Specialized in manufacturing compensators, expansion joints, baffle doors

Find out what non-metallic compensator is first: compared with metal compensator, where is it stronger and weaker?

The core structure of non-metallic compensator, also called non-metallic expansion joint (fabric fiber expansion joint), is flexible fabric band, thermal insulation filler layer and metal frame. It is different from the metal corrugated compensator: metal absorbs displacement by the deformation of the corrugated thin wall, while non-metal absorbs displacement by the flexibility of the fabric band.

First, the amount of compensated displacement is large, especially the lateral and angular displacement, which is often several times that of metal; Second, the thrust is small, because the stiffness of the fabric loop is extremely low, and the load requirement on the pipe support is low; Third, it has good corrosion resistance and can resist corrosive media such as sulfide and chloride ions in flue gas. There are also shortcomings-poor pressure bearing capacity, which can generally only be used in low pressure or even slightly negative pressure conditions, and fabric belts are consumables, and their life is not as good as that of metal bellows.

Therefore, the use of non-metallic compensator is not to replace metal, but to make up the shortcomings of metal. The following working conditions are its home field.

Application 1: Large-diameter low-pressure pipes such as air ducts and flues of power plants can be easily compensated by rectangular cross sections

The air ducts and flues of power plants are often two meters, three meters or even larger in diameter, and many of them are rectangular in cross section. Metal corrugated compensator for this occasion? Material and molding costs are ridiculously high, and metal bellows are sensitive to cross-sectional shape, making rectangular bellows extremely difficult to manufacture.

Nonmetallic compensators don't have this concern. Its ring belt is flat, and it is made into a rectangular cross section by the frame. This is how rectangular non-metallic expansion joints come from. Large diameter and low pressure just avoid the short board of non-metal pressure difference, and give full play to its advantages of large compensation and small thrust.

And guess what? A rectangular flue of DN4000, the heat displacement may reach fifty or sixty millimeters, and the non-metallic compensator can easily absorb it. What about the metal ones? Honestly calculate the fatigue life.

Use 2: How can fabric fibers and rubber materials hold high temperature and corrosive smoke environment?

Flue gases and corrosive gases are another typical type of operating conditions. The temperature of the flue gas at the inlet of the desulfurization tower may reach 150℃, as well as corrosive components such as SO₂, SO₃ and HCl, and dust washing in some places.

The band material of the non-metallic compensator is a composite structure such as glass fiber, polytetrafluoroethylene and silicone rubber, which can withstand the temperature above 200℃, and its corrosion resistance is much better than that of metal. Metal bellows are prone to stress corrosion cracking in chloride ion environment, but non-metallic bands become more and more solid.

In addition, the insulation layer of the non-metallic compensator can be designed as a multi-layer structure, which can not only compensate for displacement, but also reduce heat loss. This kind of structural design flexibility, metal compensator can't compare.

Application 3: Vibration and noise reduction of equipment interface, and "fault tolerance" function of installation deviation

The inlet and outlet of rotating equipment such as pumps, fans and compressors can't avoid vibration. If the pipes are connected rigidly, vibrations are transmitted directly to the piping system, and both noise and stress are large.

The fabric band of the non-metallic compensator itself has damping effect, which can absorb part of high-frequency vibration. A non-metal compensator is installed at the outlet of the fan, and the vibration transmission rate can be reduced by an order of magnitude. Rubber compensator and rubber PTFE compensator are the same way, which is suitable for vibration reduction of fluid media pipelines.

There is also a particularly practical use – fault tolerance. During on-site installation, the pipeline alignment deviation is several millimeters or even more than ten millimeters, which is normal. Hard connections can't be installed, so soft connections are much more convenient. The non-metallic compensator can absorb the installation deviation, which saves the user the time of field adjustment, which is considerable.

Application 4: Special applications in desulfurization, dust removal and other systems, used with baffle doors and other equipment

Flue gas baffle door, electric plug-in type insulation door, manual plug-in type insulation door of desulfurization system, these devices will have thermal displacement in the pipeline when switching and starting and stopping. The baffle door body is rigid and cannot absorb displacement, so it must be digested by the peripheral compensator.

