There were no leaks during the heat exchanger production process; it was stopped, and upon resuming operation multiple leaks were detected
Thread Content
My company has a 2-million-ton atmospheric and vacuum distillation unit. During normal operation, everything worked properly, and the color of the oils from unit 1 and unit 2 was also good. Recently, the unit was shut down without addressing the oil seals; it was restarted after 10 days, only to find that the color of the oil from the atmospheric side stream was very poor. Upon investigation, it was discovered that more than 10 tubes in unit 1 were leaking. Initially, it was thought that the gasketing on the heat exchanger’s floating head was loose, but it turned out to be leaks in the stainless steel tubes, which are made of material 321. Corrosion in unit 1 is likely caused by naphthenic acids and sulfur. Given such extensive leakage, why didn’t contamination occur in the side stream during previous operations? Why did so many tubes start leaking suddenly this time? The temperature of the oil exiting unit 1 is 210 degrees, while that of the oil returning is 140 degrees. I would appreciate your advice
Was pressure testing done before starting work? Is the shutdown based on the cooling curve?
Large temperature fluctuations during startup and shutdown, as well as the operation of start-up and shutdown pumps, cause pressure to be applied to one end of the heat exchanger, making leaks likely to occur
Only stainless steel will leak; carbon steel won’t. If it’s stainless steel, intergranular stress corrosion may have occurred!