Hydrogen Diffusion In Steels And Hydrogen Permeation Sensor

The steel equipment was destroyed seriously by hydrogen, which was generated inindustrial production. In order to prevent the occurrence of malignant accidents, thesensor was developed to detect/monitor hydrogen content produced by corrosionreactions and to evaluate the hydrogen corrosion degree of steel equipment. It is ofgreat significance that effective safeguard procedures are taken to solve the corrosionproblem, to guide the production practice and finally to realize safety production andlong period running. The researches about different types of electrochemicalhydrogen sensors have been reported at home and abroad. However, it was worth tostudy in-depth whether the consistent measure results were obtained or not throughthe measurement with different type sensors. It had vital socioeconomic benefits thatthe sensor was developed to monitor the hydrogen permeation rate of equipment inreal-time and nondestructively, to evaluate the safety operation state of equipment,and to prevent occurrence of enormous loss in economy and servant socialconsequence in production operation.The atomic hydrogen permeation rate was detected by the Devanathan-Stachurskicell. The sensor for detecting hydrogen permeation rate was developed in thedissertation. The influence of the catalytic coatings on the measured equipment on theperformance of amperometric-type and potentiometric-type hydrogen permeationsensors was studied. The performance of the sensor composed of double electrolyteswith gelatiniform electrolyte was investigated. The results were shown as follow:（1）The sensor could not oxidize the atom hydrogen when the detected workpiecesurface did not plate catalytic coating, but the catalytic activity of oxidizing hydrogenatoms was improved by the coating of nickel or palladium. The catalytic activity ofoxidizing hydrogen atom, or the sensor sensitivity, directly depended on thecompactness of coating. When the electroplating was conducted for8¹0min by0.333A-dm^-2cathode current density, the compact palladium plating on the steelcould be obtained in our developed palladium electrolyte. When the cathode currentdensity of1.00A-dm^-2was applied to electroplate nickel for over5min, the compactnickel plating on the detected surface of equipment was obtained. Therefore, not onlythe background current could be reduced effectually via plating nickel or palladium,but also the catalytic activity for oxidizing the hydrogen atoms could be improved. （2） The safe potential interval of hydrogen oxidation on nickel and palladiumcoating was+0.3⁺0.4V_Niand+0.2⁺0.5V_Ni, separately. Under the lower oxidationpotential, the catalytic activity of palladium coating was slightly higher than that ofnickel coating. We can raise the oxidization potential to reach the same catalyticactivity on palladium coating. The optimum oxidation potential on nickel coating was0.35V_Ni.（3） Both of the amperometric-type and potentiometric-type hydrogen permeationsensors could be applied to the detection of hydrogen permeation rate. Under the sametemperature conditions, the steady state potential was increased with the rise ofcharging current density. The nearly agreeable results were obtained on the two typesensors under the same density of charging current. The minimum relative deviationwas only3.0%between them.（4） The response time of amperometric hydrogen permeation sensor was shorterand the sensitivity was higher relatively. The two types of the sensors had goodreproducibility.（5） An amperometric hydrogen sensor with double electrolytes composed of agelatiniform electrolyte and KOH solution were developed to detect the permeationrate of hydrogen atoms in steel equipment. The hydrogen permeation sensor hadsuitable viscosity and high electrical conductivity, which could prevent effectively theleakage when it was fixed and it had good reliability.（6） The field monitoring tests showed that the designed corrosion monitoringsystem could accurately display the hydrogen permeation information of the equip-ment. It was applied in the real-time, on situ and nondestructive detecting atomichydrogen concentration in the steels. It could provide the reliability for the safeoperation of the equipment.The innovative points of our researches were shown as follows:（i）The optimumcatalytic coatings for oxidization of atomic hydrogen and plating processes wereascertained.（ii）The performances of the amperometric-type and potentiometric-typehydrogen sensors were studied and it was found out that the amperometric hydrogenpermeation sensor was more suitable to detect the hydrogen permeation rate.（iii）The leakage problem was solved using double electrolytes system when the sensorwas fixed. The correctness of measuring signal was verified by experiments.（iv）Theresult of field monitoring showed that the developed electrochemical monitoringsystem could realize the real-time, online and nondestructive detection of atomichydrogen concentration and the estimation of the susceptibility of hydrogen induced cracking.