Here non-metallic compensators are pretty much the only option. The temperature of desulfurization flue gas is not high but it is extremely corrosive, and the cross section of pipeline is often rectangular, so the space is limited. The non-metal compensator can be made into a flat shape, connected on both sides of the baffle door, and used in cooperation with the desulfurization flue gas baffle door, which just meets the technical requirements.

The same goes for dusting systems. The fabric ring belt compensator at the inlet and outlet of the dust collector can not only compensate the displacement, but also block the vibration transmission and protect the body of the dust collector.

Pits to be avoided in model selection: pressure, temperature, displacement, none of which can be taken for granted

Finally, talk about selection. What are non-metallic compensators most afraid of? Stress. Some people think that the fabric loop is soft anyway, so the pressure should not matter, right? Wrong. Under positive pressure, the ring belt will bulge, and the skeleton will be subjected to additional pressure load, which will tear if the design is not good.

Temperature is also a red line. Silicone rubber bands and fluorine rubber bands have different temperature resistance grades, and they will age and crack if they exceed the upper limit. The displacement is more accurate, and the deformation of the ring belt must be controlled within the safe range, otherwise creep fatigue will shorten the life.

The usefulness of non-metallic compensators?In the final analysis, it is born for specific working conditions such as large diameter, low pressure, high corrosion, large displacement and vibration reduction. When selecting the model, give the working condition parameters to the manufacturer and let the engineer help you check it-don't take it for granted.

I met a customer two days ago. The non-metallic expansion joint on the flue gas pipe was used for less than a year, and the skin leaked. When it was removed, the surface of the silicone cloth was cracked in a large area, and the reinforcing layer was exposed. After asking around, I realized that when I selected the model, I looked at the temperature resistance data and ignored the small amount of SO₂ in the medium. This thing turns into dilute sulfuric acid when it encounters condensed water, and ordinary silicone cloth can't hold it at all.

So,Material of non-metallic compensator skin?This problem is by no means just flipping through the samples and picking the one with the highest temperature resistance. If the skin is chosen wrong, it can be replaced in advance at least, and production can be stopped at worst. Today, break up these five questions and explain them clearly to help you avoid detours.

1. The skin is not a layer of cloth: the structure determines the lower limit of performance

Many people think that the skin is just a piece of cloth, and it is done by holding the medium. If it is so simple, why divide it into non-metallic expansion joints (fabric fiber expansion joints) and rectangular non-metallic expansion joints?

Temperature resistant layer, reinforcing layer, heat insulating layer, outer protective layer。 The temperature-resistant layer directly contacts the medium and is responsible for blocking high temperature and corrosion; The reinforcement layer is a skeleton, usually made of glass fiber or steel wire mesh, which bears the pressure tension; The heat insulation layer is made of ceramic fiber felt or the like to prevent heat from transmitting outside; The outer protective layer shields the whole structure from wind and rain and prevents mechanical damage.

Each of these four levels does its own work, and one is indispensable. The inner layer burns through, and the enhancement layer follows; The outer layer is damaged and watered, and the inside is no matter how good it is, it is useless. Therefore, when choosing skin, don't just stare at a certain layer, but look at the overall structural design and matching between layers.

2. Silicone cloth, fluororubber cloth and polytetrafluoroethylene film: how to compare the three mainstream materials

The most common skin surface materials in the market are these three kinds, each with its own temper.

Silicone clothTemperature resistance-60℃ to 250℃, good flexibility, cheap price, it is a cost-effective choice for general working conditions. However, it is afraid of strong acid and alkali, oil, especially corrosive flue gas containing sulfur. The client mentioned above is planted on this.

Fluorine rubber clothTemperature resistance-20℃ to 200℃, chemical corrosion resistance is one grade higher than silica gel cloth, and it has good resistance to acid, alkali and oil. The disadvantage is that it is easy to harden at low temperatures, has poor elasticity and is more expensive. It is much more reliable than silica gel cloth when used in desulfurization flue gas and chemical medium pipelines.

