Failure Analysis On High-pressure Steam Pipeline Of Cracking Furnace

High temperature and high pressure steam pipeline is widely applied in heating furnace and cracking furnace in oil refinery, chemical plant, thermal power plant ect. The safe operation of the steam pipeline is an important guarantee for the sustainable operation of device. If the temperature of the steam medium in pipelines frequently fluctuates, alternating thermal stress will produce in pipeline body, which is easy to result in thermal fatigue cracking and igniter cartridge failure, and cause serious casualties and economic losses.In order to study the mechanism of the steam pipelines thermal fatigue failure and to reduce the loss caused by thermal fatigue cracking, this text will intensively study on a typical of high temperature and high pressure steam pipe cracking failure. Through analysis of high temperature and high pressure steam pipe cracking of various testing and failure, the results indicate that the failure mechanism is fatigue cracking. Qualitative factors and steam medium don't cause the cracking for the pipeline. Pipe trench wall processing is one of the reasons to crack initiation. The microscopic analysis found that pipeline surface fatigue cracks of microscopic evidence - fatigue striations, crack initiation in pipeline inner processing trench. Because the fracture surface chemical ingredient does not contain corrosive medium, this rules out the possibility of fatigue and corrosion. Through the micro-cracks of fracture morphology and crack tip shape analysis, the results accord with extension fatigue crack characteristics. Based on the service conditions, a preliminary deduce of the steam pipeline fatigue cracking belongs to thermal fatigue. The temperature and pressure reducer in front of pipeline of non-uniform mixed water-drop is the main cause of thermal stress.When water 100℃splash into pipe inwall 500℃, simulation which for water splash into the inner pipe produces alternating thermal stress of show that local will generate enough thermal stress due to the unmatchable heat bilges cold shrink.Comprehensive failure analysis and simulation results show that high temperature and high pressure steam pipe cracking of failure properties is thermal fatigue. Water and steam non-uniform mixed in the temperature and pressure reducer, water-drop into steam pipeline is the main reason. Further study on the steam piping hot fatigue life analysis shows that the fatigue longevity about pipeline is 2×104 times and belongs to the low cycle fatigue. According to the low cycle fatigue stress level and considering the pressure inside the pipeline stress value, the study guesses water quality is mostly about 0.002g in line.This research results, especially the water splash into the inner pipe produces alternating temperature field and thermal stress, not only provide important technical references for high temperature and high pressure steam pipeline of design layout and the temperature and pressure reducer of structure transformation, but also have certain theoretical significance for thermal fatigue failure analysis of research in the field of route.