Specialized in manufacturing compensators, expansion joints, baffle doors

Metal expansion joint desoldering? Don't hurry to scold the manufacturer, the problem may lie in this

Two days ago, I met a customer who said that the metal expansion joint weld of their pipeline was cracked, and asked me if the quality was not good. Alas, who is not in a hurry when it comes to such things-media leakage, production line shutdown, or safety accidents. But let's say, don't rush to throw the blame on the manufacturer. For the problem of desoldering, we must first look at where the welding is located. Is it the bellows and end pipe connection? Or a deflector weld? Or is it a tie rod mount? The causes of desoldering in different positions vary a hundred and eighty thousand miles.

The cracking of the circumferential weld between the bellows and the end pipe is most likely due to fatigue or stress concentration. If the weld of the guide tube is cracked, it is mostly because the guide tube is worn through by the medium or the guide tube is installed backwards, causing the airflow to directly scour the weld. Tie rod bearing desoldering? You have to check whether the tie rod nut is loosened during installation, and whether the limit is regarded as a fixed support. And guess what? Many so-called "quality accidents" were checked over and over again. Either the installation team was fooling around, or the selection didn't match the working conditions at all.

The three most common pits for desoldering

First, fatigue.The pipeline system expands and contracts thermally every day, and the expansion joint expands and contracts repeatedly. Once the stress concentration at the weld exceeds the allowable value, cracks will slowly grow out. Especially the large-diameter thick-walled expansion joint or high-temperature axial expansion joint, the more extreme the working condition, the more sensitive the fatigue life. For example, the temperature of high-temperature flue gas pipelines in the cement industry often fluctuates above 400℃. Every time the bellows expands and contracts, the welds accumulate damage.

Second, corrosion.When there are chloride ions and sulfide in the medium, the weld seam will be corroded preferentially, and the strength will drop linearly. The expansion joint behind the desulfurization flue gas baffle door has a bad corrosion environment. If the right material is not selected or the corrosion resistance treatment is not done, the weld will become slag in less than half a year.

Third, the installation error.When leaving the factory, the tie rod nut was not loosened, the guide tube was installed backwards, and the cold drawing amount of the pipeline was not enough... These operations caused additional stress to be fully pressed on the weld. Many customers complained that "it took three months to desolder". As a result, when they went to the scene, they found that the direction of the guide tube arrow pointed to the opposite direction of the medium flow, and the airflow directly hit the bellows. Tsk, is this pot manufacturer wronged?

What about that?

Let's see the working conditions first. If it is a pipeline at normal temperature and low pressure, such as a general-purpose corrugated expansion joint, the cracking of the weld joint is probably a problem of the welding quality itself-the current is excessive, the welding electrode is wrong, and the groove is not handled properly. You have to re-weld if you should cut it off and re-weld it. Don't feel distressed. However, if it is a high-temperature steam pipeline or a high-temperature flue gas pipeline in the cement industry, desoldering is often a wrong selection. At this time, we have to consider changing the high-temperature axial expansion joint or the external pressure single axial expansion joint, so that the bellows can avoid the high-temperature area. Another situation: the displacement of the pipeline is too large, and the general-purpose type can't bear it at all, so it is necessary to use the double hinge transverse expansion joint or the straight pipe pressure balance expansion joint to share the stress.

On-site emergency treatment is also particular. Small cracks can be repaired in non-critical parts, but they must be welded with the same material electrode, preheated and controlled cooling speed. If the bellows itself is cracked, don't repair welding-the wall thickness of the bellows is thin, and it will burn through as soon as it is repaired, so replace it directly. In addition, it should be noted that before repair welding, check whether the guide tube is in good condition. If the guide tube is also worn out, the medium will directly wash the inner wall of the bellows, and desoldering is only a prelude. When replacing, it is best to check the adjustment status of the expansion joint tie rod nut simultaneously to ensure that the pre-tension or pre-compression meets the design requirements. As for how to adjust the tie rod nut? After screwing the nut to the limit position, reverse back half a turn to one turn, so that the expansion energy saving can expand and contract freely. Look at the design drawings for specific values, don't screw them blindly by hand feel.

