Li Yantao

Study on rust layers on steel in different marine corrosion zone

The Mossbauer spectra for corrosion products formed on A3 carbon steel and low alloy 16Mn steel exposed in the Chengdao sea area for 2 years by the electro-connected method were determined. The phase composition and content of the rust layers on the two steels in four marine corrosion zones were analyzed and studied. Although the phase composition of the two steels were different, their main phase was β-FeOOH. The different content of FeOOH and Fe3O4 in the rust layers illustrated that FeOOH in the inner rust layer participated in the cathodic process as an oxidant accelerating the corrosion rate of steel under wet/dry cycle condition. Moreover, for the alloy elements in 16Mn steel, the rust layers with simple composition and fine and close texture formed a good barrier layer lowering the corrosion rate of low alloy steel.

Electrochemical measurement of steel corrosion in seabottom sediment with “MD” method

The through one year corrosion potential and polarization resistance for 3 kinds of steels in seabottom sediment of Liaodong Bay were measured with the “MD” method.The measurements will have some theoretical and practical values. The theoretical value lies in that the recorded changing process of the practical corrosion case can be basis for indoor discussion and electrochemical research on the corrosion process. The practical value lies in that the obtained data can be basis for designing and controlling electrochemical protection systems. In fact, it is very difficult to measure in situ the corrosion parameters of steels in sea sediment.

Simulation test apparatus for marine corrosion

This paper describes the setup and working mechanism of a simulation test apparatus for marine corrosion. Experimental results showed the apparatus can basically reflect the corrosion behavior of steel in various marine environments, and is simple, convenient, and reliable for testing steel used for marine engineering.

Alloy elements' effect on steel corrosion in marine environment

Investigation of the effect of alloy elements on the corrosion resistance of 18 types of low alloy steel in marine atmospheric zone, splash zone and seawater zone by the electric connection method showed that the corrosion resistance of low alloy steel was obviously affected by Cu, P, Mo in the marine atmospheric zone, by P, Mo, Cu in the splash zone, and by Al, Cr in the seawater zone. The experimental results were used to derive three regression equations to describe the corrosive behavior of these steels.

IMPEDANCE CHARACTERISTICS OF CARBON STEEL UNDER CATHODIC PROTECTION

The potential dependence of the faradiac impedance of carbon steels in 3.5% NaCl solution was measured by ac impedance technique. The polarization resistance, and also the cathodic protection efficiency obtained from weight loss, maximized at 0.70 V with respect to saturated Ag/AgCl electrode. Consequently, the potential at faradaic impedance maximum corresponds well to the optimum cathodic protection potential. The study results showed that the ac impedance technique is a promising method for monitoring and determining the optimum cathodic protection potential.

Corrosion and adherence at sea oil-platform

Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oil platforms under different cathodic protection showed corrosion still occurred on these platforms under their designed protective potentials. Preliminary conclusions from indoor experiments on the relation between adhesive corrosion and cathodic protection showed adhering organisms caused the corrosion on these platforms.