Specialized in manufacturing compensators, expansion joints, baffle doors

Take a look at the deformation scene first to judge whether it is "true necrosis" or "false fatigue"

When it comes to compensator deformation, 90% of people's first reaction is "it's broken, change it quickly". But have you ever thought that some deformations are actually normal displacements? For example, if the bellows is compressed or stretched at a certain angle, it can recover itself as long as it does not exceed the design limit. Don't call the manufacturer when you are nervous. Calm down first and do a physical examination yourself.

Specific operation:

• 1. Take a photo first to record the deformation state (front, side, local close-up). This picture saves big trouble when communicating with the technology later.
• 2. Touch the temperature of the deformed part with your hand and compare it with other positions of the pipeline. If it's ridiculously hot, it's probably overheat.
• 3. Check whether there are any signs of liquid leakage and air leakage around. There's a leak, that's really bad.
• 4. Confirm the design displacement parameters by comparing the model on the product nameplate, such as [Universal Corrugated Expansion Joint] or [Rubber Compensator]. The nameplate generally has the maximum compensation amount, temperature and pressure, write it down.

If it is only slightly twisted and there is no leakage, there is a high probability that the thermal displacement is not completely released, so don't scrap it in a hurry. Look at the pipe when it cools down, sometimes it retracts itself-believe it or not?

Step 2: Find out the "mine burial" during installation

Irregular installation is the number one culprit of compensator deformation. Look through the installation records of your home and focus on these 3 locations:

① Fixed bracket and guide bracket

Check if the retaining bracket is actually holding the pipe in place? Some construction sites are fooled with expansion bolts, and the pipeline is directly displaced when it is hot. Is the guide bracket spacing correct? For example, [metal hose] requires one guide per meter, and less will make the hose twist and form an S-shaped bend. Take a tape measure and measure it. It's over spaced? Hurry up and make up.

② Installation direction

Look at the arrow logo! [High-temperature axial expansion joint] and [straight pipe pressure balance expansion joint] have strict requirements on the flow direction, and installing it backwards is equivalent to making the bellows hard to resist the lateral force. Tip: Use a level ruler to measure whether the flanges at both ends of the expansion joint are parallel. If the error exceeds 2mm, you should readjust it. Almost, the transformation came.

③ Pre-stretching/pre-compression

The [Sleeve Type Pipe Expansion Joint] and [Rotary Compensator] usually leave the factory with a pre-stretch amount, and the locking device needs to be loosened after installation. Did you let go? If you don't release it, the compensator will be damaged as soon as the pipe expands. Two days ago, I met a customer who said that [double hinge transverse expansion joint] was seriously deformed. I asked him to check whether the transportation fixtures were removed during installation, but the result was really not removed... It would be fine after dismantling. Alas, this kind of wasted money is painful to spend.

Step 3: Calculate whether there is "anti-aircraft gun to fight mosquitoes" in the selection

If you choose small, you can't bear it, and if you choose big, you waste money, but it is more common to "choose the wrong type". Have you made any of these mistakes?

• The displacement of the pipeline is very large, but the [general corrugated expansion joint] is chosen instead of the [compound straight pipe bypass pressure balance expansion joint] or the [curved pipe pressure balance expansion joint] -as a result, the corrugated pipe is forcibly elongated, resulting in permanent deformation. Do you want to recover? There's no way.
• The medium is corrosive, but ordinary metal bellows are used, and [PTFE-lined hose] or [PTFE compensator] should be used. Corrosion causes thinning of wall thickness, and deformation comes. Have you looked at the inner wall with an endoscope?
• Under high temperature working conditions, non-metallic [rubber compensator] or [rubber PTFE compensator] is easy to age and bulge, so it has to be replaced with [corrugated expansion joint for power station industry] or [external pressure single axial expansion joint]. Don't try to be cheap, the money saved is all pasted and repaired.

Action checklist:

• Take out the site pipeline drawings and confirm the design displacements (axial, transverse, angular). Don't tell me that the drawings are lost... If they are lost, they will be measured.
• Compare the product parameter table you selected to see if the compensation amount is within the safe range (it is generally recommended to leave a 30% margin). It is common sense to leave an allowance, so don't use it at the limit.
• Medium temperature, pressure, corrosivity-three parameters must correspond one to one. For example, it is no problem to use [non-metallic expansion joint (fabric fiber expansion joint)] for flue gas pipelines, but after desulfurization, the wet flue gas has to use [desulfurization flue gas baffle door] with corrosion-resistant expansion joint.

