Specialized in manufacturing compensators, expansion joints, baffle doors

The metal expansion joint, to put it bluntly, is a flexible joint, which absorbs the thermal expansion and contraction of the pipe by the deformation of the bellows. But if you think it can carry any working conditions, it will have to roll over sooner or later. Two days ago, a customer asked me why the expansion joint he installed leaked after only three months. When I removed it, the bellows cracked like a cracked riverbed. What's the problem? When you select a model, you just stare at the compensation amount, and everything else is ignored. Let's break it down today,Disadvantages of Metal Expansion Joints?Where the hell is hidden.

1. Fatigue life: Bellows are not perpetual motion machines, and the number of cycles is the hard threshold

Many people think that the expansion joint can be used for a lifetime, so they dream. Every time the bellows expands or contracts, a micro-damage accumulates inside the material. The fatigue life written in the design standard is usually between a thousand and several thousand cycles-this is not blindly determined, it is measured. If you think about it, steam pipes start and stop once a day, 365 times a year, and thousands of times in three years. If the circulation frequency is high and the displacement amplitude is large, the life time will be cut in half directly.

What about that? Not for you not to use it, but to figure it out. First calculate the total thermal displacement of the pipeline, and then see whether the working condition belongs to low frequency or high frequency. Like those used in the power station industryCorrugated expansion joint for power station industryThe number of cycles requirements must be specified when designing. Don't buy the general-purpose corrugated expansion joint to make do, the fatigue life is not matched, and it is too late to cry later.

2. Media compatibility: There are boundaries in corrosion resistance, so don't use it as a panacea

Stainless steel bellows corrosion resistant? That depends on the medium. Working conditions with high chloride ion content, such as desulfurization flue gas and seawater, 316L will still pitting for you. Two days ago, a case in a chemical plant, usedMetal hoseThrough hydrochloric acid, it leaked within a few months. ChangePTFE-lined hoseOrPolytetrafluoroethylene compensator, instead, lasted for more than two years.

Before the selection, you must get the media composition list, and the temperature, concentration and flow rate must not be less. High-temperature flue gas contains sulfur, ordinary stainless steel can't bear it, have toHigh temperature axial expansion jointOr non-metallicNon-metallic expansion joint (fabric fiber expansion joint)。 Don't gamble on experience, the corrosion boundary is much narrower than you think.

3. Installation and maintenance: pull rod, guide tube, pre-stretching, one step wrong, one step wrong

Installing this thing is really not just a few screws. Let me ask you, what is the tie rod on the expansion joint for? Many workers removed the tie rod directly at the scene, thinking it was a transportation fixture. As a result, as soon as the pipe heated up, the bellows was pulled to the head and torn directly. The correct way is: after installation, adjust the tie rod nut so that the bellows is in the designed position-pre-stretched or pre-compressed, according to the cold tightness requirements of the pipe system.

Let's talk about the guide tube, which not only prevents scour, but also affects the flow direction of the medium. If it is installed backwards or missed, the high-speed fluid rushes directly into the bellows, vibrates and erodes, and the hole will be perforated in less than a month. We have a client usingMetal Corrugated Expansion Joints in Cement IndustryBecause of the reverse installation of the guide tube, three were replaced in three months.

As forCorrect installation method of expansion joint of large tie rodThe tie rod absorbs the internal pressure thrust. During installation, the nuts at both ends of the tie rod should be tightened in place, and the bellows should not be pressurized-this work has to be done step by step according to the instructions, and don't take it for granted.

4. Cost account: Is one-time purchase cheap? Later replacement and downtime losses are deadly

The metal expansion joint itself is not expensive, and a general-purpose corrugated expansion joint may only cost a few thousand yuan. But what about a change? Pipeline venting, thermal insulation dismantling, replacement operation, re-pressurization, plus the loss of production shutdown, six figures per minute. Especially in chemical industry, power plants and cement lines, it is hundreds of thousands to stop a day.

