How "bad" is the dense area under the blast furnace? — — First talk about working conditions, then talk about type selection
Blast furnace density, to put it bluntly, is the sealing pipe near the hearth, iron mouth and slag mouth. The temperature always soars above 800℃, the liquid slag iron splashes from time to time, and the dusty gas washes the pipe wall like sandpaper. Plain bellows on it? It cracked in less than three months, and the crack followed the trough, leaking gas to make your scalp numb. At this time, metal expansion joints must be put on, and it is not any kind. We have one in our stationHigh temperature axial expansion joint、Corrugated expansion joint for power station industryHowever, for the lower dense area, the key is not to choose the expensive one, but to choose the right one-material and structure are the life gate.
The core requirements of "lower density" for metal expansion joints are three points: high temperature resistance, wear resistance and dust accumulation prevention
What does high temperature resistance rely on? Rely on stainless steel, but don't use 304, at least 316L, and the temperature can be as high as Incoloy825. Moreover, the bellows cannot be single-layer thin-walled, it must beMultilayer structureThe number of layers can not only share the thermal stress, but also stop the gas leakage when local micro-cracks appear. What about wear resistance? It has to be installed on the outside of the bellowsWear resistant sheathOrguide tube——Function of Expansion Joint Guide TubeNot just diversion, the key is to block high-speed dust from blowing the bellows directly. Think about it, there is coke powder in the gas, and if the trough is directly exposed, it will wear out in half a year. Anti-ash accumulation is even more pitted. The dust content of the lower dense gas is large. Once ash accumulates in the valley of the bellows, the ash will get stuck at the bottom of the valley during thermal expansion and contraction, and the bellows will either not be pulled to cause overload, or local stress concentration will directly tear. Tsk, this detail is overlooked by many people, and it is only regrettable until it is missed.
Then how to choose? Don't just look at diameter and pressure
The displacement of tight pipe under blast furnace mainly comes from thermal expansion, the axial displacement accounts for the majority, occasionally with angular displacement. In this case, the preferredStraight pipe pressure balanced expansion jointOrExternal pressure single axial expansion joint。 Why is external pressure recommended? Because the external pressure structure can put the bellows outside the medium, the high-temperature gas does not directly contact the bellows surface, and the service life is at least doubled. If you run into a pipe that needs lateral displacement,Compound hinge transverse expansion jointIt can also be on, but remember-the hinges and tie rods must be made of heat-resistant alloy steel. Don't save that money. Ordinary carbon steel creeps frighteningly fast at 800℃. There is also a pit: the installation direction of the guide tube must be consistent with the flow direction of the medium, and the direction of the arrow is the direction of the airflow. If the guide tube is installed backwards, it will be washed out first, which is equivalent to white installation.
There are several pits in installation and routine maintenance, and you have to replace them if you step on them
The tie rod nut and screw on the expansion joint at the factory are for transportation and fixation, and must be loosened after installation.How to adjust the expansion joint tie rod nut?Just lock it after adjusting it to the pre-stretched amount. Don't screw it to death or completely dismantle it. The second pit: the direction of the arrow of the guide tube-specifically talked about in the FAQ in the stationThe direction of the arrow of the expansion joint refers toMedium flow, loading backwards is equal to chronic suicide. The third pit: the space in the lower dense area is narrow, and the furnace has to be shut down after maintenance, which is extremely expensive. It is recommended to install it at both ends of the expansion jointElectric plug-in insulation doorOrManual plug-in insulation doorIt can quickly cut off the pipeline when the furnace is shut down, which is convenient for replacement or inspection. Is that the truth? Usually spend more money and make it back if you stop the furnace less.
Two days ago, I met a customer of a steel mill. The common corrugated expansion joint used in the blast furnace was leaked three times in half a year
Later, it was changed to the one we recommendedHigh temperature axial expansion jointWith wear-resistant lining and deflector, it has been used for more than two years without any problems. To put it bluntly, this kind of place is not cheap. If you choose the right material and structure, you will be worried later. If you are interested, you can flip through our siteService life of expansion jointIn that article, the actual life data under different working conditions-multi-layer 316L bellows at 800℃ were compared, and the measured fatigue life was more than four times that of a single layer. Do you still think that model selection is just about diameter and pressure?