It's the same corrugated pipe. Why do some expand and save energy for ten years, while others leak in three years?
High-end metal expansion joints are not expensive in the word "metal", but in the three links of bellows design, material matching and constraint structure. Under the working conditions of power station, cement and desulfurization, ordinary expansion joints simply can't withstand the double attack of high temperature and corrosive media. For products such as high-temperature axial expansion joint, external pressure single axial expansion joint and straight pipe pressure balance expansion joint, the temperature, pressure, displacement and fatigue life have to be calculated clearly in the selection stage, which is almost impossible. Think about it, a steam pipe is thousands of degrees, and once the expansion joint fails, the downtime loss is enough to buy hundreds of expansion joints.
Only when you choose the right materials can you pass the high-end threshold
High-end metal expansion joints and bellows are basically inseparable from austenitic stainless steel. 304 and 316L are the most common, and there are high-temperature resistant alloys. But the more expensive the material is, the better, it depends on the medium. The expansion joint used behind the desulfurization flue gas baffle door faces sulfur-containing wet flue gas. 304 can't last long in this environment, and it must be 316L or even more corrosion-resistant. However, the metal rectangular expansion joint used in the smoke air duct of power station boiler has to consider thermal fatigue and abrasion. In the final analysis, "high-end" is the accuracy of material selection, not brainless stacking. When you choose a model, if you only look at the price and don't look at the media ingredients, what is the difference between prescribing a medicine and not looking at medical records?
Structural design is the real watershed
Many people think that the expansion joint is a bellows, and it is done once the two ends are welded. In fact, high-end metal expansion joints have to be constrained for different displacement forms. For example, the transverse expansion joint of the compound hinge absorbs the transverse displacement by the hinge structure, and does not allow axial displacement; The directly buried (fully buried) expansion joint is used in underground pipelines, which should bear the covering pressure and external pressure; For large diameter thick-walled expansion joints, the wall thickness and stiffness directly affect the compensation amount. These products correspond to different mechanical models, and if they are selected wrongly, the compensation amount will be insufficient at least, and the pipeline system will be unstable at worst. Two days ago, I met a customer who took an ordinary axial expansion joint to absorb the lateral displacement. As a result, the pipe brackets were all pulled askew-this is not called saving money, but laying mines.
This little thing, the guide tube, hides a great deal of attention
Deflector tube. The specific function of the expansion joint guide tube is to reduce the scouring of the medium to the inside of the bellows and reduce the flow resistance at the same time. The high-end metal expansion joint will not be sloppy in the design of the guide tube-the material, thickness and gap size are all particular. Especially for dusty airflow, such as the application scenario of metal corrugated expansion joint in cement industry, there is no qualified guide tube, and the bellows are quickly worn out. This detail, many low-priced products won't tell you at all. Think about it, the deflector looks inconspicuous, but it directly determines the life of the bellows. Is this a hard indicator of "high-end"?
How to judge whether you need high-end metal expansion joints?
Design temperature, design pressure, compensation amount, fatigue life, medium characteristics. Steam pipeline usually chooses external pressure single axial expansion joint, external pressure design can improve stability; In order to absorb the displacement in multiple directions, it is necessary to consider the compound straight tube bypass pressure balanced expansion joint or the curved tube pressure balanced expansion joint. There are more than 30 categories listed in the product information, each category has its reason for existence, and none of them is omnipotent. Is your site overhead pipeline or buried? Is the bracket fixed or sliding? What is the cold tight state? Are there chloride ions in the medium? Take all these data to the manufacturer and let the manufacturer calculate it for you. The result of the calculation is what you should pay for.
High-end metal expansion joints are not necessarily the highest priced, but they must match your working conditions most accurately. Don't just look at the parameter table on the sample, but explain the real data of your site-pipe layout, support type, cold tightness state, media composition-all clearly. This thing is not about buying cabbage, so you can't fool it.