Boiler tube economizer, superheater tubes, reheater tube and the water wall tube are common in thermal power plant parts prone to failure, the analysis of these causes burst pipes are over-temperature heat pipe failure caused by the operation, these are the cause of overtemperature tube blasting operation caused by the failure of tube overheating. Usually, according to the deformation mechanism, the boiler tube is divided into short-term and long-term overheating tube, the first with instantaneous high temperature tensile deformation, the latter for long-term creep deformation limit; Or divide a certain critical temperature as the short-term and long-term overtemperature of the line, the main deformation of the super soft degree as the main influence factors of overtemperature detonation tube. Through in-depth analysis test of overtemperature tube and provide experience in test found that of 300 mw boiler tube failure is material, the environment, a result of the combined action of factors such as temperature, stress, even overtemperature tube for a long time, also can present a variety of damage form, its mechanism is also different.
In the long term over-temperature, the pipe in the grain boundary carbides gathering grew carbide ball occurs, the precipitation of graphite and carbon, as well as heat-resistant steel alloy redistribution of alloying elements, these are a time course. Therefore, the long-term overheating burst pipes, we pearlite spheroidization phenomenon common organizational change. While short-term overheating burst pipes also have a few instances of this form of injury, indicating that in the short term over-temperature tube burst pipes have long ago over-temperature operation. Visible, this damage can not afford a leading role for burst pipes, boiler tubes ball but levels can be used as assessment level and duration of overtemperature basis. The tubes are short-term high-temperature heat pipe explosion. Role of the media in the internal stress and deformation is the dominant factor in failure of the tube, but there are inner and outer walls thicker oxide surface oxidative damage and Xianghuo moderate pearlite spheroidization of aging damage, which indicates that the tube in the short term overheating burst pipes have long-term over-temperature prior experience running state.
For short-term overheating tube, pipe diameter swell is given priority to with intracrystalline deformation caused by the stress, wall thinning and detonation tube. For the high stress level of the main steam superheater pipe, it can be found by the stress caused by the long-term creep deformation and overtemperature damage occur creep cavity. For superheater pipe stress level of medium, damage caused by stress long-term overtemperature creep holes may not seen, but make selective the intergranular oxidation micro crack extension speed to the matrix, and caused overheating tube together with the oxidative damage. When operating conditions change, produce thermal stress cycle, because the expansion coefficient of metal oxide coating and the magnesium substrate is different, and break the scale or even fall off, stress damage is the protection to the metal surface can't intact oxide film.