So don't just focus on the money of expansion joints when choosing a model. Working conditions are bad, such as high temperature and high pressure, strong corrosion, rather buyExternal pressure single axial expansion jointOrStraight pipe pressure balanced expansion jointThis structure is more reliable. Although it is twice as expensive, it can be used for five years without accidents. Rubber compensators are cheap, right? However, as soon as the medium temperature exceeds 80℃, it will immediately become soft. You said chooserubber compensatorOr metal? Depending on the working conditions, calculate the general ledger.

5. Special working conditions do not work: vacuum, buried ground, large displacement scenes have to be requested to be smart

Metal expansion joints are not a panacea. Under the vacuum condition, the bellows has a large external pressure and is easily unstable. We have dedicatedSpecial hose for vacuumThe structure is different and can resist external pressure. You take an ordinary metal expansion joint to vacuum, and the bellows are like a flattened can, which is directly scrapped.

What about buried pipes? Buried directly in the soil, corrosion, soil pressure and uneven settlement, the metal expansion joint can't bear it at all. UsefulDirect buried (fully buried) type expansion jointOr simply use a sleeve typeSleeve type pipe expansion joint。 There are also large displacement scenarios-several hundred millimeters of lateral displacement, or axial displacement beyond the bellows limit, then you have to considerCompound hinge transverse expansion jointOrRotary compensatorDon't push on the universal model.

Alas, in the final analysis, choosing an expansion joint is not a set of formulas, but a solution of equations. Media, temperature, pressure, displacement, life, cost, every variable has to be counted. Picked right, it is a buffer for the plumbing system; Wrong choice, it's a ticking time bomb.

Find out one thing first: What role exactly do metal expansion joints play in pipes?

To put it bluntly, it is the "expansion joint" of the pipe-absorbing thermal expansion and contraction, buffering vibration and compensating for installation deviation. There are rubber compensators and non-metallic expansion joints on the market, but metal expansion saves energy and carries high temperature and high pressure, such as the main steam pipeline of power station and the high-temperature air duct of cement industry. Ordinary rubber parts will be wasted when they go up. Then what is its advantage? Let's tear it down layer by layer from the structural design.

The first hard-core advantage: "iron bone clanging" with temperature and pressure resistance

The main body of the metal expansion joint is stainless steel bellows, like our sideUniversal corrugated expansion joint、High temperature axial type expansion joints can operate at temperatures above 600℃, and the pressure level ranges from PN0.6 to PN6.4 or even higher. The rubber compensator begins to age when it exceeds 150℃. Although the non-metallic fabric fiber expansion joint can reach 1000℃, its pressure bearing capacity is weak. Metal expansion joints are just needed in the environment of high temperature, high pressure and medium corrosion such as power station boilers and desulfurization flue gas pipelines. A customer has asked: "What to choose for steam pipe?" We recommend directlyExternal pressure single axial expansion jointOrStraight pipe pressure balance typeThe reason is that it can balance out the internal pressure thrust and the pipe is not subjected to additional axial force. Think about it, if you put a rubber piece on the main steam pipe of a power plant, let alone heat it up, the steam pressure alone can blow it up.

The second advantage: there are many tricks of displacement compensation, which is not a "new trick"

The displacement of the pipeline system is not only linear expansion and contraction, but also may have lateral misalignment and angular deflection. The corrugated structure of the metal expansion joint can naturally absorb the axial displacement, but the composite displacement can be accomplished by adding a tie rod, a hinge and a universal hinge. Such asCompound hinge transverse expansion joint, specializing in absorbing lateral displacement;Curved tube pressure balance type expansion joint is used for simultaneously absorbing axial and transverse displacement at the curved tube;Double-hinged expansion joints of air-cooled island vacuum pipes adapt to large angles of thermal displacement. comparisonSleeve type pipe expansion joint (by sliding seal), metal corrugated expansion joint has no leakage point, small maintenance. Think about it, if the air-cooled island pipeline of the power plant uses a rubber compensator, can the vacuum degree be kept? The rubber will deflate under negative pressure, and the sealing ring will leak as soon as it ages, and the system efficiency will drop a lot.

