What impact does a high concentration of naphthenic acids in crude oil have on refinery equipment, particularly in the absence of sufficient neutralization?

A high concentration of naphthenic acids in crude oil significantly increases the risk of naphthenic acid corrosion (NAC) in refinery equipment, especially when adequate neutralization is lacking. Naphthenic acids, also known as cycloaliphatic carboxylic acids, are organic acids present in certain crude oils. These acids become particularly corrosive at elevated temperatures, typically between 400°F (204°C) and 750°F (399°C), where they can react with carbon steel components in distillation towers, transfer lines, and other process equipment. The corrosion mechanism involves the acidic attack of the metal surface, forming iron naphthenates, which are soluble in the hydrocarbon stream, thus removing the protective oxide layer and leading to continuous metal loss. This corrosion is exacerbated in areas of high turbulence and velocity, such as elbows and restrictions in piping. Without sufficient neutralization, the naphthenic acids remain active and aggressively corrode the equipment. Neutralization is typically achieved by injecting alkaline chemicals, such as ammonia or caustic soda (sodium hydroxide), into the crude oil upstream of the distillation units. These chemicals react with the naphthenic acids, forming less corrosive salts that can be removed in downstream processes or remain as less harmful deposits. Insufficient neutralization leaves the equipment vulnerable to accelerated corrosion, leading to potential leaks, equipment failures, and unscheduled shutdowns, resulting in significant economic losses and safety hazards. The severity of NAC depends not only on the concentration of naphthenic acids but also on factors such as temperature, flow rate, and the presence of other corrosive species like sulfur compounds. Effective monitoring and control of naphthenic acid levels and the implementation of robust neutralization strategies are crucial for mitigating NAC and ensuring the reliable operation of refinery equipment.