Specialized in manufacturing compensators, expansion joints, baffle doors

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.

Boiler Separator Outlet Expansion Joint Leaking? Three-step troubleshooting method, teach you how to deal with it step by step

Once the expansion joint at the outlet of the boiler separator leaks, the steam carries water, the system vibrates, and even stops for maintenance, which is enough for you to have a headache. Two days ago, a friend from a power plant called me in the middle of the night, saying that there was a white steam at the scene, and the pressure dropped badly, and asked me if I could block it first. Don't worry, let's find out where the leak is first, and it's not too late to start.

1. Don't rush to replace the parts yet-find out where the leak is

Many people directly place an order to buy a new one as soon as they see a leak. However, at the outlet of the boiler separator, the working temperature is high and the medium flow rate is fast, so there is often more than one possibility of leakage point:
- Damaged bellows: Most common. High-temperature steam washing + long-term fatigue, thinning of bellows wall thickness, pinholes or cracks appear. Use a flashlight from one side, and see if there are any light-transmitting spots on the other side.
- Weld cracking: Especially for circumferential and longitudinal welds, if the welding quality is poor or the thermal stress is concentrated, the cracks will extend along the fusion line. You can use colored penetration inspection, and there are generally reddish-brown marks at the leakage point.
- The guide tube is worn out: The function of the guide tube is to guide the medium and protect the bellows from direct scouring. Once the guide tube is worn out, the high-speed steam directly hits the bellows and quickly perforates. Disassemble and look at the end of the guide tube for any penetrating wear marks. Many old factories have encountered this problem, thinking that the bellows was broken. After changing it twice, it was found that the deflector tube had a problem first.

Judge which one first, then decide on the scheme. Don't come up and change something, that's a problem with the money in your pocket.

2. Temporary emergency treatment on the spot: How long can leak plugging last? Which circumstances require immediate shutdown?

After discovering a leak, if it is only a small amount of leak, you can useMetal wound gasketAddHuff FestivalTemporary hoops. But note: this will only last a few shifts, and leakage changes must be monitored continuously.
Situations where immediate shutdown is necessary:
-The leakage medium temperature exceeds 400°C, the pressure exceeds the design value by 80%, and the amount of leakage continues to increase.
-The bellows is obviously bulging or twisted, indicating that it has become unstable and may burst at any time.
-The leakage point is close to the weld or the fixed end of the guide tube, and once the weld cracks, the whole may fall off.

Temporary plugging is just to buy time for maintenance. Don't think of "waiting for overhaul for a few more days". Boiler Separator Outlet This high pressure and high temperature working condition, you can't afford to gamble.

3. Professional maintenance plan: replace metal or non-metal? How to choose a model without stepping on a pit

For what? That's the core issue. Boiler separator outlet, preferredCorrugated expansion joint for power station industry。 Specially designed for power station boilers, these products are resistant to high temperatures and fatigue, and generally use austenitic stainless steel (such as 316L or Incoloy 825).
But-if your pipe has a particularly large axial displacement because of space constraints, or needs to absorb multi-directional displacement, consider High temperature axial expansion joint。 There is a big difference between the two: the former mainly deals with the outlet of large-diameter and low-pressure boilers, while the latter is better at absorbing the axial expansion and contraction of long-distance pipes. Choose the wrong model, and it leaks after less than a year of installation.

In addition, some working conditions (such as desulfurization flue gas with low temperature but strong corrosion) can be consideredNon-metallic expansion joints (fabric fiber expansion joints)However, it is generally not recommended to use non-metal at the outlet of the boiler separator, because the temperature often exceeds 400℃, and the non-metal layer is easy to age and brittle. Remember: The more expensive the selection is not the better, it is the matching working conditions. Refer to the pages of "Corrugated Expansion Joints for Power Station Industry" and "High Temperature Axial Expansion Joints" of this site, and compare your parameter table: displacement, pressure grade, temperature, medium composition, and don't miss one item.