Third point: Fatigue life is supported by data

The design life of metal expansion joints is usually calculated according to the number of cycles, and the standard ranges from 1,000 to 10,000 times, depending on the waveform, number of layers and material. We have done testing, 304 stainless steel corrugated pipe under reasonable design, the actual operation of 15-20 years a lot. The rubber compensator is affected by ozone and ultraviolet rays, and it has to be replaced in 3-5 years. Two days ago, there was a cement factory customer. The non-metallic expansion joint used in the kiln head pipeline leaked ash in two years, so it was replaced withThe metal corrugated expansion joint of the cement industry has been running for six years without any problems. This is not metaphysics, it is rolling of material science-metal bellows are formed by cold stamping, stress distribution is optimized, plus multi-layer structure increases flexibility, and the fatigue life is more than 5 times that of rubber. Think about it, a production line stops once and loses hundreds of thousands. Who is willing to change the compensator frequently in order to save thousands of dollars?

The fourth hard-core scene: "special students" in extreme working conditions

For example, the expansion joint matched by the desulfurization flue gas baffle door should not only be resistant to SO2 corrosion, but also adapt to the low pressure and large displacement of 0.1MPa. This environmentPTFE compensators can also be used, but the cost is high and the installation is complicated. Metal expansion joints are lined with PTFE liners, or directly with high-nickel alloys (such as Inconel), get it done. AndDirectly buried (fully buried) type expansion joint, directly buried underground, wrapped with anti-corrosion coating and insulation layer, to bear soil pressure and groundwater erosion.Special vacuum hose, the wall thickness is made thin and dense, and it can bear negative pressure without deflating. These non-standard requirements and non-metallic parts are basically stopped. To be honest, choosing expansion joints means choosing "who carries it more". Metal expansion joints are a proper main force in heavy industries such as power stations, cement, chemical industry and metallurgy.

Finally, let's talk about something real: how to pick?

Don't be superstitious about "universal models". Also a metal expansion joint,Corrugated expansion joints for power station industry andMetal corrugated expansion joints in cement industry have different corrugation parameters, end connection forms and guide tube design. For example, the function of the guide tube is to prevent high-speed airflow from washing the corrugated body. When selecting the type, it depends on the flow rate and medium particle size. If there is severe vibration in the pipeline, a tie rod or limit device should be installed. You take a general-purpose corrugated expansion joint and install it on the high-temperature steam pipe. If the angle is wrong, the fatigue life is incorrectly calculated, and it will crack in three months, you can't blame the product. Our product line ranges from general-purpose type, high-temperature axial type, straight pipe pressure balance type toDouble sealed baffle door matching, each model corresponds to specific working conditions. Before the next selection, calculate the temperature, pressure, displacement and medium clearly. Don't think that "metal" is universal. Tsk, if it were that simple, there would be no technical threshold in this business.

How to determine the design temperature of the expansion joint? Three Key Points Engineers Must Understand

Nine times out of ten, people who select expansion joints have stumbled at the design temperature. Either I patted my head to get the medium temperature, or I missed the external heat source. This article is not false, and it directly dismantles the three decisive links.

1. Working temperature and design temperature: Don't regard "highest" as "design"

The maximum operating temperature of pipeline medium is 400℃, which is directly filled in the selection sheet when the design temperature is used. When the corrugated pipe material couldn't bear it, it was discovered that the allowable stress had long failed. The design temperature is not the operating temperature, which is clearly written in the standard-GB/T 12777 and ASME B31.3 both require a safety margin on the operating temperature. But this margin is not a fixed value, depending on the working conditions: continuous operation or intermittent operation? Is there a risk of local overheating? For example, the corrugated expansion joint used in the power station industry (such as the "corrugated expansion joint used in the power station industry" in our station), the temperature of the steam pipeline fluctuates greatly, and the peak value may rush to 550℃, while the average value is only 450℃. If you choose according to the average value, the bellows directly deforms plastically at the peak value. Therefore, the design temperature has to be calculated according to the extreme peak value, and the thermal shock margin at start-up has to be superimposed, generally from +20℃ to +50℃.

