Tube rupture in boiler superheaters and its treatment methods

This post was last edited by gjn1970 on 2011-8-30 at 13:57. Tube rupture in the superheater occurs: the negative pressure in the furnace decreases or even turns positive; the negative pressure curves in the various flue ducts of the boiler change from flat to serrated. Airflow sounds can be heard near the superheater or in the furnace flue ducts. The feedwater flow rate is abnormally higher than the steam flow rate, and the current drawn by the induced draft fan increases. In the event of a tube burst in the superheater, the furnace must be shut down immediately; the burst tube can damage other nearby tubes, potentially leading to a vicious cycle that results in an escalation of the accident. Turbine overheater tube failures are generally caused by excessive temperature, and can be divided into short-term overheating-induced failures and long-term overheating-induced failures; the rupture pattern in the former is trumpet-shaped, while that in the latter is lip-shaped. Another cause is wear and tear. Treatment for cracked pipes: In principle, pipe replacement is carried out. If the defect is minor and the expansion of the pipe diameter does not exceed the allowable limits (for alloy steel pipes, the creep expansion shall not exceed 2.5% of the original diameter; for carbon steel pipes, it shall not exceed 3.5%), then patch welding can be used as a solution. It is also necessary to check whether the creep expansion of the damaged pipe and other pipes exceeds the allowed limits; in principle, pipes that exceed these limits should be replaced as well. Otherwise, they represent a hazard when left inside the furnace, with a risk of pipe rupture at any time, resulting in significant losses (such as losses due to shutdowns, losses from restarting the furnace, and production losses caused by interruptions or reductions in steam supply). Finally, it is necessary to analyze the cause of overheating in the superheater tubes – whether it is due to scaling inside the tubes or other factors such as operating at excessive temperatures or blockages caused by foreign objects inside the tubes – and take timely measures to eliminate it. As for tube failures caused by overheating due to wear and thinning of the superheater tubes, resulting in insufficient strength, the common solution is to replace or weld the tubes back together; at the same time, it is necessary to analyze the causes and take timely measures to eliminate them.

1. Phenomena of superheater tube rupture accidents ⑴ Decrease in steam flow, with the steam flow being abnormally lower than the feedwater flow. ⑵ The pressure in the combustion chamber and furnace changes suddenly from negative to positive; in severe cases, smoke and steam are ejected outward through the openings. ⑶ There is a sound of steam spraying near the superheater. ⑷ Changes in superheated steam temperature. (It cannot be determined whether it is definitely rising or falling.) ⑸ The flue gas temperature decreases, and the color of the flue gas turns grayish-white or white. ⑹ The flue gas temperature drops after the superheater, resulting in an increased temperature difference between the flue gas before and after the superheater. ⑺ The load on the exhaust fan increases, resulting in a higher current. Handling of superheater tube rupture accidents: (1) If the superheater is only slightly damaged and the accident is not likely to spread rapidly, the load can be reduced temporarily while closely monitoring the leakage situation. Report to superiors and request to shut down the furnace ； Start the backup boiler as soon as possible to put it into operation, and then shut down the main boiler. If the backup boiler cannot be put into use in time and the fault worsens, the boiler should be shut down immediately. ⑵ If the superheater is severely damaged, the boiler should be shut down immediately. ①Stop the fuel supply. ②Stop the supply fan and keep the exhaust fan running to remove the smoke and steam from the furnace. ③Isolate from the system and other boilers, and close the main steam valve and feedwater valve. Maintain the water level at normal levels. ④After the smoke and steam in the combustion chamber have disappeared, stop operating the exhaust fan. ⑤Conduct inspections after shutting down the furnace