If the metal expansion joint is not maintained, all the money saved will have to be lost-please keep this practical guide away

I met a customer two days ago and bought usUniversal corrugated expansion jointIt was installed and used for two years, and it was never maintained. As a result, the steam pipe leaked last week, and it was shut down for three days, resulting in a direct loss of more than 100,000 yuan-how much does it cost to replace a new expansion joint? A few thousand dollars. He was so regretful that he said that if he had known earlier, he would have had a regular check-up. This makes me have to talk to you today about how important the maintenance of metal expansion joints is.

Why is maintenance more important than model selection? Don't wait for the downtime to regret it

Type selection is really critical, such as the main steam pipeline for power stationsHigh temperature axial expansion jointFor desulfurization flueNon-metallic expansion joints (fabric fiber expansion joints)If you choose the right one, you will be safe for five years. But if you don't maintain it, no matter how good the product is, it can't handle it. Take a real case: The cement kiln tail of a cement factory was usedMetal Corrugated Expansion Joints in Cement IndustryAs a result, the guide tube was worn out by dust and not treated in time, and the bellows wore out and leaked, so the whole production was forced to be interrupted. Calculate an account: the loss of an unplanned shutdown is enough to maintain all expansion joints in the whole plant for ten years. Do you say, is it worth saving that maintenance fee?

Don't think everything will be fine after installation. The metal expansion joint will repeatedly bear thermal displacement, pressure fluctuation and medium corrosion during operation, the wall thickness of the bellows will gradually decrease, the tie rod will loosen, and the guide tube will wear out-these can't be solved by type selection. Maintenance is not an additional burden, and it is the means of equipment maintenance with the highest ROI.

Don't go through the motions in daily inspection: visual, thickness measurement and recording, none of them can be missed

Many unit inspections are to send someone to the scene for a circle to see if there is no air leakage. What's the difference between that and no inspection? A real inspection needs to do three things:

• visual: Focus on whether there is rust, cracks and scratches on the surface of the bellows, and whether there are any traces of liquid accumulation at the trough. EspeciallyExternal pressure single axial expansion jointThe outer wall is prone to dust accumulation to accelerate corrosion.
• Thickness measurement: Use ultrasonic thickness gauge to measure the wall thickness of bellows, and measure the key parts (near troughs and welds) once a quarter. If the wall thickness is found to be thinned by more than 10%, it is necessary to arrange a replacement or repair welding plan. Some masters use vernier calipers to measure the change of wave height, and they can also judge the degree of fatigue.
• record: Write down the data of each thickness measurement, visual abnormality and ambient temperature to form a trend chart. Such asCorrugated expansion joint for power station industryIt is usually required to record the displacement monthly, compare the design value, and dispose of it in advance once it exceeds the alarm line.

These three points are indispensable. Guess what? Many faults appear three months before they happen, but nobody records them or compares them. When I really missed it, I didn't think of checking the records. There was not even a reference data.

Different working conditions differ greatly: Maintenance key points of steam pipeline, cement kiln tail and desulfurization flue in power station

Metal expansion joints are not one-size-fits-all. The failure modes of different working conditions are completely different, and the maintenance emphasis is also very different.

Steam pipeline of power station

High temperature and high pressure, material creep and fatigue are the main causes. Focus onCompound hinge transverse expansion jointAndStraight pipe pressure balanced expansion jointIn the weld area, check for microcracks every month. In addition, when the steam quality is poor, the water impact will damage the bellows. If abnormal noise is found, stop the machine immediately for investigation. During maintenance, it is recommended to do a pressure test every two years to confirm the sealing performance.

Cement kiln tail

High temperature (up to 1000℃ +), high dust, guide tube is a consumable part. Once the guide tube is worn out, the high-speed dusty air flow directly washes the bellows, and the life of the tube decreases by a cliff. Maintenance core: Check the thickness of the guide tube regularly, and you have to change it if you wear it off half. In additionRectangular non-metallic expansion jointIt is also common in the kiln tail, and its skin is easily ablated. If it is found to be hardened or blistered, it will be replaced immediately.

Desulfurization flue

Low temperature acid corrosion (below the acid dew point), ordinary stainless steel can't bear it. Maintenance focuses on the anti-corrosion layer, such asPTFE-lined hoseOrRubber PTFE compensatorWhether the fluorine layer is bulging or falling off. In additionDesulfurization flue gas baffle doorThe sealing surface should be cleaned and fouled regularly, otherwise it will be stuck and cause the action to fail. Here is a home-grown method: purge the flue with low-pressure steam every time the machine is shut down to reduce acid accumulation.

