Specialized in manufacturing compensators, expansion joints, baffle doors

The flue expansion joint is leaking air, or it looks deformed? Don't rush to get started and dismantle it, maybe the more you repair it, the worse it gets. This article is specifically written for you-every step tells you exactly how to do it, just follow it, and don't waste money.

Step 1: Don't be in a hurry to remove it, find out what type of expansion joint you have

Is this thing in front of you metal or non-metal? This is a mistake, and the rest is all for nothing. Metallic ones are commonly corrugated, such asCorrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement IndustryOr the kind of squareMetal rectangular expansion joint。 Nonmetallic, usuallyRectangular non-metallic expansion jointOrNon-metallic expansion joint (fabric fiber expansion joint)It feels like cloth. How to distinguish? Simple: take a magnet and suck it, the metal one can suck it; The non-metallic ones are fabric or rubber composite at first glance. And the ones with tie rods, mostly metal. If you are still unsure, flip through the equipment nameplate or the previous purchase order. It is clearly written on it. Don't guess by your feeling-two days ago, a customer forced non-metallic ones as metallic ones. As a result, the welding gun caught fire. Do you think it was wrong?

Step 2: Safety first, shutdown and pressure relief!

This step is life-saving! There may also be high-temperature flue gas in the flue, or residual corrosive gases (such as acid gases after desulfurization). You must wait until the system is completely cooled, emptied, and ventilated before you can do it. How to operate it? Turn off the heat source, open the release valve, and let the pressure in the pipe drop to zero. Then test it with a gas detector to confirm that there are no flammable or harmful gas residues. Don't forget to hang a "under overhaul" sign on the operation switch-don't say I'm long-winded. Some people really think it's troublesome to do it directly, and as a result, they get a big blister. Safety, if you save one step, the hospital may charge you 2,000 yuan more.

Step 3: How to fix the metal expansion joint?

Local crack of bellows, falling off of guide tube and aging of flange gasket. Let's talk about cracks first-if it's just a small surface crack, you can sand it clean with an angle grinder and then repair welding. But pay attention! The wall of the bellows is very thin, and the ordinary welding heat is directly deformed. It is necessary to use stainless steel welding electrode of the same material, adjust the current, and adopt jump welding method (weld for a section, stop for a while, and wait for cooling). If the crack is in the trough, or has already penetrated several layers-then don't bother, just replace it with a new one. Recommended BuyUniversal corrugated expansion jointOrHigh temperature axial expansion jointJust select according to your working condition and temperature.

What should I do if the deflector falls off? Check, if only the screws are loose, just tighten them; If it has fallen and is stuck in the pipe, remove the flange and refix it. Refer to the "Specific Function of Expansion Joint Guide Tube" written in our previous Q&A. This thing is mainly to protect the bellows from being washed by high-speed airflow. If it falls off, it must be put back.

Also, don't forget to check the tie rod nuts. The tie rod of many metal expansion joints is used to limit the displacement, and the nut will loosen over time. How to adjust? Refer to the question and answer "How to adjust the tie rod nut of the expansion joint"-first loosen the nut, let the expansion joint reset naturally, and then preload it again according to the designed displacement. Generally, it is screwed to about 80% of the design value, leaving some margin. And guess what? Many air leakage problems are actually that the tie rod is not adjusted properly, resulting in the bellows being overstretched and cracked.

Step 4: The repair routine of non-metallic expansion joints (fabric fibers) is different

Such expansion joints (such asRectangular non-metallic expansion joint) It is easiest to wear out at corners, or be corroded by acid and alkali to make a hole. If the damaged area is not large-for example, less than a slap-you can buy silicone cloth or fluorine tape of the same material, then apply high-temperature sealant, and stick two layers inside and outside like a patch. Attention! When sticking, ensure that the surface is clean and dry, compact and exhaust, and then wait for the glue to be completely cured before turning on. Generally, it takes 6 hours in summer and more than 12 hours in winter. Don't worry, the glue turns on before it dries thoroughly, and it collapses when it blows.

If the damaged area exceeds 30%, or the whole ring is aging and brittle, and it breaks when pinched-then don't make it up, and it won't last long. Buy spare parts directlyNon-metallic expansion joint (fabric fiber expansion joint)To replace. When dismantling the old ring belt, take a photo with your mobile phone and write down the original number of layers (single or multi-layer) and the specifications of the beading bolts (M10 or M12). After the new ring belt is installed, tighten the bolts symmetrically-first twist the diagonal corners, and then gradually apply force to prevent deviation. Many people will ignore this step. As a result, after installing it, it is loose and tight, and it leaks again.