Polytetrafluoroethylene membrane (PTFE)It is almost corrosion-resistant ceiling, can carry almost all strong acids and alkalis, extremely low friction coefficient, and does not adhere to dust. However, the temperature resistance is generally about 180℃, the mechanical strength is poor, and it is easy to tear, so it is usually used on glass fiber cloth or fluororubber cloth, rather than as a skin alone.

Is there anything else? Yes. LikePTFE compensatorIt is all-PTFE structure itself, but that belongs to another class of products, so I won't go into it here. When choosing the skin of the non-metallic compensator, directly throw the working condition parameters to the manufacturers, and let them give the scheme according to the matching of these three types of materials, which is less trouble than yourself.

3. Select the skin according to the working conditions: high-temperature flue gas, corrosive medium and high-temperature dust are different

Not long-winded, just say the conclusion.

Flue gas pipeline at the tail of boiler and cement kiln in power stationThe temperature is often above 200℃, the dust is large, and there may be sulfur corrosion. In this working condition, the inner layer of the skin must be laminated with fluororubber cloth or PTFE glass fiber cloth, the reinforcing layer must be made of stainless steel wire mesh, and the heat insulation layer must be thickened to more than 80mm. Mentioned in the information on the siteCorrugated expansion joint for power station industryAndMetal Corrugated Expansion Joints in Cement IndustryAlthough the main body is a metal bellows, the matching non-metal skin is the same routine.

Desulfurization system, wet dust removalThis kind of corrosive medium environment, the temperature is not high but the pH is very fierce. PTFE or fluororubber cloth is the first choice for the skin layer, and attention should be paid to the problem of condensate accumulation-even if the medium temperature is low, the inner material must be able to withstand the long-term soaking of acid and alkali liquid.

Dry dust removal, pneumatic conveyingIn high-temperature dust conditions, wear is more deadly than corrosion. The inner layer of the skin should be made of fluororubber cloth with good wear resistance, and a layer of wear-resistant protective layer should be added between the heat insulation layer and the reinforcing layer. Otherwise, the dust will wear the skin out in a few months like sandpaper.

Selection is not single-point optimal, but system matching. You go to the manufacturer with the working condition and ask: Which skin structure do you recommend for this working condition? Those who know the business naturally know which plan to use.

4. Composite lamination process: why is the life of the same material several times worse

It is also silicone cloth + glass fiber cloth + ceramic fiber felt. The products of Factory A will be used for 5 years, and the products of Factory B will leak for 2 years. What's the difference? Craft.

Instead of layers of cloth simply sewn together, the skin is created byHigh temperature vulcanization, rolling composite, interlayer bondingWait for the process to be made into a whole. The bond strength between layers is not enough, and it will delaminate, bulge and crack after several times of thermal expansion and contraction. The vulcanization temperature and time control are not in place, and the temperature resistance of silicone cloth is directly discounted.

When you look at the skins that have problems, nine times out of ten, it is not the wrong material choice, but the rough composite process. The most typical is to use ordinary glue to stick between layers, which is not used. Genuine manufacturers will use special high-temperature adhesives to control the process parameters in the whole process of internal mixing, calendering and vulcanization, and each batch has a test record.

So don't just compare the thickness and weight of the sample, and ask one more question: What glue do you use for composite? Is there a temperature resistance aging test report? This is more real than anything else.

5. Installation and routine maintenance: Don't wait for a leak to regret it

No matter how good the skin is, it will be for nothing if it is not installed properly.

First, the pipe flange must be flat, and the bolts should be evenly tightened diagonally. If the local pressure is too tight, the skin will be pressed out of marks or even fractured. Second, do not stretch or twist the skin when it is installed. The reserved displacement is adjusted from the factory, so do not move on the spot. Third, sealant and gasket should be added to the place of riveting or bolting, which is the most easily overlooked leak point.

