Characteristics on Seawater Corrosion of Intensely Weathered Surrounding Rock of Subsea Tunnel

Existing studies on the durability of subsea tunnel mainly focus on the concrete deterioration and steel corrosion,while there are few on the infuence of mechanical properties deterioration of surrounding rock on the durability of sub-sea tunnel.To improve the accuracy of long-term stability prediction,seawater corrosion tests of intensely weathered surounding rock of subsea tunnel are car-ried out.In this study,the strength characteristics of remolded samples of inten-sely weathered granite under different seawater concentrations are investigated,the strength attenuation equation under seawater corrosion is established,and the chemical damage evolution equation and model parameters are formulated,The findings provides the basis for analyzing the influence of corosion and weak-ening of surrounding rock on the durability of tunnel within the operation period.

Corrosion Resistance of Deformed Cu-Ni Alloy in Seawater

After solutionized, 70Cu 30Ni alloy was deformed in different degrees and then exposed both in NaCl solution and in seawater. The results show that with the increase of deformation, the E c and R p -1 of 70Cu 30Ni alloy decrease more quickly and fluctuate less when the exposure time increases, and the corrosion product films contain more nickel and less chloride because the distribution of dislocations tends to be homogeneous.

Effect of Microstructure and Sulfide on Corrosion of Cu-Ni Alloys in Seawater

The microstructure and the corrosion product films have been investigated on Cu-Ni alloys by TEM, SEM, AES and electrochemical technique as well as natural seawater exposure tests. Experimental results showed that the alloys had two kinds of microstructure, i.e. recrystallizatjon and incomplete recrystallization. In synthetic seawater containing 2x10^-6 S^2-, the stability of the alloy increased with the increase of deformation and annealing temperature, i.e., the degree of recrystallization. After exposure to natural seawater for different periods of time, the corrosion product films of the recrystallized alloy were rich in Ni and compact, and there were cracks in the outer layer which contained a small amount of S; the films of the alloy of incomplete recrystallization became thick, loose and porous, and obviously of layered structure, and the intergranular corrosion took place in the underlying substrate Besides, a great amount of seawater substance existed in the outer layer and some sulfur was found within the grain boundaries that prefer to corrode. The accelerating effect of sulfides in corrosion of Cu-Ni alloys in seawater is attributed to the coexistence and absorption of sulfides and carbides promoting the preference of corrosion where they absorb, and the formation of dissolvable Cu2S results in keeping the surface of the alloys in the active state.

INFLUENCE OF THE MICROSTRUCTURE OF Cu-Ni ALLOY ON ITS CORROSION RESISTANCE

The microstructures of two kinds of Cu-Ni alloys were observed by TEM.The results show that one of the alloys is a homogeneous solid solution.The other contains discontinuous precipitates at some grain boundaries,and the precipitate is a phase rich in Fe-Ni.By monitoring the corrosion potential(E_(con))in artifical seawater and exposure to natural seawater for a long time,it is found that the E_(con)of the former alloy steadily decreases,while the E_(con)of the latter decreases a little and fluctuates,and the corrosion rate of the former is clearly lower than that of the latter.Aanalyses of SEM and EDX show that the corrosion product film of the former is thin,uniform,compact and rich in nickel,and the film of the latter is thick,loose and covered with numerous deposits.Additionally serious intergranular corrosion occurs in the underlying substrate of the latter.The author proposes that the intergraular corrosion results from preferential dissolution of discontinuous precipitates at grain boundaries.In addition,the protective characteristics of corrosion product films are related not only to the enrichment of nickel but also to their compactness.

Influence of microstructure and surface condition on antifouling property of 90Cu-10Ni alloy in seawater

Through the experiment of natural seawater exposure corrosion, the antifouling properties of the plate specimens of 90Cu 10Ni alloy were studied, which were processed by different deformations, annealing treatments and surface treatments. The results indicate that after exposure corrosion for half a year, the antifouling properties of the specimens are quite different. The specimens processed by suitable deformations, annealing treatment at 650?℃ and pretreatment of surface film possess both good corrosion resistance and antifouling properties. However, the specimens processed by different deformations and annealing treatment at 450?℃ possess lower corrosion resistance, although they are also treated by the pretreatment of surface film; their antifouling properties change with different deformations. The relationships among the corrosion morphology and microstructure with the antifouling property of 90Cu 10Ni alloy are observed under the scanning electron microscopy (SEM).

Evaluation and classification of seawater corrosiveness by environmental factors

According to the data of main environmental factors and the depth of localized corrosion of carbon steel and low alloy steels in China seas, combined with the result of grey interrelation analysis, double-factor method was proposed to evaluate and classify seawater corrosiveness. According to the temperature of seawater and the biologically adhesive area on steels, the corrosiveness of seawater from low to high level is classified into five levels （C l-C5）, which was identified by the data of corrosion depth of carbon steel immersed in water for one year.

Synergistic effect of seawater's parameters on the corrosion rate of the austenitic stainless steel 304

In this article the corrosion rate of the austenitic stainless steel type 304, under the synergistic effect of environmental factors has been assessed via potentiodynamic polarization scan.Salinity, velocity, pH and temperature are the factors which induce effects on the corrosion rate of the considered metal.Quantitative analysis is applied using the full two-level factorial experimental design method, which results in the contribution value of each parameter in changing the quantity of average corrosion rate in both individual and synergistic cases.Besides this quantitative analysis, qualitative analysis has been used to predict the variation direction.These two analyses show the important role of the synergistic action, which changes the variation direction of corrosion rate and the contribution percentage of each parameter in varying the value of corrosion rate.Applying both these analyses can show the magnitude and quality of each parameter＇s effect, which is remarkably valuable in marine applications.

Discussion on Cathodic Protection of HZ 21-1 Platform

The environmental conditions around the first offshore HZ 21- 1 steel wellhead platform in the South China Sea are characterized by deep water, frequent typhoons, rough waves, high water temperature, severely corrosive seawater, and thick fouling organism attachments. The design and effectiveness of galvanic anode protection system are presented, and several methods are described, which are the calculation method of the protective current density considering the variation of water depth, the method of determining protection parameters considering various factors, the arrangement of anodes based on potential distribution and current requirements at different water depths, and the method of anode installation. Finally the effect of the accuracy of selected cathodic protection parameters on the economic benefits of offshore projects is also discussed..