What are the criteria for evaluating and analyzing the effectiveness of corrosion inhibitors used in atmospheric and vacuum distillation units? ? ? ? ? ?

Of course, I hope everyone can provide the usage ratio of your corrosion inhibitors. Thank you.

The iron ion content should be no more than 3 ppm. As for the chloride ion content, different people have different opinions on it. Because if there is corrosion, then naturally the iron ion content will increase, but this seems to have nothing to do with the chloride ion content. Generally, chloride ions come from the raw materials; corrosion inhibitors do not guarantee this value. Corrosion inhibitors are divided into water-soluble and oil-soluble types; the concentration of water-soluble inhibitors is generally 20–30 ppm, and that of oil-soluble inhibitors is also in this range. Corrosion inhibitors usually need to be used in combination with neutralizing agents. The amount used varies depending on the acid value of the crude oil. Nowadays, most crude oils processed are high-sulfur oils, and ammonia is generally not added; as a result, a larger amount is required. Of course, this also depends on the materials used in various facilities and their operating conditions. There are many more details; I won’t go into them.

So what methods do everyone use for analyzing iron ions? ?

Regarding the effectiveness of corrosion inhibitors, the iron ion concentration is generally required to be less than 2PPM; the pH value is also a key parameter, and the point at which the corrosion inhibitor is injected is equally important.

My system uses two types of neutralizing corrosion inhibitors; one is from Fushun Dongyuan, but its effectiveness is poor, while the one from Lanzhou performs better. The effectiveness of these inhibitors can be assessed by the level of iron ions in the wastewater – it’s generally necessary to keep this level below 3PPM. Such neutralizing corrosion inhibitors have little impact on the pH value of the wastewater. We have six injection points in total: at the top distillation line (before it enters the cooler) and on the top reflux line, and their performance is good.

The product used in our factory is manufactured in Xiantao, Hubei, and it performs fairly well; it is water-soluble. In the past, we mainly checked for iron ions and chloride ions, as well as the color of the water.

What are the ratio concentrations and injection amounts? What criteria should be used?

The iron ion content in water is generally kept at no more than 3PPM. Current corrosion inhibitors include conventional ones and those designed for high-temperature conditions. In addition to measuring the iron ion content in water, it is also possible to measure it in oils, especially in second-generation and third-generation oils, where naphthenic acid corrosion is quite severe! 　One should pay close attention to the acid value of crude oil at all times; it is important to keep an eye on it from 240 degrees onward until before secondary processing.

The iron ion content should not exceed 2 ppm. As for chloride ions, their level is generally below 200 ppm. A pH value between 6 and 7 is ideal. Corrosion inhibitors come in water-soluble and oil-soluble forms; the concentration of water-soluble inhibitors is usually around 20–30 ppm, and that of oil-soluble inhibitors is also within this range. Oil-soluble corrosion inhibitors are generally preferred, as using water-soluble ones along with water can increase the COD level of the wastewater discharged; otherwise, a neutralizing agent must be added.

The iron ion content in water should generally be kept at no more than 3PPM. The neutralizing and film-forming corrosion inhibitors available in Cangzhou also perform well, with a dosage of around 40ppm.