Corrosion of carbon steel caused by sulfur in carbon dioxide gas

Found online; let’s see if it’s helpful. If sulfur is involved, check out this article: The Effect of Sulfide Ions on the Corrosivity of Carbon Steel. I. On the Corrosivity of Carbon Dioxide – The term “CO2 corrosion” was first used in 1925 by API (American Petroleum Institute). In 1943, corrosion of the tubing below oil wells in the Texas oil fields was first identified as CO2 corrosion. CO2 in aqueous media can cause rapid general corrosion as well as severe localized corrosion of steel; early corrosion of pipes and equipment often leads to serious consequences. In the former Soviet Union, CO2 corrosion of oil field equipment was first identified during the development of the Krasnoyarsk Krai oil and gas fields in 1961–1962. The corrosion rate on the inner surfaces of the equipment reached 5–8 mm·a-1, leading to equipment damage and potential accident risks. During the CO2 flooding tests in the Little Creek oil field in the United States, without any inhibiting measures, the tubing walls of the production wells corroded and perforated in less than 5 months, with a corrosion rate as high as 12.7 mm·a-1. Such catastrophic accidents in oil and gas fields are a direct result of CO2 corrosion; they not only cause substantial economic losses but also lead to serious social consequences. Similar CO2 corrosion damage incidents have occurred at the South China Sea oil fields and the Sichuan oil and gas fields. CO2 corrosion also often occurs in chemical equipment such as those used in fertilizer production. For example, the high-pressure CO2 water coolers in the large fertilizer plant of Zhenhai Petrochemical Complex are used to cool the CO2 gas to an appropriate temperature before it enters the high-pressure synthesis system. This device is a U-tube heat exchanger. The first U-tube was made of 3074L stainless steel with a wall thickness of 3 mm; it developed leaks one and a half months after being put into operation due to severe pitting corrosion. The material of the second tube was changed to 2RE69 stainless steel; it was scrapped after being in use for over 40 days due to too many leaks. In components such as feedwater preheaters and coolers in hydrogen production plants, CO2 corrosion damage often occurs due to the transmission of gases containing CO2 and CO. This corrosion mainly takes place near the dew point; it manifests as pitting corrosion. The higher the pressure and the more moisture present, the lower the dew point, and thus the more severe the corrosion becomes. For carbon steel, at a pressure of 15×105 Pa, the corrosion rate can reach as high as 17 mm/a. The explosion of a gas pipeline and a gas storage tank (with a diameter of 3 meters) in the Dutch city of Zeist in 1996, as well as the cracking in the welding areas of carbon steel fittings and nozzles in the piping system of Japan’s first large-scale organic pharmaceutical manufacturing plant in June 1966, which led to the release of gas from within, were both later found through investigation to have been caused by stress corrosion cracking in a CO2-CO-H2O medium. II. Factors affecting CO2 corrosion: Dry CO2 gas is not corrosive in itself. CO2 dissolves easily in water, and when dissolved, it has a highly corrosive effect on certain metal materials; the damage to these materials resulting from this is collectively referred to as CO2 corrosion. At the same pH value, since the total acidity of CO2 is higher than that of hydrochloric acid, its corrosion effect on steel is more severe than that of hydrochloric acid. CO2 corrosion is influenced by numerous factors, which can be broadly categorized as follows: 1. Environmental factors include CO2 partial pressure (Pco2), medium temperature (T), the mineralization degree of the aqueous medium, pH value, the concentrations of Cl2, HCO3, Ca, Mg, trace amounts of H2S and O2, as well as bacteria in the solution; the wax content in oil-gas mixtures; the load on the medium, flow rate, and flow pattern; and the structure and properties of the scale on the material surface. 2. Material factors include the type of material, the contents of alloying elements such as Cr, C, Ni, Si, Mo, Cu, Co, etc. in the material, and the surface coating of the material. CO2 can cause general corrosion (also known as uniform corrosion) in equipment, as well as localized corrosion. In the case of uniform corrosion, the entire or most of the metal surface is damaged uniformly; the rate of uniform corrosion is commonly expressed as the mass of material lost per unit time and per unit area, or as the average thickness of material lost per unit time. When local corrosion occurs, severe corrosion takes place in certain areas of the steel surface, while other areas are either unaffected or only experience mild corrosion. Different types of local corrosion exhibit distinct morphologies. For example, pitting results in pits with smooth surrounding areas, while platform corrosion creates larger recessed platforms with a flat bottom and vertically recessed edges. Flow-induced local corrosion takes the form of grooves, namely knife-shaped channels parallel to the direction of flow. III. Control of CO2 corrosion: CO2 dissolved in water is highly corrosive to steel; therefore, it is necessary to take certain protective measures in the chemical and petroleum industries to control the corrosion caused by CO2. These protective measures mainly fall into the following categories: 1. Adjusting the composition of carbon steel and low-alloy steel to enhance the metal’s corrosion resistance, or even using non-metallic materials ； 2. Change the environment in which the metal is used to reduce corrosion of the metal by the environment ； 3. Use a corrosion inhibitor ； 4. Electrochemical protection ； 5. Use a protective covering layer.

:victory: What a great thing