2. Internal media vs external environment: who has the final say?

This question is different from the occasion. If it is a high-temperature axial expansion joint, the internal medium temperature is naturally dominant. However, don't ignore the temperature gradient at the flange connection and near the guide tube-where local stress concentrations occur and lead to early cracking of the bellows. On the other hand, like directly buried (fully buried) expansion joints, the external soil temperature and the performance of insulation layer are the keys. Two days ago, a customer who made metal corrugated expansion joints in the cement industry had a medium temperature of only 450℃, but the site was close to the rotary kiln, and the radiant heat made the external temperature soar to 600℃. As a result, the outer wall of the bellows failed first, but the inner wall was still fine. Which do you say the design temperature should be taken? It must be the maximum of the two heat sources, and then the material creep strength is checked. Don't be lazy only measure the medium temperature, the ambient temperature is often the fatal blow.

3. Material selection: When the temperature is high, money and life have to be counted

When the temperature rises, the allowable stress of ordinary austenitic stainless steel (such as 304) cliffs down. Over 550℃, you have to change to a heat-resistant alloy, like Inconel 625. But heat-resistant alloys are expensive, several hundred yuan per kilogram, and the cost doubles. What about that? In some cases, the multi-layer structure of high-temperature axial expansion joint can be used-the inner layer is heat-resistant, the outer layer is pressure-bearing, and the cost is reduced. Or simply put on non-metallic expansion joints (fabric fiber expansion joints), and use temperature-resistant fibers and silica gel coating, which can carry above 1000℃, and the price is lower than that of heat-resistant alloys. Note that the design temperature also directly affects the fatigue life: for every 100°C increase in temperature, the cycle life of the bellows may be reduced by half. Therefore, when selecting the model, the design temperature must be calculated together with the pressure and displacement, so as to determine whether the general-purpose corrugated expansion joint or the large-diameter thick-wall expansion joint should be used. The former is cheap but weak in fatigue resistance, while the latter has large wall thickness and rigidity, which is suitable for high temperature and high cycle.

Here's a common "pitfall": the regulations of temperature cycling and thermal shock in the standard. For example, desulfurization flue gas baffle door and flue gas baffle door, the medium is acidic wet flue gas, and the temperature is not high but fluctuates violently-jumping back and forth from 100℃ to 180℃. If the design temperature is selected only according to the highest value of 180℃, and the thermal fatigue is ignored, the weld will crack after hundreds of cycles under the working condition of high start-stop frequency. National standards JB/T 12235-2015 (non-metal expansion joint) and JB/T 6171 (metal bellows) have detailed regulations on temperature, but in actual projects, I suggest leaving an extra margin of 10% ~15%, especially in working conditions with high start-stop frequency. Don't ask why, I've seen too many live lessons.

4. Actual estimation: What if there is no data?

In the absence of detailed process data, the saturated steam temperature corresponding to the design pressure of the pipeline can be inverted. For example, the pressure is 1.0MPa and the saturated steam temperature is about 180℃, so the design temperature starts at 200℃. Or referring to similar project cases, we have the product pages of "Double Hinge Expansion Joint for Air-cooled Island Vacuum Pipeline" and "Double Hinge Transverse Expansion Joint" on our station, which list the design temperature range for conventional working conditions. Generally, the design temperature of steam pipeline is the medium temperature +20℃, but it depends on the pipeline material and insulation thickness. Finally, a reminder: after the design temperature is determined, don't forget to link with the "guide tube" design. The guide tube can reduce the direct scouring of the bellows by high-temperature medium, which is equivalent to reducing the effective working temperature by 30~50℃. This amount can save a lot of cost when calculating the fatigue life.

Find out first: Are diameter and caliber the same thing?