Prevention is really worry-free

The selection stage is not cheap. When providing information to the design institute, write clearly the temperature, pressure, displacement and corrosive medium. For example, the expansion joint behind the flue gas baffle door has a high sulfur content in the medium, so corrosion-resistant alloy or PTFE-lined scheme must be used. In the installation stage, be sure to look at the direction of the arrow on the expansion joint (flow direction mark), and one end of the guide tube faces the direction of the medium. During the operation stage, check the appearance of the weld regularly, tap and listen to the sound, and do penetration testing if conditions permit. Don't forget, the life of the expansion joint is directly tied to maintenance-you let it run over the limit, and it will strike sooner or later.

In the final analysis, 80% of the desoldering of metal expansion joints are not deliberately cut corners by manufacturers. Find the root cause, prescribe the right medicine, change the type, repair the welding, don't curse your mother as soon as you come up. Pipeline safety depends on the cooperation of three rings of selection, installation and maintenance, and one less ring will lead to moths.

1. Where are non-metallic compensators used? Don't use it in the wrong place.

Non-metallic compensator (also called non-metallic expansion joint/fabric fiber expansion joint) is mainly used to deal with low-pressure and high-temperature pipeline systems such as flue gas, hot air and dust. To put it bluntly, where the metal expansion joint can't withstand high-temperature corrosion or large displacement, it should play. For example, the desulfurization flue gas pipeline of the power station, the kiln tail waste gas pipeline of the cement industry, the blast furnace gas pipeline of the steel plant, and even the flue gas purification system of the waste incineration plant-the temperature in these occasions is always five or six hundred degrees, and some instantaneous peaks can rush above 1000℃, and the metal parts are soft for a long time.

Unlike metal compensator, it relies on fiber fabric and rubber composite layer to absorb displacement, and does not generate thrust itself, which can save a lot of trouble in bracket design. But you have to put it on a high-pressure steam pipe? That is wrong-if the pressure exceeds 0.1MPa, you have to choose the type carefully, and don't use it as a high-pressure part. A customer in our station once wanted to use a rectangular non-metallic expansion joint on a 2MPa compressed air pipe, but before it even ran, the fabric layer bulged.

2. Find out these 4 parameters before installation, otherwise it will be in vain.

The first is the displacement-you have to calculate how many millimeters the thermal expansion and contraction of the pipe are offset, and calculate the axial, transverse and angular directions separately. Many on-site pictures save trouble, and they say "come to a 200mm one" when they open their mouths. As a result, the actual displacement is only 30mm, a small horse pulls a big cart, and the fabric folds age quickly. The second is the temperature-the highest temperature and instantaneous peak temperature of the medium directly determine which layer of fabric to choose: silicone cloth can withstand the temperature of about 200℃, fluorine cloth can reach 300℃, and ceramic fiber will be required if it is higher.

The third is the media composition. Have strong acids and bases? That has to be lined with PTFE, which is the "rubber PTFE compensator" or "PTFE compensator" on our station. The fourth is the installation space-rectangular non-metallic expansion joints for square pipes and rounds for round pipes, don't get confused. Two days ago, a customer welded a round one to a rectangular air duct. As a result, the seal was not tight and it took half a month to rework. You say it was wrong or not?

3. Installation steps and the details of the easiest rollover.

Hoist in place → Adjust bolt pre-tension → Weld or flange connection → Remove transport screw. But the worst thing about the rollover is-when will the transport screw be removed? Many people dismantle it as soon as it is installed, and as a result, the compensator is pulled out before the pipe is hot. Correct practice: Wait until the pipeline is installed, the bracket is fixed, and then disassemble it before trial operation. The FAQ of our station specifically mentioned "Does the screw of the expansion joint need to be disassembled?" That's what it said.

