• Journal of Advanced Marine Engineering and Technology
• /
• v.30 no.1
• /
• pp.157-168
• /
• 2006

Recently, interest in using Al alloys in ship construction instead of fiber-reinforced plastic (FRP) has increased because of the advantages of A) alloy ships over FRP ships, including high speed, increased load capacity. and ease of recycling. This paper investigated the mechanical and electrochemical properties of Al alloys in a slow strain rate test under various potential conditions. These results will provide reference data for ship design by determining the optimum protection potential regarding hydrogen embrittlement and stress corrosion cracking. In general, Al and Al alloys do not corrode on formation of a film that has resistance to corrosion in neutral solutions. In seawater, however, $Cl^-$ ions lead to the formation and destruction of a Passive film. In a potentiostatic experiment. the current density after 1200 sec in the Potential range of $-0.68\~-1.5\;V$ was low. This low current density indicates the protection potential range. Elongation at an applied potential of 0 V was high in this SSRT. However, corrosion protection under these conditions is impossible because the mechanical properties are worse owing to decreased strength resulting from the active dissolution reaction in parallel parts of the specimen. A film composed of $CaCO_3\;and\;Mg(OH)_2$ confers corrosion resistance. However, at potentials below -1.6 V forms non-uniform electrodeposition coating, since there is too little time to form a coating. Therefore, we concluded that the mechanical properties are poor because the effect of hydrogen gas generation exceeds that of electrodeposition. Comparison of the maximum tensile strength, elongation, and time to fracture indicated that the optimum protection potential range was from -1.45 to -0.9 V (SSCE).

• Journal of Welding and Joining
• /
• v.19 no.1
• /
• pp.65-74
• /
• 2001

A study on the corrosion behavior in case of As-welded and PWHT temperature 55$0^{\circ}C$ of welding part of RE36 steel for marine structure was investigated with parameters such as micro-Vickers hardness, corrosion potential measurement of weld metal(WM), base metal(BM) and heat affected zone(HAZ), both Al anode generating current and Al anode weight loss quantity under sacrificial anode cathodic protection conditions. And also we carried out slow strain rate test(SSRT) in order to research both limiting cathodic polarization potential for hydrogen embrittlement and optimum cathodic protection potential as well as mechanical properties by post-weld heat treatment(PWHT) effect. Hardness of HAZ was the highest among three parts(WM, BM and HAZ) and the highest galvanic corrosion susceptibility was HAZ. And the optimum cathodic polarization potential showing the best mechanical properties by SSRT method was from -770mV to -875mV(SCE). In analysis of SEM fractography, applied cathodic potential from -770mV to -875mV(SCE) it appeared dimple pattern with ductile fracture while it showed transgranular pattern (Q. C : quasicleavage) under -900mV(SCE). However it is suggested that limiting cathodic polarization potential indicating hydrogen embrittlement was under -900mV(SCE).

• Corrosion Science and Technology
• /
• v.9 no.1
• /
• pp.48-55
• /
• 2010

The many vessels are built with FRP(Fiber-Reinforced Plastic) material for small boats and medium vessels. However, FRP is impossible to be used for recyclable material owing to environmental problems and causes large proportion of collision accidents because radar reflection wave is so weak that large vessels could not detect FRP ships during the sailing. Hence, Al alloy comes into the spotlight to solve these kinds of problems as a new-material for next generation instead of FRP. Al alloy ships are getting widely introduced for fish and leisure boats to save fuel consumption due to lightweight. In this study, it was selected 6061-T6 Al alloy which are mainly used for Al-ships and carried out various electrochemical experiment such as potential, anodic/cathodic polarization, Tafel analysis, potentiostatic experiment and surface morphologies observation after potentiostatic experiment for 1200 sec by using the SEM equipment to evaluate optimum corrosion protection potential in sea water. It is concluded that the optimum corrosion protection potential range is -1.4 V ~ -0.7 V(Ag/AgCl) for 6061-T6 Al alloy, in the case of application of ICCP(Impressed current cathodic protection), which was shown the lowest current density at the electrochemical experiment and good specimen surface morphologies after potentiostatic experiment for Al-Mg-Si(6061-T6) Al alloy in seawater environment.

