Specialized in manufacturing compensators, expansion joints, baffle doors

First, what is the metal expansion joint used for? — Don't be fooled by the name, the core is two words: compensation

Two days ago, I met a customer who came up and asked, "Is the metal expansion joint the same as the expansion joint on the radiator?" Alas, it means about the same, but it is far from that simple. To put it bluntly, as soon as the temperature in the pipeline system changes, the pipe will expand and contract by heat. The result of hard pulling is that the interface collapses and the equipment is crooked. Metal expansion joints do just that — they absorb displacement and release stress. You can call it compensator. These two words are common in the industry (refer to Article 14 of the FAQ in our site). There are two words at the core: compensation. Compensate for axial expansion and contraction, lateral offset, and even angular torsion. Without it, steam pipes and heat pipe networks will show you a look in minutes.

What we produceUniversal corrugated expansion jointIn chemical pipelines, they are soaked in high-temperature steam every day, and expand and contract hundreds of times all year round, relying on the elastic deformation of the thin walls of the bellows. AndCorrugated expansion joint for power station industryThe temperature of the main steam pipe of the power plant can soar to five or six hundred degrees. Without it, the pipe would have collapsed early.

Second, there are so many structural classifications, which ones are commonly used by us? — Bellows, sleeves, non-metals, each with its own temper

When you stand in our warehouse, you can see that the densely packed expansion joints are actually divided into three categories according to their structure: bellows type, sleeve type and non-metallic type.

Bellows expansion jointIt is the main force, relying on the deflection of ripples to absorb displacement. There are many sub-classes: such asHigh temperature axial expansion jointSpecialized in carrying high temperature;Straight pipe pressure balanced expansion jointIt can balance the blind plate force and be used on large pipes under pressure;Compound hinge transverse expansion jointIt can absorb lateral displacement and fit where the space turns. AndExternal pressure single axial expansion jointExternal pressure structure can withstand higher pressure, which is common in petrochemical industry.

Sleeve type pipe expansion jointIt is another way, which relies on the sliding between sleeves to compensate for the displacement. The structure is simple but the sealing requirements are high. It is generally used in low pressure and large displacement occasions, such as heating pipe network.

Besides, non-metallic ones, we have them on our stationNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion joint。 This thing is made of fabric and rubber, which can absorb multi-dimensional displacement and is corrosion-resistant, especially in smoke ducts and desulfurization systems. Oh, yeah,rubber compensatorAndRubber PTFE compensatorAlso in this category, the vibration damping effect is first-class.

Each structure has its own temper. If you choose the wrong one, the oil and water leakage in two years will be light, and the whole pipeline system may collapse.

Third, if you don't look at these three points in type selection, you will most likely step on pits-medium, temperature and displacement, one cannot be missed

After so many years of explaining metal expansion joints, I have seen too many people who pat their heads and select models. Let me tell you, first figure out these three parameters:

• Medium: What fluid goes? Strong corrosive, must be usedPTFE-lined hoseOrPTFE compensator； For dusty flue gas, wear resistance and guide tube structure should be considered.
• Temperature: Temperature directly determines the material. Use 304 stainless steel at room temperature, and you have to use heat-resistant alloy for five or six hundred degrees. Our oneHigh temperature axial expansion jointThe upper limit of the design temperature can reach more than 1000℃.
• displacement amount: How does the pipeline go? How much is axial telescoping? How big is the lateral offset? Every direction should be calculated clearly. Such asDouble hinge expansion joint for air-cooled island vacuum pipelineSpecially designed for vacuum large diameter pipeline, can absorb large angular displacement.

Don't think that these three values are enough to know. In actual engineering, they will affect each other. For example, high temperature + corrosive media, optical material selection is a knowledge. You choose an ordinary stainless steel bellows, and it won't take long to corrode and perforate. So don't be lazy and give your working condition parameters to the manufacturer honestly.

4. In installation and daily maintenance, the most easily overlooked details-the orientation of the guide tube, the adjustment of the pull rod, and whether the screw can be removed or not

Installing expansion joints looks simple, but the details determine the longevity. The first easy mistake to make is to install the deflector in the reverse direction. We have a FAQ on our siteSpecific Function of Expansion Joint Guide TubeThe guide tube is used to guide the flow direction of the medium and protect the bellows from being washed and worn. The direction of the arrow must be consistent with the flow direction of the medium (refer to Article 10 of Q&A). Install it backwards, and the guide tube is a plug, which will aggravate the wear.

