1. Harsh working conditions are the norm: which scenarios force you to choose wear-resistant types?
Let's just talk about the pain points. Two days ago, the equipment manager of a cement factory complained to me, saying that the general corrugated expansion joint on their smoke and air duct was worn out in less than half a year-the granular materials were washed at a high speed like sandpaper, and the corrugated roots were directly thinned and perforated. This is not an isolated case at all.
Think about it, which places are the most grinding? The air-swept coal mill export and raw material storage pipeline in the cement industry, where a large amount of clinker dust and particles fly; The pulverizing system and primary air duct of the power station boiler have high pulverized coal concentration and fast flow rate; Not to mention the desulfurization flue gas pipeline, the wet flue gas is wrapped in gypsum slurry, which has both erosion and corrosion. In these scenarios, ordinaryUniversal corrugated expansion jointCan't bear it at all-the geometry of the peaks and valleys is itself an "amplifier" of wear, and the particles repeatedly hit the corrugated surface, even if it is stainless steel, it is useless if it is not thick enough. Therefore, the wear-resistant corrugated metal expansion joint is not the icing on the cake, but just needed.
2. The "hard core" structure design of wear-resistant corrugated metal expansion joint-the attention of wall thickness, material and guide tube
So what kind of design is "hardcore"? Three key points: wall thickness, material and guide tube.
First, wall thickness.The wall thickness of conventional general-purpose expansion joint bellows is generally 1~1.5mm, and the wear-resistant type should start at least 2mm or even thicker. However, thickness does not mean that it is wear-resistant-if the number of layers is wrong, it will affect the fatigue life. The reasonable approach is to use multi-layer thin-walled structure to superimpose the thickness, such as two layers of 1.5mm, which not only ensures the flexibility of compensating displacement, but also increases the wear margin. This site'sMetal Corrugated Expansion Joints in Cement IndustryAndLarge diameter thick wall expansion jointIt is designed according to this logic.
Second, the material.Stop being superstitious about 304. 321 or 316L is preferred for wear-resistant conditions, and even duplex stainless steel (such as 2205) or Incoloy 825 should be used for high-wear areas. Why? Because wear resistance not only deals with hardness, but also high temperature and corrosion. For example, desulfurization flue gas pipeline, with low pH value and high chloride ion, 316L is barely selected, so special alloys have to be used.
Third, the guide tube.Many people ignore the role of the deflector. It doesn't just add a tube. The guide tube must extend into the bellows to allow the airflow to move against the wall of the tube, so as to avoid particles directly washing the corrugated surface. The FAQ of this site specifically talks about itSpecific Function of Expansion Joint Guide Tube-It can guide the medium to the center of the pipeline and build a "moat" between the bellows and the high-speed particles. The wall thickness of the guide tube of the wear-resistant expansion joint is usually 6~10mm, the material is consistent with that of the pipeline, and the upflow surface should be heat treated or cemented carbide surfaced. And guess what? Some low-priced products are not equipped with deflectors at all, which is to play hooligans.
3. Don't use the general-purpose model as wear-resistant: the three easiest pits to step on when selecting a model
Model selection stepping on pits? I've seen so many, to say three of the most common.
Pit 1: Only look at the pressure and temperature resistance, and ignore the flow rate and particle concentration.Many people place orders with thermal displacement parameters, without asking what's in the medium at all. With the same temperature and pressure, the wear amount of pulverized coal pipe and steam pipe is two orders of magnitude different. Before selection, it must be specified: media type, flow rate, particle diameter and concentration, erosion angle. Without this data, it is irresponsible to sell your generic model.
Pit 2: Blindly thicken the bellows and ignore the fatigue life.The wall thickness increases, the stiffness increases, and the pressure resistance is good, but the compensation ability decreases, the stress increases, and the fatigue life is shortened. Therefore, wear-resistant expansion joints are often not simply thickened, but adjust wave height and wave pitch, and even adopt multi-layer structure. This site'sCorrugated expansion joint for power station industryOn the pulverized coal pipeline, the design of wave pitch densification and wall thickness optimization is adopted, taking into account both wear resistance and fatigue.
