Specialized in manufacturing compensators, expansion joints, baffle doors

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.

What exactly are expansion joints "expanding"? Understand what it does first

When many customers hear the name "expansion joint" for the first time, their first reaction is: Can this thing become bigger and smaller by itself? Actually, you guessed half right-the expansion joint does "expand", but strictly speaking, it is not getting bigger, but absorbing the thermal displacement of the pipe. Simply put, when pipelines transport high-temperature media, they will expand and contract by heat. Pipelines of tens or even hundreds of meters may elongate by tens of millimeters when the temperature rises. If you don't find a way out for this stretch, pipe joints, valves and even brackets will be broken. At this time, the expansion joint comes in handy, and it "eats" this part of the displacement through its own corrugated structure.

Two days ago, I met a friend from a power plant, who told me that their main steam pipe burst welds three times a year, and finally replaced itCorrugated expansion joint for power station industryIt never went wrong again. You see, the core value of an expansion joint is not to expand itself, but to give a "safe amount of deformation" to the piping system.

Bellows is the real "actor"- -Detailed explanation of three deformation modes in axial, transverse and angular directions

How do metal expansion joints expand? The answer is all in the bellows. The bellows is made of layers of stainless steel sheet pressed, like the bellows of an accordion. It has three ways of "performing":

• Axial expansion: Bellows are stretched or compressed along the length of the pipe, most commonly. For example, when the steam pipe heats up, the bellows is compressed and absorbs the elongation. If you are usingUniversal corrugated expansion jointOrHigh temperature axial expansion jointIt mainly depends on this action.
• Lateral expansion: When the pipe is offset horizontally or vertically, the bellows will bend like a snake. However, it is difficult to complete the lateral displacement at a large angle by one section of corrugated pipe alone, so two sections of corrugated pipe are usually connected in series, and a section of connection pipe is added in the middle to makeCompound hinge transverse expansion jointOrDouble hinge expansion joint for air-cooled island vacuum pipeline。 This construction allows the pipe to sway from side to side, but the bellows themselves do not twist.
• Angular expansion: The bellows rotates at a certain center point and is usually used with a pair of hinges or universal hinges. Such asCompound hinge expansion joint、Curved tube pressure balance expansion jointAll can realize angular compensation. You see the kind of expansion joint with "a short tube in the middle of two bellows and tie rods around it" at the scene, which is mostly angular.

These three deformation modes are not mutually exclusive-many expansion joints bear axial and lateral displacements at the same time, and the selection depends on the direction of the pipeline and the position of the fixed bracket.

Different types of metal expansion joints, what is the difference between expansion methods?

Although they are called expansion joints, their internal structures are different, and the ways of "expansion" are worldly different.

Axial type

The most simple and crude, such asAxial expansion joint、External pressure single axial expansion jointThey have only one section of corrugated pipe and both ends are welded directly to the pipe. Used in large straight pipe sections, where the temperature changes greatly and the pipe has enough space to expand and contract. But the downside is also obvious-once the pipe has a lateral displacement, it is prone to "twist twists".

Complex hinge type

Just mentionedCompound hinge transverse expansion joint, with two bellows connected by a short pipe in the middle and a set of hinges on each side. The function of the hinge is to limit the axial expansion and contraction of the bellows, only allowing it to swing angularly or laterally in the plane. This structure is particularly suitable for L-shaped or Z-shaped pipes, which can absorb thermal displacement without producing huge blind plate forces.

Pressure balance type

There is a trouble in pressure pipes called "blind plate force"-the medium pressure acts on the end face of the bellows and will push the pipe like a piston. To solve this problem, there areStraight pipe pressure balanced expansion joint、Curved tube pressure balance expansion joint、Compound straight pipe bypass pressure balanced expansion joint。 They typically have two sections of bellows inside, one that absorbs displacement and the other that counteracts pressure so that there is no additional thrust on the fixed bracket. And guess what? The pressure of the main pipeline of many chemical enterprises can reach more than 4.0MPa. If there is no pressure balance structure, the bracket can't hold it at all.

In addition, rectangular flue ducts in coal mines and power plants are generally usedMetal rectangular expansion jointOrRectangular non-metallic expansion jointTheir expansion principle is similar to that of a circle, but the structure is an integral frame plus a non-metallic skin, and the folds and elasticity of the skin absorb the displacement. One thing to remember: rectangular expansion joints cannot withstand internal pressure and are only used for low-pressure or atmospheric pressure pipes.

Pits often stepped on at the installation site: how to deal with the direction of the tie rod, guide tube and arrow?