How to adjust the tie rod nut? Many customers receive the expansion joint and find that there are tie rods and nuts fixed at both ends, thinking that it is used for reinforcement, and it will not be disassembled. Wrong! These tie rods (also called transport tie rods) are used to prevent the bellows from deforming during transportation. After being installed in place, the nut should be loosened, adjusted to the working position, or removed directly (refer to Q&A 12 and 13). Otherwise, the expansion joint can't expand and contract freely at all. What is the difference between it and a steel pipe?

AndCorrect installation method of expansion joint of large tie rodThe large tie rod structure is to bear the internal pressure thrust, and the tie rod must be adjusted to the designed length during installation, and cannot be screwed randomly. Routine maintenance is to regularly check the bellows for cracks and corrosion spots, especially thoseDesulfurization flue gas baffle doorNext to the expansion joint, the acidic environment is most prone to problems.

5. Common faults and misunderstandings: Why did it leak after two years of use? — — Fatigue, corrosion, installation stress, take the right seat

"The quality of your expansion joint is not good. It leaked in two years." Every time I heard such words, I always asked about the working condition first. Nine times out of ten, it is a problem of type selection or installation. There are three common reasons for leakage:

• Fatigue failure: If the pipeline vibrates frequently, or the design displacement is smaller than the actual, the bellows bends repeatedly, and the metal fatigue causes cracks. This situation can be consideredMetal hoseOrSpecial hose for vacuumTo dampen the vibration.
• Corrosion perforation: There are chloride ions and sulfide in the medium, and stainless steel still can't bear it. Either reline PTFE or choose high nickel alloy. WeMetal Corrugated Expansion Joints in Cement IndustryOften encounter sulfur-containing flue gas, the surface has to be made with anti-corrosion coating.
• Installation stress: The pipeline is forced to be installed at the opposite side, or the tie rod is not loosened, and the force of the expansion joint exceeds the design. When installing, make sure that the expansion joint is in a free state, and don't pull hard.

Think that the expansion joint is "all-purpose" and can absorb all displacement. Virtually every model has a cap on the ability to compensate. Such asDirect buried (fully buried) type expansion jointSpecially used for directly buried pipelines, the axial compensation is large but the lateral compensation is limited. If the pipe turns too much, you have to cooperateRotary compensatorOrCurved tube pressure balance expansion joint。

This thing of expansion joint, three points depends on quality, seven points depends on selection and installation. Don't just buy a general-purpose model to save money and trouble. When you're not sure, flip through the "Explanation of metal expansion joint"Series articles, or directly find technology to talk about working conditions. Save those few minutes of communication, and the maintenance fee later will be enough for you to buy ten expansion joints.

I met a customer two days ago, and as soon as I came up, I asked, "Which is better, metal expansion joint or non-metal expansion joint?" I asked him what kind of medium was going in the tube, and he was stunned and said, "It's just normal steam." That's the problem-directly comparing the good with the bad regardless of the working conditions, like asking "which is better, a hammer or a screwdriver"-you first have to know whether to nail or screw.

First, don't worry about which one is better, it depends on what is going in your pipe

The expansion joint has one core task: absorbing the displacement caused by thermal expansion and contraction of the pipeline, and by the way, absorbing shock and noise. However, different media, different temperature and pressure, and different selection logic.
Steam pipeline, the temperature is always above 300℃, the pressure starts at 1.6MPa, and the non-metallic fabric fiber layer can't bear it at all; On the other hand, the flue gas pipeline contains sulfur and acid, and the metal bellows will corrode in a few days, while the non-metal is corrosion-resistant.
Therefore, the first step is not to compare good or bad, but to find out the four parameters of medium, temperature, pressure and displacement. Otherwise, if you choose the wrong choice, you can leak at least and explode the pipe at worst.

