مجله علوم و مهندسی خوردگی
سال دوازدهم شماره 1 (پیاپی 43، بهار 1401)

In this paper, the effect of corrosion on the ultimate strength of fixed offshore jacket structures, which are among the most widely used structures in both oil and gas and renewable energy industries, is investigated. The effects of corrosion over different periods of time have been considered as a uniform reduction in the thickness of the members and other types of corrosion and their effects have not been considered in this study. The fixed offshore jacket structure considered in this study belongs to one of the gas platforms in phase 19 of South Pars gas field, which has a lifespan of 25 years. The ultimate strength of the structure is obtained by pushover analysis and it is expressed using the reserve strength ratio. For this purpose, the structure has been modeled and analyzed in SACS software, which is one of the most widely used finite element softwares in this field. According to the results of this study, if the assumptions made about corrosion occur, the ultimate strength of the structure after it reaches its lifespan will be reduced by approximately 20%, such that the value of the reserve strength ratio of the structure is 1.7 when no corrosion is applied, but it reduces to 1.3 considering the amount of corrosion applied after the design life of the structure (i.e., 25 years). This downward trend is mainly to be continued over the following years.

The DP980, DP590, and IF steels are used in the construction of car bodies due to their unique mechanical properties. In this paper, the corrosion behavior and microstructure of the DP980, DP590, and IF steels which are used in the automotive industry are investigated and evaluated. In order to evaluate the corrosion behavior of all three alloys, the electrochemical impedance spectroscopy and potentiodynamic polarization were evaluated in 0.1 M NaCl + 0.1 M H2SO4 and 0.1 M NaCl + 0.1 M NaOH environments. The corrosion evaluations of all three alloys show much better corrosion behavior in the alkaline environment than in the acidic environment due to the formation of the passive layer. While these alloys show much less corrosion resistance in the 0.1 M NaCl + 0.1 M H2SO4 environment, the uniform corrosion occurs while there is no evidence of the passive layer formation. The DP980 and DP590 dual-phase steels show lower corrosion resistance than the IF steel due to the presence of the ferrite and martensite phases and the possibility of galvanic cell formation at the interface between the two phases. The DP980 dual-phase steel has a better corrosion behavior than the DP590 due to the lower martensite content in both acidic and alkaline solutions, but the corrosion behavior of these two sheets of steel is very close to each other.

One of the main problems in the oil and gas industry is CO2 corrosion which is known as sweet corrosion. The use of corrosion inhibitors is one of the most effective methods for corrosion control in the oil and gas industry. In this paper, the mechanism and effect of concentration of an imidazoline base derivative on CO2 corrosion of carbon steel was investigated. For this purpose, the corrosion behavior of a plain carbon steel in a NACE standard solution at ambient temperature was studied. The open circuit potential (OCP) and potentiodynamic polarization measurements in presence of different concentrations of imidazoline inhibitor were conducted to determine the corrosion rate of samples. . The results showed that the imidazoline base inhibitor reduced the kinetics of anodic reactions by adsorption on the metal surface and blocking the active corrosion sites . Also, it was observed that 15 ppm of imidazoline inhibitor provided the optimum inhibition efficiency of 89.87%.

The interrelationship between the five events in the process industries: corrosion, process deviation, energy, environment, and production cost was discussed. A significant interrelationship developed between these five events. In the meantime, it was shown why process deviations and corrosion should have the maximum volume allocated for corrosion planning, strategy edition and management decisions. These two events were also examined from the perspective that they themselves cause many other difficulties. An industrial example was provided to address the details of each event to create the clear explanation. Then, during the introduction of the events and their interrelationship with each other, another industrial example was examined to present the impacts of these events on the overall performance as well as the corresponding events.

This article is an overview of carbon steel corrosion and its corrosion product structure in acid medium containing H2S and CO2 and suitable corrosion inhibitors in this environment. Carbon steel is the main construction material for process equipment, piping system and transmission pipelines because of it’s availability and reasonable cost. However, in acidic environments, which containing H2S gas, carbon steel corrodes at high rates, especially in multiphase flows corrodes at higher rates. The use of corrosion inhibitors is one of the logical and, from an economic point of view, cost-effective strategy to combat corrosion in these environments. In this study, the development of corrosion inhibitors in acidic environments from the past to the present, including inhibitors with mineral compounds such as sodium sulfate or organic compounds, which are divided into four general categories of inhibitors of Amine, Imidazoline, Polymeric and Gemini, has been investigated.

Adjunct to underground railway (which produce DC interference currents) and overhead power transmission lines (which produce AC interference currents), underground gas pipelines have been affected severely which have brought about corrosion costs namely direct and indirect costs. The effects of both types of stray currents on the UG gas pipelines located in a street in Tehran are studied. On-site inspections were performed and then additional laboratory studies were done to analyze and characterize the corrosion products. It is founded that the coating of the pipe has been disbonded in two points which are in 10-meter distances from each other and the external pipe wall were locally corroded which has led to gas leakage. According to the standard criteria and the results of AC potential, AC interference current may not cause the corrosion in the points. However, the amounts of offpotentials were out of range according to the relevant standards and therefore DC stray current produced by Tehran underground railway has mainly led to the corrosion. Corrosion products were not uniformly covered the metal surface and mainly contains Fe3O4 and FeOOH as well as FeCl2. Thus, it is recommended that additional evaluations need to be done according to BS EN 50162 and afterwards, protective measures must be taken to eliminate the side effects of the DC stray current.