Flue metal expansion joint specifications, don't wait until you install it to find out that it is wrong

To be honest, I have been in this business for more than ten years, and I have seen too many cases of "installing it and finding it wrong". The customer took the drawing and said, "Buy it according to this model". As a result, when he arrived at the scene, either the flange hole didn't match, or the bellows was washed up by the smoke, and even worse, it cracked directly in the trial operation stage. Don't laugh, this kind of rollover has been encountered in every factory. Today, let's talk about the specifications of flue metal expansion joints, fill the pit before starting.

Before choosing the specification, ask: What is your flue for?

— — The power station is still cement, and the working conditions are much worse. The flue of the power station is filled with high-temperature smoke, with a temperature of five or six hundred degrees Celsius at every turn, and a little sulfur corrosion. What about cement production lines? In addition to the high temperature and a lot of dust, some customers wear out general-purpose bellows in less than three months in order to save money. So don't ask "Is there an expansion joint for DN800" as soon as you come up? You have to tell me the temperature of the medium, the pressure, and if there are any corrosive gases. WeCorrugated expansion joint for power station industryAndMetal Corrugated Expansion Joints in Cement IndustryAlthough the shape is similar, the material, wave height and wall thickness are completely two sets of designs. For example, stainless steel 321 or 316L is commonly used in power stations, and cement lines are more popular than 2520 or wear-resistant guide tubes. You take the goods from the power station to the cement factory, tsk, wait for the change.

There are only a few core parameters, but none of them can be sloppy

Diameter, wave number, material, compensation amount-these four parameters are like four pillars. If one is less, it will collapse.DiameterNeedless to say, it doesn't match the inside diameter of the pipe, and the flange can't fit. But many people ignorewavenumber: The more the wave number, the greater the compensation amount, but the stiffness also follows, and the waveform in the high-pressure pipeline is easy to be squashed. thatMaterialHow to choose? High-temperature environment gives priority to heat-resistant steel. For example, there are many Inconel 625 for high-temperature axial expansion joints, but the price is... If there is chloride in the flue gas, 316L can't bear it, so you have to add lining or simply put it onPTFE-lined hose。 As forCompensation amountDon't just look at the design drawings, the actual displacement and thermal expansion of the pipe frame must be measured, otherwise the fatigue life of the bellows will be directly halved if it is installed and deadpulled. Two days ago, I met a customer. In order to save trouble, I directly applied the parameters of the construction site next door. As a result, the compensation amount was reduced by 20%, and the pipe on the site was rattling-do you say fuck?

So the question is, who ranks first among these four parameters? Let me say,MaterialAndCompensation amountTied for the first place, the path and wavenumber are easy to change. However, many purchase lists only write "DN600, wave number 8", and the material is marked with "304"-brother, 304 is prone to intergranular corrosion above 400℃. Do you dare to use it? So don't just look at the model, you have to dump the working condition table to the manufacturer.

The same specification, different structures make a big difference

For example, if you all wear size 41 shoes, can leather shoes, sneakers and slippers be the same? The same goes for expansion joints.High temperature axial expansion jointSpecially used for straight pipes, the wave tube has heat insulation layer and guide structure outside, which can carry seven or eight hundred degrees Celsius.Universal corrugated expansion jointIt is much more flexible and can absorb axial, angular and transverse displacements, but the upper temperature limit is obviously low, so it is generally used in flue inlets or low-temperature sections. As forMetal rectangular expansion jointIt is used in square flues, such as the inlet and outlet of desulfurization tower. The four corners are particularly prone to stress concentration, and air leakage occurs if the design is not good. And there's alsoExternal pressure single axial expansion joint、Straight pipe pressure balanced expansion joint…They all looked like bellows, and their internal structures were completely different. You asked the production of a general-purpose de-imitation rectangular expansion joint, tsk, stop it.

Therefore, when selecting the type, first find out the direction of the pipeline: is it a straight pipe section with an elbow, or does it need to absorb the lateral displacement? WeCompound hinge transverse expansion jointAndCompound straight pipe bypass pressure balanced expansion jointIs specialized in dealing with these complex working conditions. If you take a general-purpose hard plug, the structural stability will collapse directly. Don't ask me how I know, I've seen too many.

Don't just keep an eye on the expansion joint, it has to be used with baffle doors and insulation doors

System matching is king. Many projects choose the expansion joint as an island, ignoring its front and back connectionFlue gas baffle door、Round Flap Door (Double Seal)OrElectric plug-in insulation door。 For example, a desulfurization system is equipped with a DN1200 expansion joint and an ordinary baffle door. During operation, the baffle door is not closed tightly, the smoke gas is backward, and the high-temperature gas directly burns the non-metallic seals inside the expansion joint. And guess what? Finally, it was found that there was a lack of transition tube between the baffle door and the expansion joint, which caused airflow erosion. Good thing we recommendedDesulfurization flue gas baffle door, double seal structure, and wear-resistant lining plate are added to press down the problem.

Matching is not a simple "flange to flange". Is there enough space? Can the expansion joint be removed during maintenance? Will the manual/electric actuator of the flapper door interfere with the expansion joint? These should be finalized at the drawing stage. Otherwise, when you finish installing it, you find that the wrench can't even reach in, and there is no place to cry.

A real case tells you how pitfalls it is to choose the wrong specification

Let's talk about the rollover scene of a certain power plant. Last year, there was a northern 2×350MW unit with a flue design temperature of 450℃, a pressure of 0.25MPa and a pipe diameter of DN1000. The purchase drawing saves trouble, so I directly copied the general corrugated expansion joint model of the next factory, the material is 304, and the wave number is 6. As a result, less than 1000 hours after turning on, cracks appeared at the root of the bellows and smoke leaked. On-site shutdown inspection: The oxide scale of material 304 falls off a lot at 450℃, and the number of waves is too small, resulting in excessive single wave compensation and fatigue failure of bellows. The renovation cost more than 700,000 yuan, and the construction period was delayed by half a month. Then it was usHigh temperature axial expansion joint, material 316, wave number increased to 6, and a guide tube was added-it has been running for three years now, and there is no problem at all. How much maintenance money can you save by spending more on the selection fee?

Therefore, the specification of flue metal expansion joint really can't be placed with your eyes closed. It is better to find a reliable manufacturer with the working condition parameters, even if you make two more calls, than to go to the site for rework. Our company maintainsMetal hose、Non-metallic expansion joint、Double-sealed single-axis circular baffle doorThese supporting products are afraid that customers only ask about expansion joints, regardless of the system. Finally, I'll send you a word: choose the right specifications, and save worry for ten years; Save trouble and choose the wrong thing, and run to the scene every day. Choose for yourself.