused by cyclic loading.

Generalized hysteretic constitutive model of marine structural steel with pitting corrosion

To describe the effect of the coupled damage caused by corrosion and low-fatigue hysteresis on the mechanical performance of marine steel, a generalized hysteretic constitutive model is developed based on the results of a reversed cyclic test that was conducted previously on the commonly used D36 steel considering different corrosion scenarios and loading schemes. Three typical hardening models, namely the NLISO isotropic model, Chaboche kinematic model, and combined hardening model in ABAQUS® are first studied using the parameters calibrated with the test data. The combined model is found to be capable of performing desirable simulations for all pitting corrosion cases. However, it is difficult to explicitly clarify the relation between its parameters and the volume loss ratio (VLR), which is not applicable for general purposes. The developed hysteretic model consists of a cyclic hardening skeleton segment, an unloading segment, and a reloading segment. A direct link is established between its parameters and VLR via regressive analysis. This generalized model can comprehensively account for, with desirable prediction accuracy, the influence of pitting-induced volume loss, stress concentration, and eccentricity on the hysteretic behaviour of marine steel. It can be applied to engineering practice with rational conservation.

Investigation of strain localization on marine structural steels: Uniaxial tests

Results of a series of uniaxial tests to investigate fracture initiation states of AH32 steel, a ship structural steel, are presented. Strains at fracture are obtained using digital image correlation analysis via DaVis LaVision software, and the corresponding states of stress are obtained via a plastic flow rule and a hardening relationship using the measured strains. The strain fields are calculated to the point of fracture initiation where the fracture initiation is defined as the condition when the first visible crack appears in the digital image of the test specimen. The software provides displacement and strain fields of the entire region and any specified sub-region of the imaged surface, which uses a so-called ‘geometric mask’. The strain values are mask-size dependent due to the local nature of deformation before fracture. Therefore, in the current study, strain fields are obtained for various mask sizes to investigate the effect of mask size on failure strain, i.e., strain localization phenomena, with the minimum mask size chosen at roughly the limit of the continuum scale (O (100 μm)). The evolution of the stress and strain fields as a function of loading is provided for different mask sizes. Moreover, comparison of the failure strain as mask sizes are decreased provides information on strain convergence. In this investigation, non-convergence behaviors are obtained for all experiments, as failure strain increased as the mask sizes are decreased.

Weld morphology and mechanical performance of marine structural steel welded underwater in a real marine environment

Grade AH36 ship steel plate, frequently used in offshore applications, was joined underwater by shielded metal arc welding (SMAW) using two different types of electrodes (E6013 and E7014). The ship steel plate was also joined under atmospheric conditions in order to compare both joints in terms of mechanical and metallurgical properties. The E6013 rutile electrode was isolated by wrapping before use, and the underwater welding process was carried out at a depth of 8 m under the sea. The joints were first subjected to visual inspection and then liquid penetrant, ultrasonic, and radiographic tests were performed. In order to determine the mechanical properties of the joints, tensile, bending, and impact toughness tests were also carried out. In addition to the microhardness test on the weld zones, microstructural examination was also performed on the joints. As a result of the nondestructive tests, weld defects like slag remaining between the passes, gas porosities, burn-through, and lack of penetration were seen on the joints welded underwater with the two different electrodes. The study determined that these defects had significantly influenced the mechanical properties and width of the weld zone of the joints.

Comparative study on ductile fracture prediction of high-tensile strength marine structural steels

ABSTRACT Accidental events such as collision, grounding, and explosion in marine structures can cause plastic deformation and structural damage. Various fracture models based on different mechanical concepts have been proposed to predict damage extents involving ductile fracture. In this paper, some fracture models were evaluated: Maximum shear stress, Cockcroft-Latham, Johnson-Cook, Modified Mohr-Coulomb, Lou-Huh, and Hosford-Coulomb models. The model parameters were identified for two shipbuilding steel grades: AH36 and DH36. A hybrid experimental-numerical approach was adopted. The parameters of six fracture models were identified using an optimisation algorithm based on the extracted loading paths from the numerical simulations and adopting a linear damage accumulation law. The calibrated fracture models are presented in stress triaxiality and Lode angle parameter space as a 3D fracture locus, and under plain stress condition as a function of the stress triaxiality as a 2D fracture locus. The predictive capabilities and flexibility of the evaluated fracture models were discussed.

Fatigue assessment of a marine structural steel and comparison with Thermographic Method and Static Thermographic Method

AbstractFatigue properties are of fundamental importance and extremely time consuming to be assessed. The aim of this research activity is to apply the Thermographic Method (TM) and the Static Thermographic Method (STM) during fatigue and tensile tests to correlate the temperature trend to the fatigue properties of an S355 steel. The material was retrieved from an in‐service port crane. Traditional fatigue tests were performed in order to evaluate the S‐N curve with a scatter band. Step load tests were carried out deriving the fatigue limit and the Energy Parameter of the material. Static tensile tests were performed to obtain the stress at which the temperature trend deviates from the thermoelastic behavior. The fatigue properties obtained by means of the energetic methods were compared to the traditional ones showing a good agreement.

