Specialized in manufacturing compensators, expansion joints, baffle doors

Find out first: What exactly does the "delivery status" of the expansion joint mean?

It's not simply the four words "do a good job of packing" and it's done. The delivery status of the expansion joint is a complete set of technical definitions: whether the bellows is pre-deformed, where the tie rod nut is locked, whether the direction of the guide tube is correct, how to protect the flange sealing surface, and whether the transportation tool is assembled or disassembled. These details are bundled together, which determines whether you can hoist and weld directly after receiving the goods, or you have to squat on the site to do a bunch of pretreatments first.

Two days ago, I met a customer and received a batch of general-purpose corrugated expansion joints. I opened the wooden box and welded it. Halfway through the welding, it was found that the bellows was crushed to death, and the tie rod was still locked tightly-the manufacturer issued the transportation protection state, which should have loosened the nut and adjusted the pre-deformation before installation. And the result? As soon as the welding heat comes up, the bellows bulges directly. Who takes the blame? The delivery status was not clearly written in the contract, so the manufacturer sent it in the safest way, and no one understood it on the spot. The final construction period was delayed for one week.

What are the common delivery states?

Free Condition, Pre-Stretched/Pre-Compressed Condition, With Limit Tie Rod Condition, Overall Delivery and Part Delivery。

• Free state: The bellows has no artificially applied displacement and the length is equal to the design length. Most general-purpose corrugated expansion joints are sent by default, because they are safest and are not afraid of accidental collisions during transportation.
• Pre-stretched/pre-compressed state: According to the cold tightness of the pipe, the bellows is pre-elongated or compressed for a section, and then locked with tooling. It is commonly used in corrugated expansion joints in power station industry, or straight pipe pressure balance expansion joints that need to absorb large displacements.
• State with limit tie rod: The tie rod nut is locked to limit the bellows from shaking during transportation. But there is a pit here-some tie rods are for transportation protection, and they must be disassembled after installation; Some tie rods are working components, such as the tie rods of external pressure single axial expansion joint and double hinge transverse expansion joint, which are used to restrain axial force or distribute transverse displacement. If you dismantle them, you will have a big problem.
• Block Delivery vs Part Delivery: Small calibers are usually delivered as a whole; Large diameter thick wall expansion joints or non-metallic expansion joints may be shipped separately and reassembled on site. When the parts are delivered, flange bolts, gaskets and fabrics have to be counted separately, and one less is troublesome.

Why does the manufacturer send free state by default? Because the free state has the widest adaptability surface, the site can be adjusted according to the actual cold tightness value. However, some working conditions must be pre-deformed: for example, the design temperature of the pipeline is 500°C, the installation temperature is 20°C, and the thermal expansion is very large. If the bellows is not pre-stretched during delivery, the bellows may be pushed to the limit after operation, and the life will be greatly reduced.

How is pre-stretching and pre-compression achieved? Is the tie rod disassembled or not?

By tie rod nuts, or special tooling. The manufacturer uses a jack or screw to pull the bellows to the specified displacement before leaving the factory, and then locks it with a tie rod nut. On delivery, the tie rod has a lead seal or a yellow warning label that says "loosen nut before installation" or "strictly prohibited removal". But you must not just look at the label, you must look at the structure.

How to identify? Remember one thing:There are usually only one or two transportation protection rods, which are slender and directly connected to the flanges or connecting pipes at both ends, and the bellows cannot move at all after the nut is tightened; Working tie rods tend to be multiple uniformly distributed rods with spherical washers or spherical bearings that allow the bellows to generate lateral displacement.Take a practical example: the tie rod of the transverse expansion joint of a compound hinge. If you remove it, the hinge structure will lose its constraint, and the transverse displacement will twist the bellows. However, the short tie rod that comes with the general corrugated expansion joint from the factory, if it is not disassembled after installation, the expansion joint cannot be deformed at all, which is equal to a rigid short tube.

How to check the delivery status during acceptance?

• nameplate: Model, nominal diameter, pressure, displacement, factory number. Focus on whether there is a label "pre-stretch xx mm" or "cold tightness xx mm".
• Certificate of Conformity: Material, welding process, inspection date. Compare the contract to see whether the bellows material is 304 or 316L. Don't find the wrong delivery after a few days of rust.
• appearance: Whether there are bruises, scratches and pits in the bellows, whether the flange sealing surface is bumped, and whether the direction of the guide tube is consistent with the medium flow direction (the direction of the arrow must point to the medium flow direction). Flexible products such as non-metallic expansion joints and rubber compensators also depend on whether the fabric or rubber has wrinkles and cracks. They are easier to deform during transportation, so they must be laid flat or hung, and cannot be stacked.