When the equipment arrives at the site, it is easy for the installer to make mistakes if he is not careful. Say a few of the most common questions:

Do you want to remove the tie rod and nut?When the expansion joint leaves the factory, it usually has a transportation pull rod to press and fix the bellows to prevent transportation bumps. Once installed in place, this tie rod should generally be loosened-but don't disassemble it completely. If it isPressure balanced expansion jointOrCompound hinge expansion jointSome tie rods are permanent structural pieces used to transmit blind plate force. Dismantle or not? Look at the nameplate or instructions, which will say "Installation: loosen tie rods after installation" or "remove shipping bars". You remember: All threaded tie rods, any with adjustment nuts, are mostly transport tie rods; If both ends of the tie rod are welded to the end plate, it is a permanent piece.

Direction of guide tubeA guide tube is usually welded inside the expansion joint, which guides the flow of the medium, reduces the resistance, and protects the inner wall of the bellows from being washed by the high-speed medium. How to judge the direction? The opening of the guide tube is directed in the direction in which the medium flows. If you install it backwards, the deflector will be held up and the bellows won't expand or contract properly at all. There was a client who putDesulfurization flue gas baffle doorThe expansion joint at the back was installed backwards, and the guide tube blocked the flue gas flow. After changing the bellows three times, it was not found out... Later, it was discovered that it was a direction problem.

What's the direction of the arrow?Many expansion joint shells have arrows printed on them or the words "flow direction". This arrow represents the flow direction of the medium, not the installation direction, let alone the displacement direction. Once installed backwards, the guide tube and the sealing structure will fail. Especially forFlue gas baffle door、Desulfurization flue gas baffle doorFor such equipment, the flow direction arrow must be consistent with the actual flue gas flow direction.

It is enough to focus on these four points when selecting a model: temperature, pressure, medium and displacement

"How exactly do you choose the expansion joint?" I generally only ask them to provide four parameters:

• Temperature: Maximum operating temperature and minimum temperature. Temperature determines the material of corrugated pipe-austenitic stainless steel (304, 316L) for high temperature pipeline, and ultra-high temperature (above 700 ℃) should be consideredHigh temperature axial expansion jointOrMetal Corrugated Expansion Joints in Cement IndustrySometimes thermal insulation is needed. For cryogenic pipelines below-196℃, austenitic stainless steel or copper alloy should be selected.
• pressure: Design pressure and test pressure. Pressure determines the number of layers and wall thickness of the bellows. Generally, the pressure of steam pipelines in power plants is 1.0~2.5MPa, and some chemical pipelines reach more than 10MPa.Large diameter thick wall expansion jointOrPressure balanced expansion joint。
• Medium: Gas, liquid, corrosive medium? If it is a corrosive medium, such as the wet flue gas behind the desulfurization tower, ordinary stainless steel cannot be used, it must be usedPTFE-lined hoseOrPTFE compensator。 If the medium contains particulate matter, such as cement raw material conveying pipelines, the bellows need to be wear-resistant bushings.
• displacement amount: What are the axial, transverse and angular directions respectively? Calculated by pipeline stress analysis software such as CAESAR II, or estimated by empirical formulas. The magnitude of the displacement directly determines the wave number and structural form of the expansion joint-for large displacement, use multi-wave bellows or connect multiple joints in series.

These four parameters are clear, and the selection will basically not overturn. As forMetal hose、rubber compensator、Non-metallic expansion jointThe principle of these special products is similar, but the applicable boundary conditions are different.

Does metal expansion joint belong to special equipment? Don't be fooled

Metal expansion joints are not necessarily special equipment. The key depends on these three parameters-nominal diameter, design pressure and medium. Take the corrugated expansion joint used in the power station industry as an example. For those with DN300 or more and a pressure of 1.6MPa and steam, nine times out of ten should be managed according to special equipment; However, those large-diameter thick-walled expansion joints in the cement industry take normal temperature flue gas, and the pressure is only 0.1MPa, so they basically don't need to enter the supervision catalogue. Don't hear "metal expansion joint" and think that you have to apply for inspection. It's all to scare you.

What do the regulations say?

The pressure pipeline components in the Special Equipment Catalogue include "compensator (expansion joint)", but there is a premise: the nominal diameter is ≥150mm, the design pressure is ≥1.6MPa, and the medium is gas or liquefied gas, or a liquid with a maximum operating temperature ≥ standard boiling point. If you compare the general corrugated expansion joint or the double hinge transverse expansion joint in your project, if you use steam, hot water and compressed air, you will most likely have to manage it by pressure pipe elements. If desulfurization flue gas and cement kiln tail waste gas are taken, the temperature is high but the pressure is low, so they are often exempted.