Step 5: How to accept after repair?

Don't rush to put it into use immediately after it is repaired. Do static inspection first: see if the weld seam has any leakage and wrinkles, and whether the bolt tightening torque is uniform. Then brush with soapy water on the weld and flange interface, and introduce compressed air at 80% of the design pressure to see if there is any bubbling. If it is bubbling, it means it is still leaking, and it has to be reprocessed.

Okay, okay? Get the system back up and running. But remember: heat up and pressure up slowly! The flue expansion joint is most afraid of rapid cooling and heating, and the heating speed is controlled at no more than 5℃ per minute. At the same time, observe the amount of displacement of the expansion joint-see if the expansion and contraction are within the allowable range. If you find that the displacement is abnormally large or stuck, stop the machine quickly and check whether the pipe support and hanger are stuck by sundries. This problem is often overlooked, but a lot of deformation air leaks are caused by it.

Tip: How to extend the life of flue expansion joint at ordinary times?

Pay more attention to whether the guide tube has fallen off at ordinary times (refer to the question and answer "Specific function of the guide tube of expansion joint"). Clean up ash regularly-especially the ash in the trough of metal bellows, which will scale over time and affect expansion and contraction. Also, don't let acidic condensate soak the bellows for a long time. If there is condensate in the working condition, consider installing a drain valve or doing heat insulation and tracking under the expansion joint. If the operating temperature exceeds 400℃ during model selection, preference will be givenHigh temperature axial expansion joint； If the smoke is strongly corrosive, usePTFE-lined hoseOrPTFE compensatorMore reliable. Alas, in the final analysis, choosing the right product in the early stage is a hundred times worry-free than repairing it in the later stage. Is this the reason?

Find out these three things before you start: selection, end face and direction

Many people get the expansion joint and go directly to the pipeline. As a result, they find air leakage, displacement, and even pull the bellows after installation. Don't worry, let's take five minutes to figure out three things out.

First, the choice should be correct.Are you going to connect a steam pipe, a flue gas pipe, or a pipe with a corrosive medium? Is the pressure high or not? What's the temperature? For example, in high temperature and high pressure situations, choose honestlyHigh temperature axial expansion jointOrExternal pressure single axial expansion jointDon't make do with a general-purpose corrugated expansion joint for cheap. Media corrosive? That's upPTFE-lined hoseOrPTFE compensator。 If you want to lay it in the ground, just lookDirect buried (fully buried) type expansion joint— — It comes with its own protective cover, so there is no need to do extra anti-corrosion.

Second, check the end face.The end faces of pipe joints must be flat, burr-free and rust-free. The flange connection also depends on whether the flange surface has bumps and whether the sealing groove is clean. And guess what? Two days ago, there was a customer who didn't find a small pit on the flange surface. After installation, it began to seep water when it was halfway pressed. Later, it was disassembled and repolished. Working all morning for nothing.

Third, look in the direction.There are generally arrows or marks on the expansion joints to tell you the direction of the medium flow. Some models likeCorrugated expansion joint for power station industryWith a guide tube inside, if the direction is reversed, the guide tube will become a resistance piece, and the bellows will be washed, and the life will be directly folded in half. Don't know how to argue? Refer to the article "The direction of the arrow of the expansion joint refers to" in our station, which is very thorough.

Flange connection: 90% of the occasions use it, follow these 5 steps to be sure

Flange connection is the most mainstream connection method. Universal corrugated expansion joint, rubber compensator and non-metallic expansion joint are all standard flanges. If you follow the following 5 steps, you will basically not roll over.

Step 1: Flange alignment.Lift the expansion joint to the installation position and align the flange hole with the bolt hole of the pipe flange. Caution – don't deadlift with brute force! If the deviation exceeds 1mm, you have to adjust the pipe support or level it with a gasket. Twisting the bolts hard will twist the bellows and hurt it internally before it can be used.

Step 2: Install the gasket.Select the gasket to see the medium and temperature. Rubber pads for cold water pipes, metal winding pads for steam pipes, and PTFE pads on corrosive media. The gasket should be placed in the center, not blocking the media flow channel. Tip: Apply a thin layer of sealant on both sides of the gasket to prevent micro-infiltration.