Whether the tie rod nut is loose is also a key check item. If the nut is loose during transportation and the pre-deformation amount runs away, you have to measure the actual length of the bellows and compare it with the installation length marked on the nameplate. If the difference exceeds 5mm, don't hard install it, contact the manufacturer to readjust it.

Relationship between delivery status and installation status

Don't think that you can weld it directly when you receive the goods. Especially for corrugated expansion joints used in power station industry, pipelines often have strict cold tightness requirements. For example, the main steam pipeline has a designed cold tightness value of 30mm. When the manufacturer delivers the goods, it is pre-stretched by 20mm. When the ambient temperature changes during on-site installation, you may have to pull another 10mm. If there is no adjustment allowance reserved at the time of delivery, or the tie rod has been locked to the limit, then the scene is blind.

Look at the cold tightness table of the design drawing first, then measure the actual length of the arriving expansion joint, and then correct the cold tightness value according to the installation temperature. This process is called "secondary cold tightening". Some expansion joints have adjustment marks when they leave the factory, such as engraving lines on the tie rod to tell you how much displacement each turn of the nut corresponds, which is for the field micro-tuning.

Status of delivery clause written into the purchase contract

To avoid scrambling, these five articles must be clearly written in the contract:

• Delivery status: free state or pre-stretched/pre-compressed state, what is the amount of pre-deformation in mm.
• Nature of tie rod: whether it is a transportation protection tie rod (removed during installation) or a working tie rod (strictly forbidden to remove), and whether there is any mark.
• Shipping protection: with or without additional support, anti-collision wooden frame, bellows sheath.
• Packing Method: Wooden Case, Naked Package, Pallet. If the large-diameter thick-walled expansion joint is naked, the outside of the bellows must be wrapped with a protective pad, and the bolts on the flange surface should be coated with rust-proof oil.
• Storage period: Non-metallic expansion joints and rubber compensators are stored for more than 6 months, the rubber may age and must be turned over or deflated; If metal expansion joints are stored outdoors for more than one year, check the bellows for rust.

Don't bother, these terms would rather be written in detail than slapped on the head on the spot. And guess what? Many procurement disputes, finally check the contract, it says "delivery according to the manufacturer's standard"-what is the manufacturer's standard? Of course, people come by the most hassle-free.

Attached: Common delivery status comparison table

• Free stateApplicable to universal corrugated expansion joint and rotary compensator; Delivery length = design length; The site needs to be adjusted by itself.
• Pre-stretched state: Applicable to corrugated expansion joints and straight pipe pressure balance expansion joints for power station industry; Delivery Length> Design Length; Retest according to the requirements of cold tightness on site.
• Pre-compressed stateApplicable to working conditions with large axial compensation requirements; Delivery length
• With limit tie rod (transport protection): Suitable for long distance transportation; Must be loosened and removed before installation.
• With working tie rodApplicable to external pressure single axial type expansion joint and double hinge transverse type expansion joint; It is strictly prohibited to remove, but the nut can be adjusted to adjust the displacement distribution.
• Overall deliverySmall-diameter expansion joint, metal hose; Install as soon as it arrives.
• Parts deliveryLarge diameter non-metallic expansion joint, rectangular expansion joint; It needs to be assembled on site, and the parts list should be checked.

In what state the expansion joint is delivered, this question should not be remembered on the day of arrival. Before signing the contract, throw the real needs of your site to the manufacturer-free state or pre-stretch, how to deal with the tie rod, and the packaging is not in place. It is much more reliable to say it once than to call for help when you arrive at the scene.

It is the most flexible and the most vulnerable. The wall thickness of bellows is often only a few tenths of millimeters to a few millimeters, but it has to bear the displacement compensation of the whole pipe system. When the scene is bad, it is bad to scold the material, but the real murderer is nine times out of ten scouring. Want to Solve Metal Expansion Joint Scour? First, understand the following five questions, which works better than changing the model ten times.

1. How exactly does scouring happen?

Not all wear is called scouring. Particles in the medium, excessive flow rate, gas-liquid two-phase flow, and sudden change in flow direction-at least two of these four factors account for at least two, and the bellows wall surface will be repeatedly cut. To put it bluntly, this is the high-speed friction between the medium and the metal surface, which is the same as polishing with sandpaper. If you touch the flushed bellows with your hand, the surface is shiny, and you can even see the metal texture, then it doesn't run.