Second, metal expansion joint: a tough guy resistant to pressure and temperature, but it also has weaknesses

Metal expansion joints (such as oursUniversal corrugated expansion joint、A high-temperature axial expansion joint,Corrugated expansion joint for power station industry) by deformation of stainless steel bellows to compensate for displacement. The advantages are obvious:
-High withstand voltage: Conventional energy to 2.5MPa, special design (e.g.Large diameter thick wall expansion joint,directly buried expansion joint) Can carry higher.
-High temperature resistance: With the guide tube and the heat insulation layer, the high-temperature axial type can reach above 800 ℃.
-Long life: Designed properly, fatigue times can reach tens of thousands.
But the weakness is also eye-catching:
First,Not corrosion resistant。 When it comes to wet chlorine and concentrated sulfuric acid, stainless steel is useless, and it has to be lined with PTFE (such as oursPTFE-lined hose).
Second,Unable to withstand large lateral displacement。 The single-wave compensation amount is generally 10-20mm, which requires multi-wave or double hinges (such asDuplex hinge transverse type expansion joint) to make up for it.
Third,High installation accuracy requirements。 How to adjust the tie rod nut and where to point the direction of the guide tube are all particular, and it is wasteful to install it wrongly.

Look at the structure first: the bellows is the core "spring" of the expansion joint

When you stare at a disassembled metal expansion joint, your first reaction must be: How can this thing "expand"? In fact, the secret is all in the middle circles of bellows. To put it bluntly, a metal expansion joint is a section of thin-walled tube with corrugations, with joints or flanges welded at both ends. The bellows is the equivalent of a metal spring that can be telescoped — but not a coil spring, but an annular ripple that runs in circles. These ripples are elastic in the axial direction, and when subjected to tension or pressure, the peaks and valleys of the ripples will open or close, resulting in displacement.

How much can the bellows stand? It depends on its stiffness. The smaller the stiffness, the easier it is to deform, and the greater the amount of compensation; But the stiffness is too small to hold up internal pressure. Therefore, it is necessary to look at the number of layers, wall thickness, wave height and wave pitch of bellows when selecting the type. For example, the general corrugated expansion joint we often say is generally a single-layer or multi-layer stainless steel bellows, while the high-temperature axial expansion joint under high-temperature working conditions has to be made of heat-resistant alloy and multi-layer structure.

Axial expansion: How does the bellows "expand and contract" when the pipe expands and contracts thermally?

The most common scenario is a steam pipe. When the pipe rises from cold to several hundred degrees, the length will be stretched by several centimeters. At this time, an axial expansion joint is installed in the middle of the pipeline, and the bellows is compressed-the distance between peaks and valleys is reduced, absorbing the elongation of the pipeline. In turn, if the pipe cools and shrinks, the bellows stretches. So you see, how do metal expansion joints expand? In fact, it is more accurate to say "compensate for displacement". The bellows itself does not necessarily really "expand", but eats the thermal expansion and contraction of the pipe through elastic deformation.

The amount of compensation. How many millimeters of axial displacement an expansion energy saver can absorb depends on the wave number of the bellows and the amount of single wave compensation. For example, external pressure single axial expansion joint, because the outside of the bellows bears the medium pressure, the stability is better, and the single wave compensation can be larger, which is suitable for long-distance pipelines. However, the directly buried (fully buried) expansion joint should consider external pressure and soil corrosion, and its structure is more complicated.

Lateral and Angular Displacement: Can Bellows Still "Walk Bending"?

The pipe is not a straight line, and turning, misalignment, and vibration will all produce lateral and angular displacements. Axial compression alone is not enough at this time. What to do? Let the bellows "bend". For example, the double hinge transverse expansion joint uses two sets of bellows to add a hinge structure in the middle, which can absorb transverse displacement and angular displacement. Imagine that two sets of bellows, one bent and the other extended, can make the pipe "drift" in the horizontal direction with the rotation of the hinge.

There is also a curved tube pressure balance type expansion joint, which is specially used in the curved tube part with pressure thrust. It adds a balanced bellows inside to offset the blind plate force and avoid excessive thrust on the pipe support. Two days ago, a customer asked me, saying that the bracket was always broken at the corner of the hot air duct in their factory. When asked, the blind plate force was not counted. Later, the pressure balance expansion joint of the curved tube was replaced, and the problem was directly solved.