Step 3: Thread the bolts and pre-tighten diagonally.The bolt goes through the inside of the flange and the nut is on the outside. First screw it by hand until it sticks tightly, then use a wrench in diagonal order-for example, a four-hole flange, the order is 1-3-2-4; Eight-hole flange, press cross. The preload force is controlled at about 60% of the design torque, so don't die once.

Step 4: Tighten to the specified torque in portions.Split into two or three wheels with 20% more torque per wheel. Notice,rubber compensatorAndRectangular non-metallic expansion jointThe torque of this kind of flexible flange should not be too large, otherwise it will deform the edge of the flange. See the product manual for the specific torque value, don't feel it by your hands.

Step 5: Check the gap.After all the bolts are tightened, check the clearance around the flange with a gauge, and the maximum error shall not exceed 0.5mm. If one side is loose and the other is tight, it means that the flange surface is uneven or the expansion joint itself is crooked, so you have to do it again.

Welding Joints: Hardcore Operations for High Temperature and High Pressure Scenarios

Welding is mainly used in large diameter, high temperature and high pressure occasions, such as the main steam pipeline of power plants and the kiln tail pipeline of cement plants. Common welding models areLarge diameter thick wall expansion joint、Double hinge expansion joint for air-cooled island vacuum pipeline、Compound hinge transverse expansion jointEtc.

Before welding, the grooves at both ends of the expansion joint and the pipe grooves must be polished clean to expose the metallic luster. The groove angle is generally 30°-35°, leaving a 2mm blunt edge. The welding electrode is made of the same material as the base metal, and the stainless steel corrugated pipe must be made of stainless steel welding electrode; Just use J427 for carbon steel pipes.

The welding sequence is particular:Sectional jump welding, each section is welded about 100mm, cooled to room temperature before welding the next section. Never weld to the end in a continuous circle, so the heat will be concentrated, the bellows will be thermally deformed, and the sealing will be directly scrapped.

Immediately after welding, heat insulation and slow cooling, especially stainless steel, otherwise the weld seam is prone to intergranular corrosion. After cooling, do non-destructive testing-radiation or ultrasound to ensure that there are no pores and slag inclusions. By the way, if there are no testing conditions at the site, at least a hydraulic test should be done (which will be talked about later).

Special connections: Installation points of sleeve type, direct burial type and non-metallic expansion joints

These three kinds of expansion joints are relatively unpopular, but you have to know them when you encounter them.

Sleeve type pipe expansion joint

The sliding surface of the sleeve should be coated with grease, generally using lithium molybdenum disulfide-based grease. After the outer sleeve and the pipe are welded, the inner sleeve should leave half of the designed displacement, and cannot be pushed to the head. In addition, the sleeve type is generally equipped with a guide bracket, which must be set at 4 times the pipe diameter on both sides of the expansion joint, otherwise it will be stuck.

Direct buried (fully buried) type expansion joint

The buried expansion joint directly contacts the soil, and anti-corrosion is the vital gate. Before installation, check whether the outer protective layer is damaged and whether the bellows part is tightly wrapped. When backfilling, fine sand should be used, layered and compacted, and there should be no stones. If you encounter groundwater, you have to make a drainage ditch or set up a sump. The one in our stationDirect buried (fully buried) type expansion jointIt comes with anti-corrosion coating and waterproof end cap, but the joint still needs to be heat-shrink sleeve or cold-wrapped tape on site.

Non-metallic expansion joint (fabric fiber expansion joint)

Non-metallic expansion joints are resistant to high temperatures and corrosion, but have low strength. The flange bolts should not be tightened too tightly during installation, otherwise the flange will be crushed. Its flange surface is soft, and the gasket can be rubber cushion or no gasket (see the manufacturer's requirements). Note: The non-metallic expansion joint cannot withstand axial thrust, so fixed brackets must be set at both ends of the pipe to digest the thrust away, otherwise it will be pulled and cracked.

Don't go in a hurry after installation: Tie rod adjustment and pressure test check

Installing the expansion joint is only the first step, and there are two key actions behind it.

