Do metallurgical metal expansion joint selection, the most afraid to ask "how much is a meter" as soon as you come up. The price is easy to set, but the working conditions are difficult to deal with. The temperature, dust and medium of blast furnace hot air pipe, sintering machine flue and converter dust removal pipe are different in each position. If you take a general scheme to set it, there is a high probability that it will leak after three months of installation.
Details of metallurgical working conditions: high temperature, dust, corrosive media, what is the expansion joint carrying
Look at the temperature first. Pipelines exceeding 200℃ in metallurgical system abound, and hot blast furnace pipelines can even reach above 400℃. Temperature directly determines whether the bellows should add a temperature-resistant layer and what kind of material to use. Look at the dust again-in the pipelines where sintering, blast furnace and converter are dust removed once, the dust concentration is often tens or even hundreds of grams per cubic meter, and wear is fatal. There is also corrosion. The temperature of net flue gas after desulfurization is not high, but sulfurous acid and chloride ions are not ambiguous at all.
Expansion joints do not only carry displacement, they carry pressure, temperature and media corrosion at the same time. You use it as a normal connector, sooner or later something will happen. The first step of selection is to write the media composition, temperature range, pressure and dust concentration clearly, and then talk about other things.
Select type according to displacement: what structure corresponds to axial, transverse and angular directions respectively, do not take general type hard carry
Axial, transverse and angular directions are often combined in actual working conditions. Mainly axial displacement, withUniversal corrugated expansion jointOrExternal pressure single axial expansion joint。 The lateral displacement is large, so it is necessary to useCompound hinge transverse expansion jointThe axial thrust is restrained by the hinge. Select angular displacementHigh temperature axial expansion jointWith the tie rod structure, two or three are used in groups.
To be honest, the space of metallurgical pipelines is tight. In many cases, the main pipeline has many turns and complicated branch pipes, and the displacement direction is not a single axial direction. At this time, it is useless for you to just look at the axial compensation amount on the sample. You have to let the manufacturer do stress analysis. If the general-purpose type is hard to carry the large lateral displacement, it will be a matter of time before the side of the bellows bulges and becomes unstable. Two days ago, I met a customer. A single axial expansion joint was used on the flue of the sintering machine. As a result, the thermal expansion of the pipe twisted the bellows into a twist and replaced it withCompound hinge transverse expansion jointIt works.
How to determine the materials and internal parts: corrugated pipe material, guide tube, wear-resistant lining, none can be saved
Bellows material is the core. Ordinary 304 stainless steel can't last for a few months in chloride ion environment, so 316L or high nickel alloy must be used. Heat-resistant alloy should be selected for ultra-high temperature working conditions. If the temperature exceeds 600℃, heat insulation layer or non-metal composite structure should be considered.
The guide tube must be fitted, and the direction cannot be reversed. The function of the guide tube is to let the medium go along the flow direction without directly washing the ripples. The pipe wall should be thickened, and the front end should be turned into a taper shape to reduce vortex. In dusty working conditions, high-temperature resistant heat insulation cotton must be filled between the outer wall of the guide tube and the bellows to prevent dust accumulation.
For severely worn pipe sections, the surface of the guide tube should be welded with wear-resistant layer, or designed as a detachable and replaceable structure. These inner parts cost 30% of the total price of the expansion joint is no joke. Save this money and the bellows are waiting to be worn out.
Installation and pre-displacement: how to adjust the tie rod nut, how to put the guide bracket, if the wrong installation is directly scrapped
There are more pits in the installation process than in the selection. The tie rod nut is not tightened when you go up. Pre-displacement is also called cold tightening. First, the expansion joint is stretched or compressed to half of the design displacement, and then the nut is locked. This allows the bellows to be stressed more evenly when working in the hot state. However, many people don't know that the pre-displacement amount should be corrected according to the actual installation temperature-the pre-displacement amount is different between summer and winter.
The position of the guide bracket is more critical. Guide brackets must be set at both ends of the expansion joint. The distance between the first passage and the expansion joint should be controlled within 4 times the pipe diameter, and the second passage should not exceed 14 times the pipe diameter. If the spacing is too large, the pipeline will become transversely unstable, and the bellows will bear extra bending moment, so the life will be shortened. When installing, make sure that the pull rod cannot withstand the medium pressure thrust-the pressure thrust is carried by the pipe bracket, and the pull rod is only responsible for distributing displacement.
Failure signals in operation: intergranular corrosion, fatigue crack, dust accumulation, how to find them in advance
Expansion joint failure does not happen suddenly, there is a signal in advance. Most commonly, filamentous cracks appear at the trough of the bellows, which are fatigue cracks. Most likely, the actual displacement exceeds the design value, or the bracket is loose and causes additional force.
Intergranular corrosion is not good to be found with the naked eye. If the surface of the bellows is gray-black, loses its metallic luster, or leaves a black mark after rubbing it with your fingers, you should be alert. At this time, the intergranular corrosion test by nitric oxalic acid method can confirm whether the material has been sensitized.
Dust accumulation is a problem unique to the metallurgical industry. The gap between the guide tube and the bellows is filled with dust, the bellows loses its elasticity and becomes a rigid body, and the displacement is all concentrated on the weld. This can't be seen by inspection alone. The surface temperature of the bellows should be measured regularly. If the local temperature rises abnormally, it is most likely internally blocked. It is better than anything to open the inspection hole and take a look when shutting down for maintenance.
Selection Case: From Cement Industry to Power Station Industry Experience, What Can the Metallurgical Scene Borrow
Of the cement industryMetal Corrugated Expansion Joints in Cement IndustryIt is very similar to the working condition of metallurgical sintering machine-high temperature, high dust and continuous operation. The common practice in the cement industry is to add double-layer corrugated pipe with external insulation layer and thicken guide tube. This set can be transplanted to metallurgical dust removal pipeline. of the power station industryCorrugated expansion joint for power station industryHigh pressure and safety requirements, especially the expansion joint on the main steam pipe, the material and welding process are top standard. High-temperature and high-pressure pipelines in the metallurgical industry can refer to the practices of power stations, such as selectingStraight pipe pressure balanced expansion jointTo eliminate the blind plate force and avoid the design of the pipe support being too large.
To put it bluntly, no expansion joint in any industry is exclusive. The key is to see whether the working condition parameters match or not. Cross-border is not a shame. Taking the selection ideas of mature cases and matching them with the actual data of your own production line is the proper way.
The selection of metal expansion joints for metallurgy is not urgent. The working condition data column is not clear, and no matter how beautiful the parameters are selected, it is useless.