Cargo Oil Tank Research Articles

A new insight on the corrosion behavior and mechanism of martensitic steel

The corrosion performance of martensitic steel remains a matter of dispute, with no consensus on whether it exhibits heightened or diminished corrosion resistance. In this study, the corrosion behavior and mechanism of martensitic steel were systematically investigated by simulating a cargo oil tank environment. The results indicate that under strong acidic conditions, the corrosion rate of martensite (1.1404 mm/y) is significantly higher than that of ferrite-pearlite (0.7430 mm/y) due to its increased dislocation density and internal stress. Additionally, the presence of high-energy defects provides abundant active sites for the redeposition of Cu-bearing particles, while their uneven distribution further exacerbates corrosion. Therefore, we propose a competitive mechanism that governs the corrosion behavior of martensite, complementing the understanding of its behavior and mechanism.

Risk Analysis of Occupational Health and Safety Using Hazard Identification, Risk Assessment and Risk Control (HIRARC) Method (Case Study in PT Barokah Galangan Perkasa)

PT Barokah Galangan Perkasa is a company located in East Kalimantan that is engaged in the manufacturing, repair, and maintenance of ships. The welding activity is the most dominant in shipbuilding, but the implementation of the occupational health and safety (OHS) system is not optimal. There have been several work accidents in the upper accommodation and cargo oil tank areas, such as falling from a height, being hit by welding sparks, and an electrical short circuit. The working conditions in this area are quite risky. Therefore, research on risk analysis is needed. HIRARC is a method for identifying a problem that is assessed at risk based on the likelihood and severity where the results of the assessment can determine the level of risk and give risk control for each work activity. Research results show that there were 40 potential hazards in the upper accommodation area with 77% low risk level, 12% moderate risk level, 8% high risk level, and 3% very high risk level. While in the cargo oil tank area there was 37 potentials hazard with 84% low risk level, 13% moderate risk level, and 3% high risk level. By knowing the risk level, companies can identify work activities that require prioritized improvement. They can also determine appropriate control to prevent the occurrence of such risks. Risk control in the upper accommodation area can be achieved through the implementation of administrative controls, utilization of PPE, and technical engineering controls.

Comparative study on corrosion behaviors of ferrite-pearlite steel with dual-phase steel in the simulated bottom plate environment of cargo oil tanks

The corrosion behaviors of ferrite-pearlite steels before and after intermediate quenching treatment were compared in the simulated bottom plate environment of cargo oil tanks. The results indicate that all tested steels exhibited an enhanced galvanic corrosion caused by the accumulated Fe3C. However, the corrosion resistance of steels could be improved by the change in microstructure from ferrite-pearlite to ferrite-martensite through intermediate quenching treatment, whereas a higher temperature caused an adverse effect. This was mainly due to both the Fe3C morphology and the content of cathodic phase in the steel matrix controlling the area ratio of cathode to anode during the corrosion process. Moreover, the proportion of high-angle grain boundaries and the potential difference in the galvanic couple had a limited effect on the galvanic corrosion.

Effect of cementite spheroidization on improving corrosion resistance of pearlitic steel under simulated bottom plate environment of cargo oil tank

The influence of cementite spheroidization on the corrosion resistance of a pearlitic steel used as cargo oil tank under the simulated bottom plate environment was investigated by employing microstructural characterizations, electrochemical measurements and gravimetric tests. The results indicate that for the as-forged pearlitic steel with the gradual accumulation of lamellar cementite on the surfaces, the galvanic effect between the anodic ferrite and the cathodic cementite is enhanced during corrosion evolution. This leads to intense corrosion acceleration. However, after cementite spheroidization, the discrete spherical cementite is easy to separate from the matrix when the surrounding ferrite matrix is dissolved. The area ratio of cathodic to anodic keeps at a stable value, and both the anodic dissolution of iron and cathodic HER are retarded by cementite spheroidization. As a result, the galvanic acceleration effect is restrained and the corrosion resistance of the pearlitic steel is improved significantly.

