The corrosion and erosion-corrosion behaviors of A3 carbon steel in naphthenic acid mediums at high temperature were studied in det ail.The erosion-corrosion resistance of A3 carbon steel in industrial oil-refini ng environment was also investigated.The results revealed that the total acid nu mber (TAN),the temperature and the velocity of flow play important roles in affe cting the naphthenic acid corrosion (NAC)and erosion-corrosion (NAEC)behaviors o f carbon steel,which influence the degree of NAC and NAEC by influencing the tra nsportation of naphthenic acid molecules toward the metal surface,the absorption of naphthenic acid molecules on the metal surface,the active reaction on the me tal surface,and the spallation of corrosion products from the metal surface.In g iven corrosion mediums,the control step of NAC process is mainly dependent on th e temperature.The carbon steel has little resistance to the NAC and NAEC,so this material should be used cautiously in industry oil-refining installation,especi ally in the places where the temperature,the TAN and the velocity of flow are ra ther high.

The structure,function and characteristic of expert system of Fitness-For-Service for petrochemical(ESFFSR)was introduced in this p aper .In ESFFSR,aritifical neural network(ANN)and Fitness-For-Service technology were used to evaluate the corrosion defects in refinery.ANN is used to make the rela tionship between corrosion rate and the effect factors for general corrosion.Fit ness-For-Service models are used to analyze the local corrosion.Based on the AN N and Fitness-For-Servic models,ESFFSR can make suggestions for lower temperatur e and pressure if the defect is incompetent automatically.In addition,ESFFSR wou ld give out the corrosion type,mechanism,characteristics and effect factors on l ine in petrochemical.The selected material of commended tables to anti-corrosio n for distillation,catalysis and coking equipment were also given in ESFFSR.

The composition,phase and microstructure of zinc-al uminum-chromium conversion coating were studied by XRD,SEM,EDS,EPMA and XPS etc. The mechanism of coating formation was proposed.Results showed that the main ele ments in the coating are zinc,aluminum and chromium.Zinc and aluminum existed mo stly as zero-valent zinc and zero-valent aluminum,but chromium existed mostly as trivalent chromium oxide.There were lots of zinc and aluminum particles in the coating phase,when heating the coated substrate approximately to 300℃,t he hexavalent chromium was reduced to an insoluble amorphous oxide,nCrO3·mC r2O3,by the organic substance such as succinic acid,which acted as a binde r f or the particles of zinc and aluminum to form a film.At the same time,the chromi c acid in the treatment chemical reacted with the metal surface of the substrate forming a chemical bond providing strong adhesion.

The database which is based on the summary of a lot of corrosion cases,stores a large number of data by SQL Server.In the paper the database for the corrosion cases of the pressure pipe and pressure vessel is de veloped by ASP (Active Server Page).There are a lot of cases with pictures and t exts in the database.In the database,we can inquire in all kinds of models and m aintain the database conveniently.The database can also be as an important part of expert system of the pressure pipe and pressure vessel.

The present paper studied the corrosion of 316 and 310 type stainless steels containing rare earth elements in eutectic(Li,K)2CO 3 mixture at 650℃.The results indicated that the addition of RE can improve t he corrosion resistance of 310S steel by promoting the formation of a more prote ctive Cr-rich oxide scale.316L(RE)stainless steel was corroded faster than 310S steel owing to the lower content of Cr.The corrosion mechanism of the alloys wa s discussed.

The inhibition performance and adsorption mechanism of thio -phosphate inhibitor on the carbon steel surface in high temperature na phthenic acid/white oil solution has been studied with chemical、SEM and X-ray analysis methods.It is shown that,in naphthenic acid / white oil solution,thio - phosphate can be adsorbed on the metal surface by both reacting sediment and mol ecules adsorbing cover .At the lower inhibitor concentration,the surface film is formed by reacting sediment type,but at higher concentration,it will be formed by adsorbing cover type.When the concentration is 1000 mg/L,the inhibition effic iency of thio -phosphate will be upon 94%.

This paper deals with the coking and caburizing of the used cracking tube made by HP heat-resistant steel.The experiments show that the structure on the cross-section of the used cracking tube is consisted of th e oxide and coking layer,the chromium depletion layer,and the inner carburized la yer due to serious carburizing.It is found that there is filamentary coke near t he surface of the tube but the spherical coke exists far from the surface of the tube.The initial coking behaviour of HP heat-resistant steel is investigated by quick coking experiment.During the initial coking stage,the filamentary is form ed under the catalytic action of nickel or iron elements in the steel,although t here is a Cr2O3 film on the surface of the steel.The hydrocarbon cracking in termediates can permeate the Cr2O3 film and combine with the nickel or iron elements in the steel,which arouses the catalytic coking,and causes the destruct ion of the Cr2O3 film and serious coking and carburizing.With increasing of the cracking time,the spherical coke begins to develop instead of the catalytic filamentary coke.

