Specialized in manufacturing compensators, expansion joints, baffle doors

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.

How to make expansion joint insulation layer? Think clearly why you should do it

Insulation is not a panacea, but it is not a small trouble without it. The expansion joint is responsible for absorbing heat displacement in the pipeline system. If the heat insulation is not done well, not only will the heat be lost in vain, but also may cause condensation to corrode the bellows, and even discount the overall compensation amount. Let's first find out the purpose of heat insulation-not just wrap a layer, but minimize the heat loss on the premise of ensuring free expansion and energy saving. You may ask: Wouldn't it be good to pack it thicker? Alas, it really isn't. The bag is too thick and too dead, and the bellows can't move, which is equivalent to turning the compensator into a rigid connection. Therefore, the core is one sentence: the insulation layer can't jam the bellows.

Before you start, take a look at what kind of expansion joint you are using

The thermal insulation methods of metal corrugated expansion joints and non-metal expansion joints (fabric fiber expansion joints) are very different. The bellows part of the metal must leave enough space to not be filled; The non-metallic expansion joint itself has a heat insulation layer, which in many cases only needs external protection or local reinforcement. If you have a high-temperature axial expansion joint or a directly buried (fully buried) expansion joint in your hand, the thermal insulation requirements are different-aluminum silicate fiber cotton for high-temperature working conditions and polyurethane for low-temperature antifreeze scenes. Don't get confused. Two days ago, I met a customer who stuffed rock wool directly into the ripples of the directly buried expansion joint. As a result, it stuck as soon as it ran, and the compensation amount was directly returned to zero.

Core Principle: The insulation layer cannot jam the bellows

Some construction sites save trouble, and the rock wool is directly tied to the corrugations with iron wire. As a result, the insulation layer is torn as soon as the expansion joint is stretched, or the wire strangles the corrugations. The correct way is to make a detachable thermal insulation sleeve, which is divided into two layers: the inner layer is filled with flexible thermal insulation material (such as aluminum silicate needle blanket), and the outer layer is made of stainless steel skin or aluminum skin as a shell, leaving a gap of 15-20mm between the shell and the bellows. If it is a large-diameter thick-wall expansion joint or a compound hinge transverse expansion joint, the influence of transverse displacement must be considered, and the shell should be designed as an overlapping sliding structure. And guess what? Many expansion joints that leak in the later stage are not treated properly at the junction, and water flows into the corrugated root along the insulation layer, resulting in stress corrosion cracking.

Specific construction process: four steps, bypassing three pits

The first step is to clean the surface of the expansion joint to remove oil and rust. Don't be lazy in this step, otherwise the insulation layer will not be stuck firmly, and it will be more troublesome to fall off later. The second step is to apply a waterproof layer on the inner insulation material (especially for outdoor open-air conditions). The third step is to install the removable jacket and fix it with stainless steel hoops. Be careful not to tighten the bolts too tightly to leave a margin for thermal expansion. The fourth step is to seal the junction between the insulation layer and the pipeline insulation to prevent moisture from penetrating. You have to remember these three pits: first, don't tie it with wire, second, don't wrap the bellows to death, and third, the junction must be sealed with silicone rubber. Last year, there was a power plant project, and the junction of the insulation layer was not treated properly. Half a year later, the root of the bellows was corroded and perforated. Changing an expansion joint and the loss of production shutdown was enough to buy several sets of insulation jackets.

Material selection: temperature has the final say

For conventional steam pipelines with temperatures below 200℃, rock wool felt is enough; However, in the case of flue gas pipeline or power station boiler, the temperature often rushes above 400℃, so aluminum silicate fiber or ceramic fiber must be used. If you are equipped with desulfurized flue gas baffle door or round baffle door (double seal), the insulation layer has to be extra considered for acid corrosion resistance, and a layer of PTFE film or anti-corrosion paint should be added to the outside. Another reminder, never use glass wool-the fiber is too brittle and will be powdered after a few vibrations. By the way, if it is a rubber compensator or rubber PTFE compensator, there is no need to insulate at all. Rubber itself is an insulation material, and if you wrap it hard, it will affect its displacement.