Routine maintenance is not so mysterious, just regular inspections. Check the skin surface every quarter for any cracks, aging, bulging, and dust accumulation that causes local overheating. Don't wait until the smoke comes out before shutting down the machine. That will cost you a lot.

To put it hard, in order to save money in some projects, the material of the skin of the non-metallic compensator is kept to the lowest level, and the installation and maintenance are not paid attention to. In the end, if something goes wrong, the product is blamed. This account is actually not cost-effective at all.

When choosing a skin, remember three sentences:Material matches working conditions, process determines life, installation and maintenance guarantee bottom line。 These three are achieved, and the non-metallic compensator can be used for more than ten years. If you can't do it, then wait for it to be changed every two years.

Find out what you want to measure first: 4 core sizes

Two days ago, I met a customer. On the phone, I said anxiously that the expansion joint was leaking and I needed to replace it with a new one. I asked him what the diameter of the pipe was, and he was stunned for a long time and said, "About one meter". Tsk, this "probably" is in trouble. How to measure metal expansion joints? It's really not a matter of just taking a tape measure and measuring it casually.

Before measuring, figure out what you are going to measure. There are only four core sizes:

• Diameter (DN)— — The inner diameter of the pipe, which is the first factor in the selection. The common ones are DN50, DN100, DN200, etc., according to the nominal diameter.
• Installation length— — The actual length between the end faces at both ends of the expansion joint. This directly determines whether you can fit it.
• displacement amount-Amount of axial compression, stretching, and lateral offset. This is the core parameter of the expansion joint, which will be described in detail later.
• Ripple parameters— — Wave number, wave height, wave pitch, inner and outer diameter of bellows. These determine the stiffness and compensation capacity of the expansion joint.

How to choose a measuring tool: Don't measure the inner diameter of the corrugation with a tape measure

Many on-site masters are used to walking the world with a tape measure. Tape measure the installation length is fine, but measure the corrugated inner diameter? The error can reach more than 5mm. The bellows is a thin-walled piece, and once the tape measure is pulled, the tension of the ruler itself can make the reading too large.

Install length and diameter, either with a tape measure or laser rangefinder; The corrugated inner diameter must be with vernier caliper or special inner diameter gauge; Vernier caliper for wave height and wave distance; If you need a precise corrugation profile, use a dedicated template or projector.

For 90% of on-site measurements, a vernier caliper plus a tape measure is enough. Don't be superstitious about laser rangefinders. The dust in the pipeline well is large and the light is poor, so the laser is not good to use. For what occasions do you use lasers? Large-diameter pipelines, above DN500, can't be reached by a tape measure, so it is most reliable to measure the installation length with a laser rangefinder.

Teach you step by step: standardized operation process

How to measure the metal expansion joint to be standard? Give you a set of operating procedures:

The first step is to measure the path.If the expansion joint is installed, measure the inside diameter of the flange or the inside diameter of the pipe directly. If it is removed, measure the inside diameter of the bellows. Note that measure in three directions and take the minimum value. Why? Bellows ellipticity is very common, and you can't fit it when you take the maximum value.

The second step is to measure the installation length.The distance between the end faces of the flanges at both ends is measured at 4 points evenly along the circumference, and the average value is taken. If the difference between the four points exceeds 5mm, it means that the expansion joint is crooked or the flange surface is uneven. At this time, it has to be corrected before measuring.

The third step is to measure the corrugation parameters.Use a vernier caliper to measure wave height (the vertical distance from crest to trough) and wave pitch (the distance between two adjacent crests). Count the wave numbers. There is a common mistake here-someone included the end edge wave, and the result was that the number of waves was 2 more, and the selection was directly wrong.

Step 4, record the nameplate information.If the nameplate is still there, write down the model, nominal diameter, design pressure, design temperature, and displacement on it. This information is much more accurate than you can measure yourself.