The change of electrochemical noise(ECN)patterns wi th time of 16Mn steel in 0.1 mol/L Cl-+0.5 mol/L NaHCO3 solution was inv es tigated.The experimental result showed,during metastable pit initiation period,t he pitting initiation rate λ was less than 0.002 s-1,and the average life time of current transient coupled in ECN was about 3～5 s.However,the average li fetime of potential transient was 200 s.During the transition from metastable to stable pitting,λ increased rapidly,with an increase of the lifetime of current transient and a decrease of potential transient.Then,during the stable developm ent of pitting corrosion,the lifetime of current and potential transient become almost identical,and a large-scaled fluctuation in ECN as well as a decrease of λ was observed.In addition,during the transition from metastable to stable pitt ing,noise resistance Rn decreased fast,and Rn get stable once the st abilization of pitting corrosion.

The characteristics of the cathodic potential wavef orms of the Q235 steel electrodes polarized by square wave pulsed currents (SWPC s) were studied in 3%NaCl,0.06%NaCl and tap water.The results show that polarize d by SWPCs the cathodic potential waveforms have the basic features of those in RC parallel circuits,and move negatively with increase of the polarizing time bu t their shapes do not change obviously.The solution resistance may create great influence on the measured potential waveforms so that it must be compensated to obtain the real ones.The real amplitudes of the potential waveforms are very sma ll (<10 mV) and decrease with increasing frequencies of SWPCs.So it was pointed out that the bottommost potential of the cathodic potential waveform could be us ed as the cathodic polarization potential of the electrode.The characteristics o f the cathodic potential waveforms were analyzed in the paper.

The corrosion of the ceramic coatings formed by mi cro-arc oxidation on a magnesium alloy was investigated by salt spray tests.The results indicated that the corrosion-resistance of the coating prepared in mixe d salt solution was best.The difference of the corrosion-resistance between the ceramic coating formed by micro-arc oxidation and the chromate conversion coat ing and sealing mechanism were analyzed by SEM.The results indicated the corros ion-resistance of coatings obtained by micro-arc oxidation was far better than t hat treated by chromate.The corrosion-resistance of the coating after sealing by paraffin was improved significantly.

By means of corrosion test of flower of sulfur vapo r,corrosion test under ultraviolet photallochromy acceleration and measurement o f polarization curve,the inhibition performance of 1-phenyl-5-mercaptotetrazole (PMTA),2-mercaptobenzoxazole (MBO),2-mercaptobenzimidazole (MBI) and the built i nhibitor (PMM) were evaluated.The result of corrosion test showed that PMM was t he most prominent for silver in the four inhibitors and the PMM took on the syne rgistic effect.The anti-tarnishing films were studied by the means of Auger elec tron spectroscopy (AES) and X-ray photoemission spectroscopy (XPS).Results showe d that the anti-tarnishing film formed by PMM is more compact and stabilized tha n that of mono-component inhibitor,so the mixed tarnishing inhibitor was more ef fective than mono-component inhibitor.

The effect of hydrogen on stress corrosion cracking (SCC) of the high-strength LC4 aluminum alloy in 3.5%NaCl solution has been stu died using slow strain rate tension technique.The experimental results showed th at the alloy is susceptible to SCC in humid air,especially in NaCl solution.SCC may occur in the mechanisms of anodic dissolution and hydrogen embrittlement,but the mechanisms would be varied under various conditions.In humid air,or under t he condition of anodic polarization in 3.5% NaCl solution,the mechanism of SCC i s mainly anodic dissolution.Under the condition of hydrogen pre-permeation or ca thodic polarization,hydrogen embrittlement plays a key role during the SCC proce ss.The results also indicated that the SCC resistance of LC4 alloy decreases wit h increasing the time of hydrogen pre-permeation.

In the present paper a review was given on water di ffusion behaviors in polymer films and coating impedance according to Fickian pr ocess.In the case of linear Fickian diffusion,a mathematical relationship betwee n the water-uptake in organic coatings and capacitance,C,of coatings was est ablished.The change rate of coating capacitance was mainly depended on the water diffusion coefficient,D,in coatings.In the initial stage of water-uptaking, a linear relationship is shown in the curves lnC(t)～time0.5,with the slope proportional to D0.5.Under the non-linear diffusion,water prefe rentiall y penetrated through the cracks or the boundaries of foreign particles by sheari ng diffusion,while in the bulk coatings by linear one.The contribution by linear diffusion could be eliminated with the presence of obvious porosity,and the coa ting capacitance was mainly determined by the porosity of coatings,θ.The sl ope of the linear part in lnC(t)～t0.5 curves was proportional to θ 0.5.

The formation and definition of acidic rain are des cribed respectively.Usually the rain with the pH value less than 5.6 is called a cidic rain.The corrosion due to the acidic rain is the most important type of th e atmosphere corrosion.The area where acidic rain falls covers one third of all over Chinese areas.With the developments of Chinese economy,acid precipitation a rea increased,the corrosion loss also increased.The direct corrosion loss due to the acidic rain on the material in 1999 was estimated to be 3.0 billion RMB or so by the experience estimation and Uhlig method.