Fresh and sea water immersion corrosion testing on marine structural steel at low temperature

ABSTRACT The aim of the present study is to experimentally examine the corrosion progress characteristics of steel associated with fresh and sea water immersion at low temperature. Three types of steel, namely mild steel (Grade A) and high tensile steel (Grades A and D) are tested under various corrosive conditions in the fresh water, in the sea water and in the air at a temperature of 18°C, 0°C and −10°C. Mass loss of test specimen due to corrosion is measured at a monthly interval and it is converted to a loss of steel plate thickness. Based on the test database, the effects of parameters affecting the corrosion progress are discussed. Test database obtained in the present study is documented.

HC-DSSE 조합 파단 변형률 정식화에 기반한 선박해양 구조물용 강재의 연성 파단 예측

HC-DSSE 조합 파단 변형률 정식화에 기반한 선박해양 구조물용 강재의 연성 파단 예측

A New Method for Analyzing the Dimension Error of Marine Steel Structures

With the strengthening of offshore oil exploitation, the construction of marine steel structures such as offshore oil platforms has been carried out on a large scale. During the construction process, the dimensional control and error analysis of marine steel structures is an important point. The dimensional error of marine steel structure is an important indicator reflecting the quality of marine steel structure construction. The marine steel structure is completed from structural design to offshore installation. The structural dimensional error must be strictly controlled and analyzed at each stage. It has important guiding significance for the design and construction of marine steel structure, ensuring final installation and safe production. Based on the summary of traditional size control and analysis methods, this paper introduces a new method of size control and analysis. The new method introduced in this paper uses the minimum two-passenger fitting technique, that is, the sum of all the deviation values is the smallest, so that the measured data can best match the design data, and the size error of the marine steel structure is represented by the magnitude and direction of the three-dimensional deviation. The three-dimensional deviation of each node is reflected objectively and actually, intuitive and reasonable, and the calculation program is written by AUTOCAD VBA, and the deviation value is quickly calculated, which has a good effect on on-site construction adjustment and error analysis.

Experimental study on constitutive relation of the high performance marine structural steel under extreme cyclic loads

Jacket offshore platform serving in the marine environment is often subjected to severe dynamic loads such as winds, waves, currents and earthquakes. The alternating stress state of jacket offshore platform will lead to the degradation of mechanical properties of the structural steel, which results in the decline of the overall bearing capacity. In this paper, eighteen types of cyclic loading program designed according to the characteristics of the steel and extreme cyclic loads are presented for the first time. The hysteresis behavior of structural steel NV-D36 under various cyclic loading program is studied. The changing process of energy dissipation capacity of the steel under different loading program is compared. The hysteresis skeleton curve of steel under variable amplitude cyclic loading is fitted based on the basis of the classical Ramberg-Osgood model. The parameters of combined hardening of the steel based on Chaboche constitutive model are calibrated. The results of the cyclic loading are numerically simulated with the obtained hysteresis skeleton curves and parameters. The combined hardening criterion can be used to analyze the responses of the steel under cyclic loading, and the parameters can be applied to study the dynamic properties of the jacket offshore platform of structural steel NV-D36.

On the failure behaviour to striking bow penetration of impacted marine-steel structures

Abstract Demands for water transportation modes are continuously increasing as rapid economic and industrial growths in the recent decade. Ship as representative of the water transportation is generally needed to carry various products from one location to another. Besides as product carrier, ship also acts as public facility to transport human across islands for number of reasons, such as tourism and vehicle. Considering its importance, structural damage due to accidental loads or so-called impact can cause unacceptable casualties which threat ship passenger, shipping industry and maritime environment in same time. The most frequent impact phenomena occur in forms of collision and grounding, which are targeting side structure and double bottom consecutively. However, since responses of the impacts on structure are highly nonlinear and vary due to development of ship structures, sustainable analysis as an update of pioneer calculation can be beneficial as rational reference for improving safety and navigational instruments. This work aims to assess failures of the side structures subjected to penetration of striking bow in ship-ship collision scenario. Locations of impact are idealized to happen on after-end, midsection and fore-end to provide complete assessment. Striking bow is to be deployed by varying input velocity to observe significance of the fractures on the side structure. This configuration is implemented on the designed collision scenario, and later calculated using nonlinear finite element method (NLFEM). Summary of the solution indicated that the midsection produced the highest resistance against side collision. Breaching of the inner shell was successfully avoided on the fore-end, but the critical damage to the cargo was observed during bow penetration to the after-end region. This location was recommended to be added by longitudinal framing to increase its resistance against ship collision.