Influence of Sn and Mo on corrosion behavior of ferrite-pearlite steel in the simulated bottom plate environment of cargo oil tank

This work investigated the influence of Sn and Mo on corrosion behavior of ferrite-pearlite steel in the simulated bottom plate environment of cargo oil tank. The results indicate that the corrosion rate of three ferrite-pearlite steels increased with extending the immersion time due to the continuous accumulation of the residual Fe3C. However, the addition of Sn or the combined addition of Sn and Mo could reduce the corrosion rate of Sn containing steel and Sn-Mo containing steel to 37.5% and 20% of that of carbon steel, respectively. Moreover, the cathodic reaction of Sn containing steel and Sn-Mo containing steel was always controlled by the charge transfer step during the whole immersion test, while that of carbon steel was gradually transformed into the diffusion-controlled process. These results were mainly related with the deposition of metallic Sn and Mo on the steel surface. The metallic Sn and Mo with uniform distribution restrained the galvanic effect through suppressing both the anodic dissolution of ferrite and cathodic hydrogen evolution reaction on the residual Fe3C.

Corrosion behavior of low alloy steel for cargo oil tank under upper deck conditions

A simulated corrosion test apparatus was used to investigate the corrosion behavior of a low alloy steel under simulated upper deck conditions in a cargo oil tank. The estimated corrosion loss of conventional E36 class ship plate steel is 4.27 mm, which is clearly inadequate compared with the standard adopted by International Maritime Organization. Outer rust layer of specimens starts to peel off after 77 days and becomes fragmented after 98 days. X-ray diffraction, scanning electron microscopy, and Raman spectroscopy revealed that the resulting rust is composed of σ-FeOOH (the main protective phase), Fe2O3, FeS, elemental S, and FeSO4. FeSO4 in the interface of the base and rust layer leads to localized corrosion. Elemental sulfur forms on the surface of σ-FeOOH, and the quantity and size thereof increase with increasing corrosion time. Furthermore, layered elemental sulfur promotes fracture and peels off the rust layer.

Effect of Cu on corrosion behavior of low alloy steel under the simulated bottom plate environment of cargo oil tank

The effect of Cu on the corrosion behavior of low alloy steel under the simulated bottom plate environment of cargo oil tank was investigated by using gravimetric test, SEM, EDS, XPS, XRD and electrochemical measurements. The results indicate that the corrosion resistance of 16MnCu steel was higher than that of 16Mn steel, which was related to the deposition of nano-sized Cu particles on the surface. The deposited Cu might suppress both the anodic dissolution of the ferrite and hydrogen evolution reaction on the cementite, leading to the reduction of the galvanic effect caused by the residual cementite.

In-Service Hull Inspections for Avoiding Dry Docking Safely

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 26750, “In-Service Hull Inspections for Avoiding Dry Docking Safely,” by D. Constantinis and P. Davies, EM&I Group, prepared for the 2016 Offshore Technology Conference Asia, Kuala Lumpur, 22–25 March. The paper has not been peer reviewed. Copyright 2016 Offshore Technology Conference. Reproduced by permission. Current methods for external inspection of floating assets on station use divers or remotely operated vehicles (ROVs), but these methods incur high safety, people-on-board (POB), and cost penalties. The data produced by these methods are restricted by marine growth and limited access to isolation valves. The Hull Inspection Techniques and Strategy (HITS) joint-industry project (JIP) called for new methods to be developed that minimize or eliminate diving. This has been achieved by carrying out many of the inspections from inside the hull. Introduction The exploration and production of deep-water hydrocarbon reserves requires evermore-complex and high-capital-value floating assets. There are a number of key drivers required to optimize profitable operations, including managing the integrity of the topside and hull while reducing cost and POB and complying with client, corporate, and regulatory requirements. Floating production units can be designed for 25 years or more on station, and the new-generation ultradeepwater (UDW) drilling units also need to plan their integrity-management strategies without dry docking for extended periods (Fig. 1). These requirements have driven the development of innovative methods for inspecting, testing, and maintaining pressure systems as well as hull structures, the latter sometimes not getting the integrity attention it deserves. The HITS JIP was formed to address these issues, with membership from regulators, oil majors, class societies, lease operators, service companies, and educational bodies representing all sectors of the industry. The HITS JIP drew opinion from the industry and concluded that there are principally four challenges that should be addressed: Minimizing diving operations for hull in-water inspections Minimizing man entry for inspection of confined spaces Developing a capability to inspect cargo oil tanks with minimal cleaning requirements Developing competency standards for hull inspectors The HITS JIP does not carry out any developments itself but encourages industry to develop or adapt technology to improve hull-inspection techniques and evaluates the results. An industrywide survey concluded that the first priority should be given to minimizing diving operations for hull inspection, and, accordingly, three of the HITS member organizations cooperated in the development of an alternative method. This paper describes the new methodology; details how it has been applied to floating production, storage, and offloading vessels (FPSOs) and UDW drillships; and presents the lessons learned through site implementation.