Common Errors Demonstration

Once I went to the scene, I saw a master put a tape measure on the ripples to measure the length. Ripples have peaks and troughs, and he measures the length of the arc between the peaks, which is several centimeters longer than the actual installation length. This kind of error is particularly hidden. After testing, I took it to correct the model. If I didn't match it, I thought it was the manufacturer who did it wrong.

The most difficult thing to measure is actually the displacement

The previous ones are easy to handle, but the real test of kung fu is the measurement of displacement. Why? Because the displacement is divided into cold state and hot state, the data of the two states are completely different.

How to measure cold pre-stretch?Before the expansion joint is installed, it is generally necessary to pre-stretch or pre-compress. Universal corrugated expansion joints and axial expansion joints usually leave the factory with transport rods to hold the bellows in a predetermined position. When installing, what you want to measure is the change in the amount of displacement from the natural state to the installed state. Specific method: After installation, adjust the tie rod nut, and measure the distance change of the flanges at both ends of the bellows with a vernier caliper. Stop when you pull to the design value, and the nut locks.

How to estimate hot operation data?This really can't be measured directly-the pipe is so hot that you can't touch it. How do you measure it? It can only be calculated. The thermal expansion coefficient of the pipe material is multiplied by the length of the pipe and multiplied by the temperature difference, and the theoretical thermal displacement is calculated. For example, a 20-meter-long carbon steel pipe, with a temperature difference of 200℃, has a thermal expansion of about 20×0.012×200=48 mm. This means that the expansion joint has to absorb at least 48mm of axial displacement.

What about that? The reliable way is to look at the running traces. After the expansion joint is installed, if there are strains or scratches on the bellows surface, or the tie rod bolts are bent, it means that the actual displacement exceeds the design value. Conversely, if there is dust accumulation on the bellows surface but not locally, the boundary of that clean area is often the actual displacement range. Earth methods are sometimes more accurate than instruments.

Don't hurry to place an order after testing: How to convert data into model

After measuring for a long time, the data is all written in the notebook, and then what? Just take the size and buy it? Wrong. The expansion joint is not a standard part, not that you can buy it in stock by quoting a DN200 with a length of 500mm. It is a non-standard part designed according to working conditions.

After you get the data, you have to do three things:

First, check the displacement amount.Multiply the measured displacement by the safety factor (usually 1.2~1.5), and report it to the manufacturer. For example, if you calculate that the thermal displacement of the pipeline is 48mm, then you have to report the compensation requirement of about 60mm. Why? The actual working condition is more complicated than the calculated working condition, with vibration, installation error and occasional working condition fluctuation.

Second, check the medium and temperature.The diameter and length are just the shell. What really determines the material and number of layers of the bellows is the medium, pressure and temperature. Stainless steel bellows for high-temperature steam pipelines, PTFE-lined hoses may be used for corrosion-resistant media, and flue gas pipelines should consider wear resistance, so guide tubes must be added. It is also the expansion joint of DN200, room temperature air and 500℃ flue gas, and the material and thickness of the corrugated pipe used are different from one thousand miles.

Third, choose the right structural form.General corrugated expansion joints are used for straight pipe sections, compound hinge transverse expansion joints are used for transverse displacement, and straight pipe pressure balanced expansion joints may be used for large displacement and high pressure. If the structure is chosen wrong, no matter how accurate the measurement is, it will be useless.

There is one of the worst things here-the expansion joint is installed cold during measurement, but you have to tell the manufacturer the displacement direction under hot working conditions when selecting the model. Is axial displacement compression or tension? Is there a lateral offset? If this information is not provided, the manufacturer can only do it according to the most unfavorable working conditions, and the products made are big and expensive, so you can't complain yet.

In the final analysis, how to measure the metal expansion joint is the measurement of the size and the understanding of the working conditions. Dimensional measurement is a basic skill, and what really opens the gap is whether the field data can be converted into accurate selection parameters. Only after measuring the right amount and asking about the working conditions can you buy the right expansion joint.

