The process operations for the heating furnace tubes must be properly controlled to prevent carburization and tube rupture

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It is necessary to properly control the process operations of the heating furnace tubes in order to prevent carbon infiltration and tube rupture. Example: A hydrogen heating furnace belonging to an oil company came to a stop due to tube rupture and combustion caused by 1Cr18Ni9Ti stainless steel tubes. A hydrogen heater is a key device for heating the cycle gas, which is primarily composed of hydrogen. Liquefied gas burns in the heating furnace chamber to heat the furnace tubes, and the circulating gas passes through these tubes, causing its temperature to rise. It then merges with the injected mixed oil to form a reduced-pressure mixed oil, which flows toward the hydrocracking reactor. The cause of tube rupture in the furnace tube is severe carburization resulting from a large amount of oil coke adhering to the tube wall. Although carburizing largely preserves the original metal surface, it alters the internal surface structure and causes the material to become brittle. The large stress between the carburized layer and the matrix leads to cracks and fissures, and in severe cases, perforation and tube rupture occur. Analysis: The furnace tube is in a high-temperature and high-pressure environment; under normal operation, there should be no coke inside the tube. Coking occurs due to an imbalance in the control of the mixing point between hydrogen and reduced-pressure oil, which causes the mixed oil to flow back into the furnace tubes, bringing in some oil particles. Therefore, this type of tube burst accident is caused by poor process operation.