Thread Content
Gonglenghui recently learned about a YS dual-mode unit; 8 months after it was put into use, leaks appeared in the copper tubes of the evaporator. Upon inspection of the tubes, a large amount of brown sediment was found in the water sample, as well as numerous brownish-black fine particles on the inner walls of the tubes, which were primarily iron oxide. Chemical analysis of the water quality showed that the coolant solution was acidic, with a pH value of 5.7. Below are the precipitates in the ethylene glycol solution, as well as the deposits on the inner walls of copper pipes. Next, focusing on the \"ethylene glycol aqueous solution\", this study will investigate whether it is corrosive, the reasons for its corrosiveness and the associated hazards, as well as the anti-corrosion measures to be adopted for the refrigerants used in YBC units, water-cooled dual-mode units, and industrial refrigeration units. I. Whether the ethylene glycol aqueous solution is corrosive: Analysis of the ethylene glycol solution sample using an industrial cooling unit revealed that the ethylene glycol content was 15.04%, the acid value was 0.15 mgKOH, the chloride (Cl ions) content was 0.0037% (37 ppm), and the pH value was 5.74. The main components of the precipitate in the solution are: Ca at 0.24%, Fe at 68.13%, S at 0.40%, and Si at 0.59%. Spectral analysis of the main components of the fine particulate matter attached to the copper tubes showed a Ca value of 0.42%, an Fe value of 63.18%, an S value of 0.78%, a Si value of 1.55%, a Cd value of 1.01%, and a Cu value of 3.50%. Investigating the source of iron oxide reveals that it is a corrosion product of the solution on steel pipes. According to Gonglenghui, the evaporator tube side system of this unit requires a 25% ethylene glycol aqueous solution as a coolant; this solution is acidic and does cause corrosion to steel pipelines. Research has found that EPS Company in the UK conducted tests on the corrosion of iron by ethylene glycol-based cooling fluids with and without corrosion inhibitors in the refrigeration industry; without corrosion inhibitors, rust formation occurred within two weeks. The article from the Naval Facilities Engineering Service Center states that only through proper testing and the timely addition of the correct corrosion inhibitors can ethylene glycol solutions be used in cooling systems for 20 years. II. Reasons for the corrosive effect of ethylene glycol aqueous solutions: Firstly, the corrosivity of ethylene glycol is lower than that of water. Secondly, ethylene glycol aqueous solutions have a slight acidity. Thirdly, they become acidic as they oxidize into organic acids during use. Lastly, the corrosivity of these solutions increases as the solution temperature rises and as exposure to oxygen increases. Ethylene glycol is colorless and odorless, has low volatility, and is low in corrosivity; it mixes easily with water and other organic compounds. It is one of the most common organic refrigerants. Data shows that nearly half of the production of ethylene glycol is used as coolant and refrigerant in the automotive and refrigeration industries. III. Hazards of corrosion 1. Corrosion of pipes leads to early leakage in the piping system. 2. Induce electrochemical corrosion, exacerbating pipeline leaks. 3. In pipeline systems, the pipes, pumps, valves, as well as various welding and brazing joints used to connect the pipelines, can suffer from corrosion caused by the deposition of corrosion products in acidic electrolyte solutions; this can lead to phenomena such as galvanic corrosion and concentration cell corrosion. IV. Corrosion prevention and control measures 1. Select the appropriate coolant. The requirements for a coolant are that it remain in liquid state throughout the operating temperature range, have a high boiling point and a low freezing point, as well as a high specific heat, low density, and low viscosity. It exhibits good chemical stability at operating temperatures, does not corrode pipes and equipment, does not burn, is harmless to humans, is inexpensive, and is readily available. The table below shows the common types of refrigerants and their corrosivity. 2. Control and monitoring of reserve alkalinity. In most cases, the reserve alkalinity should be 10–12 milliequivalents. ASTM D1122 specifies that the reserve alkalinity for long-lasting antifreeze should be 10–20 mg/100 ml. The frequency of testing and adjusting the system solution depends on the level of reserve alkalinity in the solution; a simple pH measurement shows that it should be above 7.5 and not below 6.5. 3. Reduce contact between the solution and oxygen by using a closed saline circulation system. The ethylene glycol corrosion inhibitor solution is composed of a buffer and a passivator; the buffer is used to neutralize the organic acids generated by the oxidation of ethylene glycol, and can be substances such as borax or triethanolamine. A passivator is a substance that forms a passive film on the metal surface, resulting in electrical polarization and thereby preventing corrosion. It can be phosphates, molybdates, etc. The corrosion-inhibiting capacity of a solution refers to its resistance to acidification; the specific measure for this is the number of milliliters of 0.100N hydrochloric acid required to titrate 10 ml of an ethylene glycol solution to pH 5.5. 4. Add the appropriate corrosion inhibitor to monitor and control the corrosion of the pipelines by the solution. The selection of corrosion inhibitors is well-established in the automotive industry, with inhibitors tailored for different types of gasoline and diesel as well as various vehicle models. In the refrigeration industry, there are also corresponding products abroad such as TYFOCOR-L(EPS). Specifically, corrosion inhibitor suppliers conduct system analysis to develop specialized formulas and control methods suitable for that particular system, including requirements regarding water quality, so as to make the corrosion inhibitors more effective for the machinery. 5. Improve water quality. Shandong Gonglenghui Network Information Technology Co., Ltd. is an industrial internet company whose vision is to create a one-stop MRO service platform for industrial refrigeration, aiming to become a trusted partner for its customers. Its e-commerce platform, \"Gonglenghui\", operates on a B2B+O2O model to supply customers with lubricants and filters for daily maintenance, as well as sensors, valves, controllers, electrical components, heat exchangers, compressors, and control centers for repairs. It also provides parts such as bearings, seals, shaft seals, rotors, slide valves, balance pistons, and impellers for major overhauls. The platform offers comprehensive remote and on-site technical services. With the mission of \"creating more value for customers in the field of industrial refrigeration through an efficient supply chain and high-quality services,\" it aims to ensure customer satisfaction and deliver value to them at all times. The brands that our company primarily serves at present include York, GEA (Grasso), Wuleng, Daleng, Yanceng, Carrier, Trane, McQuay, and others; we handle the maintenance of these units. Our engineers possess high technical skills, enabling them to carry out maintenance work efficiently and with high quality in terms of unit repair, system adjustment, and electrical control, while also striving to achieve new successes through a sincere attitude.