Tie rod adjustment.Many expansion joints come from the factory with tie rods and nuts, such asLarge tie rod expansion joint、Straight pipe pressure balanced expansion joint。 These tie rods are locked when transported and installed to protect the bellows. After installation and pipeline butting, it is necessary to loosen the tie rod nut until the bellows can expand and contract freely. How much looser exactly? Generally, leave a gap of 5-10mm between the tie rod nut and the ear plate. If you don't understand, look through "How to Adjust the Expansion Joint Tie Rod Nut" in our station, with pictures and texts.

Pressure test check.Clean the air in the pipe before pressurising. The test pressure is usually 1.5 times of the design pressure, and the pressure is held for 30 minutes. The pressure drop does not exceed 5%. During pressure test, people should not face the expansion joint to prevent bursting and injuring people. Focus on checking flange surfaces, welds, bellows troughs – these are the places most prone to leaks. If water seepage is found, re-tighten the bolts or repair welds after pressure relief.

Pits stepped on by old drivers: 6 common mistakes in expansion joint connections

Tell me a few blood and tear lessons, and you can avoid detours after seeing them.

• Error 1: Use the expansion joint directly as the pipeline compensator, and forget to set the fixed bracket.The expansion joint can only absorb displacement and cannot withstand pipe thrust. Without fixing brackets, the whole line will twist like a snake. EspeciallySingle-axis double-flapper doorFixing brackets must be in place before and after such equipment.
• Mistake 2: The flange bolt was tightened too tightly and crushed the bellows.Some people feel that the tighter the better, and as a result, the flange deforms, the bellows wave pitch is elongated, and the fatigue life plummets.
• Mistake 3: There was no protection during welding, and the splash burned through the bellows.Cover the bellows part with asbestos cloth before welding, and clean the welding slag after welding.
• Mistake 4: Use large stones when backfilling with directly buried expansion joints.The earth and stone directly hit the protective layer and cracked, and after two years, it will corrode and perforate.
• Error 5: The non-metallic expansion joint is installed in the horizontal section of high temperature pipe, neglecting drainage.The internal water is bubbled for a long time, and the fabric layer is rot. Drainage outlets must be provided or the installation direction must be sloped.
• Mistake 6: Forgot to remove the transport tie rod.This is the silly one, but someone has done it. The tie rod is not loose, and the expansion joint is equivalent to a rigid connection. The thermal expansion and contraction of the pipeline directly pulls the pipeline bracket, and finally the bracket is bent.

Okay, how to connect the expansion joint to the pipe? These four methods are enough for you. If you are still unsure, flip through the installation instructions of each product in our station, or ask the technician directly. It's better to take a second look before you start, rather than rework it after installation. Do you think that's the case?

I met a customer two days ago. I just installed a batch last yearflue expansion jointIt leaked before it was used for a full maintenance cycle. When I removed it, I saw that the guide tube was washed up by the smoke like a knife-it was installed backwards. No one looked at the direction of the arrow. You say it was wrong or not? There is no problem with the equipment itself. As soon as there is a mistake in the installation link, it will be completed later. Today, break these five steps into pieces and explain them clearly. Follow them, and at least step on half the pit.

First, recognize the model number and arrow direction before installation

Don't rush up when you get the expansion joint. One glance at the nameplate, one glance at the arrow. That arrow is not an ornament, it represents where the medium flows. Once the orientation of the guide tube is reversed, the high-temperature dusty flue gas directly washes the root of the bellows, and it will wear out in less than a few months. Common ones areMetal rectangular expansion jointAndNon-metallic expansion joints (fabric fiber expansion joints)— — The former carries high temperatures, such as the flue of power station boilers; The latter is corrosion resistant, and the wet flue gas working conditions in the desulfurization system all depend on it. If you select the model correctly, you must confirm that the arrow is consistent with the actual pipe flow direction before installation.

In addition, the nuts on the tie rods are in a pre-tensioned state when they leave the factory. In order to protect the bellows from being stretched or compressed during transportation, the manufacturer will adjust a fixed position. Don't loosen it in advance, and adjust it according to the drawings when the hoisting is in place.

Second, bracket arrangement is the real technical activity

Many people think that the expansion joint is a flexible joint, and it is finished by welding it. And the result? Once the pipe heats up, the bellows are either jacked to death or pulled apart. The problem is with the bracket arrangement. Both sides of the flue expansion joint must be setFixed bracketAnd in the middleguide bracketEnsure that the displacement only goes in the design direction.