Two days ago, a customer asked with the drawings, saying that he wanted to change the expansion joint, but he didn't know how to report the parameters. When he asked, he threw over a blurry picture of the scene. I've seen this way too many times. The expansion joint looked like a bellows, but if the parameters were not selected correctly, it would bury a mine if it was installed. Today, break it apart and crumble it into pieces to make it clear-what are the detailed parameters of the expansion joint? Remember the following 7 items, and you can also be a half-expert.

1. Pipeline diameter and connection method: first fix DN, everything else is easy to say

There's no room for negotiation on caliber. DN50 is DN50, DN2000 is DN2000, the wrong measurement is not a joke. Especially large-diameter thick-walled expansion joints, which can't be used when made, and scrap iron can't be sold at a high price.

The flange connection is convenient to disassemble and assemble, but there are more leakage points with more flange surfaces; Welding the connection once and for all, but it can be difficult to cut off the expansion joint during overhaul. Choose flange or welding, ask your on-site maintenance worker's opinion, it is more effective than flipping the design specification.

2. Compensation amount: axial, horizontal and angular, don't just stare at one number

When many people report the parameters, they say "compensation amount 50mm"-axial 50? Horizontal 50? How many degrees in the angular direction? Something completely different.

Axial displacement is the pipeline expanding and contracting along the axis direction, lateral displacement is the pipeline running sideways, and angular displacement is the pipeline turning at an angle. The universal corrugated expansion joint mainly absorbs axial displacement, while the compound hinge transverse expansion joint specializes in dealing with transverse displacement. If it is at the corner of the pipeline, it has to rely on the angular direction.

If you think about it, as soon as the main steam pipe heats up, displacements in three directions tend to exist simultaneously. Only staring at one number report, who will carry the remaining two directions?

3. Pressure and temperature: four numbers, none of which can be less

Design pressure, test pressure, operating temperature, instantaneous temperature-these four items are the lifeblood of expansion joints.

The design pressure is the maximum pressure that the bellows can bear. The test pressure is generally 1.5 times the design pressure, and each unit must be hit before leaving the factory. The working temperature determines what material the bellows uses, instantaneous temperature, how much the temperature can soar when you drive and stop in your factory, you have to tell the truth. Before, I met a cement factory customer, the working temperature was 200℃, and the instantaneous temperature rushed to 450℃. The direct material of 304 bellows was deteriorated, so it was better to change it to 316L. You said that this parameter is not complete, who dares to do it for you?

4. Corrugated material and number of layers: How to choose 304, 316L and Inconel

This piece of material, 304 is cheap, 316L is resistant to chloride ion corrosion, and Inconel alloy carries high temperature. For corrosive medium in desulfurization pipeline, it is correct to choose 316L; The gas turbine exhaust temperature is five to six hundred degrees, and Inconel can withstand it.

The number of layers is interesting. Under the same pressure capacity, multi-layer thin-walled bellows have longer fatigue life and better flexibility than single-layer thick-walled bellows. However, one more layer will make it more difficult to process, and the cost will rise. Many of the corrugated expansion joints used in our power station industry are multi-layered, but the cement industry is uncommon-the working conditions are different.

5. Stiffness and fatigue life: These two determine how long your pipeline can last

The rigidity of the bellows is too great, the thermal deformation of the pipe can't be absorbed, and the force is all transmitted to the support; The stiffness is too small, and it can't hold up the internal pressure. How do you give this number? Generally, it is calculated by the manufacturer according to the EJMA standard, and you will have the measured stiffness value on the parameter table.

There is a concept in the design of fatigue life called "equivalent cycle times". Designing 1000 times does not mean that it can be used 1000 times-if the actual displacement in each operation is smaller than the design value, it may be okay to use it tens of thousands of times; On the contrary, if it exceeds the design displacement, it may crack hundreds of times. This is not a math problem, it is an empirical account.

6. Guide tube, tie rod and pressure balance: accessory parameters really can't be saved

What does a deflector do? When there is high-speed airflow or particulate media in the tube, the corrugations will be directly washed away. A guide tube was added, and the wear and tear were all carried on it, and the bellows were clean.

