How harsh are the working conditions of steel mills? Why can't ordinary expansion joints hold up?
The environment in the steel mill is really not something that ordinary equipment can carry. The temperature of blast furnace hot air pipeline can rush above 1300℃, the converter flue gas is full of iron oxide dust, the pressure of continuous casting cooling water system fluctuates seven or eight times a day, and the rolling steam pipeline starts and stops at every turn. You put a universal corrugated expansion joint on it, and something will happen in a few months-either the bellows is worn out by dust, or the high temperature causes the material to creep and fail, or the water hammer directly crushes the bellows. To put it bluntly,Special metal expansion joint for steel millsIt is not a marketing gimmick, but a specially designed material, structure and seal for these extreme working conditions. If ordinary goods go up, they will add chaos to the steel mill.
Selection is not a pat on the head: Which expansion joint should be used in different parts of steel mills?
High temperature flue gas pipeline, steam pipeline, process fluid pipeline. The working conditions of each part are completely different, so the right medicine should be prescribed in the selection.
High temperature flue gas pipeline
Like hot blast stoves and sintering machine flues, the temperature is always thousands of degrees, and there is more dust. Recommended useHigh temperature axial expansion jointOrMetal rectangular expansion jointThe temperature resistance grade must be heat-resistant stainless steel, and the inner insulation layer must be added if necessary. If the flue gas contains sulfur or chlorine, consider corrosion-resistant coatings. In addition, the desulfurization and denitrification system should be matchedFlue gas baffle doorAndDouble-sealed round flapper door, achieving reliable isolation-after all, an air leak means a downtime fine.
Steam pipeline
Extraction of steam turbine and heating of factory area have high pressure and large displacement. Straight tube pressure balanced expansion joint orCompound hinge transverse expansion jointIt can effectively absorb axial and transverse displacement and avoid huge thrust from pipeline to support. Note that there is often condensed water in the steam pipeline, and the guide tube must be installed in the right direction, otherwise the bellows will be scrapped by a few water hammers.
Process fluid pipeline
Cooling water, hydraulic oil, etc., the pressure and temperature are relatively mild, useUniversal corrugated expansion jointOrStainless steel metal hoseJust do it. However, the direction of the deflector must be consistent with the flow direction-the arrows are clearly marked, and don't install them backwards. In addition, large-diameter thick-walled expansion joints ordirectly buried expansion jointYou need to install a leak monitoring interface, otherwise you won't know if it leaks underground.
The easiest mistake to make during installation: the tie rod nut is reversed from the pre-tension
Two days ago, I met the equipment supervisor of a steel mill, saying that their newly installed expansion joint leaked after half a year. When removed and looked, the bellows twisted and deformed – guess what? During installation, the transportation tie rod was not disassembled, and the equipment was directly pushed hard, and the bellows suffered extra torque. The correct way is to confirm that the model of the expansion joint is consistent with the design drawings before installation, and first remove the transportation fixings. The tie rod nut usually needs to be adjusted to the installation length and then locked. Don't screw it to death. For high-temperature pipelines, pre-stretching or pre-compression should be carried out-see the design calculation book for specific values, and don't blindly estimate them by experience. In addition,Double-sealed flapper doorWhen installing, pay attention to the parallelism of flange surface and the gap of sealing surface, otherwise it will not be closed tightly, and air will leak and ash will leak.
Someone uses a rubber compensator in the high temperature flue gas section. Alas, the temperature resistance of rubber usually does not exceed 200℃, while the flue gas temperature of steel mills often exceeds 400℃, so it is strange that nothing happens. Remember,rubber compensatorOnly suitable for normal temperature and low pressure occasions.
Maintenance also has tricks: don't wait for a leak before replacing it
The maintenance cycle of steel mills is long, and the loss of one shutdown is hundreds of thousands, so the daily inspection of expansion joints is particularly important. Focus on several places: whether there are corrosion pits or cracks on the surface of the bellows (especially near the weld), whether the guide tube falls off, and whether the tie rod nut is loose. For large-diameter thick-walled expansion joints or directly buried expansion joints, a leak monitoring interface can be installed, and replacement can be arranged in advance if any abnormalities are found. In addition, don't use rubber compensators instead of metal expansion joints for high-temperature flue gas sections-that is to lay mines for yourself.
Maintaining records is also critical. Record the state, displacement, temperature and pressure data of the bellows in each inspection to form a trend. If it is found that the deformation of the bellows suddenly increases, nine times out of ten there is a problem with the pipe bracket, so you have to check the bracket first and then replace the expansion joint.
Two real cases help you see the importance of model selection
Case 1:A common axial expansion joint was used in hot air duct of blast furnace in a steel mill. As a result, the bellows cracked frequently within one year. switch toExternal pressure single axial expansion jointAfter that, the bellows was moved to the outside to avoid direct washing by high-temperature flue gas, and the life time was directly doubled by three times. You see, when the structure changes, the effect is vastly different.
Case 2:In a steel rolling workshop, the steam pipeline used a general expansion joint without a guide tube. As a result, the condensed water in the steam impacted the bottom of the bellows at high speed, resulting in premature fatigue failure. modifyCompound straight pipe bypass pressure balanced expansion jointAfter, the problem is solved. Only when the type is selected correctly can the equipment withstand the harsh environment of steel mills.
So, uh,Special metal expansion joint for steel millsIt's not a gimmick, it's a real need. From selection to installation to maintenance, every link must be serious. Otherwise, the time cost and downtime loss of changing the expansion joint once are enough for you to buy several sets of special parts.