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Recently, everyone is more concerned about the causes of tube bundle corrosion in petrochemical water coolers. I wrote "Causes of Tube Bundle Corrosion in Gasoline Water Coolers" to introduce it to you so that you can have a preliminary understanding of the tube bundle causes. Depending on the corrosion situation, methods for anti-corrosion can be considered to extend the service life of the pipe bundle. Reasons for corrosion of gasoline water cooler tube bundles 1. Corrosion status of cold exchange equipment Cooler and condenser are one of the key equipments of the production device. Most of them are made of carbon steel, which generally accounts for about 30% of all heat exchange equipment. About 60% of the daily emergency repairs of a large number of faults and accidents are caused by corrosion and leakage of pipe bundles in cold exchange equipment. It seriously affects the safety, stability and full-load operation of the production equipment. In addition, when the cooling water exchanges heat with a medium with a higher temperature (most of the water travels through the tube), the water is prone to scale, forming a rust layer, which increases the thermal resistance, seriously reduces the heat exchange efficiency, and cannot meet the needs of production. Due to the corrosion and scaling of the cooler tube bundles, the service life is short, and most tube bundles are scrapped and replaced in advance. 2. Reasons for Corrosion of Cooler Tube Bundle 2.1 Corrosion and scaling of oil phase side corrosion equipment are common problems in the operation of refinery production units, especially the condensation and cooling systems of low-temperature parts at the top of the tower such as atmospheric and vacuum, catalytic cracking, delayed coking, etc. of primary and secondary processing units. Corrosion is more serious, and the cooler is one of the more prominent parts. Because the shell medium of the cooler is oil or oil gas (its operating temperature is about 80 to 150°C), it exchanges heat with the cooling medium circulating water (its operating temperature is about 28 to 40°C). Judging from the morphology and metallographic analysis results of the corrosion parts, they are all electrochemical corrosion, but the corrosion medium and operating conditions are different. Generally, the corrosion of the vapor phase part is slight, while the corrosion of the liquid phase part is severe, especially the vapor-liquid two-phase phase transition part (dew point part) is the most serious. The corrosion forms are comprehensive corrosion and local corrosion, with pitting corrosion being more prominent in some cases. The maximum local corrosion rate is as high as 6mm/a or more, with an average between 1.2 and 5mm/a. Severe corrosion damage to primary processing equipment is due to the mutual promotion of HCl and H2O, forming cyclic corrosion. The reaction formula is: Fe + 2HCl → FeCl2 + H2↑ FeCl2 + H2S → FeS↓+2HCl Fe + H2S → FeS + H2↑ FeS + 2HCl → FeCl2 + H2S The cause of corrosion in the condensation system of secondary processing equipment is different from that of primary processing equipment, but the degree of corrosion at the gas-liquid phase transition part in the condensation area is the same. From the appearance of the corroded tube bundles, the spaces between the tube bundles are blocked by loose corrosion products and dirt, and corrosion pits appear on the metal surface. 2.2 Corrosion on the circulating water side is caused by the cooling water containing bicarbonates, carbonates, chlorides, phosphates, etc. Among them, dissolved bicarbonates such as Ca(HCO3)2 and Mg(HCO3)2 are the most unstable. When the cooling water flows through the heat-transmitting metal surface, the following reaction occurs: Ca(HCO3)2 → CaCO3 ↓ + H2O + CO2↑ Mg(HCO3)2 → MgCO3 ↓+ H2O + CO2↑ When a large amount of calcium chloride is dissolved in water, the following displacement reaction will also occur: CaCl2 + CO-23 → CaCO3↓ + 2Cl- When polymeric phosphate is added to water as a corrosion inhibitor, calcium will be converted into calcium phosphate. The reaction is: 2PO4-3 + 3CaCl2 → Ca3(PO4)2↓ + 6 Cl- In addition, the oxygen dissolved in the cooling water can also cause metal corrosion and form rust. The reaction is as follows: 2Fe+2H2O+O2 → 2Fe(OH)2 ↓ The result of the reaction is gradual scaling on the heat transfer surface, accompanied by the formation of rust. When the cooler is running, the heat exchange effect is seriously reduced due to the influence of the scale layer. Some individual tube bundles have been blocked within the heat exchange tubes after less than a year of use. In addition, due to the presence of scale, it is easy to cause corrosion under the scale on the inner wall of the pipe, reducing the service life of the pipe bundle. The corrosion of metal surfaces by water is mainly electrochemical corrosion. In the corrosion battery, the cathode reaction is mainly the reduction of oxygen, and the anode reaction is the dissolution of iron. The corrosion reaction of carbon steel in water is: anodic reaction: 2Fe → 2Fe+2 + 4e cathodic reaction: O2 + 2H2O + 4e → 4OH- Overall reaction: 2Fe + 2H2O + O2 → 2Fe(OH)2↓ During corrosion, iron forms iron hydroxide and precipitates out of the solution. Because this ferrous iron compound is unstable in oxygen-containing water, it will further oxygenate to form iron hydroxide. 2Fe(OH)2 + 2H2O + 1/2O2 → 2Fe(OH)3↓ After that, the iron hydroxide dehydrates and forms rust. 2Fe(OH)3 → FeOOH ↓+ H2O Reddish-brown Fe(OH)3 is basically insoluble in water. As long as the dissolved oxygen in the water continues to increase, this conjugate reaction that corrodes the battery will continue. In addition, the content of other components in the water, as well as temperature, flow rate and the action of microorganisms, will all affect the progress of the above-mentioned conjugation reaction process. The presence of dissolved solids, especially oxides and sulfates, can exacerbate corrosion. The presence of suspended solids and dirt in the water will cause local accumulation of dirt, making it difficult for the metal protective film to form or forming an oxygen concentration difference battery to cause pitting corrosion. Therefore, metal corrosion under scale will accelerate the corrosion of metal due to the autocatalytic effect of electrochemical corrosion itself. 3. Attention In short, for petrochemical companies, the amount of money spent every year on replacing pipe bundles of cold replacement equipment due to corrosion accounts for a relatively large proportion of the entire overhaul and update. Therefore, the rational selection of pipe bundle materials and control methods for cold exchange equipment to reduce corrosion is an issue that our scientific and technical personnel have always been concerned about.