In some working conditions, the flow rate is not high, but the medium is steam with water, and the water droplets hit the trough at high speed, which still cuts iron like mud over time. What is more hidden is the sudden change of flow direction, such as the elbow immediately behind the expansion joint, and the medium directly turns against the bellows, which is equivalent to opening a sandblasting machine locally.

Second, how long does it take to scouring to destroy an expansion joint?

Three months, or even less. The wall thickness of the bellows is inherently thin. Once it is washed and thinned, the pinhole leaks first, and then it tears apart along the trough. Many scenes thought that the material was not good, so they changed 316L and 254SMO, but it still leaked. The roots are washing away, not corroding.

So the deflector is not an optional accessory, it is a shield for the bellows. The expansion joint without the deflector is equivalent to going to the battlefield without body armor. When selecting, if the medium has particles, high flow rate and gas-liquid two phases-any of these three words appear, the guide tube must be matched.

Third, how to prevent scour in design?

Add the guide tube, change the material and change the structure, all three tricks are indispensable. The guide tube guides the high-speed medium into the inside of the tube, so that the bellows avoid direct flushing, which is the first line of defense. When the dust content of the medium is large, you can consider surfacing cemented carbide on the inner wall of the pipe. Don't be reluctant to give up this cost. The replacement cost of an expansion joint is enough for surfacing for several years.

If the working temperature is high, choose high-temperature axial expansion joint or external pressure single axial expansion joint, and move the bellows to a position that is not directly impacted by the medium. The external pressure structure is particularly easy to use. The bellows is outside, the medium goes through the internal channel, and the trough can't be touched on the scour path at all. Two days ago, I met a cement factory customer. The temperature of the smoke duct was 800℃. It used to be an ordinary axial type, and it wore out in three months. Later, the external pressure single axial expansion joint was changed, and it took more than a year to see that the bellows was intact when disassembled.

4. What can be done by on-site operation?

Don't think everything will be fine if you put it on. Controlling flow rates, avoiding running at critical flows for long periods of time, checking bellows troughs for bright spots or pits during shutdowns — these details are more important than anything else. And guess what? Many scour accidents are caused by incomplete pipeline purging in the early stage of driving and welding slag stuck in the gap of the guide tube. The welding slag tumbles inside at a high speed, which is equivalent to filing the bellows every day.

When the expansion joint is installed, the direction of the guide tube must be consistent with the flow direction of the medium. The arrow is clearly marked, but someone is acting backwards. The consequence of reverse installation is that the medium is directly poured into the interlayer between the bellows and the guide tube, so it is not called washing, but cutting.

5. How to avoid stepping on pits when selecting models?

Calculate the medium first, then check the flow rate, and finally determine the structure. Flue gas pipeline uses non-metallic expansion joints or rectangular non-metallic expansion joints. The erosion resistance depends on the skin material. Don't just look at the thickness of the frame. The skin is the layer that directly contacts the medium. For general-purpose corrugated expansion joints or metal hoses for liquid pipelines, focus on the length and wall thickness of the guide tube-the front end of the guide tube should extend beyond the turbulent zone of the medium, and the wall thickness should be at least the same as that of the connection tube.

For power plant desulfurization system, corrosion-resistant expansion joints matched with desulfurization flue gas baffle doors have to be used. The concentration of chloride ions in desulfurization slurry is high and there are many particles, which ordinary stainless steel can't bear at all. Non-metallic or fluorine-lined structure is the correct solution. All in all, don't take the general structure to harden the bad working conditions. The first principle of type selection is to choose the structure under any working condition.

VI. Handling sequence of scour accidents

First stop the machine for inspection, then judge the degree of damage, and then decide whether to repair the weld or replace it as a whole. If the bellows is not perforated but thinned obviously, replace it directly-the strength and fatigue life of the thinned bellows are discounted, and the welding repair will only leave the stress concentration point. If only the guide tube is worn out, you can only change the guide tube, and the cost can be saved by half.

Remember, the expansion joint is the weak link in the pipe system, but it is because of its weakness that it protects the whole pipe system for you. When it is broken, I think of replacing it. It's better to ask more questions when selecting a model: Will this medium be washed? What is the flow rate? How big are the particles? — — This sentence can save hundreds of thousands of parking losses.

It is also a corrugated expansion joint. Why is the height difference of the wave sidewall so much? Find out exactly where this parameter refers first

What is the sidewall height of expansion joint wave? To be honest, there is a problem with this question itself-the height of the wave sidewall is not a fixed value, it follows the working conditions. Don't rush to ask "how much" first, find out which paragraph it refers to.