Used by a cement plantMetal Corrugated Expansion Joints in Cement IndustryNo guide brackets were installed at both ends, and the thermal expansion twisted the bellows into a twist, which was scrapped in two months. The strength of the fixed bracket should be able to withstand the pressure thrust of the pipeline. The expansion joint itself does not bear this force, it is only responsible for absorbing displacement. Don't let the expansion joint carry it on its own, it can't carry it.

3. Hoisting alignment and welding sequence

Never use wire rope to directly strangle the corrugated part when hoisting. When the wire rope is strangled, the corrugation is deformed, the local stress is concentrated, and the life is directly discounted. The correct way is to hold the end tube with a sling and lift it smoothly. The gap between counterparts should be uniform, generally controlled at 2~4mm, too big or too small.

Weld one end first and naturally cool to room temperature before welding the other end. Both sides are welded simultaneously or continuously, and the thermal stress will deform the bellows. If it is a flange connection, tighten it symmetrically with a torque wrench, and the sealing gasket should be temperature-resistant and corrosion-resistant-non-metallic expansion joints are usually equipped with fluorine rubber pads, so don't use ordinary asbestos pads for cheap. Don't rush to remove the tie rod after welding, wait until the pipeline system is completely fixed.

4. Cold tightening amount and tie rod adjustment

The operating temperature of the flue is always several hundred degrees Celsius, and the thermal expansion of the pipe is very large. Therefore, when leaving the factory, the expansion joint often hasPre-stretchingOrPre-compressionThis value is called cold tightness. The tie rod nuts must be adjusted according to the values specified in the design drawings during installation. Tighten the locking nut after adjustment to prevent loosening.

After the system heats up to the design temperature, the transport rod needs to be removed. How to dismantle it specifically? This site has a special question and answer "Does the screw of the expansion joint need to be disassembled", which is very clear. Anyway, remember: without removing the tie rod, the bellows can't expand and contract freely, and the pressure is all held on the corrugation, which will bulge soon.

V. Post-installation acceptance and common pits

An airtightness test must be done before smoking. Focus on checking the weld and flange surface, and use soapy water or leak detector. During trial operation, observe whether the displacement is smooth, and stick your ear to the pipe to listen to any abnormal noise. If it is found that one side of the expansion joint is bulging and the other side is overstretched, 80% of it is that the guide bracket is stuck or the tie rod is not adjusted in place.

Expansion joints near desulfurization flue gas baffle doors are particularly prone to corrosion. Wet flue gas contains sulfuric acid and sulfurous acid, and the corrosion rate is several times faster than dry flue gas. SoDesulfurization flue gas baffle doorThe matching expansion joint must be checked to see if the anti-corrosion coating is intact. Even if a small piece of the coating falls off, it can be pierced in half a year.

Install this work, the details make or break. The drawings do not match the actual object? Then stop and ask, don't push it. Find a reliable manufacturer (such as us), and do a thorough technical briefing, which will be much less worried later.

1. Core question: Will the expansion joint of desulfurization flue expand and contract? The answer is yes, but the key depends on how you understand "telescoping".

Two days ago, a customer came to me and asked, "Does the expansion joint of desulfurization flue expand and contract?" I asked him back, "What do you understand about expansion and contraction?" He was stunned for a moment and said that it was like a spring to pull and contract. In fact, the working conditions of desulfurization flue are not so simple.

The expansion joint will, of course, "expand and contract", but this "extension" does not necessarily mean axial elongation, and "contraction" does not necessarily mean axial compression. In the desulfurization system, the diameter of the flue is often two or three meters, and the temperature rises from normal temperature to 150℃ or even higher. The thermal expansion of the flue wall is calculated in millimeters, but what is more troublesome is the relative displacement between pipes-angular, lateral and even torsional. So,Does the desulfurization flue expansion joint telescope?The answer is: it must be able to adapt to multi-dimensional displacement, not just a single direction of expansion and contraction.

Look at our product listMetal rectangular expansion joint、High temperature axial expansion joint, andNon-metallic expansion joint (fabric fiber expansion joint)The structure is designed to absorb axial and radial displacements. So don't expect the expansion joint to go straight like a rubber band, it's more like a joint, flexible but not blind.