Computation of Corrosion Rates of Steel with Variation of Cl-, SO4 2-, CO3 2-, HCO3 -, O2, CO2, pH and Temperature, Developed by Modeling with Artificial Neural Network

Background: Corrosion of carbon steel in ocean water is dependent on several parameters, such as, chemistry of seawater, temperature, and pH. Its chemistry is also not fixed but varies from one geographical location to another as well as along the depth from surface to sea bed. The fact causes unpredictable corrosion failures of marine steel structure that leads to economic losses, oil spilling, environment pollution and accidents. This is because; corrosion mechanisms are complex with high degrees of interaction among the corrosion species, products and metallurgies. Methods: For better understanding of the mechanisms of the effects of co existences of these parameters and prediction of the unpredictable life of the structures, ANN model was developed using 170 sets of experimental data, varying the corrosion influencing parameters SO4 2-, Cl-, HCO3 -,CO3 2-, CO2, O2, pH and temperature as input and the corrosion current as output. About 60% of experimental data were used to train the model, 20% for testing and 20% for validation. The model was developed by programming in Matlab. Results: 80% of the validated data could predict the corrosion rate correctly. Corrosion rates predicted by the ANN model are displayed in 3D graphics which show many interesting phenomenon of the conjoint effects of multiple variables that might throw new ideas of mitigation of corrosion by simply modifying the chemistry of the constituents. The model could predict the corrosion rates of some real systems. Conclusion: It can be summarized that corrosion of carbon steel in aqueous marine environment is strongly influenced by various anions present in sea water, pH and temperature. The conjoint effect of two or more parameters jointly shows interesting phenomenon that even with high Cl- content the corrosion rates can be lower in the presence of high concentration of carbonate and sulfate. Keywords: Modeling Corrosion; Neural Network; Seawater chemistry; Carbon steel, Prediction Corrosion rate, Matlab programming.

Corrosion Crack Nucleation Mechanism in the Welded Structures of X65 Steel in Natural Seawater

The nucleation mechanism of corrosion cracks in welded structures in natural seawater has been revealed through investigation on the corrosion behavior of X65‐welded structures in natural seawater. The evolution laws of surface corrosion morphology, residual stress, and areas of welded structures with the most serious corrosion damage were analyzed by microstructure observation, corrosion morphology observation, residual stress detection, and magnetic field detection. The results show that the main factors of determining surface corrosion morphology evolution law of welded structures are microstructures of the weld joint, heat‐affected zone (HAZ), and the fusion line. Due to the difference of corrosion rates between the weld joint, HAZ, and the coarse Widmänstatten structure in fusion line, the fusion line of welded structures receives the most serious damage while being corroded. Meanwhile, mutual reinforcement of residual stress and corrosion damage on the surface of welded structures further accelerate the nucleation of corrosion cracks. Under the influences of microstructure, residual stress, and corrosion, corrosion cracks that are parallel to weld joints generate first in the fusion line of welded structures. Therefore, it makes welded structures the source of marine steel structures’ corrosion failure.

Controlling the failure of marine structures attached to the bottom of the sea under dynamic loading

PurposeAnalysis of designing and controlling the failure of marine structures attached to the bottom of the sea under dynamic load obtained from the sea waves is one of the main engineering challenges in recent years. The circumstances of the onshore marine structures have their own complexity and the difficulty due to the effect of hydrodynamic factors and dynamic responses which are dominant in the marine environment. The paper aims to discuss these issues.Design/methodology/approachThe structure elements are composed of the metal pipe with a length of 5 m, outside diameter of 20 cm and thickness of 1.5 mm. the failure control with a safety factor of 2 indicates the absence of the above marine structure failure. It has been diagnosed to be trustworthy and reliable.FindingsIn this study, the control of marine steel structure failure with the height of 60 m under the dynamic load of the sea water waves having sinusoidal shape in the Caspian Sea has been studied and analyzed.Originality/valueIn this paper, the minimum and maximum internal force and movement in six directions of freedom were obtained for each element. To analyze and control the failure, the combination of stresses caused by static and dynamic loads has been used. According to the regulation of 10-360-AISC, the control was conducted.

Ductile Fracture Predictions of High Strength Steel (EH36) using Linear and Non-Linear Damage Evolution Models

A study of the damage evolution laws for ductile materials was carried out to predict the ductile fracture behavior of a marine structural steel (EH36). We conducted proportional and non-proportional stress tests in the experiments. The existing 3-D fracture strain surface was newly calibrated using two fracture parameters: the average stress triaxiality and average normalized load angle taken from the proportional tests. Linear and non-linear damage evolution models were taken into account in this study. A damage exponent of 3.0 for the non-linear damage model was determined based on a simple optimization technique, for which proportional and non-proportional stress tests were simultaneously used. We verified the validity of the three fracture models: the newly calibrated fracture strain model, linear damage evolution model, and non-linear damage evolution model for the tensile tests of the asymmetric notch specimens. Because the stress evolution pattern for the verification tests remained at mode I in terms of the linear elastic fracture mechanics, the three models did not show significant differences in their fracture initiation predictions.

A fuzzy system for evaluation of deteriorated marine steel structures

A fuzzy system for evaluation of deteriorated marine steel structures