مجله علوم و مهندسی خوردگی
سال یازدهم شماره 3 (پیاپی 41، پاییز 1400)

Measuring the instant off potential of pipelines in order to specify the cathodic protection condition of the pipelines and provide an overview of the quality of the coating is inevitable. However, there are many challenges in measuring this quantity for urban gas distribution networks due to interconnected structure, current interferences, especially interferences of local station networks, connection of new and old networks with different required potential levels, existence of networks with Different coatings in one area, worn urban structures, traffic and number of test points, large number of stations in the target area, have been identified. In this paper, an attempt has been made to provide solutions to the above-mentioned challenges resulting from IOP measurement experiences in the Ahwaz metropolitan gas distribution network and the requirements that facilitate project implementation, as well as data collection with higher accuracy. The measurement was based on the use of interrupter and fast data logger synchronizable that could be connected to pc. However, the contents can be generalized when using other equipment, such as trans-rectifier timers and usual voltmeters (in accordance with the instructions for use).

Failure analysis was carried out on yellow brass tubes that leaked after five years of service in a heat exchanger. The leaked tubes had numerous longitudinal cracks. The service fluid inside the brass tubes was cooling water used to exchange the temperature with hot steam at the shell side. Microscopic examinations and energy dispersive spectroscopic analyses were carried out on the brass tube inside and outside surfaces to understand the root cause of the failure. Microscopic examinations of the tubes at the fracture edges and cracked areas revealed that the tubes suffered severe dezincification, and cracks initiated and propagated from the regions that suffered dezincification, causing the failure of tubes. It is suggested to control the corrosive species in cooling water and select proper material for tubes to avoid the premature failure.

For fire water storage tanks internal corrosion will occur due to internal surfaces are in contact with water. In oil and gas industry in addition of coating, cathodic protection is used to reduce or mitigate internal corrosion. According to dimensions of fire water tanks in petrochemical plants and refineries and high current density requirements, impressed current system used for tanks internal protection. Generally suspended MMO tubular anodes in string form used. These strings placed on circle with some offset from tank wall for uniform distribution of current and potential. Due to close distance between anodes to tank shell and bottom plates, using conventional formulas that assume reference potential at infinite distance will introduce error in calculated resistance, also anodes distribution along string is not addressed in conventional methods. Anode system resistance affect transformer-rectifier size in impressed current system, for tank internal cathodic protection this matter is important due to effect on nozzles quantity and location for suspending anode strings that affect tank construction. In this paper finite element analysis by COMSOL software and mathematical derivation used for calculation of anode system resistance and results compared by conventional methods. According to the results it is observed that error in calculated anode system resistance by conventional methods is more than 17% in comparison with finite element analysis results.

In this paper, the failure analysis of 2E-17131-B heat exchanger tubes (second stage condenser of the CTA2 unit) of Shahid Tondgooyan Petrochemical Company made of DSS 2205 steel has been studied. To reach the aim, visual inspection, chemical analyses, microstructural studies and cyclic polarization tests were carried out. Visual inspection of failure tubes showed that through-thickness pitting in 6 o’clock position caused the leakage and shutdown of the production line. Review of the manufacturing history revealed that there were two hold-ups for 24-48 hours.As a result, the hot current fluid lost its velocity and heat during this period, followed by condensing and accumulating the fluid on the bottom of the tube. Optical emission spectroscopy and portable X-ray fluorescence confirmed the chemical composition of the studied DSS 2205 steel based on relevant standards and data sheets. Microstructural investgations of the tube material revealed the typical microstructure of the duplex stainless steels. In addition, no microstructural changes were observed in the tubes after the service so that the pitting resistant was not weakened by a detrimental secondary phase formation. According to energy dispersive spectroscopy results, the corrosion products in the pits were rich in bromine. Therefore aggressive bromide anions ascertained as the main cause of the pitting corrosion. Given the obtained results of cyclic potentiodynamic polarization tests, the pitting resistance of DSS 2205 in the media containing bromide was lower than that of in chloride media, concluding that this steel is not appropriate for using as a 2E-17131-B heat exchanger tube material.

In self-healing coatings, corrosion inhibitors should be properly incorporated into the coating so that smart release of the inhibitor can occur in case of corrosion process. In this work, for the first time, multi-layered nanostructured self-healing coatings including sol-gel/ PEI-PAA polyelectrolyte pair / benzotriazole corrosion inhibitor / graphene oxide have been prepared to protect the surface of 2024 aluminum alloy. Local pH changes due to corrosion trigger the smart release of corrosion inhibitors, thus protecting the substrate surface. The presence of graphene oxide layer also prevents the penetration of water and corrosive agents to the substrate surface. SEM and EDS tests were used to study the morphology, chemical composition and distribution of constituent elements. The release of corrosion inhibitor in response to local pH changes was studied by UV-vis spectroscopy. FTIR and RAMAN tests were used to ensure the formation of a graphene oxide layer. Self-healing ability and corrosion protection of the coatings was studied by electrochemical impedance spectroscopy (EIS). The results showed that the smart multilayered coatings have superior corrosion protection performance compared to hybrid sol-gel monolayer.

One of the biggest and most dangerous problems in combined cycle power plants, which has reduced efficiency, degraded reliability and also created a lot of human and financial risks, is the problem of boiler corrosion. Most events in boilers occur suddenly. In this study, the flow accelerated corrosion (FAC) phenomenon in HRSG boilers of Kahnouj combined cycle power plant is investigated. Also, by examining the effect of pH increasing on reducing the FAC corrosion rate in deaerator’ evaporators and the conditions for this phenomenon, it can be said that changes in pH indicate that with increasing the FAC corrosion rate should be drastically reduced, which leads to a change in chemical control operation and condition improvement. Finally, the ideas are expressed to reduce these problems.