Select different "expansion methods" for different working conditions: high temperature type, pressure balance type, double hinge type... Don't choose the wrong one

Choosing the wrong expansion joint is equal to laying a mine. Simply a few points:

• High temperature flue gas pipeline(For example, power stations and cement industries) -use high-temperature axial expansion joints or non-metallic expansion joints. Non-metallic fabric fibers can carry hundreds of degrees, and there is no internal pressure thrust, but the strength is not as strong as metal.
• Steam Supervisor(High pressure, high temperature) -Straight pipe pressure balanced expansion joint or double straight pipe bypass pressure balanced expansion joint. They absorb axial displacement while balancing pressure thrust and do not require a primary fixing bracket.
• Air-cooled island vacuum pipe— — The double hinge expansion joint of air-cooled island vacuum pipeline is used, and the sealing requirement in vacuum environment is extremely high, and the double hinge structure can absorb complex displacement.
• Large diameter thick-walled pipe(For example, desulfurization flue) -large-diameter thick-walled expansion joint, strengthened wall thickness, and guide tube has to be added to prevent scour.
• Insulated parts requiring frequent overhaul— — With manual plug-in type insulation door or electric plug-in type insulation door, use expansion joint to compensate pipeline displacement, and then use baffle door to cut off the medium.

You see, the "expansion method" is different for each working condition. When selecting the model, you have to compare the model and size table of the expansion joint, calculate the compensation amount, pressure and temperature, and don't just look at the price.

"Expansion" doorways in installation and use: the key points of deflectors, tie rods, pre-stretching

Only when the expansion joint is installed correctly can it "expand" normally. Article 1:guide tube。 The guide tube is installed on the inner wall of the bellows, and its function is to guide the flow medium to avoid the direct washing of the bellows by high-speed fluid. Especially in the flue gas pipeline with particulate matter or high flow rate, the bellows will wear out in a few months without the guide tube. The specific function can refer to the question and answer in our station.

tie rod。 Many expansion joints come out of the factory with tie rods or transport screws, which is to prevent the bellows from being crushed or pulled during transportation and installation. How do you adjust the tie rod nut after installing it in place? It is generally required to loosen the nut and allow the tie rod to float freely, but in some cases it is necessary to adjust the tie rod length to pre-compress or pre-stretch the expansion joint. For example, when the temperature of the pipeline is lower than the operating temperature, it has to be pre-stretched. After the temperature rises, the expansion joint just returns to the free length, and the compensation efficiency is the highest. Does the screw of the expansion joint need to be removed? The transportation screw must be disassembled, and the pull rod depends on the situation, and some are reserved as limits.

Pre-stretching。 It's a practical trick. For example, the design compensation amount of an axial expansion joint is 50mm. If the installation temperature is 20℃, the operating temperature is 200℃, and the pipeline is extended by 80mm, the expansion joint has to be pre-stretched by 30mm, installed on the pipeline and then welded. This operates without exceeding the compression limit of the bellows. This is often done in the cement industry and power station industry with corrugated expansion joints.

Don't reverse the installation direction of the expansion joint. The direction of the arrow of the expansion joint refers to the flow direction of the medium. If it is installed backwards, the guide tube will not play the role of diversion, but will become a throttling piece, and the pressure loss will increase greatly. Many on-site accidents are caused by reverse directions.

To be honest, I have been doing pipeline compensation for a long time, and customers often ask, "Where are non-metallic expansion joints generally used?" In fact, behind this problem, they often have suffered from the loss of metal expansion joints-cracking at high temperatures, corrosion and perforation, or can't fit in at all. Today, I will not take a detour, but directly break these main battlefields apart and crumble them into pieces. All of them are actual combat experience.

Power station boiler and flue gas system: the main battlefield of non-metallic expansion joint

How big can the temperature difference be in the air duct, flue and desulfurization tower inlet and outlet of thermal power plant? Cold to hot, the temperature difference of several hundred degrees is common. Moreover, the flue gas carries sulfide and chloride ions, which is extremely corrosive. The metal expansion joint often can't last a maintenance cycle here, and the weld cracks and intergranular corrosion can't be repaired. At this time, non-metallic expansion joints (especially fabric fiber materials) become standard.

The inlet and outlet of desulfurization tower must be matchedDesulfurization flue gas baffle doorUse. Think about it, when the smoke baffle door is switched, it will produce impact and vibration, and the metal expansion joint can't absorb the three-dimensional displacement at all. The result of hard carrying is cracking. The same cannot be said for non-metallic expansion joints, which also isolate vibrations and protect the entire flue system. We distributed a batch to a power plantRectangular non-metallic expansion jointIt is used between the outlet of the induced draft fan and the desulfurization tower, and it has been operated for three years without any problems. Remember, under the working condition of power station, the non-metallic expansion joint should not only consider the thermal displacement, but also the design and sealing structure of the guide tube. Otherwise, the high-temperature flue gas directly washes the fiber layer, and the life of the non-metallic expansion joint is greatly reduced.

