| With the rapid development of petrochemical industry, high temperaturecentrifugal cast furnace tube has been widely used in petrochemical plant crackingfurnace, hydrogen furnace, the furnace pipe working environment is very bad, highworking temperature of700℃-1050℃. In the long term high temperature, tubematerial will gradually produce tissue injury, tube material high-temperature injurymainly as follows: the spheroidization of pearlite and graphite, creep cavity, carbideprecipitation, these are caused by the tube material embrittlement and carryingcapacity decline. At the same time as a result of the production process of tube walltemperature change frequently and strong gas scouring effect, often make the furnacetubes in does not reach the design life before serious damage and destruction.According to the American Petroleum Institute API RP530, furnace tube isdesigned to last for100000hours. However, depending on the operating conditionsand material properties is obtained for the effective service life is30000~15millionhours. Cracking furnace tube run many has far exceeded its design life, the furnacetube still can continue to run and run long, it is the problem that solves urgently. Forthis kind of problem at home and abroad, many research results, but a variety offurnace tube production process, environment as well as the original furnacemetallurgical quality and organizational performance differences, therefore, it isnecessary to organize different furnace tube, performance test and residual lifeassessment.This research through observation and contrast of a petrochemical enterpriseunder super high temperature service of the ethylene cracking furnace tubes inconvection section of parent material microstructure in operation before and after thechanges, analysis of furnace tube damage and organizational performance, using theL-M parameter method of extrapolation to predict furnace tube remaining lifeassessment of furnace tube, can serve to the next overhaul cycle, analysis of cause thecauses of the deterioration of furnace tube, ensuring long-term safe operation ofethylene furnace. The main research contents and conclusions are as follows:(1) the old furnace tubes of metallographic analysis, the results showed that withthe increase of the service time, furnace tube tissue precipitates more and more, thegrain integrity becomes worse.(2) has been operated for tube enduring high temperature tensile testmetallographic analysis of visible, with the increase of temperature and the increase of the service time, precipitate a propensity for aggregation, twin features reducetrend is more obvious.(3) by scanning electron microscope (SEM) and energy dispersive spectroscopy(EDS) analysis, the results show that service20000hours old furnace tube crosssection along the inner wall of the inner wall of the furnace tube is uneven, and thegrain boundary wear and corrosion damage traces, crystal within a certain amount ofbulk precipitation, analysis results show the existence of C, S, part of Cl, K, Caelement segregation, and the existence of a large number of cracks; the inner wall ofthe furnace tube in service30000hours old, there are a lot of loose particles anduneven.(4) by means of a tensile test can be seen, along with the increase of the servicetime, furnace tube strength parameters--tensile strength while increasing, and plasticparameters--elongation, shrinkage rate is reduced in different degrees, hightemperature service so that the tube material had a certain degree of brittleness.(5) through high temperature endurance test and service life prediction, usingL-M formula to predict new furnace and furnace tube in service life are far exceed thedesign life, the temperature and pressure in service during the limited impact, mainlycarbide precipitation embrittlement. After normalization served for20000hours on theold furnace tube remaining life for more than2years overhaul cycle, served for30000hours on the old furnace tube remaining life of over1years. |
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