Practical case: Negative textbooks are more valuable than positive textbooks

Two years ago, there was a cement plant project, which used metal corrugated expansion joints in the cement industry, and the insulation layer was made into a whole wrapped type. As a result, the bellows leaked after half a year's operation. When I disassembled it, I found that the insulation cotton was full of water, and the bellows was pitted like a honeycomb. Later, it was replaced with a segmented detachable insulation sleeve, and each section was sealed with silicone rubber. So far, there has been no problem for three years. Another negative example is the general-purpose corrugated expansion joint used on gas pipelines. The thickness of the insulation layer is not enough, and the outer shell is rusted through due to condensation in winter. Therefore, don't be too troubled. The thickness should be calculated clearly, and the gap should be left enough, so that the insulation layer can really work. If you use air-cooled island vacuum pipe double-hinged expansion joint or sleeve-type pipe expansion joint, the insulation design has to be confirmed with the manufacturer-this structure with hinges and sleeves has complicated displacement direction, and the insulation jacket must be specially customized.

How to make expansion joint insulation layer? There are three cores-select the right material, leave enough gaps, and seal well. Don't think about the one-time package. Make it detachable, and it will be convenient for future maintenance. If you are not sure, ask the expansion joint manufacturer directly for the insulation scheme, and don't think about it yourself. After all, an expansion joint is tens of thousands of thousands, and it is scrapped in advance because of improper insulation. Is it distressing?

Can the expansion joint carry bending moment at all? Things the designers didn't tell you

Two days ago, I met a customer, and without covering the heat of the drawings, he threw over: "Can this expansion energy saving withstand bending moment?"-I guess you have been asked a similar question. The answer is not simply "yes" or "can't", but many designers just wait for you to give a quick word. Today, let's puncture this layer of window paper and talk about what bending moment means to the expansion joint, and why this thing is the most common pit in model selection.

Find out first: The job of expansion joint is not to carry bending moment

The original design of the expansion joint is to absorb the axial displacement, transverse displacement and angular displacement caused by thermal expansion and contraction of the pipe. The bellows itself is a flexible, thin-walled structure — think of it like the bellows of an accordion, which stretches with a gentle pull, but if you push it on the side, it immediately deflates. Explained by the concept of stiffness (for details, refer to the question and answer "Stiffness and Calculation Formula of Bellows" of this site), the bending stiffness of bellows is only a fraction or even lower than the axial stiffness. Once the bending moment exceeds the design range, it can lead to instability of the bellows (local bulge or depression), or directly tear the weld in the worst case. Therefore, letting ordinary expansion joints carry bending moments is equivalent to letting gymnasts lift weights-the professional is not right.

Where the hell does that bending moment come from? Pipeline vibrations, wind loads, earthquakes, support settlements, and even installation errors can produce bending moments. Some designers mistakenly believe that as long as an expansion joint is installed, the pipe can "automatically adapt" to all external forces. Alas, this idea is more brittle than paper.

Some expansion joints are inherently bending moment resistant materials

But then again, there are indeed expansion joints on the market that are specifically designed for bending moments. Such asCompound hinge transverse expansion jointIt converts the bending moment into a force couple through two sets of hinges, and the bellows only bear pure lateral displacement;Curved tube pressure balance expansion jointAndThe straight pipe pressure balance expansion joint uses the pressure balance structure to cancel out the internal pressure and thrust, thus allowing the bellows to remain stable when subjected to bending moment. These products have to be treasures when selecting models-you let them carry bending moments, and not only do they not lose their temper, but they do a good job.

In turn, some expansion joints are inherently "soft persimmons":Universal corrugated expansion joint、External pressure single type axial type expansion joints, they have no limiting structure or hinge inside, and the bellows are directly exposed. You let them carry bending moments? That's not trust, that's murder. Remember: Expansion joints without limiting devices can't bear bending moments, even if the designer patts his chest and says "it should be fine".

The Biggest Myth of Field Installation: Expansion Joints Are Not Fixed Brackets

I have seen too many sites where workers use the expansion joint as a fixed bracket-the pipe is not equipped with a guide bracket, and it is all relied on the expansion joint to carry it hard. And the result? The bellows is twisted and twisted, the flange surface is skewed, and finally the medium leaks before going back to the manufacturer. In practice, if there is additional bending moment in the pipeline system (such as vibration, wind load, earthquake), guide brackets or tie rods must be provided on both sides of the expansion joint. This site's question and answer "How to adjust the tie rod nut of expansion joint" and "Correct installation method of large tie rod expansion joint" make it clear: the function of tie rod and screw is to limit excessive displacement and prevent the bellows from being pulled out or crushed to death, instead of bearing bending moment. The tie rod itself is a rigid connection. If the bending moment acts directly on the tie rod, the tie rod will also deform and fail. Therefore, we must distinguish the difference between "limit" and "load-bearing" when installing.

