| Because more and more crude oil containing high sulfur is used in the process of refining petroleum, H2S corrosion is extensively existed in the refining petroleum industry. It can lead to many accidents which cause enormous economic loss and personnel casualty.In this paper, according to the principle of electrochemical hydrogen permeation and the losing weight method of corrosion, the H2S corrosion rate and hydrogen permeation has been investigated by modelling the field condition in the industry. A practical sensor in which Pd alloy membrane is used as sensitive component for monitoring hydrogen permeation rates and software and hardware of a probe have been developed in order to provide a feasible monitoring method for valuating H2S corrosion situation of propane tank (made of 16MnR steel) of removing pitch in the Maoming Corporation of Petroleum Refinery. The results are indicated as follows:(1) The electroplating solution was composed of NiSO4·7H2O 215 g·L-1; NaCl 11 g·dm-3; H3BO3 33 g·dm-3; Na2SO4 25 g·dm-3; MgSO4 35 g·dm-3. On the side of collccting hydrogen, the surface of the steel was electroplated at the condition of pH 55.5 with the current density of 0.8 A·cm-2 at room temperature. After 35 min, a uniform nickel layer with highly catalytic activitiy was obtained on the collecting hydrogen side. A three-nickel-electrode cell consisted of a nickel-plated coating on collecting hydrogen side (as working electrode), a pure nickel silk (as reference electrode) and a nickel stick (as auxiliary electrode). An electrolytic cell, which was composed of 0.2 mol·dm-3KOH solution and the three-nickel-electrodes, was used to monitor atomic hydrogen permeation rate. The value of background current density of the cell was lower than 0.5 μA·cm-2. Pure nickel silk with steady potential in KOH solution could be used as reference electrode. The optimal potential range for oxidation of atomic hydrogen was +0.2+0.3 V (vs NiE).(2) Between 293 K and 328 K, the hydrogen diffusivity of A3, 08F, 16MnR and 20G was determined by Devanathan-Stachurski electrochemical method.(3) Based on the experiment results, it was found that at 318 K the corrosion rate of 16MnR steel and the steady permeation hydrogen current density obviously increased with increase of H2S concentration in the low concentration range(0 -4). However, the corrosion rate decreased with the increase of H2S concentration in themoderate concentration range (1.59 ×10-4 < w <1.02×l0-3). The steady permeation hydrogen current density continued to increase with the increase of H2S concentration, but its increase rate became smell. While the concentration of H2S solution approached saturated value (w ≥1.02×10-3), the rate and current density did not change with the increase of H2S concentration. The H2S concentration affected efficiency of permeating hydrogen. While the concentration approached saturated value, the efficiency kept constant. The calculational equations between the corrosion rate of 16MnR steel and the steady permeation hydrogen current density obtained from the sensor were established based on simulant experiment and mathematical derivation.(4) Pd alloy membranes were used as sensitive component and auxiliary electrode while a pure nickel silk as the reference electrode. Electrolyte solution was 0.2 mol·dm-3 KOH. Thus, a closed sensor like the anodic room in Devanathan-Stachurski cell was made. The value of the background current density of the sensor was lower than 0.5 μA·cm-2. Temperature impact affected slightly to the output of sensor signal; the recurrence of the sensor was good, but the response time of the signal was long. The monitoring result was reasonable in the field. The sensor was able to be applied to monitoring H2S corrosion rate of propane tank.(5) Monitoring hardwares were consisted of sensor, computer and potentiostat in the field. The design of monitoring software included the functions of automatic calculation of H2S corrosion rate and displaying of the curve... |
PDF Full Text Request