Today, refineries do not have the technology to neutralize organochlorine compounds (OC) or reliably protect equipment. Some experience in the fight against chlorine at refineries has already been obtained, but, in our opinion, none of the proposed developments is yet effective enough [1-5]. Control of the inorganic chloride salts content in oil is carried out by the extraction of metal chlorides (mainly chlorides of sodium, calcium and magnesium, which are soluble in water), followed by titration of the aqueous extract. A more complex task is to methodically ensure the determination of OC content in oil. Solving this problem has its own specifics: first, oil is a complex mixture of hydrocarbons with a low content of OC, measured in parts per million (ppm); second, the oil contains organosulfur compounds that interfere with the determination of chlorine. Diesel fuel commodity, the indicators of which met the requirements of SSTU 7688: 2015, was used as a medium for corrosion research of metal plates - steel St 20, components from the pipeline, the tank, from the pipeline from Czech steel. The oils used for research (export mix 1) were analyzed and indicated as follow: • Sample 1 with OC content of 0.8 ppm; • Sample 2 with OC content of 170 ppm; For this study, the most corrosive compounds - dichloroethane, methylene chloride and trichlorethylene - were mixed in 1:1:1 ratio: • Sample 3 - OC content of 430 ppm; • sample 4 - OC content of 438 ppm. According to oil companies, the main share of organochlorine, which is found in oils, consists of dichloroethane, dichloromethane, chloroform, trichlorethylene, perchlorethylene, and of these products the content of trichlorethylene is the highest. These chlorine-containing products are fed into the oil to dissolve paraffin deposits and reduce their amount in the pipeline but, at the same time, it was established that the greatest corrosion was caused by these compounds, specifically dichloroethane, methylene chloride and trichlorethylene. The material, used to investigate the corrosion effect, was a metal plate taken from different components: a pipeline, a tank, and a Czech steel pipeline. The experimental conditions were: temperature of 30 ºС and 40 ºС; exposure time of 2 hs. To evaluate the reproducibility two control tests were conducted in the same conditions of commercial diesel fuel. An oil mixture with OC content of 438 ppm (sample 4) was added in the amount of 30%v to each control test, since it should have the greatest active corrosive effect on the pipelines and welded joints components. The experimental results revealed that the corrosion rate is negligible in the tested materials: metal plates taken from pipeline, tank, Czech steel pipeline showed resistance to the aggressive condition in a “stable” level; the corrosion activity of the aggressive state was assessed as "average". The corrosion effect of chloroform, dichloromethane, methylene chloride, trichlorethylene and perchlorethylene on metal plates, using a concentration of OC in the range from 10 to 1000 ppm in mixture with commercial diesel fuel at a temperature of 20° C was studied; also in this study the corrosion effect was evaluated on metal samples - steel St 20, metal from the pipeline, tank, metal pipeline from Czech steel. Among the studied OCs, the most corrosive compounds were found - dichloroethane, methylene chloride and trichlorethylene. The effect of chemical composition and concentration of OC mixture on corrosion of steel 20 was investigated. Dichloroethane, methylene chloride and trichlorethylene were mixed in 1:1:1 ratio. It was found that the content of this OCs mixture in the range of 10-500 ppm in diesel fuel at temperature of 30-40ºC increased the corrosive activity of the system to a maximum of "average" corrosion activity; in this condition, steel St 20 showed the corrosion resistance at a "stable" level in the scale of corrosion resistance of metal, and corrosion activity of the system in accordance with GOST 9.502. Using a mixture with OC content of 1000 ppm on St20 steel, the corrosion resistance changes to “reduced” level, and the corrosion activity of the aggressive system was assessed as "increased". The corrosion effect of mixture of the most corrosive OCs added to commercial diesel fuel in the amount of 500 ppm was evaluated on the metal components of main oil pipelines, tanks and process equipment. It was found that the obtained corrosive system at 30 ºC caused a low corrosion rate, while the studied metal plates showed resistance to aggressive environments at “stable” level; the corrosive activity of aggressive system was assessed as "medium". The increasing of the temperature experiments up to 40 ºC had a negligible effect on the corrosion rate under the action of OCs. The corrosion effect of mixture with the highest OCs content of 438 ppm, added to diesel fuel in the amount of 30% ppm was evaluated on the metal based components of main oil pipelines. Metal plates from the pipeline, tank, Czech steel pipeline showed resistance to the aggressive environment at “stable” level, and the corrosion activity of the aggressive system was assessed as "average". The increase of temperature experiments up to 40 ºC had a negligible effect on the corrosion rate under the action of OCs. Finally, considering the corrosive effect of OCs and the corrosion rate of main oil pipeline components, tanks and process equipment, it could be stated that the content of OCs in oil up to 500 ppm at temperatures up to 40 °C has little corrosive effect. Process equipment exhibited corrosion resistance at “stable” level in the scale of assessment of corrosion resistance of metal in accordance with GOST 9.502-82 (corrosion rate up to 0.1 mm/year).
