Weekly Topic: Leakage Issues in Hydrogenation High-Pressure Heat Exchangers – Issue 18, June 12–18, 2011
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This post was last edited by lijianhuai on 2011-6-11 09:06. The weekly topic discussion sessions in the refining area welcome active participation from everyone, and we hope that you will come up with more valuable topics. Please do not hide your responses to this question. Our hydrogenation high-pressure heat exchangers developed tube-side leaks after another year of use; after shutting down the system and plugging 59 tubes, operation was resumed, but leaks occurred again just a few days later. The shell of these heat exchangers is made of 2.25Cr1Mo, while the tube side is made of 0Cr18Ni10Ti. The leaks occurred in the part of the heat exchanger where water was injected. What are the factors that cause corrosion and perforation in the tube side of hydrogenation high-pressure heat exchangers? Some say it’s sulfur corrosion; I don’t think so. Others say it’s chlorine corrosion, but we haven’t tested the chlorine content in the raw materials. I’m aware that chlorine is destructive to 0Cr18Ni10Ti. Please share your opinions – what level of S, Cl, etc. should be maintained in the hydrogenation feedstocks? If the properties of the raw materials cannot be changed, what type of material should be used for the tubes?
Reply to 1# lijianhuai: There are two reasons. One is the material quality of the pipes, and the other is corrosion. Regarding the Cl ion corrosion mentioned by the moderator, it is necessary to analyze the Cl ion content in the medium, as Cl ions do cause rapid corrosion of stainless steel.
The S content of the raw materials used in processing, as well as the operating temperature and pressure, and the manufacturer of the equipment.
Upgrade the duplex steel, increase water injection, and reduce the salt content in the raw materials
Reply to 1# lijianhuai: The quality of the water used for hydrogenation and water injection needs to be well controlled; it is best to use deionized water with a chloride content of less than 3 ppm in order to reduce the chlorine concentration in the heat exchangers； Leakages in the raw material heat exchangers are usually caused by intergranular corrosion cracks due to chloride ions. Sulfur corrosion proceeds more slowly in lower temperatures, and a small amount of chloride ions has little effect on carbon steel; therefore, the final stage of heat exchanger cores as well as air-cooled and water-cooled coolers can be made of 10# steel ； Finally, the material for the second-stage heat exchanger can be 316L ； In environments with relatively high temperatures, chlorine exists in the gas phase, which causes little corrosion to equipment and pipelines; therefore, other heat exchangers operating at temperatures above 280 degrees generally do not experience corrosion-related leaks
Cl—has a severe destructive effect on stress corrosion of austenitic stainless steels. The important factors affecting stress corrosion in austenitic stainless steels are temperature, the medium, the shape/size and distribution of non-metallic inclusions, as well as the influence of processing stresses. The fracture direction of stress corrosion is generally perpendicular to the direction of the stress, and it propagates in a dendritic pattern. Stresses originate from residual stresses resulting from cold deformation, welding, and metal impact; the occurrence of these stresses disrupts the stable structure within the metal, causing dislocations to form slip steps under the action of the stress. The presence of these slip steps provides an opportunity for Cl– to adsorb and penetrate. Chloride stress corrosion resistance test: In the aforementioned corrosive environment, both ultra-pure ferritic stainless steels and duplex stainless steels withstood a testing period of over 1000 hours without experiencing fracture. It can be seen that ordinary austenitic stainless steels are not resistant to chloride stress corrosion.
How is it the same as our workshop’s situation?
Reasons: One is the material issue of the pipe, and the other is corrosion. Use desalinated water with a chloride content controlled at less than 3 ppm to reduce the chlorine concentration in the heat exchanger ； Leakages in the raw material heat exchangers are usually caused by intergranular corrosion cracks due to chloride ions. Sulfur corrosion proceeds more slowly in lower temperatures, and a small amount of chloride ions has little effect on carbon steel; therefore, the final stage of heat exchanger cores as well as air-cooled and water-cooled coolers can be made of 10# steel ； Finally, the material for the second-stage heat exchanger can be 316L.