The waveform of the corrugated expansion joint, you can understand it as a wave. The hypotenuse between the peak and the trough, that is, the vertical distance from the bottom of the trough to the top of the peak, is called wave height in the industry, but when the engineering drawings are actually processed and inspected, it is actually the "wave sidewall height"-it refers to the vertical projection size of the inclined wall on the side of the bellows. Many people confuse it with wave height, which is not exactly the same thing. When you measure with a caliper, you measure the height from the trough to the peak, but the height of the wave sidewall should also consider the transition radius between the peak arc and the trough arc. The measured value will be slightly different from the wave height.

This size directly determines the stiffness, pressure resistance and compensation amount of the expansion joint. The same nominal diameter, high wave side wall height, good flexibility, large compensation, but the pressure resistance will decrease; On the other hand, if the wave side wall height is low, the pressure bearing capacity is strong, but the compensation capacity is limited. So do you say that this parameter is heavy or not? When you can't figure out the selection, most of the problems will occur when you install the pressure test later.

Is there a fixed standard for wave sidewall height? From GB/T 12777 to the actual product, see how it is determined

Some people think that the national standard will specify an exact wave sidewall height for each path, which is overthinking. GB/T 12777 General Technical Conditions for Expansion Joints of Metal Corrugated Pipe mainly stipulates the design, manufacture, inspection and acceptance requirements of corrugated pipe, and gives framework things such as design calculation method, material selection principle and fatigue life test method, which will not determine the height of wave sidewall alone.

There is a parameter table of bellows section dimensions in the standard, which lists the recommended values such as wave height, wave pitch, wave number and wall thickness, but these are design references, not mandatory standards. The same corrugated expansion joint of DN200 is used in low-pressure and large-compensation applications and high-pressure and small-compensation applications, and the wave side wall height is likely to be more than double. For this reason, you can't find a "standard answer" in the national standard. What about that? It has to be pushed from the design source.

There are four key factors affecting the height of wave sidewall: pressure, caliber, material and compensation amount

Let's talk about how the height of the wave sidewall was "forced" out in actual design. Four factors are indispensable:

Stress.This is the first deciding factor. The higher the internal pressure, the greater the circumferential stress on the bellows wall. If the height of the sidewall of the wave is too high, the stress is easy to concentrate at the trough, and the pressure resistance is immediately discounted. Therefore, under high-pressure working conditions, the height of the wave side wall is usually pressed relatively low, the wave shape is flat, and multi-layer thin walls are used to make up the flexibility. On the other hand, in the working conditions of low pressure and large displacement, such as non-metallic expansion joints or large-diameter metallic expansion joints for smoke ducts, the height of wave sidewall can be made higher, and the waveform can be stretched, so that the compensation amount can go up.

Caliber.The larger the diameter, the larger the pressure bearing area, and the greater the total thrust under the same pressure. The design requirements of the expansion joints of DN100 and DN2000 are completely different from the same order of magnitude. Large diameter expansion joint should control the ratio of wave side wall height to avoid excessive plastic deformation of wave trough. For example, the rectangular expansion joint on the smoke duct of power station, which has a super large diameter, is often iterated by finite element analysis, instead of copying the empirical value of small diameter.

Materials.The yield strength and fatigue characteristics of austenitic stainless steels (e.g. 304, 316L) determine how much bending strain the bellows can withstand. The material strength is high, which can make the height of the wave sidewall larger, and the wave shape can hold it anyway; If the material is low in strength or thin in thickness, the situation is the other way around. There is also the problem of material creep under high temperature working conditions. As soon as the temperature rises, the allowable stress of the material drops, and the height of the wave side wall has to be lowered accordingly, otherwise the bellows is easy to become unstable under high temperature.

The amount of compensation.The larger the displacement to be absorbed, the larger the deformation of each wave, and the height of the wave sidewall should naturally be made higher. However, the fatigue life of bellows is directly linked to the displacement of single wave, and it is not because you can increase the compensation infinitely by pulling the height of the wave sidewall hard. Axial type, transverse type and hinge type, each type has different requirements for the height of wave sidewall. Under the working condition of transverse displacement, the height of wave sidewall has a great influence on the shear deformation of corrugated pipe, so it should be specially checked during design.

The height of the wave side wall is not determined by patting the head: what data are mainly looked at in design calculation?