In addition, the direction of the guide tube must follow the flow direction of the medium, and the direction of the arrow should not be reversed. And guess what? A cement factory installed the guide tube backwards, and the high-temperature airflow directly washed the fabric layer, which was perforated in three days. We also talked in detail in the FAQ of our station that "the arrow direction of the expansion joint" is for this purpose.

4. In daily use, the three most easily overlooked pits.

Pit 1: Let the compensator bear the load.The non-metallic compensator only absorbs displacement and does not bear weight. The weight of the pipeline depends on the bracket. Even an elbow should be supported separately. Don't let it hang. Some site drawings save trouble, hang the valve directly on the compensator, and the flange leaks within a month.

Pit 2: Neglect insulation.The outer insulation layer not only insulates heat, but also prevents condensed water from corroding the fabric layer. However, many people think that "it can withstand high temperatures anyway" and don't pack it. As a result, the outside condenses and water seeps into the fabric, accelerating aging. Especially noticeable in winter.

Pit 3: Large compensator for small displacement.Some people choose oversized specifications for "insurance", which leads to wrinkles and accelerated aging of fabrics under low displacement. According to JB/T 12235-2015 standard, the working displacement of the compensator is preferably controlled between 60% and 80% of the rated displacement. You say that using a 200mm compensator to absorb a 20mm displacement, isn't that a waste of things?

5. When should I change? Don't wait until it leaks to dismantle it.

The life of a non-metallic compensator is usually 3-5 years, but depends on the operating conditions. If you find that the surface of the fabric layer is cracked, hardened, delaminated, or the flange bolt can't be tightened after it is loose (indicating that the sealing layer has collapsed), then you have to change it quickly. Another signal-the vibration of the pipe suddenly becomes louder, or there is an abnormal noise around it, which may be that the internal guide tube has fallen off. Usually check the appearance quarterly, focusing on welds and fabric overlaps.

If you want to save trouble, rubber compensators are cheaper than fabric compensators, but the temperature resistance is only about 100℃, so don't get confused. When encountering high-temperature flue gas, nonmetallic expansion joints (fabric fiber expansion joints) or rectangular nonmetallic expansion joints have to be used. In the final analysis, with the right selection, the right installation, and the maintenance keeping up, it is not a problem to use a compensator for five years.

What is radial force? Why do so many people fall on this

Anyone who designs pipelines knows that the biggest function of metal expansion joints is to absorb heat displacement. However, when the radial force was mentioned, many people began to be confused. Radial force, to put it bluntly, is the force that pushes the bellows perpendicular to the axis of the pipe, from the center outward or from the outside inward. Wrong direction, light bulge, worse bracket collapse, pipeline twist. Two days ago, I met a customer. A DN600 steam pipe was equipped with a universal corrugated expansion joint. As a result, the radial force was not calculated accurately. After three days of production, the corrugated pipe bulged like a toad's belly. Alas, this kind of thing is not rare.

Radial forces under internal pressure: Outward expansion is mainstream, but not so simple

As soon as the pressure inside the pipe comes up, the bellows expands outward like a balloon-this is the most intuitive direction of radial force, pointing from the central axis to the outer wall. But don't think it's just evenly outward. withUniversal corrugated expansion jointFor example, the radial force generated by internal pressure will make the wave peak expand outward and the wave trough contract inward. The magnitude of this force is directly related to the pressure and wave diameter. If the medium is high temperature and high pressure steam, the radial force has to be doubled instantly. What's more troublesome is that this force will be transmitted to the whole pipeline system, and if the constraint is not good, it can push the fixing bracket askew.

Don't ignore end effects

Where the ends of the bellows are close to the end pipe, the radial force distribution will change abruptly. Stress is concentrated there, and the ripples are more likely to crack. So a lotHigh temperature axial expansion jointThickened walls or reinforcing rings may be provided at the ends in order to hold the non-uniform radial forces of this piece.