Many people think that the pipeline of DN100 is equipped with the expansion joint of DN100, and they can be bought and installed. If you really do this, there will be a problem nine times out of ten. The diameter (DN) is the nominal diameter, and the pipe diameter is the actual inner diameter. The two basically correspond to the standard parts, but the structure of the expansion joint-the guide tube, the wall thickness of the bellows, and the flange sealing surface-will eat a part of the circulation area. For example,Corrugated expansion joint for power plant industryIf it is equipped with a larger guide tube, the actual flow capacity will be different from that of a straight tube. You think the DN200 tube with the DN200 expansion joint can pass the same flow? As soon as the guide tube shrinks in diameter, the flow rate directly soars. So, don't use DN as the inner diameter.

The core logic of pairing: flow rate, pressure, displacement, one cannot be less

If the diameter is large, the medium flow rate will of course be low, but the equipment cost will rise upside down, and the flange, bellows and guide tube will all have to be enlarged by one. What about choosing small? If the flow rate is too fast, it will erode the bellows, and in severe cases, it will directly cause vibration. Last year, the steam pipeline of a chemical plant was equipped with DN250 expansion joint in order to save money. As a result, the medium flow rate rose from 15m/s to 22m/s, and the bellows were worn out in three months-replacing it once is enough for you to buy three pairs.

The pressure level and the amount of displacement will also, in turn, constrain the diameter.High temperature axial expansion jointThicker bellows are required, and the actual inner diameter will shrink under the same DN, so it must be recalculated according to the effective cross-sectional area. For example, for the same DN200, the inner diameter of the normal temperature type may be 198mm, while the inner diameter of the high temperature type may only be 190mm due to the increase of wall thickness, and the flow area difference is 8%. If you don't recalculate, the flow rate will be biased.

Difference in diameter selection of expansion joints made of different materials

Metal expansion joints (e.g.Universal corrugated expansion joint、Large diameter thick wall expansion joint) andrubber compensator、Non-metallic expansion joints (fabric fiber expansion joints)The matching method is completely different. Metal parts are rigid, and the diameter usually goes in standard series, but if you useCompound hinge transverse expansion jointIn this structure with hinges, if the diameter is large, extra bending moment will be generated at the flange connection, and the hinge is easy to deflect over the limit.

The rubber compensator has good elasticity but limited pressure resistance, and its large diameter is easy to bulge-especially in large diameter and low pressure conditions. The rubber layer expands outward after being subjected to internal pressure. The larger the diameter, the higher the risk of bulging. What about non-metallic expansion joints? Such asRectangular non-metallic expansion jointIt is mostly used for rectangular smoke ducts, and the diameter needs to be matched with the hole spacing of flange bolts, so the round pipe DN cannot be copied. If you take the round pipe formula of DN1000 to calculate the rectangular flue, the bolt holes don't match, and the site has to be re-drilled.

Common mistake: What happens if the diameter is matched small? What's the pit if it's big?

Two days ago, a customer equipped DN200 pipeline with DN150 expansion joint, and the medium flow rate doubled, and the bellows were worn out in three months-as mentioned earlier. On the other hand, the diameter is larger, although the safety factor is higher, butCompound hinge transverse expansion jointIn this type of hinged structure, additional bending moment will be generated at the flange connection, which can easily lead to deflection exceeding limit. In addition, if the flange is large, it may make the flange wrong-if you take the flange of DN200 to the bolt hole of DN250, it will have to be reprocessed on the spot, and the construction period and cost will all be included.

The gap between the guide tube and the bellows. After the diameter is enlarged, if the gap between the outer diameter of the guide tube and the inner diameter of the bellows is not well controlled, the medium will form vortex in the gap, which will accelerate corrosion. EspeciallyDesulfurization flue gas baffle doorThis kind of used in wet flue gas environment, the corrosion margin is not enough, and it will be perforated in half a year.

Practical Suggestions: Three Steps of Model Selection

The first step is to confirm the actual inner diameter and wall thickness of the pipeline, and calculate the effective circulation area. Don't just look at DN, take a caliper to measure the actual inner diameter of the pipe-especially old pipes, which may have scale or corrosion on the inner wall, and the actual diameter is a section smaller than the nameplate.