Then how exactly do the designers set this size? The core path is as follows: first, according to the pipeline stress analysis, the displacement to be absorbed-axial displacement, lateral displacement and angular displacement is obtained, and then the materials and layers are selected in combination with the design pressure, design temperature and medium corrosion margin, and then the geometric parameters of the bellows are iteratively calculated by the calculation method recommended by EJMA standard or GB/T 12777. The wave sidewall height is not calculated separately, it is a related dimension that follows the wave height, wave distance and wave number.

One is the compressive strength check, to ensure that the bellows will not yield or instability under the most severe working conditions; The other is the fatigue life check, to ensure that penetrating cracks will not occur within the expected number of cycles. If you find that the sidewall height of the expansion knuckle wave reported by the two manufacturers is much different under the same working conditions, don't rush to compare the price. Let them take out the design calculation book first. If the wave sidewall height deviates too far from the conventional value, either the stiffness and fatigue life are not up to standard, or there is another mystery in the material or wall thickness.

How to confirm the wave sidewall height with the manufacturer when selecting the model? What to pay attention to in field measurement and drawing verification

If your project has entered the procurement stage, when confirming the height of the corrugated sidewall with the manufacturer, the safest way is to ask the other party to mark the expansion drawing of the corrugated pipe on the drawing, instead of simply quoting a number. The wave height, wave distance, wave side wall height, number of layers and wall thickness of a single layer should be marked on the drawing. These data are meaningful when put together. If you ask the height of a wave sidewall separately, and the manufacturer gives a number, you can't see whether it is reasonable or unreasonable.

For on-site measurement, just use a vernier caliper or depth gauge to directly measure the distance from the trough to the peak of the bellows. But one thing to remind: Many bellows have protective sleeves or insulation layers on the surface, so you have to remove the outer sheath and measure it again. The measured value is allowed to deviate from the value marked on the drawing. GB/T 12777 has requirements for the dimensional tolerance of corrugated pipe. Generally, the tolerance of wave height is about ±3%, and the wall thickness tolerance is according to the material standard. If the measured deviation exceeds 5%, we should be alert to manufacturing quality problems.

In addition, attention should be paid to distinguish whether it is a single layer or a multilayer structure during measurement. The wave sidewall height of multi-layer bellows is the total height. What you measure from the outside is the outermost contour, but there may be gaps or misalignments between each layer. This should be confirmed with the manufacturer. Two years ago, there was a customer, and the height of the wave sidewall measured by a caliper was 3mm smaller than the drawing. It was not said that the manufacturer cut corners. As a result, it was found that the outer protective ring blocked part of the measurement position. This kind of low-level misunderstanding, it is good to talk about it, but I am afraid that it will not talk about it.

At the end of the day, what is the expansion knuckle wave sidewall height? This question should not be answered by a "standard answer", but by your working condition data. Report the parameters of pressure, temperature, medium, displacement and number of cycles to the manufacturer, and ask them to take out the design calculation book. You will naturally know what range the reasonable wave sidewall height should fall in.

How to judge that non-metallic compensator should be replaced

How to replace a non-metallic compensator? In fact, before asking this question, one thing has to be clear-whether it should be replaced or not. Blind replacement not only wastes money, but also may dismantle the originally stable system.

Non-metallic compensators (often called fabric fiber expansion joints) work in high-temperature flue gas and corrosive media for a long time, and the loop belt is a loss part. When you inspect, focus on these places:crack。 If the surface of silicone rubber coating or fluororubber is cracked and the depth exceeds half of the thickness of the coating, it will basically reach its life;Aging。 Press the surface of the loop band with your hand, and the rebound is slow, hard and brittle, indicating that the material has lost its elasticity;deformation。 Use a ruler to lean on the flange surface. If the ring belt is wrinkled and the local bulge exceeds 10mm, it must be treated;leak。 This is the most direct-there is smoke running out during operation, or obvious wear and penetrating damage can be seen after shutdown. Don't hesitate to arrange replacement directly.

If the internal guide tube of the compensator falls off, or the external stainless steel wire mesh is damaged, resulting in the exposure of the fiber layer, even if the surface looks okay, it is recommended to replace it as soon as possible. This kind of damage will accelerate the overall failure of the ring belt, which won't last long.

Preparation before replacement: Don't rush to do it

How to change a non-metallic compensator? The premise is that security measures are in place. This thing is mostly used in places with harsh working conditions such as smoke duct, desulfurization system and cement kiln tail of power plants. The medium is either high temperature or corrosive gas. In the flue above 200℃, do you dismantle it directly? That's not work, it's life-threatening.