Second, why do you have to scale? -Those invisible thermal expansion, contraction and vibration displacement in the desulfurization flue

When the desulfurization system is in operation, fluctuation of flue gas temperature is the norm. Although the net flue gas temperature after gypsum slurry washing has dropped, the original flue gas section may be as high as 160℃. The flue is made of steel structure, and the linear expansion coefficient is about 12×10⁻⁶/℃. You calculate: a 30-meter-long flue, when the temperature rises by 100℃, will elongate by 36mm. If this force is held hard, it will take minutes for the weld to crack and the bracket to deform.

In addition to thermal expansion and contraction, there is more covert-fan vibration. When the induced draft fan and the booster fan are started, the vibration frequency is not high but the amplitude is large, and the flue shakes with it. Coupled with the flue self-weight, wind load, seismic load... these displacements are superimposed, and the elasticity of the pipeline itself can't bear it at all.

What about that? Expansion joints are meant to "eat" these displacements. For example, our commonUniversal corrugated expansion jointThe bellows can absorb axial displacement through compression and stretching of the corrugations;Compound hinge transverse expansion joint andCurved tube pressure balance expansion jointThen specifically deal with lateral and angular displacements. To put it bluntly, a flue without expansion joints is like a car chassis without shock absorption.

Third, metal or non-metal? Material Selection and Structural Difference of Expansion Joint in Desulfurization Flue

This question is chosen wrong, and the post-maintenance costs can make you cry. The desulfurization flue is a typical "three highs and one low" environment: high temperature (above 100℃ in some areas), high humidity (close to saturation), high corrosion (SO₂, HCl gas and condensed acid), and low pressure (slightly positive pressure or negative pressure).

Metal expansion joint(e.g.Corrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement Industry) has the advantages of high strength, strong pressure bearing capacity, and can adapt to large displacements. But the downside is also terrible: corrosion. After desulfurization, the net flue gas humidity is high, the pH value of condensed water is low, and pitting corrosion may occur in 316L stainless steel. We generally suggest addingPTFE-lined hoseOr spray an anti-corrosion coating protective layer.

WhileNon-metallic expansion joint(includingrubber compensator、Rubber PTFE compensator、PTFE compensatoras well asNon-metallic expansion joint (fabric fiber expansion joint)) is becoming more and more popular in desulfurization flues. Why? Because non-metallic materials are inherently corrosion resistant and flexible, they can absorb multi-dimensional displacements. Especially like fabric fiber expansion joint, the main body is made of silicone cloth, glass fiber wool, polytetrafluoroethylene film, etc., and the temperature resistance can reach 250℃, and the inner line is a guide tube (refer to our question and answerSpecific Function of Expansion Joint Guide Tube) It also prevents airflow from directly washing the skin. However, the short board of non-metal is low pressure. Fortunately, the desulfurization flue is a low-pressure system, which matches perfectly.

If the temperature exceeds 250°C and the pressure is greater than 0.1 MPa, preference is given to metal expansion joints with anti-corrosion liners; If the temperature is within 200℃ and the pressure is low, non-metals are the king of cost performance. From our stationRectangular non-metallic expansion jointThere are many application cases in desulfurization system of thermal power plant, and the effect is stable.

Fourth, everything will be fine if the expansion joint is installed? Common Failure Modes and Maintenance Points

Many customers think that they can be installed for ten years, but accidents happen in two years. The most failures I encounter are three:

• Corrosion perforation: If the metal bellows is not treated with anti-corrosion treatment, condensed acid will deposit at the bottom of the corrugation and leak quickly. So chooseUniversal corrugated expansion jointAsk about the material and processing process.
• Fatigue cracking: Frequent vibration leads to stress concentration in bellows. Such asLarge tie rod expansion jointIf the tie rod nut is not aligned during installation (see Q&AHow to adjust the tie rod nut of expansion joint), will limit the displacement and instead accelerate fatigue.
• Non-metallic skin tear: The reason is often that the design of the guide tube is unreasonable or the airflow rate is too high. We have a case where a power plant usedNon-metallic expansion jointThe wind speed exceeded 15m/s. As a result, the end of the guide tube was not fixed, and the skin was worn out in three months.