Pit 3: The direction of the guide tube is reversed or the material is wrong.The direction of the arrow of the guide tube must point to the direction of the medium flow, and the upward end should be chamfered to avoid vortex. Some people want to use carbon steel deflectors cheaply, but they rotten in the desulfurization flue gas for a few months, and the bellows suffered. The material of the guide tube should match the pipe or be more resistant to corrosion. This site'sDesulfurization flue gas baffle doorThe matching expansion joint and guide tube are all 316L or higher grade.
4. Installation and maintenance: If the wear-resistant parts are installed in the wrong position, the life will be directly discounted by 30%
If you choose the right product, install it incorrectly and be in vain. There are several hard requirements for the installation of wear-resistant corrugated metal expansion joints:
- The direction of that guide tube must coincide with the flow direction of the mediumAnd the gap between the guide tube and the inner wall of the pipeline should be uniform, generally controlled at 5~10mm, otherwise the local erosion will be aggravated.
- Bellows cannot withstand torsion。 The deviation of pipeline installation or the deformation of supports and hangers will lead to uneven force of bellows and wear concentrated on one side. should be usedLarge tie rod expansion jointOrIf the double hinge transverse expansion joint absorbs the transverse displacement, do not use the axial hard top.
- Regularly inspect the end of the guide tube for wear。 Many wear-resistant expansion joints are designed with reserved space for replacing the guide tube, such as the flange detachable structure. This thing is not disposable. If you find that the scouring thinning exceeds 50%, change it quickly. Don't wait for the bellows to be exposed.
Also, don't underestimate insulation. Wear-resistant expansion joints are often used in high-temperature pipelines. If the heat insulation falls off, it will cause condensation, corrosion and wear, and the life will be directly discounted by 30%.
5. Data Speaks: Real Wear Cases in Cement, Power Station and Desulfurization Flue Gas Pipelines
Tell me a few real cases for you to feel it.
Case 1: Kiln tail flue of a cement plantThe medium temperature is 350 °C, the dust concentration is 80 g/Nm³, and the flow rate is 25 m/s. Previously, a certain brand of general-purpose expansion joint was used, with a wave thickness of 1.5mm, and the bellows was worn out after 9 months. Replace it with oursMetal Corrugated Expansion Joints in Cement IndustryWith a wall thickness of 2mm, lined with a guide tube of 16Mn + surfacing wear-resistant layer, disassembled and inspected after 20 months of operation, the end of the guide tube is worn about 3mm, and the bellows is intact. Estimated service life is increased by more than 3 times.
Case 2: Pulverized coal pipeline in a thermal power plant, Specification DN800, pulverized coal concentration 0.5kg/kg, flow rate 28m/s, temperature 80℃. Original Universal Typebellows compensator, the corrugated roots cracked at 12 months. Replaced withCorrugated expansion joint for power station industryThe wave pitch is densified, the wall thickness is increased to 2.0 mm, and an anti-wear liner is added. After 30 months of operation, the depth of wear was less than 0.5mm.
Case 3: Inlet flue of desulfurization tower in a power plantThe flue gas after wet desulfurization contains water droplets and a small amount of gypsum particles, and the pH value is 3-4. Original 304 material expansion joint, 6 months corrosion perforation. Use 316L material instead (learn from this sitePTFE-lined hoseThoughts), which has been running for 4 years and is still normal.
Under these three working conditions, the average life of general-purpose products is only 1/3 to 1/5 of that of wear-resistant products. Calculate an account: the price difference of an expansion joint may be several thousand yuan, but it will lose tens of thousands or even hundreds of thousands once it is shut down. How to choose, you should know in your heart, right?