In the second step, according to the medium (steam, flue gas, corrosive liquid) and temperature and pressure, find the corresponding type of expansion joint from the product information. For example, a wet smoke environment, withDesulfurization flue gas baffle doorOrNon-metallic expansion joint (fabric fiber expansion joint)The diameter should leave a corrosion margin; For steam linesHigh temperature axial expansion jointThe effective cross-sectional area should be recalculated after the wall thickness is thickened.

The third step is to check the path comparison table provided by the manufacturer. This site hasMetal hose size comparison tableAndMetal expansion joint weight tableCheck flange standards (HG/T 20592, GB/T 9119, etc.). Finally, it is best to let the manufacturer calculate the flow field with finite element-don't save this step. Many manufacturers provide it for free. You only need to send the media parameters and pipe dimensions. They produce a calculation book, which is much more accurate than patting your head yourself.

If you useDirect buried (fully buried) type expansion jointOrDouble hinge expansion joint for air-cooled island vacuum pipelineFor this kind of special structure, the stability of external pressure should also be considered, and the relationship between diameter and wall thickness is more complicated. Go directly to the technical manufacturer for the type selection calculation book-don't be too troublesome. The cost of replacing the expansion joint once is broken is enough for you to buy three pairs.

sum up

Choose the right diameter and double the life of the equipment. The diameter matching is not simple 1:1, and needs to consider the flow rate, medium, structure and installation comprehensively. If you are unsure, flip through this siteMetal hose size comparison tableOrMetal expansion joint weight tableOr directly find the manufacturer to issue a calculation book. Remember: the cost of replacing an expansion joint is enough for you to buy three right ones.

Insufficient expansion joint displacement? Don't be in a hurry to change, start by checking these four steps

I met a customer two days ago, and I called in a hurry to say that the displacement of the expansion joint was not enough, and the pipeline was almost deformed, so I wanted to replace it with a new one directly. I asked him to take a few photos and send them to see-but after looking at the photos, I found that it was not the displacement at all. I've seen something like this more than once or twice.

What should I do if the expansion joint displacement is not enough?Don't think about tearing it down and replacing it when you don't hear enough. If you waste money, you can't afford to delay the construction period. Check according to the following four steps, and 80% of the problems can be solved by themselves.

Step 1: Confirm is it true that the displacement is not enough, or is the pipeline thrust making trouble?

Many so-called "insufficient displacement" are actually "crushed to death" by the pipeline thrust. How to distinguish?

Look at the phenomenon:When the displacement is insufficient, the bellows should be expanded but stuck; Excessive thrust will cause bellows to bulge, twist and even crack. You have to take out the design drawings first, find the rated axial/lateral/angular displacement compensation amount, and then measure the field thermal displacement value with a caliper or displacement sensor. If the measured value does not exceed the rated value, but the expansion joint has deformed and failed, it can basically be concluded that it is a problem of stiffness or pressure-regardless of the displacement itself.

Inspect the guide tube and pipe holder:If the guide tube is deformed or stuck by the medium, it will hinder the normal movement of the bellows; Pipe frame offset also forcibly transfers displacement to the expansion joint. In the question and answer of this site, we specifically talked about "the specific function of the expansion joint guide tube". The guide tube mainly protects the inner wall of the bellows, but once it is stuck, it becomes an accomplice. In addition, check whether the fixed support is loose-if the thrust that the pipe should be bearing by the fixed support is thrown to the expansion joint, the expansion joint will not be able to carry it even with 100% margin.

First exclude "false is not enough", and then judge whether you really choose small.

Step 2: Selection stepped on a pit?

Wrong selection is the most common cause of insufficient displacement, and it is often the most injustice. I've seen general-purpose corrugated expansion joints to absorb large angular displacements-that's not the job at all.

Common Error One:The system needs to absorb lateral displacement or angular displacement, so a single axial expansion joint is selected. Single type axial type can only absorb axial expansion and contraction, and forcibly twist it, and the bellows will fail fatigue soon. Correct practice: If it is multi-directional displacement, you should choose compound hinge transverse expansion joint or compound straight pipe bypass pressure balance expansion joint. The latter has the advantage that it can absorb both axial and lateral displacements, and the internal pressure thrust is balanced out and does not act on the pipe support.