Tsk, at this point, you may ask, "Then I installed the expansion joint with the tie rod, so I don't have to worry about the bending moment?" The answer is: the tie rod can only limit the excess axial displacement, but can't eliminate the direct effect of bending moment on the bellows. Only structures such as compound hinges can convert bending moments into force couples.

Real Case: Lessons from Cement Plant

Last year a cement factory approached us and said they usedMetal Corrugated Expansion Joints in Cement IndustryAs a result, after half a year of operation, the welding seam cracked. When we looked at it in the past, the root of the problem lies in the horizontal pipe-the lateral bending moment was not calculated in the design, and the pipe's own weight plus the wind load twisted the bellows into a twist. Later replaced withCompound hinge transverse expansion jointAnd adding guide brackets to the pipe, the problem was completely solved. This case tells us: When selecting the type, we must submit a complete pipeline stress analysis report, and don't expect the expansion joint to be packed to the end. The displacement, force and moment of each point will be indicated in the stress analysis report, so that the manufacturer can match the appropriate structure accordingly. If you throw over a simplified diagram and say, "You look at it," that's laying a mine for yourself.

To sum up a sentence: Don't pat your head, look for a manufacturer

Can it resist bending moments? Let's see what type of expansion joint it is first. If you are not sure, find the manufacturer, put out the working conditions, stress analysis reports and installation environment of your pipeline, and let professional people do professional things. There are so many models in this product list, from general purpose to pressure balance, each with its own temper-Universal corrugated expansion jointThe softest temper can only walk displacement;Compound hinge transverse expansion jointAndCurved tube pressure balance expansion jointYou can chew hard bones. Remember: the words "probably" and "probably" are ticking time bombs in engineering. You asked me can the expansion joint withstand bending moment?

Look at the model, look at the structure, see if there is a limit device. Don't ask if you can, ask if you should let it carry it first.

Two days ago, a customer called and said that the general-purpose corrugated expansion joint arrived, but the flange screw hole didn't match. After asking, he found out that the caliber he measured was the outer diameter of the wave peak, not the diameter. Anyone who has done this kind of thing on the spot knows it-welding the wrong flange, buying the wrong model, the construction period is delayed for a week, the boss scolds and the workers complain. The measurement of the diameter of the expansion joint looks simple, but many of them overturn. Exactly where to measure? Use what tool? What is the difference between different kinds of expansion joints? This article makes the doorway clear.

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

The caliber in the pipeline industry usually refers to the nominal diameter (DN), that is, the inner diameter of the pipe. However, the structure of the expansion joint determines that it can't directly measure the inner wall-the bellows has peaks and valleys, the flange has stops, and the guide tube extends a section. You take a tape measure and put a card on the crest of the wave, and the data is at least 10-20mm larger than the diameter. That's the margin left for deformation, not the caliber.

Circular metal corrugated expansion jointFor example, general-purpose corrugated expansion joint and corrugated expansion joint for power station industry, the diameter is equal to the nominal diameter of the pipeline connected to it. For physical measurement, measure the diameter between the sealing surfaces of the flange-that is, the diameter of the inner hole after removing the flange boss. Or measure the inner diameter of the connector directly. Remember: Don't measure the crest, and don't measure the outer diameter of the flange.

Rectangular expansion joints and non-metallic expansion jointsHow to measure? Metal rectangular expansion joints and rectangular non-metallic expansion joints, the caliber is actually the length × width of the rectangular channel. Take a tape measure to measure the long and short sides of the inner mouth of the flange, and pay attention to whether the four corners are right or chamfered. The frame of non-metallic expansion joints (fabric fiber expansion joints) is metallic and the caliber is also the inner frame size. Don't count the thickness of the outer skin when measuring, otherwise it will be too large. In addition, such as PTFE-lined hoses, lined with PTFE may affect the inner diameter. It is necessary to confirm whether to measure the diameter of the metal shell or the lining-usually calculated according to the actual diameter after the lining.

