The corrosion behavior of type 304 stainless steel and industrially pure iron, chromium, nickel in 1.0mol/L HC1 and their corrosion inhibition by piperidine (PD) were investigated by atomic absorption spectrometry (AAS), current vs time relation at constant potential and polarization curve measurements. The results showed that the dissolution of 304 stainless steel in HC1 could be inhibited effectively by PD. The passive range of Cr in HC1 would extend in the presence of PD. For Fe, PD acted as a cathodically controlled inhibitor. A new idea "selective inhibition" was suggested and applied to describe the inhibition by PD for 304 stainless steel in HC1. In the presence of PD , the dissolution rates of Cr and Ni in 304 matrix decreased obviously, and the molar percentages by which various components in 304 stainless steel dissolved were different from those in the absence of PD. AAS data indicated that regardless of the presence of PD the dissolution of Fe, Ni and Mn took the form of divalence, while Cr dissolved in the form of trivalence.

The pitting growth for 304 stainless steel in 0.5mol/L NaCl and its inhibition by piperidine(PD) were investigated by means of atomic absorption spectrometry(AAS) and pitting current-time curve measurements under potentiostatic condition. According to AAS data, Fe, Ni and Mn in pits dissolved into ions in form of divalence, and Cr in form of trivalence both in the presence and absence of PD. The ratios by which each component element of 304 stainless steel dissolved played a very important role in pitting self-propagation process. The self-propagation effect decreased with downward shift of the dissolution ratio of Cr because the decrease in pH in pits could be ascribed mainly to the hydrolysis of Cr3+. PD inhibited 304 stainless steel from pitting growth by decreasing the total amount of dissolved ions and the dissolution ratio of Cr. On the basis of pitting growth kinetics, the influence of PD on the type of pit configuration was analysed. The results showed that the addition of PD turned the pits into those with slower development rate. The possible inhibition mechanism on pitting development was also discussed.

Corrosion fatigue crack initiation(CFCI) life of LY12CZ aluminum alloy notched specimens in 3.5% NaCl solution under variable amplitude loading block spectra was investigated experimentally. It was shown that overloading in the spectrum made the CFCI life longer considerably, and the loading sequence and the overloading type had a significant effect. So the overloading effect must be considered in the prediction of the CFCI life under variable amplitude loading. According to the CFCI life curves that revealed the overloading and corrosion effect, a study was made on applying Miner's accumulative damage rule to predict CFCI life under variable amplitude loading. A model was established and was thereafter used to predict the CFCI life under the selected spectra. The predicting results showed good agreement with the testing. The distribution of the CFCI life under one spectrum was determined by using ranking methods. Corrosion effect on CFCI under variable amplitude loading was also discussed.

Thermo-elastic-plastic finite element method was employed to investigate the welding stress distribution in the multipass-girth-butt welded pipes of austenitic stainless steel (1Cr18Ni9Ti) and mild steel(0.2%C). The computed results showed that significant biaxial tensile residual stresses existed in the weld vicinity region of the inner surface of the pipes under the normal process condition. Water cooling could effectively adjust the residual stress distribution and obtain the biaxial compression residual stresses on the whole HAZ of the pipe inner surface. The residual stress measurements verified the conclusion. The compression residual stresses of the multipass-girth-butt welded 1Cr18Ni9Ti pipe could remarkably improve its resistance to stress corrosion cracking.

Corrosion behaviour of high purity aluminium(99.999%Al), industrial high purity aluminium(LGl, 99.85%), Al-Si and Al-Mg alloys immersed in molten chemically pure sodium at 350-450℃ for 25-100h have been investigated. Structural morphology and alloying element distributions of the specimens were analysed with the aid of OM, SEM, XRD and EPMA methods. Experiments indicated that high purity aluminium immersed in molten sodium was attacked slightly instead of completely immune. The molten sodium corrosivity to aluminium depended on existing impurity, especially silicon. Addition of magnesium to some content and microalloying of zirconium as grain fining agent can improve the corrosion resistance of aluminium. Corrosion product formed on the surface of aluminium and its alloys was characterized as AlNaSi phase.

Acrylic emulsion was introduced into steel reinforcing concrete as concrete admixtures or rebar coatings in order to prevent steel reinforcements from corrosion. Specimens were immersed in 3% NaCl solution as accelerating corrosion test for up to 60 days. The corrosion behavior of each specimen at different immersion time was investigated with electrochemical impedance spectroscopy(ELS) method. The results showed that breakdown of the passive layer on the steel surface were deferred when incorporating 20% acrylic emulsion into concrete while its permeability remanining unchanged. The corrosion rate can also be reduced to a considerable extent when using steel rebar coated with acrylic emulsions. The active state of steel surface under the emulsion coatings was ascertained by comparing the impedance spectroscopy before and after cathodic activation. On the basis of these results, some proposals were presented to enhance the anticorrosion ability of the emulsion coatings. All above showed that acrylic emulsion is a promising material for corrosion prevention of reinforcing concrete.