Common error two:Use the universal corrugated expansion joint to cope with the high temperature steam pipe of power station. The temperature of high-temperature steam pipe is always five or six hundred degrees, and the material of general-purpose bellows is not temperature-resistant enough, so the bellows will soften and deform in advance. In this case, high-temperature axial expansion joints must be used-this category is specially available in our station, and the temperature resistance grade and compensation amount are designed according to the working conditions of the power station.

Common mistake three (save money instead):In the air duct of cement industry, the temperature is not high but the dust is large. It is costly and easy to wear with metal corrugated expansion joints, so it is more cost-effective to replace them with non-metal expansion joints (fabric fiber expansion joints). Non-metallic expansion joints are corrosion resistant, absorb multidimensional displacements, and are inexpensive. The national standard JB/T 12235-2015 also has clear specifications for it.

Therefore, first turn over the decision to pat your head when selecting the model at that time, and don't let the expansion joint take the blame.

Step 3: The pit dug in the installation link

There is a problem with installation, which is more concealed than the selection. And guess what? Most of the so-called displacement is not enough, in fact, it is not installed in place.

Tie rod nut not adjusted in place:The tie rod nut of the expansion joint is for pre-tightening, not for transport locking. Specifically, we have a question and answer in our station "How to adjust the tie rod nut of the expansion joint"-simply put: after the installation, the tie rod nut should be screwed to the specified position to release the initial displacement capacity of the bellows. If it is not adjusted, the bellows is equivalent to being pressed all the time, and the natural compensation amount will be discounted.

The pre-stretch is done backwards:Some pipes need to be pre-stretched (for example, steam pipes are pre-stretched for a section when installed in cold state, and just reset when hot state), but workers have gone in the opposite direction-what should have been stretched becomes compression. After the system heated up, the expansion joint was directly pushed to death. Of course, the displacement was not enough. This phenomenon is common on power station steam pipes.

Failure of pipe fixed support:The function of the fixed support is to guide the thermal displacement of the pipe to the expansion joint. Once the support is loosened or fallen off, the pipe will be turbulent, and the displacement that should have been absorbed by the fixed section is all superimposed on the expansion joint. Check for any loose welds or bolts on the holding bearings-don't underestimate this step, it can solve a lot of problems.

Step 4: Classification of Remedial Protocols – Mild, Moderate, Severe

To be honest, after the first three steps of troubleshooting, most problems can be found at the root. But what if the selection is really small or the working conditions change? According to the degree of excess tolerance, there are three situations:

Slightly out of tolerance (actual displacement exceeds rating by less than 10%):Adjust the tie rod nut to redistribute the displacement, or add a limiting device (such as adding a limiting plate next to the expansion joint) to limit the out-of-range displacement so that the expansion joint only works within the safe range. This operation is simple and low cost.

Moderate deficiency (more than 10% ~30%):Change! But you don't have to change the full pipeline. If space allows, switch to a general-purpose corrugated expansion joint of the same caliber but with more wavenumbers-the more wavenumbers, the more compensation. Or simply change it to a double straight pipe bypass pressure balancing expansion joint, which doubles the compensation amount by combining two bellows and can also balance the pressure. Note that the thrust and support load of the pipeline should be recalculated before replacement.

Serious insufficiency (more than 30%):Don't expect to change the same type of expansion joint, there is no room for design. The entire pipeline needs to be recalculated and the combined compensation scheme is used instead. For example, use a rotary compensator (which can absorb large angular displacement by rotation, suitable for long straight pipes) with a sleeve-type pipe expansion joint (absorbing axial displacement), or change single-point compensation to multi-point segmented compensation. Our station has two mature products, rotary compensator and sleeve-type pipe expansion joint, and the technical scheme can be customized for customers.

What should I do if the expansion joint displacement is not enough?The core is "diagnose first and prescribe medication later". Don't change it for a new one at every turn, maybe it won't work if you change it. Follow the above four steps, 90% of the problems can be solved on the spot, and the money saved is enough to buy several sets of equipment.