The first step is to stop the machine and relieve pressure. Reduce system pressure to zero and temperature to ambient temperature. Don't save this step-some pipes have dead ends, and the dust accumulation inside is still slowly storing heat. I have seen more than once that the surface can't be seen but the internal temperature is still very high. In the second step, use blind plates or baffle doors to separate the pipes on both sides. Speaking of this, the circular baffle door (double seal) in our station is designed for this kind of maintenance scenario. After locking, it can ensure zero leakage, and the later operation is safe. The third step, padlock, hanging tag and gas detection, is completed according to the factory's LOTO process.

Check spare parts at the same time. The specifications and parameters of non-metallic expansion joints are different for each item-diameter, pressure, temperature, displacement, flange hole distance, which must be compared one by one. Don't think you can pretend just by looking at it. Last year, a customer took a short 50mm rectangular non-metallic expansion joint to the site, but the hole position didn't match. Finally, it was reworked, and the construction period was delayed for three days.

Practical details of old compensator removal

When disassembling, the first thing is to draw the installation positioning line with a marker on the outer ring of the flange, and measure the diagonal size. There is no cost to this step, but it saves you a lot of adjustment time when you reinstall it.

There is no technical content in bolt removal, but pay attention to protecting the flange surface. This is especially true when cutting-some welds join structures that need to be fired, and make sure there are no combustible around before cutting. When hoisting, use a sling or soft rope, and the wire rope directly strangled on the loop belt will crush the fabric fibers. You're dismantling old pieces, but the equipment and plumbing next to it are still good.

Flange surface cleaning is a link that many people ignore. After the old compensator is removed, the flange surface is covered with aging cement, rust residue and old gasket residue. Use an angle grinder with a steel wire wheel to polish it clean until the metallic luster is exposed. If the flange surface is uneven, it will still leak if a new non-metallic compensator is installed.

Critical steps for new compensator installation

When installing new pieces, alignment is the most error-prone step. The alignment of the flange holes is not complete, and the centerline of the compensator must coincide with the centerline of the pipe. How to check? Take four points evenly on the circumference of the flange, and measure the distance to the pipe wall, so long as the deviation does not exceed ±3mm.

Then there is pre-compression/pre-stretching. When the non-metallic compensator leaves the factory, the manufacturer presets an installation length based on the design displacement. You can work according to the drawing-how many millimeters are marked on the drawing for pre-compression, and you can adjust the tie rod nut to how much. Here's an easy mistake: thinking that pre-compression is just pressing a little. No, the amount of pre-compression directly affects the displacement compensation range during operation. Too much pressure, insufficient positive displacement; Less pressure, not enough reverse displacement. Specifically, how to adjust the tie rod nut? Our technical department has specially written an instruction on how to adjust the tie rod nut of the expansion joint, which contains detailed data of torque and adjustment sequence.

The first pass is all put on, and the torque is screwed to 30%; The 2nd pass is screwed to 70% in diagonal order; Third pass again in order to 100%. The four corner bolts are tightened one last time. Such a simple process can avoid local leakage caused by warping of the flange surface.

Acceptance after reinstallation: Don't rush to turn on the machine

After installation, the final step in how to replace the non-metallic compensator is verification. Direct power supply to power on? That won't work.

Do the tightness test first. Brush with soapy water on the flange joint surface and the ring belt surface, pressurize the pipe to 1.25 times the design pressure, and stabilize the pressure for 30 minutes. If there are bubbles coming out, it is the leakage point, so mark, relieve pressure and treat it immediately. No air bubbles indicate that the seal is qualified.

Confirm the displacement compensation effect again. This is particularly important for non-metallic compensators, whose fabric fiber bands require some room to move to absorb thermal displacement. You check whether there is enough space on both sides of the compensator, and watch for abnormal bulging or stretching on the surface of the loop belt while running. If conditions permit, record a set of data for each cold state and hot state: temperature, pressure, and displacement. This data is back to the draft of the device file.

Finally, write the replacement date, reason for replacement, model of new compensator, pre-compression amount during installation, and torque value of fastening bolts into the operation record. I don't remember it now, but I can't find it if I want to check it the next time I overhaul it.

It is difficult to replace the non-metallic compensator, but it must not be careless. Each step has stringent process requirements, and which step is skipped will end up being exposed in the run. If you encounter specific problems on the spot, such as uncertain ring belt selection and special installation conditions, go directly to the manufacturer for technical confirmation, which is more reliable than thinking about it yourself.

Expansion joints without pre-deformation when they leave the factory will be scrap iron at the site

The factory state of the metal expansion joint directly determines whether it can work after being installed. Many people receive the goods and see that the bellows are shiny and the paint is intact, and they feel that everything is okay-wrong. If the expansion joint is not pre-deformed when it leaves the factory, it is basically a decoration when transported to the site, and may even become a potential safety hazard of the pipeline system.

