Corrosion of high-temperature naphthenic acid in distillation equipment
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The original sulfur content is increasing nowadays, and the corrosion caused by high-temperature naphthenic acids during the processing of crude oils with high acid values is posing an increasingly serious threat to atmospheric and vacuum distillation units. This corrosion mainly affects the constant third line, constant bottom line, vacuum second, third, and fourth lines, the oil transfer line, and the heating furnaces; it also impacts the heat exchangers used for fractionated oils. The measures taken to protect against high-temperature naphthenic acids consist primarily of using materials resistant to corrosion, with the addition of corrosion inhibitors serving as a supplementary measure. Friends in the refinery industry, please discuss based on your respective experiences the issue of high-temperature naphthenic acid corrosion in atmospheric and vacuum distillation units, as well as the materials used for equipment and pipelines, and the specific types, properties, and effectiveness of corrosion inhibitors!
During the renovation in 2001, the process pipelines operating at temperatures above 250 degrees were upgraded from carbon steel to Cr5Mo, while 316L was used for the pressure-reduction side lines. The current performance of these pipelines is excellent; this facility processes Luning crude oil, whose acid value is around 1.5, and can reach 2.0 at times. At present, the degree of pipeline corrosion and thinning is considered acceptable. No corrosion inhibitors are used in this facility. In the facility used for processing light oil, high-temperature corrosion inhibitors from Nanjing Wanermei were adopted in 2007. According to the data, the iron content in the products from the side lines using these inhibitors decreased by more than 50%, indicating a certain level of corrosion protection. The main issue in this facility is high-temperature sulfur corrosion.
Corrosion by high-temperature naphthenic acid in atmospheric and vacuum distillation units http://bbs.hcbbs.com/viewthread.php?tid=113718&highlight=
The average acid value of the crude oil processed by my unit is around 2 mg KOH/g. The materials used for the various side lines of the vacuum distillation tower were originally 304L; however, upon inspection during maintenance, it was found that the second and third vacuum lines were severely corroded. These lines have now been replaced with 316L material. We have also added a high-temperature corrosion inhibitor to the second vacuum line. This inhibitor is made from high-molecular-weight, high-boiling-point organic polymers, and it forms an adsorptive protective film on the surface of the metal materials. At the same time, some corrosion inhibitors react directly with naphthenic acid to form naphthenate esters. These high-molecular-weight naphthenate esters can establish an adsorption equilibrium on the metal surface, isolating organic acids such as naphthenic acid from the metal surface thereby protecting the material. Based on the analyses from various side lines after injection, the iron ion concentration decreased significantly, indicating that it should have had a certain effect. The high-temperature corrosion inhibitor we use is model LX-213. This post was last edited by seea on 2008-1-16 at 13:53.]
Has corrosion inhibitors been added to crude oil to address naphthenic acid corrosion?
In the past, alkali was injected into crude oil to slow down naphthenic acid corrosion. It’s basically nowhere to be found in China now, but it still exists abroad.