Corrosion Behavior of Welded Joints for Cargo Oil Tanks of Crude Oil Carrier

E32 grade corrosion resistant steel was welded with welding wires with three different S contents. The microstructure, mechanical properties, inclusions, and corrosion behavior of welded joint were investigated. The joint coupon corrosion test and potentiodynamic polarization test were carried out under the simulated corrosion environment of the inner bottom plates of cargo oil tanks. The pitting initiation and propagation mechanism of the weld metal were studied by scanning electron microscopy and infinite focus. The results indicated that the microstructures of three kinds of weld metals are all composed of acicular ferrite, ferrite side-plate and proeutectoid ferrite. The microstructure of heat-affected zone is composed predominantly of bainite. Joint welded with low S filler wire has good mechanical properties. S can decrease free corrosion potential and increase the corrosion tendency. The pitting initiation is oxide inclusion or sulfide-oxide inclusion complex. S can induce the formation of occluded area and promote the corrosion propagation. The chemical compositions of weld metal is similar to base metal, which can limit the galvanic corrosion between weld metal and base metal, and avoid formation of corrosion step.

Sustained effect of remaining cementite on the corrosion behavior of ferrite-pearlite steel under the simulated bottom plate environment of cargo oil tank

This investigation aims to study the sustained effect of remaining cementite on the corrosion of ferrite-pearlite steel in an acidic chloride solution (i.e. simulated bottom plate environment of cargo oil tank). The results show that the corrosion rate of ferrite-pearlite steel was continuously accelerated with extending the immersion time, caused by the continuously enhanced galvanic effect between the remaining lamellar cementite and exposed ferrite phases. Electrochemical impedance spectroscopy (EIS) data further indicated that the promoted dissolution of ferrite phases was controlled by charge transfer process. Meanwhile, the hydrogen evolution reaction occurred on cementite was controlled by the diffusion process.

Effect of rolling process on comprehensive properties of corrosion resistant steel for bottom plate of cargo oil tanks

A new kind of corrosion resistant steel for cargo oil tanks (COT) was developed. The influences of final rolling temperature, cooling rate, and final cooling temperature on microstructure were investigated. The proper rolling process parameters were obtained through multi-pass thermal simulation test. The final rolling temperature is about 820 °C, the final cooling temperature is about 600 °C, and the cooling rate should be controlled between 10 °C/s and 20 °C/s. Based on the above analysis of the results, three groups of rolling samples by thermo mechanical control process are prepared. The tensile strength, yield strength, and toughness of the corrosion resistant steel are measured, which meet the requirements of DH36 steel, it can instruct the actual rolling production. The corrosion behaviour is also researched by weight loss and electrochemical impedance spectroscopic method, and it is found that the steel has good corrosion resistance performance, the best one is No.3 steel, the corrosion rate of which is about 1/4 of the accepted criterion.

