Heat exchangers are widely utilized in the petroleum refining industry, and their importance is self-evident. The utilization efficiency of heat exchange equipment directly impacts the overall efficiency of the refining process as well as operational costs. Statistics indicate that heat exchangers account for approximately one-fifth of the total investment in chemical plant construction projects. Consequently, the utilization efficiency and service life of heat exchangers constitute critical subjects worthy of in-depth investigation. An analysis of the causes of heat exchanger failure reveals that corrosion is a primary culprit; indeed, corrosion in heat exchangers is a widespread and pervasive issue. Effectively resolving the problem of corrosion is, therefore, tantamount to addressing the fundamental root cause of heat exchanger failure.
Corrosion Inhibitors: Corrosion inhibitors based primarily on chromates are commonly employed in cooling water systems. The chromate ion acts as an anodic (process) inhibitor; when combined with appropriate cathodic inhibitors, it yields corrosion protection results that are both satisfactory and economically viable.
Chromate-Zinc-Polyphosphate: Polyphosphates are utilized for their ability to clean metal surfaces and for their inherent corrosion-inhibiting properties. Polyphosphates can undergo partial hydrolysis to form orthophosphates, which, in turn, can react with calcium ions to generate large colloidal cations, thereby inhibiting the cathodic process.
Chromate-Zinc-Phosphonate: This method is similar to the aforementioned approach, with the exception that sodium phosphonate is substituted for polyphosphate. Aminomethylene phosphonates are particularly suitable for applications involving pH levels higher than those typically prescribed for polyphosphate-based systems. Aminomethylene phosphonates effectively prevent scale formation and can control the precipitation of calcium salts, even at pH levels as high as 9.
Chromate-Zinc-Hydrolyzed Polyacrylamide: This system leverages the dispersing action of hydrolyzed polyacrylamide-a cationic copolymer-to prevent or inhibit the formation of scale and fouling deposits.
Electrochemical Protection: This approach involves the application of both cathodic protection and anodic protection techniques. Cathodic protection entails utilizing an external DC power source to render the metal surface of the equipment the cathode, thereby achieving protection. However, this method is characterized by high power consumption and significant operational costs. Anodic protection, conversely, involves connecting the heat exchanger requiring protection to the anode of an external power source; this process induces the formation of a passive film on the metal surface, thereby providing corrosion protection.