• Journal of the Korean Society for Heat Treatment
• /
• v.20 no.4
• /
• pp.195-202
• /
• 2007

Corrosion resistance and torque of M10 bolt coated with Magni 565 were investigated. Corrosion protection mechanism were also studied with the microstructure of coating film. The bolts with the optimum conditions showed around $10{\mu}m$ layer thickness, a great corrosion resistance in salt spray test and a proper torque in torque/tension test. But torque coefficient k increased with the number of bolting and clamping force of M10 bolt showed significantly lower than that of specified value 28.3kN. It was thought that the repeated bolting made the coating film peel off and powdery. The sample coated with optimum coating conditions showed more higher polarization resistance and corrosion potential than the specimens of top and base coat only. The base coating film was composed of lamellar zinc flakes, which provides a large sacrificial cathodic protection. Meanwhile, the top coating film was composed of organic aluminium pigments layer, which provides barrier protection to the corrosion circumstances.

• Journal of Advanced Marine Engineering and Technology
• /
• v.24 no.4
• /
• pp.460-469
• /
• 2000

A study on the corrosion behavior of RE36 steel for marine structure was investigated with parameters such as micro-Vickers hardness, corrosion potential and corrosion current density measurement of weld metal(WM), base metal (BM) and heat affected zone(HAZ), Al anode generating current and Al anode weight loss quantity in case of cathodic protection. And we carried out slow strain rate test(SSRT) in order to research mechanical properties such as stress at maximum load, percent strain, time to fracture and strain to failure ratio etc and to find out limiting cathodic polarization potential for hydrogen embrittlement with applied cathodic polarization potential. Hardness of HAZ part was the highest among those three parts and also galvanic corrosion susceptibility was the highest in HAZ part among those three parts due to the lowest corrosion potential than other parts. However corrosion current density was the highest in WM part among those three parts. And the optimum cathodic polarization potential showing the best mechanical properties obtained by SSRT method with applied constant cathodic potential was from - 770mV to - 875mV(SCE). However it is suggested that limiting cathodic polarization potential indicating hydrogen embrittlement on the mechanical properties was under - 900mV(SCE).

• Journal of Advanced Marine Engineering and Technology
• /
• v.13 no.4
• /
• pp.54-62
• /
• 1989

When some kinds of inhibitors, i.e. $1{\times}10{-3}mol/l$ arsenic trioxide, 0.2 mol/l 2-mercaptoethanol, 0.2mol/l thiourea were added to 3% NaCl solution, there were some considererable effects to decrease corrosion current density in natural potential condition and the effect fo solution temperature increasing corrosion rate was smaller than that of no addition to 3% NaCl solution. However the susceptibility of hydrogen embrittlement due to over-protection in case of cathodic protection was much greater than that of no addition, especially was the greatest in case of addition of 2-mercaptoethanol. Therefore adding inhibitors for anti-corrosion effect, it is suggested that selection of the optimum protection potential is important from the view point of prevention against hydrogen embrittlement due to over-protection in case of cathodic protection.

• Proceedings of KOSOMES biannual meeting
• /
• 2005.05a
• /
• pp.161-165
• /
• 2005

Recently, it is on the increase interest for Al alloy with new material for ship application to substitute for FRP ship. The reason is thatAl alloy ship has beneficial characteristics such as high sea speed, increase of loadage and easy to recycle compared with FRP ship. In this paper, mechanical and electrochemical properties are investigated by slow strain rate test experiment in various applied potential condition. These results will provide as reference data to design ship by deciding optimum protection potential regard to hydrogen embrittlement and stress corrosion cracking. In general, Al and Al alloys are not corroded with forming film which has the corrosion resistance property in neutral solution. However, it was observed that formation and destruction of passive film by $Cl^-$ ion in sea water environment. At comparison of current density after 1200 sec in potentiostatic experiment, the current density in the potential range of -0.68 $\~$-1.5 V is shown low value. The low current density means protection potential range. Elongation in applied potential of 0 V was high. However, the corrosion protection application in this condition is impossible potential because the toughness is low value by decreasing strength by active dissolution reaction at parallel part of specimen. The film composed with $CaCO_3$ and $Mg(OH)_2$ has a corrosion resistance property. However, the uniform electrodeposition coating at below -1.6 V potential is not formed since the time to form the uniform electrodeposition coating is short. Therefore, it is concluded that mechanical property is poor because effect by hydrogen gas generation is larger than that of electrodeposition coating. It is concluded that the optimum protection potential range from comparison of_maxim urn tensile strength, elongation and time to fracture is -1.3$\~$0.7 V (SSCE).