Research on the optimization approach for cargo oil tank design based on the improved particle swarm optimization algorithm

Based on the improved particle swarm optimization (PSO) algorithm, an optimization approach for the cargo oil tank design (COTD) is presented in this paper. The purpose is to design an optimal overall dimension of the cargo oil tank (COT) under various kinds of constraints in the preliminary design stage. A non-linear programming model is built to simulate the optimization design, in which the requirements and rules for COTD are used as the constraints. Considering the distance between the inner shell and hull, a fuzzy constraint is used to express the feasibility degree of the double-hull configuration. In terms of the characteristic of COTD, the PSO algorithm is improved to solve this problem. A bivariate extremum strategy is presented to deal with the fuzzy constraint, by which the maximum and minimum cargo capacities are obtained simultaneously. Finally, the simulation demonstrates the feasibility and effectiveness of the proposed approach.

Research on Quick Decision Technology of Liquid Cargo Supply’s Program

The liquid cargo replenishment decision based on ship’s stability, strength and the floating state is a multiobjective optimization problem. The mathematical model of multi-objective is built in this paper. Aiming to obtain the feasible solution, the adaptive step ergodic of permutation and combination is applied in terms of the cargo oil tank and the water ballast tank. particle swarm optimization (PSO) algorithm is applied into the project. On the basis of constraint conditions, the multi-objective optimization function is proved and take it into real operating mode for calculation and analysis. Improved objective function that is built based on multi-objective mathematical model. Taking real calculation example to verify the effectiveness of improved function and PSO algorithm. The result is good and the time complexity and mathematical precision are both improved effectively.

Effects of Sn and Sb on the corrosion resistance of AH 32 steel in a cargo oil tank environment

Effects of the alloying elements, Sn and Sb, on the corrosion resistance of modified AH 32 steel for the cargo oil tanks (COT) were examined using an electrochemical test and weight loss measurement. All experiments were carried out in acidic chloride solution (0.14 M HCl and 10 wt% NaCl, pH 0.85) at 30 °C, simulating the inner bottom plate of COT. It was clearly found that the small amount addition of Sn and Sb improved the corrosion resistance of modified AH 32 steel, which is confirmed by the higher polarization resistance of AH 32 steel modified with Sn and Sb addition compared with that of the base steel. X-ray photoelectron spectroscopy analysis of the corroded surface after immersion of 72 h presented that the AH 32 steel modified with Sn and Sb addition created the protective corrosion products including SnO2 and Sb2O5. These oxides act as high corrosion inhibitor to anodic corrosion reaction, and hence leading to the improvement in the corrosion resistance of the modified AH 32 steels.

Influence of Chromium on Corrosion Behavior of Low-alloy Steel in Cargo Oil Tank O2-CO2-SO2-H2S Wet Gas Environment

As international maritime organization (IMO) draft 289 was adopted to develop a low-alloy anti-corrosion steel for the deck of cargo oil tank and to understand corrosion mechanism, corrosion behavior of a low-alloy steel with chromium contents was studied in O2-CO2-SO2-H2S wet gas environment. Corrosion rate was measured, and the microstructure and morphology of corrosion product film were characterized by scanning electron microscopy (SEM). The phase and chemical composition of the corrosion product film were investigated by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), respectively. The effect of misorientation distribution on corrosion resistance of steel was evaluated by electron backscattered diffraction (EBSD). The results showed that corrosion rate decreased with increasing chromium content in the low-alloy steel, and the corrosion type was general corrosion. The phenomenon of chromium enrichment was found in corrosion product film consisting of α-FeOOH, γ-FeOOH, sulphur, FeS2 and Fe1–x S. The increase of chromium content decreases the amount of high-angle grain boundaries, thus resulting in the improvement of corrosion resistance.

Electrochemical Corrosion Performance of Low Alloy Steel in Acid Sodium Chloride Solution

The corrosion behavior of low alloy steel for cargo oil tanks (COT) is investigated by thermo mechanical control process (TMCP) at various cooling rates. The corrosion rate is estimated by accelerated corrosion test in strong acid sodium chloride solution. The corrosion mechanism is studied by potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS) measurements. It indicates that the acicular ferrite is refined as the cooling rate increases, the CR15 steel with higher cooling rate exhibits good corrosion resistance with a less weight loss, lower corrosion current density and bigger impedance modulus than steels CR10 and CR12.