The function of the tie rod and the nut is to limit the displacement of the bellows, which is used to adjust the pre-deformation during installation, which really needs to be adjusted. But note that the tie rod is not designed to absorb lateral displacement-that's what hinges and gimbals do.

There are also internal and external pressure balance expansion joints, such as straight pipe pressure balance type, whose core function is to eliminate blind plate force. If you choose an ordinary expansion joint, install it near the fixed bracket, and directly overturn the bracket during the pressure test of the pipeline, then you will really cry without tears.

7. Implementation standards and special working conditions: Act according to rules and do not step on red lines

For metal corrugated expansion joints, look at GB/T 12777 in China, and EJMA for design calculation. Non-metallic expansion joints follow JB/T 12235-2015, and there are rigid regulations on materials and test methods.

There are more rules for special working conditions. Flue gas baffle door and expansion joint in desulfurization system, corrosion resistance is the first priority; The expansion joint of the cement kiln tail, high temperature and wear resistance is the core; The vacuum double hinge expansion joint used in air-cooled pipelines of power stations should also consider the vacuum degree. Like a mountain, professional manufacturers are used to which industry, you better find deep cultivation in this field.

After so much verbose, the core is one sentence: What are the detailed parameters of the expansion joint? Pipe diameter, compensation amount, pressure and temperature, number of material layers, stiffness life, accessories, standards-seven things, each falling on the paper, the manufacturer can make something reliable for you. When you select the model next time, sort out these seven parameters before calling, and the efficiency will at least double. "

After many people get the expansion joint, the first thing they ask the manufacturer is: Where does this thing fit? Honestly, this question hit the nail on the head. Installing the expansion joint in the wrong position is more fatal than choosing the wrong model. If the selection is wrong, the service life will be shorter at most, and the position will be wrong. The bellows will be stretched, twisted and unstable, ranging from abnormal noise in the pipeline to tearing the bellows and leaking the medium. We have done pipeline compensation schemes all the year round, and have seen too many such cases. Today, we will break up the location and make it clear.

Which section of the pipeline should the expansion joint be installed: first distinguish the fixing bracket and the guide bracket

To find out where the expansion joint is installed, two roles must be recognized first: the fixing bracket and the guide bracket. The fixing bracket is the anchoring point of the pipe, it locks the pipe firmly and does not allow displacement in any direction. The guide bracket only limits lateral displacement and allows axial sliding. The mission of the expansion joint is to absorb the displacement caused by thermal expansion and contraction between these two types of brackets.

The expansion joint must be located between the two fixed brackets and mounted close to one of the fixed brackets. Leave enough straight pipe segments on the other side to cooperate with the guide bracket to allow the pipe to expand and contract in a predetermined direction. In other words, the expansion joint is not installed wherever you want, it is a link in the pipe support system. You set the fixed bracket first, and the position of the expansion joint will be set by 70% to 80%.

Is the expansion joint close to the fixed bracket or the device end? Force differences between two typical layouts

Pipe layouts typically come in two typical forms. One is that the expansion joint is close to the fixed bracket, which is called "single axial layout". At this time, the expansion joint bears pure axial compression or stretching, and the bellows has the most uniform force and the longest service life. LikeHigh temperature axial expansion jointUnder this layout, the maximum compensation ability can be exerted.

The other is that the expansion joint is close to the equipment end, such as connecting sensitive equipment such as steam turbines, pumps and fans. In this case, the expansion joint has to not only absorb the thermal displacement of the pipe, but also bear the additional displacement caused by the thermal expansion of the equipment. The stress state is much more complex, and sometimes it is necessary to useCurved tube pressure balance expansion jointOrCompound hinge transverse expansion jointTo defuse. Which one you choose depends on whether the equipment can withstand pipe thrust.

Selection of connection position under different working conditions: How to determine high-temperature steam, large-diameter flue gas and corrosive medium

Different working conditions have different ideas for location selection.