4. Installation details determine life: how to adjust the tie rod nut? Is the guide tube oriented correctly?

With new expansion joints installed, don't think everything will be fine. If the installation details step on a pit, they will have to be changed after three months.
Tie Rod Nut Adjustment:Many installers screw the tie rod nut to death, feeling that the tighter it is, the safer it is. Wrong! The tie rod of the expansion joint is used to withstand the internal pressure thrust of the pipe, and the nut should be adjusted to the position designed to be pre-tensioned or pre-compressed. Generally, the manufacturer will mark the installation length when leaving the factory, measure the actual distance between the two ends of the bellows on the spot, adjust the tie rod nut to the free state, and then fine-tune it according to the requirements of cold tightening or hot tightening. How to adjust the tie rod nut? For details, please refer to the question and answer of "How to adjust the tie rod nut of the expansion joint" on this site, which has a detailed step diagram.
Guide tube orientation:The direction of the arrow of the guide tube must coincide with the direction of the medium flow. In some factories, it is installed backwards. As a result, the opening of the guide tube faces downstream, and the medium directly impacts the root of the bellows, which will wear out in a few months. After installation, be sure to check the direction, don't wait for it to leak before disassembling it.

There is also the grounding jumper. Don't forget-the steam flow rate at the outlet of the boiler separator is high, which is easy to generate static electricity. If it is not jumped, it may cause electric sparks. How many of these pits have you stepped on?

5. What indicators should we focus on in daily inspection? Two years or five years? Don't wait until you miss it before you regret it

- Displacement indicator scale: There is generally a scale on the outer wall of the expansion joint to record the initial position. If the deviation of the scale value exceeds 20% of the design displacement, it means that the pipeline stress is abnormal, and the bracket and guide need to be checked.
- Bellows surface temperature: Sweep the infrared temperature measuring gun once regularly. If the temperature difference on the same section exceeds 50℃, it may be fouling on the inner wall of the bellows or bias flow of the medium.
- Deflector outlet sound: Listen to it with an auscultation stick. If there is an abnormal "hissing" sound, it means that the guide tube may have been perforated and the airflow is howling inside.
- Tie rod nuts and bolts: Check for looseness and rust. The bolts are prone to slack at high temperatures, and it is recommended to re-tighten the torque every time the machine is stopped for maintenance.

As for the replacement cycle, don't stick to "every two years" or "every five years". If the working conditions are stable and the inspection data are normal, many power station industries will use corrugated expansion joints for 8-10 years without any problem. However, if there is a leakage or an overtemperature or overpressure event, it must be replaced regardless of how long it has been used. Remember: Do it regularlyLife Assessment of Bellows (S-N Curve)It is much more reliable than patting your head to set the cycle.

After all, what if the boiler separator outlet expansion joint leaks? Step 3: First locate the fault point, then choose the right product to replace it, and finally make it use for a few more years by installation and inspection. Don't wait until there is white steam at the scene to flip through the manual, when every second is money.

1. Why do you have to install an expansion joint at the pump outlet? Can you not pretend?

Many people think that the pump outlet pipe is hard, so it is more troublesome to weld it directly. But think about it, as soon as the centrifugal pump is started, the pressure pulses like a heartbeat, coupled with the impact of the water hammer in the pipeline, and the thermal expansion and contraction caused by the temperature change-if these forces are hard on the pump body, the mechanical seal will leak at least, and the pump housing will directly crack at worst. Expansion joints do just that: absorb displacement, dampen vibration, protect pumps and pipes.

But don't be too happy. Install the wrong position and choose the wrong type, that is to dig a hole for yourself. I've personally seen people putUniversal corrugated expansion jointOn the high-pressure pipeline at the pump outlet, the corrugated pipe was washed to pieces and scrapped in two weeks. Expansion energy saving solves the problem, but the wrong choice is the source of new accidents. What about that? Look down.

2. The first level of selection: pressure, temperature, medium, one wrong is all in vain

Pump outlet pressure is usually not low, and it is common for multi-stage pumps to dry to several MPa or even higher. At this time, don't rush to look at the design pressure of the pipeline, but you have to include the peak value of water hammer-the instantaneous pressure of water hammer may be more than 30% higher than the normal value, and ordinary expansion joints can't bear it at all. Therefore, the nominal pressure level must leave sufficient margin.