• Corrosion Science and Technology
• /
• v.2 no.6
• /
• pp.283-288
• /
• 2003

The cathodic protection method is being widely used in marine structural steel, however a high tensile steel like RE 36 steel for marine structural steel is easy to get hydrogen embrittlement due to over protection during cathodic protection as well as preferential corrosion of HAZ(Heating Affected Zone) part. In this paper, corrosion resistance and mechanical properties such as elongation and hydrogen embrittlement were investigated with not only in terms of electrochemical view but also SSRT(Slow Strain Rate Test) method with applied constant cathodic potential, analysis of SEM fractography in case of both As-welded and PWHT(Post-Weld Heat Treatment) of $550^{\circ}C$. The best effect for corrosion resistance was apparently indicated at PWHT of $550^{\circ}C$ and elongation was increased with PWHT of $550^{\circ}C$ than that of As-welded condition. On the other hand. Elongation was decreased with applied potential shifting to low potential direction which may be caused by hydrogen embrittlement, however the susceptibility of hydrogen embrittlement was decreased with PWHT of $550^{\circ}C$ than that of As-welded condition and Q.C(quasi cleavage) fracture mode was also observed significantly according to increasing of susceptibility of hydrogen embrittlement. Eventually it is suggested that an optimum cathodic protection potential range not causing hydrogen embrittlernent is from -770 mV(SCE) to -850 mV(SCE) in As-welded condition while is from -770 mV(SCE) to -875 mV(SCE) in PWHT of $550^{\circ}C$.

• Journal of Welding and Joining
• /
• v.18 no.5
• /
• pp.70-76
• /
• 2000

The effect of Post Weld Heat Treatment(PWHT) of RE36 steel for marine structure was investigated with parameters such as micro-vickers hardness, corrosion potential and corrosion current density of weld metal(WM), base metal(BM) and heat affected zone(HAZ), and both Al alloy anode generating current and Al alloy anode weight loss quantity etc. Hardness of post-weld heat treated BM, WM and HAZ is lower than that of As-welded condition of each region. However, hardness of HAZ was the highest among those three parts regardless of PWHT temperature and corrosion potential of WM was the highest among those three parts without regard to temperature and corrosion potential of WM was the highest among those three parts without regard to PWHT temperature. The amplitude of corrosion potential difference of each other three parts at PWHT temperature $550^{\circ}C$, $650^{\circ}C$ are smaller than that of three parts by As-welded condition and corrosion current density obtained by PWHT was also smaller than that of As-welded condition. Eventually, it was known that corrosion resistance was increased by PWHT. However both Al anode generating current and anode weight loss quantity were also decreased by PWHT compare to As-welded condition when RE36 steel is cathodically protected by Al anode. Therefore, it is suggested that the optimum PWHT temperature with increasing corrosion resistance and cathodic protection effect is $550^{\circ}C$.

• Corrosion Science and Technology
• /
• v.14 no.5
• /
• pp.226-231
• /
• 2015

In spite of highly advanced paint coating techniques, corrosion damage of marine metal and alloys increase more and more due to inherent micro-cracks and porosities in coatings formed during the coating process. Furthermore, flowing seawater conditions promote the breakdown of the protective oxide of the materials introducing more oxygen into marine environments, leading to the acceleration of corrosion. Various corrosion protection methods are available to prevent steel from marine corrosion. Cathodic protection is one of the useful corrosion protection methods by which the potential of the corroded metal is intentionally lowered to an immune state having the advantage of providing additional protection barriers to steel exposed to aqueous corrosion or soil corrosion, in addition to the coating. In the present investigation, the effect of flow velocity was examined for the determination of the optimum corrosion protection current density in cathodic protection as well as the corrosion rate of the steel. It is demonstrated from the result that the material corrosion under dynamic flowing conditions seems more prone to corrosion than under static conditions.