Don't use non-metallic expansion joints. The non-metallic expansion joint has JB/T 12235-2015 national standard, but it is not in the special equipment catalogue because the fabric fiber has limited pressure bearing capacity. However, as long as the parameters of metal rectangular expansion joints and high-temperature axial expansion joints are sufficient, the design, manufacture, installation and inspection must comply with TSG D0001, GB/T 12777 and other standards. Two days ago, a customer took our straight pipe pressure balance expansion joint and asked me why there was no TS logo on the nameplate-I said that your pipe diameter was only DN80 and the pressure was 0.6MPa, which was not within the scope of supervision at all. It was a waste of money to do TS.

How to judge whether your expansion joint should be monitored or not? Three steps.

Is the nominal diameter ≥150mm? Is the design pressure ≥1.6MPa? Is the medium a gas or a high temperature liquid? The second step is to look at the structure: such as sleeve-type pipe expansion joint and rotary compensator, although they are also compensators, they are not considered bellows, and the supervision and determination in some places are controversial. The third step is to look at the pipeline category: if the whole pipeline belongs to GC1 and GC2, the expansion joint will naturally follow. For example, the metal expansion joint connected behind the desulfurization flue gas baffle door directly skips the flue gas at normal pressure and temperature.

In case of monitoring and inspection, how to choose the type without stepping on the pit? If you clearly know that the project belongs to the category of special equipment, be sure to purchase products from manufacturers with corresponding manufacturing licenses. However, if you buy the "non-standard" one cheaply, the on-site supervision will not recognize it, and the rework loss will be ten times more expensive than the expansion joint itself. On the other hand, if your project clearly doesn't need monitoring and inspection, don't listen to people fool you and add money to do TS. The budget saved is enough to buy a few electric plug-in insulation doors.

Whether the metal expansion joint is special equipment or not depends on the three axes of "diameter, pressure and medium". Don't be intimidated by the word "expansion joint", and don't take it seriously. If you really want to judge it, look through the Pipeline Grade Table or Pressure Pipeline Summary Table given by the design institute, which will clearly write whether the pipe section is a pressure pipeline. If it doesn't work, send the parameters of your metal hose, PTFE-lined metal hose or large-diameter thick-walled expansion joint to our technology to help you close it-don't let compliance problems get stuck in your project acceptance.

So, back to that core question:Are metal expansion joints special equipment?The answer is clear – look at the parameters. The pipe diameter is less than 150, the pressure is less than 1.6MPa, and the medium is water or low-temperature liquid, so it is appropriate to leave it alone; On the other hand, no one can avoid the monitoring and inspection of DN200 and 2.5MPa bellows on steam pipelines.

1. There is no fixed answer to the life of metal bellows expansion joint: design, working conditions and materials have the final say

Two days ago, a customer called and asked, "How many years will your bellows expand and save energy?" I asked him, "What working conditions do you use it in? What is the temperature? Is the medium corrosive?" He was stunned. To be honest, there is no standard answer to this question. Metal bellows expansion joint life? It is not a true or false question at all, but a comprehensive question determined by design, working conditions and materials.

The same general-purpose corrugated expansion joint, placed on a clean steam pipe, may run steadily for ten years; It is not unusual to throw it into the dusty environment of the cement industry and scrap it in three years. So don't believe those sales talk that pat your chest and say "guarantee for 10 years"-those are theoretical values measured under certain conditions.

Five core factors affecting life: temperature, pressure, medium, displacement frequency and installation quality

If the expansion joint of metal bellows fails, 90% of them can't escape these five pits.

• Temperature: If the design temperature exceeds 10℃, the fatigue life may be directly discounted by 50%. For example, corrugated expansion joints are used in power station industry. If high-temperature axial expansion joints run above 600℃ for a long time, the material must be heat-resistant alloy, and ordinary stainless steel can't last a maintenance cycle.
• pressure: The higher the internal pressure, the greater the circumferential stress on the bellows wall. Frequent pressure fluctuations can easily lead to low-cycle fatigue.
• Medium: Chloride ions and sulfides in the chemical industry are invisible killers. PTFE-lined hoses or PTFE compensators are specially designed to deal with corrosive media, but if you touch hydrochloric acid with ordinary stainless steel, the life is calculated by day.
• Displacement frequency: A pipeline that starts and stops several times a day has a much shorter life than a pipeline that runs continuously. Frequent expansion and contraction is equal to repeatedly bending the wire, and it will break sooner or later.
• Installation quality: Most overlooked. During installation, the tie rod bolts are not removed, or the pre-offset is not done correctly, and the expansion joint directly enters the limit state before it runs. I saw a scene two days ago, and the screw of the expansion joint of the big tie rod was not disassembled, but it was directly welded to death-that would compensate for a fart.