Other working conditions such as air-cooled island pipelineDouble hinge expansion joint of air-cooled island vacuum pipeMaintenance focuses on hinge lubrication and vacuum sealing; For directly buried pipeDirect buried (fully buried) type expansion jointIt is necessary to prevent groundwater from infiltrating the insulation layer-each has its own doorway.

The deflector is worn out? The tie rod is loose? On-site disposal scheme for common faults

The fault will not greet you in advance, but there are some quick methods to deal with it on the spot, which can last a while longer to avoid downtime.

• Guide tube wear down: If it is only partial perforation, you can use stainless steel welding electrode for repair welding, pay attention to the matching of base metal material. However, if it is a large area of wear, it must be shut down and replaced-the deflector is a wear part anyway. Refer to the function of the expansion joint guide tube in our product information, it is to sacrifice itself to protect the bellows.
• tie rod loose: This is the most common question. The loosening of the tie rod nut will cause the expansion joint to lose its restraint and the displacement to exceed the limit. Adjustment method: first confirm the structure, such asCompound straight pipe bypass pressure balanced expansion jointThe pull rod plays a position limiting role and cannot be used as a tightening device. When tightening the nut, operate symmetrically, twisting 1/4 turn each time to keep both ends balanced. Don't think of the tie rod as a stretching tool-see the Q&A "How to adjust the tie rod nut of the expansion joint" on this site for details.
• Bellows leakage: Small pinholes (less than 2mm in diameter) can be temporarily plugged with epoxy resin repair agent, and the pressure does not exceed 0.3MPa. But don't expect to repair large cracks or pieces of rust, just replace them with new ones. In case of leakage, first close the front and rear valves to reduce pressure, and then determine whether to remove and weld according to the leakage location-someLarge diameter thick wall expansion jointYou can repair welding online, but it is risky and not recommended.
• Non-metallic expansion joint skin damage: If it is a small crack, it should be repaired on site with high-temperature resistant silicone gel and glass cloth, but more than 20% of the damaged area must be replaced as a whole. Specific standards refer to the national standard JB/T 12235-2015 for non-metallic expansion joints.

On-site disposal is only temporary life-saving, and regular maintenance or replacement must be arranged for follow-up. Don't gamble your luck with "still make do with it".

The old master may not tell you all of the five local methods to prolong your life

I learned these tricks from drinking from the old fitter on the scene. They didn't cost much, but they worked.

1. Pre-stretched or pre-compressed before installationFor example, the design displacement is 100mm. During actual installation, pull or press 30-50mm in advance according to the ambient temperature, so that the bellows can work in the best deformation range. This matter has to be calculated against the design drawings, but many installation teams don't do it to save trouble.
2. Regularly lubricate tie rods and guides: Tie rod threads and spherical washers are easy to rust to death. Apply molybdenum disulfide grease once every six months to ensure free movement. Be careful not to rub oil on the bellows-some rubber parts can be corroded by oil.
3. Water accumulation in insulation layer: The insulation layer of the expansion joint on the steam pipeline is most afraid of water, and chloride ion corrosion will be formed as soon as water accumulates. It is recommended to make waterproof iron sheet outside the insulation layer and leave a drainage hole. This is the right moveSleeve type pipe expansion jointEspecially effective.
4. Avoid frequent overtemperature and overpressure: Occasionally, it is not a big problem, but if the temperature exceeds 50 degrees every day, the fatigue life of the bellows will be directly halved. You have to communicate with the process department and let them control the operation. Don't say, many old masters record the temperature curve of the expansion joint, and in turn urge the process improvement.
5. Periodically cold tighten the bellowsFor example, after the high-temperature expansion joint runs for a period of time, the bellows will produce certain plastic deformation (creep). After the machine is stopped and cooled, press the bellows back a little with a tie rod or adjustment bolt to restore its elasticity. This technique is a bit difficult, so it is recommended that experienced masters operate it, otherwise it may be overstressed.

These methods do not require additional equipment, the key is to develop a habit. To be frank, I have seen hundreds of thousands of dollars spent on importedCurved tube pressure balance expansion jointYes, as a result, it broke in two years, just because I didn't do cold tightening. Imported goods can't handle rough raising.

The product information of this site has detailed parameters of various expansion joints, such asMetal hose size comparison table、Expansion Joint Weight Table、Metal hose pressure standardCheck it when you maintain it. Don't make the wrong model. The maintenance of metal expansion joints is at ordinary times, so don't wait for something to happen before regretting it.