Step 4: Check the medium and environment, don't let "warm water boil the frog"

Many times deformation accumulates slowly, not collapses at once. It's like boiling a frog in warm water, it's too late by the time you find out.

① Temperature exceeds limit

The actual operating temperature is more than 10℃ higher than the design, and the bellows of [metal corrugated expansion joint] will soften and creep, and the first deformation is irreversible. How to check? Use an infrared thermometer to measure the surface of the expansion joint, and continuously record the maximum temperature within 1 hour. Exceeding the design cap? Then you have to consider switching to a high temperature resistant model.

② Pressure fluctuation

[Rubber Compensator] is most afraid of frequent pressure shocks. The pressure rose sharply from 0.5MPa to 1.2MPa, and the rubber layer bulged directly. Operation recommendation: Install a buffer tank or pressure reducing valve before the expansion joint to reduce the water hammer effect. Otherwise, it would be useless if you changed a hundred.

③ Corrosion and wear

The acidic condensate in the desulfurization flue gas pipeline will corrode [flue gas baffle door] and [stainless steel corrugated expansion joint]. Check whether there is liquid accumulation at the bottom of the expansion joint, and install a drain port if so. [Cement Industry Metal Corrugated Expansion Joint] used in the cement industry, dust particles will wear the bellows wall, regularly use an endoscope to see the inner wall. Don't wait for a piercing to regret it.

Note:Don't just look at the expansion joint itself, the state of upstream and downstream equipment also affects the deformation. For example, if the [electric plug-in board insulation door] is not closed tightly, the medium will flow backwards, which will also make the compensator stress abnormally. Check is the valve closed tightly?

Step 5: How many pits have you stepped on in operation and maintenance?

Many deformations are man-made disasters, not natural disasters.

① "Pull" caused by misoperation

When pipeline pressure test, do you regard the compensator as a fixed point? Before the pressure test, the pipeline must be fixed with temporary support, otherwise the [large-diameter thick-walled expansion joint] will be directly deformed as soon as the pressure comes up, just like twisting. Winter parking and restarting, some pipes need to be preheated. It heats up quickly without preheating, and [Double Seal Single Axis Circular Baffle Door] or [Air Cooling Island Vacuum Pipe Double Hinge Expansion Joint] will twist due to thermal shock. You say it was wrong or not?

② Improper maintenance

The fabric fiber layer of [non-metallic expansion joint] is easy to accumulate dust, and if it is not cleaned for a long time, the dust will expand after absorbing water and crush the internal structure. Tsk, you think it's okay if it's dirty? The fastening bolts of [Rubber Compensator] should be tightened regularly. If they are loose, the flange surface will be offset and the rubber body will be torn. Twist the bolts in five minutes. Don't be lazy.

Action checklist:

• Before each start and stop, verify whether the media in the pipeline is emptied.
• Check the surface of the compensator once a quarter for cracks, bulges and corrosion spots.
• For [directly buried (fully buried) expansion joint], because it is buried in the ground, check whether the ground has abnormal uplift or subsidence. There was a bulge on the ground, and something was probably happening underneath.

Step 6: Do-it-yourself to check the three-step method without asking for help

If you haven't found the problem in the previous steps, use this process to do it yourself:

First knife: appearance + size

Use a vernier caliper or tape measure to measure the length, diameter and angle of the compensator. Compare factory drawings to determine the amount of deformation. For example, [metal hose] has an "S" shaped bend, indicating that it has been subjected to lateral force. Where do lateral forces come from? Check if there is a hanger beside it that is crooked.

Second knife: reproduction of working condition data

Adjust the operating temperature, pressure and flow change curves to see whether the high deformation period corresponds to a steep rise/drop. If the [Universal Corrugated Expansion Joint] is twisted, it is mostly due to the torsional load of the pipeline. Check whether there is a valve nearby to open and close quickly. Closing the valve quickly creates torque that the compensator can't handle.

Third Knife: Disassembly Verification

If convenient, remove the compensator and check the internal guide tube (refer to the Q&A "Specific Function of Expansion Joint Guide Tubes" on this site). The misalignment or fall of the guide tube will cause the medium to directly impact the bellows, resulting in local deformation. For [vacuum special hose], use soapy water to detect leakage, and the leakage point is often the deformation and cracking point. Spray with soapy water and where it bubbles is the problem, simple and rude.

Finally, a word:Compensator deformation is not necessarily a product quality problem. Many times, as long as you follow the above steps to troubleshoot, adjust the installation or operation, you can save a replacement fee. If you really can't find the reason, contact our technical support, bring your on-site photos and data, and we can analyze it together. Don't change it blindly. After changing it, it is still broken. That's bad.

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.