Radial force reversal under displacement condition: axial compression, transverse tension, direction change accordingly

Internal pressure is only the basic working condition, and what really makes the radial force "discolor" is displacement. When the pipe is heated and elongated, and the expansion joint is axially compressed, the relative positions of the peaks and valleys of the bellows change, and the direction of the radial force will be partially reversed-the place that originally wanted to be pushed out may be retracted inward at this time. Conversely, if it is a lateral displacement (such as a pipe route turning), the radial force will become a complicated state of "pulling and pressing at the same time". At this time, useCompound hinge transverse expansion jointOrLarge tie rod expansion jointCan effectively restrain and avoid the radial force runaway.

I've seen a case in the cement industry, usingMetal Corrugated Expansion Joints in Cement IndustryOriginally, the axial displacement was handled well, but the radial force reversal was not considered after the lateral displacement was added, and the spacing between the guide brackets was too large, so the bellows was directly twisted into a twist. Tsk, it's more expensive to fix than to buy a new one.

Differences in Radial Force of Different Types of Expansion Joints: From Universal Type to Pressure Balance Type

Different structural designs, the performance of radial force is very different.

• Universal corrugated expansion joint: The radial force caused by internal pressure is the largest. If there is no guide tube, the bellows will easily become unstable under high pressure.
• Straight pipe pressure balanced expansion jointAndCurved tube pressure balance expansion joint: Most of the internal pressure thrust is offset by balancing the bellows, and the radial force mainly comes from media flow disturbance and installation deviation, which is relatively easy to control.
• Compound hinge transverse expansion joint: The radial force is concentrated on the hinge structure, and the bellows itself is more stressed, but special attention should be paid to the fatigue life of the hinge.
• External pressure single axial expansion joint: On the contrary, its bellows is compressed on the outside, and the radial force generated by the internal pressure is squeezed inward, in the entire reverse direction. Don't get confused when designing.

You see, it is also called an expansion joint, and the direction of radial force varies widely. When you don't see clearly when you select the model, you have to cry at the scene as soon as you sign the drawings.

Common consequences of misdesigning radial forces: bulging, twisting, stent collapse

The radial force is not counted correctly, how serious are the consequences? Tell me a few real things:

• bulge: The internal pressure radial force is too large, the bellows peak excessively expands outward, and the material forms permanent bulge after yielding. Common inLarge diameter thick wall expansion jointAlthough the wall thickness is large, the stress is concentrated in the zone of abrupt curvature change.
• Twisted: The direction of the radial force is inconsistent during lateral displacement, causing the bellows to twist like twisting a towel. Generally occurs in the middle of long pipelines, when the spacing between guide brackets exceeds the standard.
• Stent collapsed: The radial force is transmitted to the fixed bracket through the end tube, and if the bracket is not designed according to the thrust, it will tear the base directly. There was a desulfurization flue project last year, usingDesulfurization flue gas baffle doorAndNon-metallic expansion jointCombination, just because the radial force is not counted, the fillet weld of the steel support is broken.

These problems can actually be avoided by preliminary calculation. The point is, you have to know exactly where the radial force is pushing.

How to judge the direction of radial force during installation? Look at arrows, calculate thrust, set guidance

Don't have time to do finite elements for on-site installation? There are shortcuts, too.

First, look at the arrows.Products in the station (such asUniversal corrugated expansion joint) Before leaving the factory, arrows are basically made, and the direction of the arrows is the flow direction of the medium, which also corresponds to the main direction of the radial force after installation-the flow direction side is the peak expansion side, and the reverse side is the trough contraction side. Don't act backwards.

Second, count thrust.The internal pressure thrust formula is not complicated: F = p × A (A is the effective area of the bellows). However, the radial force has to be multiplied by a coefficient, which is related to the shape and height of the wave. In the stationStiffness and Calculation Formula of BellowsThe detailed algorithm is listed in the question and answer, so just apply it directly.

Third, set the guidance.Whether the radial force can be controlled or not, the guide bracket is the key. normalUniversal expansion jointThe first set of guide brackets is required to be Direct buried (fully buried) type expansion jointIt is another set of calculation logic to consider the influence of soil lateral constraint on radial force.