Influence of Inclusion on Corrosion Behavior of E36 Grade Low-alloy Steel in Cargo Oil Tank Bottom Plate Environment

Corrosion behavior of low-alloy steel was investigated in simulated cargo oil tank (COT) bottom plate service environment (10% NaCl solution, pH = 0.85). The corrosion behavior of inclusion was studied by in-situ scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was found that pitting corrosion was inclined to occur around the place where inclusions exist. After initial corrosion, an area of 10–20 μm in diameter was formed as a circinate cathode around the edge of inclusion. MnS inclusion dissolved in the simulated COT corrosion solution before low-alloy steel matrix, and pitting was formed at the place where MnS dissolved. TiO2 inclusion dissolved in the simulated COT corrosion solution after low-alloy steel matrix, and pitting was formed at the place where steel matrix dissolved. The corrosion tended to occur at the area where the curvature radius of inclusion is smaller. The size of round TiO2 inclusions had little influence on corrosion behavior in this certain environment.

Effect of TMCP Parameters on Microstructure and Mechanical Properties of Cargo Oil Tanks Steel

The effect of TMCP parameters on the microstructure and mechanical properties of cargo oil tanks (COT) steel is investigated. The microstructure characteristics are performed by optical microscope, and the mechanical properties are researched by tensile test at ambient temperature and impact test at different temperatures (-20°C, -40°C). The results show that the microstructures of COT steel are a mixed microstructure consisting of ferrite, granular bainite and pearlite, which are resulted from the special TMCP parameters. The COT steel has good comprehensive mechanical properties by analyzing the experimental data, satisfying the international standard. Furthermore, impact fracture surfaces appear small dimples and a few of large ones, most of the dimple with a certain direction, and the inclusion with the fracture is mainly composed of MnS, CaS and Al2O3 composite product.

Cyclic Corrosion Behavior of E36 Low-alloy Steel in a Simulated Cargo Oil Tank Upper Deck Environment Corresponding to IMO Standard

The full-system cycle corrosion behavior of E36 grade low-alloy steel was studied by a homemade device to simulate the cargo oil tank upper deck corrosion environment which was established corresponding to the international maritime organization standard.The corrosion rate and reduction of thickness of the steel were measured respectively,and an extrapolation of the thickness reduction for 25 years corrosion was calculated by fitting formula and curve.Surface morphology of steel tested for different cycles before and after the removal of corrosion product films was observed by scanning electron microscope(SEM).The distribution of element and phase constituent of corrosion product film were analyzed by energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD) respectively.The results showed that the extrapolation of thickness reduction for 25 years corrosion was 2.21 mm.In the early stage of the corrosion,acid condensing droplets were formed on the surface of corrosion product film due to the existence of sour gas and the alternating temperature and humidity,and then the corrosion scale was gradually blistered.In the later stage of the corrosion,the size of the blisters grew up,and then most of which cracked and falled off.At last,the outer corrosion scale was completely detached,and the inner corrosion product scale was exposed to the corrosive environment.The rather loose outer corrosion scale of the steel formed in wet O2- CO2-SO2- H2S gas environment was mainly consisted of α-FeOOH,γ-FeOOH,S,FeS2,Fe1- xS and FeS.However the rather compact inner corrosion product scale was consisted mainly of α-FeOOH.

Effects of Cu on Corrosion Resistance of Low Alloyed Steels in Acid Chloride Media

The corrosion resistance of two kinds of low alloyed steels was studied according to the test procedures for qualification of corrosion resistant steel for cargo oil tanks issued by International Maritime Organization. The results indicated that the addition of Cu improved the corrosion resistance of the NS-D36 steel to more than three times that of the conventional D36 steel in the strong acid solution containing chloride (10% NaCl, pH = 0. 85). The anodic polarization behavior of the copper-bearing steel was studied by polarization curves and electrochemical impedance spectroscopy (EIS), and alloying element Cu showed beneficial effects including an active potential range, low current density and high transfer resistance of electric charge. The rust layer was analyzed by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES), and the results pointed out that the mechanism of copper's beneficial effects was based on the suppression of anodic dissolution by metallic copper re-deposition on the steel surface immersed in the strong acid chloride media.