3. Life difference in different application scenarios: from high temperature of power station to cement dust, to chemical corrosion

Come on, let's talk about a few practical scenarios.

Power station industry: Boiler outlet, turbine bypass, high temperature, high pressure, and frequent start-and-stop. In this scenario, the power station industry uses corrugated expansion joints and air-cooled island vacuum pipeline double-hinged expansion joints, and the design life is usually about 10 years. However, in fact, due to overtemperature and overpressure, it is the norm to change a batch in 5-8 years.

Cement industry: There is much dust, strong grinding property, and high temperature. If the metal corrugated expansion joint in cement industry is not added with wear-resistant guide tube, the corrugated pipe will be impacted by particle flow and perforated quickly. The specific function of the guide tube is to protect the bellows body, but the guide tube itself is also a wear part.

Chemical industry: Corrosive media are enemy number one. PTFE-lined metal hoses and rubber PTFE compensators are standard here. But even with a PTFE compensator, the liner needs to be checked regularly to see if it has fallen off-once the medium penetrates the metal matrix, the rate of corrosion will make you doubt your life.

Flue gas desulfurization system: The non-metallic expansion joint (fabric fiber expansion joint) behind the desulfurization flue gas baffle door has a long life, but the acid dew point corrosion of the metal corrugated expansion joint is particularly serious in the low temperature and high humidity environment of wet desulfurization. We advise customers to give preference to rubber compensators or non-metallic compensators in this case.

4. Common failure modes: fatigue fracture, corrosion perforation, instability deformation, which one have you encountered?

For so many years, what I have seen the most isFatigue fracture。 Under the cyclic displacement of the bellows, micro-cracks gradually appear in the stress concentration areas of the peaks and valleys, and finally there is a click. And guess what? Many owners have to wait until they leak before changing, so why did they go early?

Secondly,Corrosion perforation, especially point corrosion. Stainless steel is most afraid of chloride ions. Even if the concentration is very low, it will penetrate quickly at the stress concentration point. Therefore, on chemical pipelines, we recommend using vacuum special hoses or directly buried (fully buried) expansion joints plus external protection.

Unstable deformationWhat? That's caused by too much pressure or skewed installation. The bellows is like being twisted and twisted, with uneven wave pitch and bulging directly in severe cases. Structures with restraints, such as double hinge transverse expansion joints and straight tube pressure balance expansion joints, are designed to prevent instability. However, some masters regard the tie rod as a reinforcement when installing it, which should be dismantled or not, and the result becomes an accomplice.

5. Practical operation method of prolonging life: one-stop selection, installation, inspection and maintenance

To say a thousand words, if you want to prolong the life of metal bellows expansion joint, you have to start from the root.

Don't make do with the selection: The working condition parameters must be given accurately. For high temperature, choose high-temperature axial expansion joint, for corrosion, choose PTFE-lined or rubber compensator, and for large diameter and high pressure, choose large-diameter thick-walled expansion joint. Don't buy a general-purpose model cheaply to handle harsh conditions-that's equivalent to running a rally with a Xiali.

Installation should be standardized: How to adjust the expansion joint tie rod nut? It's all clearly written in the instructions, but field workers often get it wrong. Remember: the transport tie rod should be removed after installation, and the adjustment tie rod should adjust the pre-bias according to the compensation amount. Does the screw of the expansion joint need to be removed? Depending on the situation, but by no means means welded to death.

Patrol inspection cannot be omitted: Look at the bellows surface every month for cracks, corrosion spots and deformation. Focus on checking whether the guide tube is loose and whether the tie rod is bent. The national standard JB/T 12235-2015 for non-metallic expansion joints also stipulates the periodic inspection cycle, so just follow it.

Maintaining records is done: What day it was changed, what model, and the change of working condition parameters-take a note, and there will be a basis for the next change. Products such as rotary compensators and sleeve pipe expansion joints are relatively simple to maintain, but don't ignore them.

The life of a metal bellows expansion joint is like asking how many years a car can run- -how you drive it, where you drive it, and how you maintain it. Choose the right product, install the right position, and check it out regularly. There will be no problem for ten or eight years; On the contrary, it is not unusual to lie down in a nest in three or two months. What scenario are you using for the equipment at hand? Comparing the above few, you probably have an idea in your mind.