How many hundreds can a piece of cloth carry? Talk about the underlying logic of the temperature range of non-metallic expansion joints

When many people come into contact with non-metallic expansion joints for the first time, they will think that this thing is just a piece of "cloth"? If you can hold a hundred or two hundred degrees, it will top the sky. But the reality is that in places such as cement kiln tail and boiler flue, it has to work in flue gas at 300 to 400 degrees Celsius or even higher. Isn't it a little counter-intuitive?
In fact, the truth is very simple: non-metallic expansion joints do not rely on a single layer of fabric to carry the temperature at all. Its temperature capability depends on the synergy of the entire composite structure-fabric, insulation, sealing layer, each with its own division of labor. But the outermost layer of cloth determines "whether you can carry it", and the hidden insulation layer inside determines "how long you can carry it". If you don't understand this logic, the selection is blind.

Silicone cloth, fluorine tape, polytetrafluoroethylene-where is the temperature ceiling of different fabric layers

Let's go straight to the hard goods. There are only a few kinds of fabrics most commonly used for non-metallic expansion joints, and the upper temperature limit is basically the industry consensus:

• Silicone cloth: The continuous working temperature is about 200~250 DEG C. The advantages are good flexibility and aging resistance, but once it exceeds 250 ℃, the silicone coating begins to decompose and the fabric becomes brittle. Therefore, silicone cloth is suitable for compensators from room temperature to medium temperature, such as air conditioning air duct and drying equipment.
• Fluorine tape: Can carry it to the beginning of 300℃. The high temperature resistance of fluororubber is stronger than that of silica gel, and it is also resistant to oil, acid and alkali. It is often used for the front flue of the desulfurization tower, but it won't work further up.
• Polytetrafluoroethylene (PTFE) film or coated cloth: This is the "carrying handle" in non-metallic fabrics at present. The long-term service temperature of pure PTFE can reach about 260℃, but the glass fiber cloth + PTFE composite layer after special impregnation treatment can reach 350℃ or even higher in a short time. Note, it is short-term. When continuous operation exceeds 300℃, PTFE will slowly soften and creep, resulting in leakage.

Many people look at this table and run to choose PTFE cloth, thinking that everything will be fine. Hey, don't worry-the fabric is only the first line of defense, and the real trick is in it.

Don't just look at the fabric: insulation and sealing structures are the real protagonists of high-temperature conditions

Two days ago, I met a customer, saying that his non-metallic expansion joint at the tail of the cement kiln leaked after less than half a year. On disassembly, the fabric layer is intact, but the insulation layer in the middle — ceramic fiber felt — has been sintered to powder by high temperatures. This is the typical "strong outside but dry inside".
The function of the insulation layer is to block the heat flow inside through porous materials (ceramic fibers, aluminum silicate wool, glass fiber felt). If the insulation layer is not thick and dense enough, the heat penetrates directly into the inner surface of the fabric, and the fabric soon becomes unbearable. A standard non-metallic expansion joint such as oursNon-metallic expansion joint (fabric fiber expansion joint)It is usually designed in 3~5 layers: an outer layer of fluorine tape or PTFE cloth, 2~3 layers of heat insulation felt in the middle, and an inner layer of corrosion-resistant sealing film (such as F46 film).
More critical is the sealing structure. At high temperature, the pressing force between the metal flange and the cloth surface will be loosened due to thermal expansion, so it is generally necessary to match stainless steel pressing strips and high-temperature sealing gaskets. Don't underestimate this. The root cause of many leaks is the failure of the seal at the flange, not the broken fabric itself.