Cement Industry: Flexible Responsibility in High Temperature Dust Environment

On the cement production line, from the preheater to the dust collector, the inside of the pipeline is full of high-temperature and high-dust gas, and the temperature is above 350℃ for a long time, occasionally rushing to 500℃. The metal corrugated expansion joint is prone to dust accumulation and stuck here, and once worn out, a new one will have to be stopped for a few days. The advantages of non-metallic expansion joints come out-wear resistance, easy replacement, and adaptation to large angle deflections of pipes.

Many cement factories like to putMetal Corrugated Expansion Joints in Cement IndustryAndNon-metallic expansion joints (fabric fiber expansion joints)Used with: metal bellows is responsible for axial compensation, and non-metal is responsible for lateral and angular displacement, both without delay. When selecting, it should be noted that the dust of cement plant contains silicon and has high hardness. The skin of non-metallic expansion joint must be thickened with wear-resistant layer, and the guide tube should be detachable to facilitate dust cleaning. Before, a customer had a cheap picture and used a general-purpose non-metallic expansion joint. As a result, it was worn out in half a year, which was not worth the loss.

Metallurgy and Steel: "Soft Connection" in High Temperature Flue Gas Pipeline

The working temperature of flue gas pipelines of blast furnaces, converters and heating furnaces often exceeds 500℃, even above 800℃. Metal expansion joints fatigue crack quickly at this temperature for a simple reason-the yield strength of the metal decreases at high temperatures, and the cyclic stress is wasted as soon as it is superimposed. The multilayer structure of non-metallic expansion joint (including thermal insulation layer) can effectively block the heat radiation, and can absorb the lateral and angular displacement caused by thermal expansion of the pipe.

Then exactly how to choose? Depends on the temperature range. When the temperature exceeds 600℃, ordinary silicone cloth skin won't work, so ceramic fiber cloth with multi-layer insulation felt has to be used. We have made a batch for the steel millHigh temperature axial expansion joint, but that was metal; In the position where three-dimensional compensation is needed, non-metallic expansion joints are used. Another point: the pipe diameter of the metallurgical industry is often very large, circular and rectangular. Non-metallic expansion joints can be made into any shape, and it is convenient to install on site, unlike metal expansion joints that have to adjust the flange surface when they correspond.

Chemical Industry and Environmental Protection: Corrosion Resistance is the Last Word

In the desulfurization, denitrification and pickling process sections, the medium contains sulfur, chlorine and acid, and the pH value is often below 1. Even if the metal expansion joint is lined with rubber and PTFE, the matrix will rot immediately as soon as the edge gap leaks. But here comes the problem:PTFE compensatorAndrubber compensatorAlthough they are corrosion resistant, they have limited pressure bearing capacity and are difficult to make into large rectangles structurally. At this time, the advantages of non-metallic expansion joints are reflected-they can be made into rectangular or circular structures, which are suitable for various irregular flues, and the overall cost is low.

"Can I replace the non-metallic expansion joint with a rubber compensator?" I said you depend on the working conditions: rubber is acid and alkali resistant but not high temperature resistant, and it softens when it exceeds 120℃; The PTFE film and silica gel layer in the skin of non-metal expansion joint can be combined, which is both temperature-resistant and corrosion-resistant, and the cost is 30% to 40% cheaper than that of metal expansion joint fully lined with PTFE. If you happen to have a circular flue, you can also considerRound Flap Door (Double Seal)With the use of non-metal expansion joint, the sealing effect is better.

Selection reminder: Don't just look at the material, the working condition details determine the life

AgainNon-metallic expansion joints (fabric fiber expansion joints)Used in power stations and cement plants, the thickness of fiber layer, sealing structure and guide tube design are different. Did you do it according to JB/T 12235-2015 standard? Does the installation location reserve enough access space? In order to save space, many customers install the expansion joint in the corner. As a result, when changing the skin, they can't even reach in the wrench, so they can only cut the pipe. There are really quite a few people who have stepped on these pits.