To the Problems of Corrosion of Oil Transportation Equipment
Elena Dilonardo
Ultimo
2022
Abstract
Today, refineries do not have the technology to neutralize organochlorine compounds (OC) or reliably protect equipment. Some experience in the fight against chlorine at refineries has already been obtained, but, in our opinion, none of the proposed developments is yet effective enough [1-5]. Control of the inorganic chloride salts content in oil is carried out by the extraction of metal chlorides (mainly chlorides of sodium, calcium and magnesium, which are soluble in water), followed by titration of the aqueous extract. A more complex task is to methodically ensure the determination of OC content in oil. Solving this problem has its own specifics: first, oil is a complex mixture of hydrocarbons with a low content of OC, measured in parts per million (ppm); second, the oil contains organosulfur compounds that interfere with the determination of chlorine. Diesel fuel commodity, the indicators of which met the requirements of SSTU 7688: 2015, was used as a medium for corrosion research of metal plates - steel St 20, components from the pipeline, the tank, from the pipeline from Czech steel. The oils used for research (export mix 1) were analyzed and indicated as follow: • Sample 1 with OC content of 0.8 ppm; • Sample 2 with OC content of 170 ppm; For this study, the most corrosive compounds - dichloroethane, methylene chloride and trichlorethylene - were mixed in 1:1:1 ratio: • Sample 3 - OC content of 430 ppm; • sample 4 - OC content of 438 ppm. According to oil companies, the main share of organochlorine, which is found in oils, consists of dichloroethane, dichloromethane, chloroform, trichlorethylene, perchlorethylene, and of these products the content of trichlorethylene is the highest. These chlorine-containing products are fed into the oil to dissolve paraffin deposits and reduce their amount in the pipeline but, at the same time, it was established that the greatest corrosion was caused by these compounds, specifically dichloroethane, methylene chloride and trichlorethylene. The material, used to investigate the corrosion effect, was a metal plate taken from different components: a pipeline, a tank, and a Czech steel pipeline. The experimental conditions were: temperature of 30 ºС and 40 ºС; exposure time of 2 hs. To evaluate the reproducibility two control tests were conducted in the same conditions of commercial diesel fuel. An oil mixture with OC content of 438 ppm (sample 4) was added in the amount of 30%v to each control test, since it should have the greatest active corrosive effect on the pipelines and welded joints components. The experimental results revealed that the corrosion rate is negligible in the tested materials: metal plates taken from pipeline, tank, Czech steel pipeline showed resistance to the aggressive condition in a “stable” level; the corrosion activity of the aggressive state was assessed as "average". The corrosion effect of chloroform, dichloromethane, methylene chloride, trichlorethylene and perchlorethylene on metal plates, using a concentration of OC in the range from 10 to 1000 ppm in mixture with commercial diesel fuel at a temperature of 20° C was studied; also in this study the corrosion effect was evaluated on metal samples - steel St 20, metal from the pipeline, tank, metal pipeline from Czech steel. Among the studied OCs, the most corrosive compounds were found - dichloroethane, methylene chloride and trichlorethylene. The effect of chemical composition and concentration of OC mixture on corrosion of steel 20 was investigated. Dichloroethane, methylene chloride and trichlorethylene were mixed in 1:1:1 ratio. It was found that the content of this OCs mixture in the range of 10-500 ppm in diesel fuel at temperature of 30-40ºC increased the corrosive activity of the system to a maximum of "average" corrosion activity; in this condition, steel St 20 showed the corrosion resistance at a "stable" level in the scale of corrosion resistance of metal, and corrosion activity of the system in accordance with GOST 9.502. Using a mixture with OC content of 1000 ppm on St20 steel, the corrosion resistance changes to “reduced” level, and the corrosion activity of the aggressive system was assessed as "increased". The corrosion effect of mixture of the most corrosive OCs added to commercial diesel fuel in the amount of 500 ppm was evaluated on the metal components of main oil pipelines, tanks and process equipment. It was found that the obtained corrosive system at 30 ºC caused a low corrosion rate, while the studied metal plates showed resistance to aggressive environments at “stable” level; the corrosive activity of aggressive system was assessed as "medium". The increasing of the temperature experiments up to 40 ºC had a negligible effect on the corrosion rate under the action of OCs. The corrosion effect of mixture with the highest OCs content of 438 ppm, added to diesel fuel in the amount of 30% ppm was evaluated on the metal based components of main oil pipelines. Metal plates from the pipeline, tank, Czech steel pipeline showed resistance to the aggressive environment at “stable” level, and the corrosion activity of the aggressive system was assessed as "average". The increase of temperature experiments up to 40 ºC had a negligible effect on the corrosion rate under the action of OCs. Finally, considering the corrosive effect of OCs and the corrosion rate of main oil pipeline components, tanks and process equipment, it could be stated that the content of OCs in oil up to 500 ppm at temperatures up to 40 °C has little corrosive effect. Process equipment exhibited corrosion resistance at “stable” level in the scale of assessment of corrosion resistance of metal in accordance with GOST 9.502-82 (corrosion rate up to 0.1 mm/year).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