Temperature and pressure are husband and wife, who has the final say when fighting? Synergistic Relationship Must Be Considered in Model Selection

When the temperature goes up, the pressure goes down. These two parameters are like a couple fighting-one is always pressing the other. For example, the same PTFE fabric compensator can withstand 0.3MPa at 200℃, and it may not even be able to withstand 0.1MPa at 300℃. Why? Because the strength of the fabric decreases with the increase of temperature, and at the same time the aging rate of the seal ring accelerates.
Therefore, when selecting the model, we must get the "temperature-pressure" combination of working conditions, instead of simply asking "how many degrees can this expansion joint withstand". For example:rubber compensatorGenerally used for normal temperature and low pressure (0.1~0.2MPa), andRectangular non-metallic expansion joint350 ℃ and slightly positive pressure are common in the boiler flue. If you throw the rubber compensator into the 250℃ flue, it will be wasted in less than a month. Conversely, if high-temperature resistant non-metallic expansion joints are used on high-pressure pipes, the flange connections will also be pushed open.

Cement kiln tail, boiler flue, desulfurization tower-three real cases teach you to calculate the applicable temperature

It's boring to talk about theory. Let's look at the case directly:

• Cement kiln tail: The typical temperature is 350~400 ℃, and the flue gas contains dust and alkaline substances. The selection scheme isNon-metallic expansion joint (fabric fiber expansion joint), PTFE impregnated glass fiber cloth for the fabric, three layers of ceramic fiber felt in the middle (20mm each), and an inner F46 film for corrosion protection. The sealing structure adopts stainless steel corrugated press strip + graphite gasket. The actual operating temperature is 380℃, the pressure is-3kPa, and the life can reach more than 2 years.
• Boiler flue: The temperature is generally 150~250℃, but an instantaneous peak of 300℃ may occur when starting and stopping. At this time, silicone cloth or fluorine tape is enough, and the price is also cheap. However, it should be noted that the boiler flue gas has a large moisture content, so waterproof fabrics should be selected, such asRubber PTFE compensator(lined with PTFE) can be solved well.
• Desulfurization tower import and export: The temperature is 80-120 DEG C, but the medium contains dilute sulfuric acid, which is highly corrosive. Conventional non-metallic expansion joint fabrics are prone to corrosion, so it is recommendedPTFE compensatorOr rubber compensator lined with PTFE, although the temperature is low, anti-corrosion is the first priority.

Do you see the doorway? Each working condition should be calculated separately: first set the temperature section, then look at the medium and pressure, and finally combine the number of layers.

Three-step self-examination method: You can also judge by yourself that non-metallic expansion energy saving can't be used in your working condition

Well, after talking about so many dry goods earlier, finally give me a grounded self-examination method, so as to save you from being fooled by sales:

1. Step 1: Find out the working condition parameters-Maximum continuous operating temperature, instantaneous peak temperature, medium (whether containing acid, alkali, particles), working pressure (positive or negative pressure?). These data are indispensable.
2. Step 2: Check fabric and insulation— — Take a product sample and ask what material the outer cloth is made of (silica gel? Fluorine glue? PTFE?), which kinds of felt are used for the insulation layer, and how thick each layer is. If the total thickness is less than 50mm, it basically can't bear long-term operation above 250℃.
3. Step 3: Look at the seal and connection structure-Is the flange surface flat or with stops? Stainless steel 304 or 316 for beading? Is the gasket asbestos rubber or expanded graphite? If the seal is not good, no matter how good the fabric is, it will be for nothing.

After these three steps, he felt confident in his heart. Finally, the national standard for non-metallic expansion joints is JB/T 12235-2015, which can be used as a reference when selecting. However, the practical application depends on practical experience. After all, the standard is only the lower limit.

Two days ago, a customer called and asked, "Which is the radial direction of the expansion joint?" I asked him back, did you use the arrow as a radial reference when you installed it? He froze for a moment. In fact, this problem is particularly typical. Many field engineers and technicians will confuse radial and axial directions. The consequence of confusion is very direct-the selection is wrong, the pipeline will still be broken after installation, and the compensator will be installed for nothing. Today, let's make this direction clear at once.

Let's make it clear: What is radial?

