Corrosion of heat exchangers in the ethylene glycol unit
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Dear sea friends, in an ethylene glycol brine unit, corrosion has occurred on the ammonia side of the heat exchanger. Please take a look to determine what type of corrosion it is and what caused it. One heat exchange tube is leaking. Thank you all
The tube fluid is ethylene glycol and saline, right! What’s the temperature like?
Describe in detail the operating conditions of the tube train, such as temperature, medium, pressure, etc., as well as the material of the tube bundle and the duration of use, so that analysis can be carried out more easily.
Vortices form at the pipe ends, which can lead to erosion corrosion. The pipe ends are welded flat; whereas per the standard, the tube sheet extends 3 mm beyond the tubes, the pipe ends in this case are welded in a circular pattern, which provides better corrosion resistance. The tubes can be made of stainless steel, or they can be coated to enhance their corrosion resistance!
Judging from the picture, it doesn’t seem to be tube media corrosion. It is likely that the shell-side fluid caused corrosion; axial scratches were formed during the drilling of holes in the tube sheet. After welding and expansion operations were completed, there was still a gap between the tubes and the tube sheet, and gap corrosion occurred during operation, leading to leakage. It’s just my personal opinion; I’m not sure if it’s correct. Please forgive any mistakes if there are any.
Corrosion: Judging from the image, it does not seem to be corrosion of the tube-side fluid. It is likely that the shell-side fluid caused corrosion; axial scratches were formed during the drilling of holes in the tube sheet. After welding and expansion operations were completed, there was still a gap between the tubes and the tube sheet, and gap corrosion occurred during operation, leading to leakage. It’s just my personal opinion; I’m not sure if it’s correct. Please forgive any mistakes if there are any.
The working fluid is ammonia, at a temperature of about -8°C. Thank you
This post was last edited by ytzyl on 2022-5-25 08:51. The medium on the tube side is ammonia; the evaporation temperature is around -8°C and the pressure is about 2.15 bar. The heat exchange tubes are of type 9948, model 10#, and have been in use intermittently for over a year. Thank you
I have done this many times before, and it’s the standard practice in the industry. Erosive corrosion, I don’t think so
Yes, the tube side contains ammonia, and ammonia does not cause corrosion. The shell side contains ethylene glycol saline, and corrosion inhibitors may not be added. I would like to ask: does ethylene glycol cause corrosion in the welds by creating small pits?
Generally, ethylene glycol is highly corrosive. Ethylene glycol causes cavitation in equipment when in contact with air. Erosion caused by cavitation tends to produce locally concentrated clusters of honeycomb-like pores, leading to corrosion of the equipment. At the same time, factors such as the instability of ethylene glycol due to its hydroxyl groups and its tendency to acidify can corrode carbon steel as well as ordinary stainless steels (304 stainless steel). This also results in very high levels of impurities such as rust in the solution system, with the impurity content reaching around 1%.