Why do you say that? Because the displacement compensation ability of bellows is achieved by the elastic deformation of corrugations. If the bellows is at a completely free length when leaving the factory, once the pipe heats up after installation, the bellows will be forcibly compressed (or stretched) from the free state to absorb the heat displacement. The problem is that the fatigue life of bellows is calculated according to the number of cycles, and it is installed directly in the free state, which is equivalent to overdrawing a part of the displacement quota that should be left for cold state to hot state in advance. For example, if a general-purpose corrugated expansion joint with a design compensation of 100mm is pre-stretched by 50mm before leaving the factory, it will be in a semi-compressed state in the cold state, and then compressed by 50mm in the hot state. If it is not pulled when it leaves the factory, it will be installed directly at the site. When it is hot, it will be compressed by 100mm, the stress of the bellows will be directly doubled, and the life will be reduced by a cliff.

So, what is the factory status of metal expansion joints? It is not "what you receive", but "what the manufacturer should be according to your working conditions". This point is confused, and there are pits behind it.

Several common conditions at the time of leaving the factory, which one do you have

Expansion joints with different working conditions have completely different factory conditions. There are generally four types.

The first, the free state.This is most commonly found in small diameter, low pressure, and little temperature change. For example, some non-metallic expansion joints (fabric fiber expansion joints) used in ventilation ducts have low stiffness, and their absorption displacement mainly depends on structural rotation rather than corrugation stretching, so they don't need pre-deformation when they leave the factory. However, note that the expansion joints of metal bellows, especially the high-temperature axial expansion joints used in power stations and cement industries, will not leave the factory in a free state.

The second is pre-stretched or pre-compressed.This is the most particular category. Straight pipe pressure balance expansion joint, external pressure single axial expansion joint, curved pipe pressure balance expansion joint, etc. Before leaving the factory, the manufacturer will pre-stretch or compress the bellows for a certain distance according to the cold tightness (also called cold drawing) of the pipeline. Pre-stretching is used to compensate for thermal expansion (pipes become longer when heated), and pre-compression is used to compensate for thermal shrinkage (pipes become shorter when cooled, such as cryogenic lines). How much to pull and how much to press are written on the drawings and nameplates. Just work according to the drawings during installation.

The third type, with a limiting device.Many tie rod and hinge expansion joints will be equipped with temporary limit screws or limit blocks when they leave the factory to prevent the bellows from being accidentally stretched, compressed or twisted during transportation and hoisting. For example, compound hinge transverse expansion joint and compound straight pipe bypass pressure balance expansion joint have large transverse displacement. Once the bellows is twisted during transportation, the corrugations will produce plastic deformation, and the whole process will be wasted. The limit device is used to lock the displacement, and then remove it after installation and alignment at the site.

The fourth type, with protective support.Large-diameter thick-walled expansion joints, directly buried (fully buried) expansion joints, such as large self-weight, thick bellows wall and large wave height, will be wrapped with a protective sleeve or support frame on the outer ring of the bellows when leaving the factory to prevent bumps, extrusions and scratches on the corrugated surface during transportation. Because any pit or scratch in the bellows is a potential stress concentration point.

The factory position of the tie rod and nut, whether to dismantle or not

This question has been asked countless times in the background. Every time I rhetorically ask: Have you seen the nameplate?

There are two kinds of tie rods on the expansion joint, one isStructural tie rod(Permanent tie rod), such as the tie rod on the single hinge expansion joint and the large tie rod expansion joint. This set of rods participates in the force and is used to bear the blind plate force generated by the internal pressure of the pipeline. The nut on this tie rod is in a locked state, which is set after leaving the factory. It must not be loosened or disassembled during installation. You remove it, and the pipe is pressed, and the bellows bulge out like a balloon.

The other istransport tie rod(temporary tie rod), which only serves the transportation and hoisting stages. It is usually made of thinner screws or angle steel, with one end welded to the end pipe and the other end locked with a nut to the flange or tube sheet. The role of this tie rod is to maintain the factory length of the bellows while locking in the amount of pre-tension/pre-compression. After installation and alignment, the tie rod must be removed or loosened to the extent that it is completely unstressed. If it is not disassembled, the expansion joint becomes a rigid short joint, which can't absorb any displacement. All the thermal stress of the pipeline is transferred to the equipment and bracket, and the root of the bellows will crack after a few heat cycles.