In addition, don't forget to consider it together with other products. For example, the flue is fittedManual plug-in insulation doorOrElectric plug-in insulation doorConvenient isolation during maintenance; If you need a higher seal grade, you can chooseDouble-sealed single-axis circular baffle doorOrSingle-axis double-flapper door。 The non-metal expansion joint and the baffle door are a perfect match. One is responsible for compensation and one is responsible for cutting off. Only when the two cooperate well can the whole pipeline system run stably.

Your current working conditions, is there high temperature, corrosion, or large displacement? Find the crux, then select the corresponding non-metallic expansion joint, and don't blindly follow the material. For specific models and sizes, you can compare the expansion joint model and size instructions on our website, or consult the technology directly to avoid detours.

Let's give a quick answer first: Yes, and it's the most common one.

"Are stainless steel corrugated Expansion joints and metal compensators the same thing?" To put it bluntly, Expansion joints and compensators are different names for the same thing in industrial pipelines-the general-purpose corrugated Expansion joints and high-temperature axial Expansion joints in our factory, and there is nothing wrong with you calling them metal compensators. But strictly speaking, metal compensators are a big category, and stainless steel corrugated expansion joints are just one of them. Just like the relationship between "car" and "sedan", a sedan is a car, but a car also includes trucks and vans.

Why is stainless steel corrugated expansion energy saving used as a compensator? By the folds of the bellows.

The pipeline expands by heat, shrinks by cold, or displaces due to equipment vibration. If it is hard, the weld will crack and the flange will leak. Stainless steel bellows eat this displacement through the elastic deformation of its own corrugations-axial expansion and contraction, lateral deflection and angular displacement can all be absorbed. The core of the directly buried expansion joint and the external pressure single axial expansion joint in the station is stainless steel bellows. To put it bluntly, it relies on physical deformation to "compensate" the thermal displacement of the pipe, which is the business of metal compensators.

Bellows aren't the only ones in the metal compensator family.

The sleeve-type pipe expansion joint is compensated by the sliding of the inner and outer sleeves, and the rotating compensator absorbs torsion by the rotating shaft. Even the rubber compensator and PTFE compensator are considered compensators-only the material is not metal. Therefore, "metal compensator" specifically refers to the compensation equipment made of metal. Stainless steel corrugated expansion joint is the most widely used among them, but it is by no means the only one. For example, when you encounter high-temperature and high-pressure steam pipelines, you may have to use high-temperature axial expansion joints; If a large amount of compensation is needed and there is no space, it depends on the lateral type of double hinge or the pressure balance type of curved tube. The matter of model selection has to be based on the working conditions.

One point that many people confuse: Are expansion joints and compensators the same thing or not?

Two days ago, I met a customer, who insisted that the "compensator" and "expansion joint" he bought were not of the same type, and then took the product manual to check the model. I directly dug out the fourteenth question and answer in the station and showed it to him-expansion joints and compensators actually refer to different designations for the same type of equipment in industrial piping systems. Another example is the non-metallic expansion joint, which is called "non-metallic compensator" in the national standard JB/T 12235-2015. So don't dwell on the name, look at the structure and use. Stainless steel corrugated expansion joint is a kind of metal compensator, but many people are used to calling it "stainless steel" according to the material and "compensator" according to the function.

How to judge which one to use when choosing a model? Remember a simple principle:

If the medium temperature is high, the pressure is high, and the seal is tight, stainless steel corrugated expansion joints are preferred (such as corrugated expansion joints for power station industry and metal corrugated expansion joints for cement industry); If the diameter of the pipeline is oversized or it needs to absorb multi-dimensional displacement, it may be necessary to use compound hinge and pressure balance type; If there is corrosion in the medium, a PTFE-lined hose or PTFE compensator is more suitable; Non-metallic expansion joints (fabric fibers) are commonly selected when the flue gas pipe temperature is not high but low-cost solutions are required. The more than 30 types of products in the station are actually revolved around the purpose of "compensating displacement".

To sum up: stainless steel corrugated expansion joint is the main force of metal compensator, but don't regard "metal compensator" as its exclusive hat.

When selecting, don't just look at the name, but the material of the bellows (304, 316L or superalloy), wave number, wall thickness, and whether it has a guide tube (the specific function of the guide tube is explained in detail in Article 7 of Q&A in the station). If you need a product size or weight reference, the station has a metal expansion joint weight chart and a page for the model and size of the expansion joint. In the final analysis, if you can solve the compensation problem with stainless steel bellows, don't go around the bends-it is cheap, mature, reliable and sufficient.