Mild steel (0.24wt% C) can be passivated in triaxial composite flooding solution containing 1.2% NaCl+ 0.6% petroleum sulfonate + 0.12% polyacrylamide(wt%). The composition and structure of passive film formed on the steel were investigated by XPS. The results showed that the passive film was composed of Fe3O4, FeOOH, Fe2O3 and Fe(OH)2, and its thickness was about 7nm. The valence of elemental iron varied at different depth of the passive film. At the outer surface of the passive film, the valence of iron was +3, and at the interface near the matrix, +3 and +2 iron were detected.

The electrochemical behavior of aluminum in 0.5mol/L NaCl and 0.49mol/L NaCl+0.01mol/L NaX (X=Cl-, Br-, I-, F-, NO3-, SO42-) solutions was studied by potentiodynamic method and potentiostatic hydrogen gathering measurements. When the above-mentioned anions were added into the solution, the breakdown potential and negative difference effect (NDE) of aluminum were found to change. The breakdown potential shift resulted from the anion competitive adsorption on aluminum surface in the solution. The change of NDE could be explained by the theory of hard-soft-acid-base (HSAB). The inconsistency ofchanging trend of the breakdown potential with NDE implied that NDE of aluminum was probably caused by low valence Al+ chemical reaction in solution.

The determination methods and relevant models of crack propagation rate in environmentally assisted cracking were summed up and reviewed. The advantages and shortcomings as well as application range of these methods and models were analyzed and evaluated. The main purpose of the review was to provide convincing basis not only for the most suitable determination of crack propagation rate in various complex material/environment combinations but also for the life-prediction of components in practical service.

It is a quite complicated and heavy work to calculate potential distribution in a regional cathodic protection system with boundary element method (BEM). The node numbers of the model for calculation can be reduced and computer operation time can be shortened by using cylindrical element discreting method, if the geometric shape of the object to be protected is suitable for partitioning into cylindrical elements and the potentials on cross-section periphery are approximately equal. In previous work, the variable error polyhedron method was used to optimize the model. Since the fitting of the cathodic polarization curve was simplistic, the stability of the optimization was poor. In this paper, the piecewise linear fitting is applied, thus the stability of the optimizing process is improved. This improved calculation method has been used for the cathodic protection design of some oil well cases.

Oil pipes and their corrosion products of WEN23-1 and 23-8 wells in Zhongyuan oil field were studied by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron probe microanal-yser (EPMA). Corrosion tests of carbon steel in solutions containing CO2 were carried out. The results showed that CO2 and condensate water were the primary factors causing corrosion of gas well. Nonmetallic inclusion (MnS, Al2O3) in oil pipe was another cause to accelerate localized corrosion and cracking failure of oil pipes in the medium with CO2. The possibility of application of inhibitor to prevent CO2 corrosion of gas well was discussed.

Type 310 stainless steel foils were precharged with hydrogen at different current densities. The effects of hydrogen on the pitting susceptibility were investigated by carrying out the ASTM-G48 standard ferric chloride tests. The variations of pit density, pit size distribution, average pit diameter and apparent pit area percentage with hydrogen charging current density and immersion time were statistically examined. Hydrogen in 310 stainless steel greatly promoted the pitting initiation and the pit growth. Average pit diameter D increased linearly with logarithm of immersion time t, i.e., D=αlnt+β. The value of constant a increased with the rise of charging current density. The hydrogen interactions with defects both in surface film and metal substrate were used to explain its deleterious effects on the resistance of pitting corrosion. It was considered that hydrogen accelerated pitting corrosion mainly by formation of positive charge regions around defects in the surface film.

The effect of La2O3 on microstructure and corrosion resistance of laser clad Ni-based alloy coatings was investigated. The experimental results showed that the addition of La2O3 could modify the microstructure and improve corrosion resistance of these coatings. Their microstructure was refined and purified. In the clad coatings containing La2O3, both secondary dendrite space and inclusion percentage were reduced. The corrosion weight loss of the clad coatings with different amounts of La2O3 was much smaller than that of the coatings without La2O3 in HNO3 solution. The anodic polarization curves also proved that the corrosion resistance of the laser clad coatings in HNO3, H2SO4, HCl and NaCl solutions, was significantly improved with the addition of La2O3.