Measuring tools and hands-on details

Choose the right tool and save half the detour. The vernier caliper is the most accurate and suitable for small calibers (below DN200). Use a tape measure for large diameter (DN300 or above), but it must be straightened and fit the end face. Measurement position: Select the inner circle of the flange end face to avoid welds and burrs. Measure two to three directions and take the average value-the pipeline may have ellipticity, especially large-diameter thick-walled expansion joints or directly buried expansion joints. Excessive ellipticity will lead to lax seal.

Does the expansion joint come with a deflector? The inner diameter of the guide tube is generally consistent with the diameter, but the front end of the guide tube may shrink. When measuring, it should be measured from the flange surface to the inner wall of the guide tube. Don't be lazy and only measure the outer port, otherwise install it and find that the guide tube holds up against the pipeline, so rework it as well.

So what to do? If conditions permit, it is best to actually remove and measure, or check the original equipment nameplate-the model and size of the expansion joint are generally marked DNxx on the nameplate. Before buying, take a photo of the nameplate and send it to the manufacturer for confirmation, which is more reliable than your own quantity.

It is not enough to have the caliber alone, but to give all these 4 data in the selection

Caliber is just the first step. When buying an expansion joint, you must also report the connection mode (flange or take-over), nominal pressure (PN), working temperature, medium, and compensated displacement (axial, transverse and angular). For example, high-temperature axial expansion joint is used in steam pipeline, and the temperature is not reported, so the consequences of choosing the wrong material are serious. Another example is the expansion joint matched by the desulfurization flue gas baffle door. The medium is corrosive, so the sulfur content, temperature and pressure must be indicated. Also, the number of flange bolt holes, the diameter of the distribution circle, and the form of the sealing surface (convex, flat) must be provided-this directly affects the ability to match your existing pipe flange.

Do you find it troublesome? The price of trouble is that the arrival can't be loaded, the return freight is paid out of pocket, and the construction period is delayed by yourself. Thinking back, it is much more cost-effective to spend 10 more minutes writing all the parameters than tossing for a month.

Finally, let's talk about a few places that are prone to fall into pits

FirstDon't take the mounting size of the non-metallic expansion joint as the caliber. The mounting size is typically larger than the through diameter because the outer edge of the flange is covered. You report the installation size in the past, and the manufacturer produces it according to the diameter. When you install it back, the flange edge is exposed outside, and the sealing gasket is not compacted.

Second, rubber compensator or rubber PTFE compensator is soft, gently press when measuring, do not deadlift, otherwise the data is on the big side. Soft materials deform as soon as they are pulled. You measure 300mm, but in fact, the diameter is only 250mm. It is best to gently lean against it with a caliper, not hard.

ThirdWhen the old equipment is replaced, it is the most hassle-free to check the original nameplate. If you can't see the nameplate clearly, remove it to measure the inner diameter of the flange, or look for the design drawings. If it doesn't work, take the outer diameter of the pipe minus the wall thickness to estimate it-but this method has a large error and is only suitable for emergencies.

Place an order after the quantity is accurate, so as to save returning and exchanging back and forth and delaying the construction period. Remember: the diameter of the expansion joint measures the diameter, not the crest; The inner diameter is measured, not the outer diameter of the flange; Clearance is measured, not hemming size.How to measure the expansion joint diameter?The answer is one: measure the diameter of the inner hole between the end faces of the flange, the diameter of the circle, the length and width of the rectangle, and the attention of the guide tube to avoid the shrinkage. Choose a caliper or tape measure as a tool, and measure three directions to take the average. When the data is complete, the rest will be smooth.

1. Why does the food industry have "special" requirements for expansion joints? It's not just the material.

It's not just any fluid running through the food processing pipeline. Milk, juices, sauces, beer…these media require extremely high hygiene levels. Even the slightest dead angle or trace precipitate in ordinary expansion joints may contaminate the whole batch of products. From the light to the scrapping of the whole pot, from the worst to the start of product recall, the loss is easily hundreds of thousands.

The core of food-grade expansion joints is not "whether it can compensate for displacement" at all-that is a basic function, and even an expansion joint should do it. The real hard indicator is: whether food safety can be guaranteed. Behind this is a series of hard levers involved in materials, construction, surface treatment, cleaning verification, and more.

Two days ago, I met a customer who made condiments, saying that their last batch of tomato sauce was found to exceed the standard of heavy metals. At the end of the investigation, the problem was a stainless steel hose on the pipeline that was not passivated. Tsk, just this one oversight, the whole batch of goods was dumped. So don't think that "stainless steel is food grade", it's far from it.