To judge what kind of tie rod it is, look at two points: first, thickness, structural tie rods are generally thick, and high-strength bolts are used; The second is to see if there is a mark for adjusting the spacing of nuts. The transport tie rod is usually marked with the words "remove after installation" with paint. Really unsure, turn out the factory information, it is clearly written on it.

What records are left behind by factory inspection to be considered qualified

The factory status of the metal expansion joint is not only the physical posture, but also the inspection record. When a qualified expansion joint leaves the factory, these things must be attached with the box: hydraulic test record, air tightness test record (when gas medium is required), stiffness test data and displacement data.

Hydraulic pressure test, generally according to the design pressure of 1.25 times or 1.5 times the water pressure, hold the pressure for 30 minutes without leakage, this is a hard index. Air tightness test is used for pipelines transporting flammable, explosive or toxic media, and the requirements are stricter. Usually, low-pressure air tightness of 0.05~0.1MPa or helium mass spectrometry leak detection is directly performed. The most critical stiffness data are axial stiffness, transverse stiffness and bending stiffness. These three values are directly calculated into pipeline stress analysis. Whether the data is correct or not, and whether the values deviate greatly from the design must be verified on the spot. The displacement data refers to the maximum compensation amount allowed by this expansion joint in all directions, axial, transverse and angular directions. Comparing it with the drawings, you can know whether the manufacturer has cut corners.

After you get this information, don't rush to put it away, check it with the product nameplate. The nominal diameter, design pressure, design temperature, compensation amount and factory number on the nameplate should be aligned with the certificate. If you don't, call back to the manufacturer.

Shipping and storage, which state parameters can be quietly destroyed

There is a saying that "it is good when you leave the factory, but it is bad when you go to the construction site". During the period from the factory to the installation of metal expansion joints, there are three state parameters that are most prone to problems: pre-stretching amount, limiting device and surface protection.

What does the amount of pre-stretch maintain? By the limit rod. However, the practice of many construction sites is that the equipment is thrown in the yard directly in the open air, exposed to the sun and soaked in rain. If the limit tie rod is exposed to humid environment for a long time, the thread will rust, and it can't be removed even if it wants to be removed during installation. Rust is not the worst thing. The worst thing is that someone tries to save trouble by cutting the tie rod directly with gas cutting-that's how the expansion joint is treated as scrap iron.

For surface protection, there is generally stainless steel or spray protective layer on the outside of the bellows, but if the sling is bound at the position of transportation and hoisting without a rubber pad, the wire rope will be directly corrugated, and a strangulation mark will be a crack source. In a dusty environment such as cement plants and power plants, dust accumulates in the trough of corrugated pipes. If it absorbs moisture and chloride ions are enriched, stainless steel corrugated pipes can't withstand pitting corrosion.

Pad sleepers below, above 30cm from the ground, cover with rainproof cloth on top, oil the limit rod regularly to prevent rust, and don't pile any heavy objects on the bellows. There are not many projects that can be done with such a small thing.

On-site acceptance three-minute self-inspection checklist

No nonsense, just give you a set of moves.

• Touching the nameplate:Is there a nameplate? Are the model, pressure, temperature, compensation amount and factory number on the nameplate clear and unaltered? Expansion joint without nameplate, refuse to sign for it.
• Second, look at the ripples:Are there any pits, scratches, welding slag splashes and arc damage on the corrugated surface? Is the corrugation spacing even? If the wave distance is wide or narrow, it means that plastic deformation has occurred during transportation, and the product will be returned.
• Three pairs of limits:Pre-tensioned/pre-compressed expansion joint, is the limit rod intact and the locking nut loose? Is the paint mark on the tie rod clear? If the mark is gone, confirm with the manufacturer what the pre-deformation amount is.
• Quad core records:Are there any factory hydraulic test reports, stiffness data and displacement data? Are the data consistent with the nameplate? Is the stamp on the document complete?
• 5. Check the attachments:Is the deflector installed? Is the direction of the guide tube consistent with the direction of the medium flow (along the direction of the medium flow)? Is the arrow on the nameplate in the same direction as the deflector?

These five steps can be completed in a little more than two minutes. If there is a problem, take photos on the spot, write records, notify the manufacturer, and don't drag it out until the day of installation before unpacking.

What is the factory status of metal expansion joints? It is the pre-deformation position calculated by the manufacturer according to your working conditions, and it is the reference point to ensure the safe operation of the bellows during the life cycle. The first thing you do after receiving the goods is not to rush to hoist them, but to confirm that these "states" are still there.