What about the temperature? Under high temperature medium, the material creep velocity of ordinary corrugated expansion joint will accelerate. At this time, either chooseHigh temperature axial expansion jointEither a deflector is installed to insulate the heat. Not to mention the corrosiveness of the medium-acidic and alkaline fluids must bePTFE-lined hoseOrPTFE compensatorOtherwise, the bellows will be perforated in a few months. Two days ago, a customer usedrubber compensatorI went to pick up oily sewage, but the rubber swelled and deformed, and it was wasted in two months. When selecting the product information of this site, don't rely on your feeling, that is to pay tuition.

3. Installation position and fixed bracket: 90% of installation accidents occur here

The expansion joint cannot be directly attached to the pump flange. You must leave at least a straight pipe section with a diameter length to stabilize the fluid flow. More importantly, fixing brackets or limiting brackets must be set on both sides of the expansion joint, and the main fixing bracket must be able to withstand the blind plate force. Many people think that expansion energy saving absorbs displacement and install it casually. As a result, as soon as the pipeline runs, the expansion joint is stretched to the limit, and the bellows directly cracks.

If you are usingCompound hinge transverse expansion jointOrCurved tube pressure balance expansion jointThen special attention should be paid to the adjustment of the tie rod nut. When installing, the tie rod nut must be loosened to the position corresponding to the design compensation amount, and never screw it to death. How to tune it? Refer to the question and answer of "How to adjust the tie rod nut of the expansion joint" in the station, which is very detailed. Alas, I have seen a project in which the worker screwed the tie rod so hard that the expansion joint couldn't move at all, which meant that it was not installed. Finally, the pipe stress pulled the pump body askew.

4. Flow guide and flow direction marking: Don't ignore these two small details

The medium flow rate at the outlet of the pump is fast. If the expansion joint has no guide tube, the high-speed fluid directly washes the inner wall of the bellows, and it won't take long to wear out. Especially for particulate-containing media, a guide tube is almost necessary. What is the function of the guide tube? In addition to anti-scour, it can also reduce flow resistance and avoid swirls. There is a special article in the Q&A of this siteSpecific Function of Expansion Joint Guide TubeYou can take a look.

In addition, there are generally arrows on the expansion joints to mark the flow direction-this arrow must point to the direction of the medium flow, and when installed backwards, the bellows will become unstable. Don't laugh, there are cases of acting backwards on the spot every year. EspeciallyLarge diameter thick wall expansion jointOnce installed backwards, the labor cost of disassembling and assembling will cost tens of thousands. And guess what? Last time, a brother from a power plant told me that a technician in their factory turned the arrow backwards, and as a result, the bellows bulged half an hour after turning on. So don't be too long-winded, check the direction of the arrow again against the drawing before installing.

5. Post-operation inspection and maintenance: Don't wait until you leak before you regret it

Installing expansion joints is not once and for all. The vibration frequency of the pump outlet is high, and the bellows is prone to fatigue cracks. It is recommended to check every six months: use soapy water to detect leaks, see whether there are corrosion spots or scratches on the surface of the bellows, and whether the tie rod and nut are loose. Especially for use under high temperature operating conditionsExternal pressure single axial expansion jointThe insulation layer must be done well, but don't wrap the bellows dead-leave room for inspection.

If you find that the bellows is seriously deformed, or the compensation amount has been exhausted, don't hesitate to change it directly. The service life of expansion joints depends on the working conditions: some can last ten years, and some are wasted in three years. Don't take chances and wait until it leaks before replacing it, the pump may have been damaged. By the way, there is a question and answer on this site called "The Service Life of Expansion Joints", which has a detailed analysis. You can refer to it.

Install the expansion joint at the pump outlet, not just buy one and install it. From working condition confirmation, selection, installation to maintenance, every link must be solid. Avoid these 5 pits so your pumps and pipes can live long.