The radial direction of the expansion joint refers to the direction perpendicular to the centerline of the pipe, that is, the direction radiating outward from the center of the circle. For example, if you take a round tube, the direction along the length of the tube is axial, the direction around the tube is called circumferential, and the radial direction is along the radius, pointing from the inner wall to the outer wall. Used on expansion joints, radial displacement is the compression or stretching of the bellows in a direction perpendicular to the axis. For example, when the pipeline shifts up and down or left and right, the compensator bears radial displacement. Isn't it intuitive? But why do 90% of people do the opposite? Because everyone stares at the "axial direction", the main direction of thermal expansion and contraction, ignoring the lateral offset.

What does the direction of the arrow on the expansion joint mean?

Many products, such as general-purpose corrugated expansion joints and high-temperature axial expansion joints, will be marked with an arrow on the shell. This arrow points to the direction of the medium flow, and it also reminds you that the expansion joint mainly compensates for axial displacement-that is, thermal expansion and contraction in the direction of the arrow. Arrows are not radial markers. There are no arrows in the radial direction, because the radial displacement is absorbed by the lateral stiffness of the bellows, and the amount of radial compensation allowed by expansion joints of different structures varies greatly. And guess what? Some customers took the arrow as a radial reference, and forced the expansion joint to be crooked. As a result, the bellows was twisted into a twist before it was pressurized. Alas, sorry for the tube.

What kind of expansion energy saving carries radial displacement?

Look at the type. For example, the compound hinge transverse expansion joint is specially used to absorb transverse (radial) displacement. Its structure has two sets of bellows plus hinges, so that the tube can swing in the vertical direction. There are also expansion joints of large tie rod structure (such as straight pipe pressure balance expansion joints). The function of tie rod is to limit axial displacement and guide compensation force to radial direction. Conversely, like external pressure single axial expansion joint, its design mainly eats axial displacement, radial capacity is very weak. When selecting, if the direction is reversed, the bellows will be twisted, and the flange will be cracked. This is not to scare people. There have been enough accidents at the scene to write a case book.

How to judge in actual operation?

Here are three stupid ways for you to remember and not step on pits:

• First, look at the product nameplate or drawings.It will be marked with "lateral compensation amount" or "radial displacement", generally in millimeters. If not, look for the technical parameter table, which is written separately in the axial and radial directions.
• Second, find the guide tube of the expansion joint.The guide tube is usually along the axis direction. If there is a significant gap between the guide tube and the inner wall of the pipe, this expansion joint allows certain radial deflection. On the contrary, with minimal or even no clearance, it is a pure axial type.
• Third, look directly at the structure.There is a high probability that those with tie rods and hinges can eat radial, while those without such constraints are mostly pure axial. For example, in our products, compound hinge transverse expansion joint and straight pipe pressure balance expansion joint are good at radial compensation, while general-purpose corrugated expansion joint and external pressure single axial expansion joint should not be expected to carry radial direction.

Whichever of these three methods you use is better than blind guessing. One more detail: How to adjust the expansion joint tie rod nut? If you buy the model with a tie rod, be sure to loosen the tie rod nut to the designed position before installation, otherwise the tie rod locks the radial displacement and becomes a rigid connection. For specific adjustment methods, please refer to the FAQ of this site.

One last word of reminder

Don't use the radial direction as the axial direction, and don't expect a general-purpose expansion energy saver to hold a few millimeters of pipe misalignment. When installing, if you find that there is a deviation from the pipeline and forcibly tighten the expansion joint with bolts to make do, you are sentencing the bellows to death. The correct approach is to use double hinge transverse expansion joints or large tie rod expansion joints to specifically absorb this radial deviation. I really can't figure it out. Looking through the product information of this site, the displacement parameters of each model are clearly written-how much in the axial direction and how much in the radial direction, at a glance. For example, for straight pipe pressure balance expansion joints, the radial compensation amount is clearly marked in the selection table, so just follow the selection.

Alas, the direction is right, and expansion and energy saving will help you carry it for ten years; If the direction is reversed, it will leak in three months.