High-temperature steam pipelines, such as the main steam pipeline of power stations, have a temperature above 400℃. At this time, the expansion joint should be as close to the fixed bracket as possible, and enough guide brackets should be set in the middle straight pipe section. If the straight pipe section is too long, the bellows will be unstable, and if the straight pipe section is too short, the fixed bracket will bear excessive blind plate force.Corrugated expansion joint for power station industryThe installation spacing is generally controlled at 20~40 meters for a compensation unit, depending on the pipe diameter and medium temperature.

Large-diameter flue gas pipelines, like the inlet and outlet flues of desulfurization towers, have low pressure but large cross-section, and are usually rectangular structures. At this time, where to install the expansion joint depends more on the drop point of the flue support and the arrangement of the baffle door. Generally, it is recommended to set a fixed point on both sides of the flue, and the expansion joint is placed in the middle section, so that the displacement in both directions is concentrated in the middle.

What about corrosive media pipes? The position of the expansion joint must avoid dead angles and fluid accumulation sections. When the medium flow rate is low, corrosive liquid is easy to accumulate at the bottom of the bellows, so in addition to selecting the correct position, it is also necessary to selectRectangular non-metallic expansion jointOr a structure with a guide tube to ensure smooth passage of the medium without staying in the bellows area.

How the expansion joint is connected to the pipe: welded, flanged or sleeved? Position Determines Joint Form

The connection method is not randomly determined, but is directly related to the spatial conditions of the installation position.

The welding connection is the most reliable and suitable for high temperature and high pressure pipelines, but it requires welding conditions and flaw detection means at the site. The flange connection is convenient for loading and unloading, and is suitable for pipelines that need regular maintenance and cleaning, such as desulfurization flue and sewage treatment pipe. The sleeve connection is not welded, without flange, and is sealed by packing. It can be selected in compact spaceSleeve type pipe expansion joint。

If the expansion joint is installed in a narrow pipe gallery with limited access space, preference should be given to flange or sleeve connections. If the position is at the end of the overhead pipeline, which is convenient for hot work, welding is a better choice.

Common installation error: What happens if the expansion joint is installed near the elbow and the distance between the two expansion joints is insufficient

Install the expansion joint near the elbow. The elbow is where the pipe produces lateral displacement and bending moment, where the expansion joint will bear additional lateral forces and bending stresses, and the bellows will soon fatigue crack. The correct way is to set fixed brackets at both ends of the elbow, and the expansion joint is placed on the straight pipe section away from the elbow.

The two expansion joints are too close to each other. Some designers put two expansion joints next to each other in order to save space in the pipeline. This will lead to the middle pipe section becoming a floating unit, the two expansion joints push each other, the displacement distribution is uneven, one is overloaded and the other is idle. The specification requires that the length of the straight pipe section between the two expansion joints, usually not less than four times its nominal diameter, and that an intermediate fixing bracket be provided to distribute the displacement.

Practical recommendations for type selection and positioning: Final installation point determined by combining the design of fixed bracket and manufacturer's data

The positioning of this matter, in the final analysis, depends on the layout plan of the fixed bracket. When making compensation design, first clear the direction of the pipeline, set the positions of all fixed brackets, and then calculate the compensation amount needed for each compensation section according to the thermal expansion amount and allowable span. Then compare the displacement parameters provided by the manufacturer to determine the specific installation point of the expansion joint.

Are temporary supports installed during the pipeline pressure test? Is the amount of pre-stretch adjusted to ambient temperature? Is there a protective sleeve on the outside of the bellows? These details can affect the quality of the installation. As a reminder,Direct buried (fully buried) type expansion jointThe installation method is completely different from the overhead pipeline and cannot be mixed.

Which position the expansion joint is connected to the pipeline is not worked out by the construction team on the spot, but it has to be calculated clearly in the design stage. If the location is selected correctly, there will be no problems with the pipeline for twenty years; Wrong choice, rework is a small matter, safety accidents are a big deal. It is recommended to send the pipe drawing to the manufacturer before purchasing, and let the technicians help you review the positioning. Many problems can be avoided in the drawing stage.