Second, the material is the bottom line: stainless steel, PTFE or rubber? How to choose to be compliant.

Food contact materials must comply with FDA, GB 4806 series and other standards. What material to choose depends on the media characteristics and process conditions.

• PTFE-lined hose/PTFE compensator: The lining polytetrafluoroethylene (PTFE) is extremely inert, can resist acid and alkali and does not precipitate. Suitable for highly clean or corrosive food media, such as CIP cleaning solution, acidic juice, vinegar. This site'sPTFE-lined hoseAndPTFE compensatorExcellent in corrosion resistance and hygiene.
• Stainless steel metal hose (304 or 316L): Suitable for high temperature steam, dry materials or purified water. However, note that the surface roughness cannot exceed the standard-Ra ≤0.8 μ m is the bottom line, and it is best to achieve 0.4 μ m. Moreover, passivation treatment must be done, and the weld should be polished and smooth. This site'sUniversal corrugated expansion jointAndMetal hoseBoth support custom polish grades.
• rubber compensator: Food grade ethylene propylene monomer (EPDM) or silicone rubber can be used, but no plasticizer migration must be confirmed. For example, when transporting dairy products or oils, if small molecules precipitate in the rubber formula, it will contaminate the product. This siterubber compensatorAndRubber PTFE compensatorAll provide food grade material certification reports.

Some suppliers say that "stainless steel is food grade", but in fact, no passivation is done and the welds are not polished. The surface roughness is large, it is easy to hang on the wall and breed bacteria, and CIP cleaning can't wash it clean at all. So don't just look at the material grade, ask about the surface treatment and dissolved substance test report.

Third, the structural design determines the "dead zone" and "cleanliness". Don't underestimate the guide tube and the dead corner.

What are food grade expansion joints most afraid of? Hiding dirt and evil. If there are steps or gaps at the connection between the bellows and the pipe, bacteria will grow after the material remains, and CIP cleaning will not clean it. What about that? Deflectors are not optional, they are a necessity.

The inner diameter of the guide tube must be consistent with the inner diameter of the pipe, and the transition must be smooth to avoid vortex and deposition. Regarding this, this siteSpecific Function of Expansion Joint Guide TubeThat question and answer said it very clearly-to put it bluntly, it is "straighten out the flow path of the medium so that the dirt has no place to hide".

In addition, it is recommended to use concave and convex surfaces or tongue and groove surfaces for flange sealing surfaces, and cooperate with food-grade gaskets (such as PTFE coated gaskets) to prevent gasket debris contamination. Structurally, dead corners such as narrow slits and exposed threads should be avoided. And guess what? In order to reduce the cost, some manufacturers saved the guide tube. As a result, the pipeline was blocked after half a year of use by the customer. When they were disassembled, they saw that the root of the bellows was full of mold spots.

IV. Manufacturing process and testing: Materials alone are not enough, surface treatment and certification should be implemented.

Just having good materials and no corresponding craftsmanship is equal to nothing. The metal inner walls of food grade expansion joints must be mechanically polished or electrochemically polished, with a roughness Ra ≤0.8 μ m (even more stringent to 0.4 μ m), and the weld must be smoothed. The welding process should adopt argon arc welding, and do acid pickling passivation treatment to restore the passivation film on the surface of stainless steel.

Before leaving the factory, it must pass the pressure test, air tightness test, and the verification of simulated CIP cleaning. In terms of certification, domestic products can issue third-party food contact material testing reports, while export products need FDA or EU 1935/2004 certification.

V. Actual selection: What should be used in different sections of the same food workshop?

The pretreatment section of a dairy factory needs acid and alkali resistant CIP cleaning, the temperature is about 80℃, we recommendPTFE-lined hoseThe lining PTFE is corrosion resistant and does not adsorb milk fat; The filling section is a normal temperature and sterile environment.Food grade stainless steel metal hose (universal corrugated expansion joint)Polished to Ra0.6 μ m and connected with a quick-assembly clamp; The pipeline displacement of steam sterilization section is large, so selectHigh temperature axial expansion jointThe inner liner is designed as a removable structure for easy access.

You see, different locations of the same factory have different requirements. The key is to match the existing product models of this site according to the medium, temperature and cleaning frequency, rather than buying a "food grade" label with your eyes closed. There is no universal solution in the food industry. Choosing the right expansion joint in each section can not only ensure safety but also save maintenance money.