Regular inspection, pay attention to whether there are corrosion marks or abnormal deformation on the surface of the expansion joint; Check that the tie rod is loose (ref.Do you need to remove the screw of the expansion joint, the transport screw after installation and commissioning must be removed); For non-metallic ones, see the skin for bulging or aging cracks. In addition,Service life of expansion jointThe general design is 10-15 years, but the actual depends on the working conditions. Suggested cooperationFlue gas baffle doorAndDesulfurization flue gas baffle doorRealize maintenance and isolation, and facilitate shutdown and replacement.

At the end of the day,Does the expansion joint of the desulfurization flue expand and contract？ It must stretch and shrink, but more importantly, choose the right type, install the right position and take care of it regularly. Understand these points, and select models without stepping on pits.

How to remove square flue expansion joint? Look at the type before you do it

Two days ago, a customer called and said that a square flue expansion joint in the factory was leaking, and he was anxious to change it. As a result, it was stuck halfway through the dismantling-the bolts were rusty, the tie rod couldn't be twisted, and the fabric layer was torn. He asked me: How should you dismantle this thing when you sell it?

Good question. How to disassemble the square flue expansion joint is really not just a matter of twisting it with a wrench. Before dismantling, regardless of the type and working conditions, hard dismantling will only pull and deform the flange surface, and even make the pipe bracket crooked. Today, I will explain the two common methods of disassembling square expansion joints, breaking them apart and crumbling them.

First, there are two main types of square flue expansion joints: metal rectangular and rectangular non-metal

Metal rectangular expansion jointAndRectangular non-metallic expansion joint。

Metal rectangular expansion joint, structurally is corrugated pipe plus flange, with tie rod and nut. Used for high-temperature and high-pressure flue gas pipelines, such as power station boiler outlets and desulfurization flues. The material of corrugated pipe is usually stainless steel, and the temperature resistance can reach above 600℃.

Rectangular non-metallic expansion joint, the main body is a fabric fiber layer (non-metallic expansion joint, also called fabric fiber expansion joint), with a guide tube inside and clamped by a metal frame outside. It has lower temperature resistance, but a large amount of compensation, which is suitable for low-pressure, large-size flues, such as dust collection pipes in steel mills.

These two things, the disassembly method is completely different things. You take the idea of dealing with metal parts to dismantle non-metal, and the fabric layer is ripped off as soon as you pull.

2. Three issues that must be clearly understood before disassembly: medium, pressure and bolt state

Before you start, ask yourself three questions. If you can't answer them, don't touch the wrench.

First, what is the medium?Is it hot smoke, cold air, or corrosive gas? If it is wet flue gas after desulfurization, which contains sulfuric acid condensate, the metal bolt may have been corroded so that only one layer of skin is left, and it will break when twisted.

Second, is there still pressure in the tube?Some maintenance drawings save trouble, and the flange is removed before the system is completely relieved. If the square flue expansion joint is disassembled under pressure, the flange surface suddenly separates, and the high-pressure gas will collapse the bolt like a bullet. It's no joke, every year there are cases of injuries as a result.

Third, what is the current state of the bolt?First, take a flashlight to see if there is rust, deformation, and whether the tie rod nut has been welded to death. There's a simple way to judge: tap the head of the bolt with a wrench and listen to the sound-crisp instructions have room for loosening, stuffy instructions have rusted to death.

3. Disassembly of metal rectangular expansion joint: loosen the tie rod first, and then disassemble the flange

There is a core principle in the disassembly sequence of metal rectangular expansion joints:Release the pre-tightening force first, then remove the connecting bolts。

Step 1: Loosen the tie rod nut.The metal rectangular expansion joints are equipped with tie rods, which are used to limit the excessive stretching of the bellows. When disassembling, first loosen all the nuts at both ends of the pull rod, so that the bellows is in a free state. Be careful not to dismantle all, leave one or two buckles to prevent falling off.

Step 2: Diagonal method to remove flange bolts.Many people are used to dismantling them one by one from one side. As a result, the flange is unevenly stressed, and the remaining bolts are stuck. The correct way to do this is: first remove the two bolts of the diagonal, then remove the other pair of diagonals, step by step like removing a tire. Every time you remove one, check the flange surface for misalignment.

Step 3: Top off the flange surface.After the bolts are all removed, the flanges may still stick together because the gaskets will carbonize and bond after high-temperature operation. Gently wedge with a flat shovel from the flange gap and shake left and right to separate the two flange surfaces. Don't smash the flange ear plate with a sledgehammer, which will deform the bolt hole.

The worker cut the bolt directly with a cutting gun. As a result, the cutting flame burned through the bellows and the whole expansion joint was scrapped. The wall thickness of the corrugated pipe of the metal rectangular expansion joint is usually only 0.5~1.5mm, and it is worn as soon as it is ironed.

4. Disassembly of rectangular non-metallic expansion joint: Pay attention to the fabric layer and guide tube

Rectangular non-metallic expansion joints are much more delicate. It is a metal press frame on the outside, a fabric fiber layer on the inside, and a flow guide tube in the middle.

Step 1: Remove the bolts of the press frame.First remove the metal press frame bolts that hold down the fabric layer. Note: This kind of bolts are usually large in number and closely spaced, so it is easy to leak when disassembled by one person. It is recommended to use a marker to make a mark between the press frame and the flange, so that it can be aligned when put back.

Step 2: Carefully separate the fabric layers.After using the fabric fiber layer for a period of time, it will be smoked hard by smoke and lose its elasticity. Do not pull hard when disassembling. Use scissors to cut off the attached spacer along the edge of the press frame. If there are tar-like deposits, spray some loosening agent first.

Step 3: Take out the guide tube.Rectangular non-metallic expansion joints usually have a guide tube inside, which is used to guide air flow and protect the fabric layer. The guide tube is inserted in the flue. When pumping out, it should follow the axial direction and not skew, otherwise it will scratch the anticorrosion layer on the inner wall of the flue.

If the fabric layer of non-metallic expansion joint has been broken, the insulation cotton inside will leak out. Before dismantling, confirm whether there is any insulation cotton leakage. If so, you need to wear a dust mask and goggles first-the glass fiber sticks to the skin and itches unbearably.

5. What about the bolts that can't be removed? Several practical treatment methods

When removing square flue expansion joints, screw rust is the most common pit. I'll list a few measured methods that work:

• Osmotic loosening agents.Spray WD-40 or special bolt loosener on the root of the thread and wait 15 minutes before screwing. If it is a high-temperature bolt, it works better with bolt coolant (instantaneous cooling creates cold shrinkage gap).
• The tapping method.Use a copper or wood hammer to tap the side of the bolt head a few times to shatter the rust layer. Don't use a hammer, it will round the bolt head.
• Heating method.Heat the nut part with oxyacetylene flame (be careful to avoid bellows), use the principle of thermal expansion and contraction to expand the nut, and then twist it quickly. This method can be used for the tie rod nut of the metal rectangular expansion joint.
• Grooving method.If it can't be twisted, use an angle grinder to cut a straight slot in the head of the bolt, and then screw it with a large screwdriver. This is a destructive means. After removing the bolts, it is wasted, but it keeps the flange.

Don't try to clamp the bolt rod with a pipe plier and turn it hard, which will break the screw rod and make it harder to remove it if it breaks in the bolt hole.

6. Don't rush to suit after dismantling, check these parts first

It was finally removed, so don't try to put on new pieces quickly. Spend 10 minutes checking the following places to save you the hassle of reworking later.

Is the flange surface flat?Lean against it with a ruler to see if there is any deformation. The flange of the square flue expansion joint may warp after long-term use because it is subjected to thermal stress. If the deformation exceeds 1mm/m, the new expansion joint will not be sealed tightly.

Are the bolt holes elongated?The bolt holes will become oval at high temperatures. When this is found, it is necessary to ream the hole with a reamer or re-drill the hole after repair welding.

Is the deflector intact?If it is a rectangular non-metallic expansion joint, check the removed deflector for wear. The head of the guide tube is the easiest to wear. Once perforated, the airflow will directly scour the fabric layer, resulting in the newly replaced expansion joint breaking in half a year.

Is there a settlement in the bracket?Settlement of the pipe supports at both ends of the expansion joint can cause the new expansion joint to be forcibly twisted when installed. Measure the actual distance between the two flanges, and compare it with the length of the new expansion joint. If the error exceeds 5mm, the bracket should be adjusted first.

In the final analysis, the disassembly of the square flue expansion joint depends on strength and experience. You have mastered these steps, and the next time you meet them, you will have the bottom in your heart. If you encounter particularly tricky working conditions-for example, all the bolts are rusted in the blind hole and the flange is seriously deformed-you should find technical support from the manufacturer, and don't carry it hard.