Flue expansion joint repair plan: from investigation to aftercare, take you step by step

1. Don't hurry to dismantle it-you have to find out which expansion joint is wrong first

There are all kinds of expansion joints in the flue. You can remove them as soon as you get started? Don't worry, see what it looks like first. Several common kinds:Metal rectangular expansion joint(Square iron box, used in large flue),Non-metallic expansion joints (fabric fiber expansion joints)(soft to the touch, like cloth),Corrugated expansion joint for power station industry(Bellows plus guide tube, the most common outlet of power plant boilers),Metal Corrugated Expansion Joints in Cement Industry(High temperature and wear resistant, often wrapped in thermal insulation cotton). AndHigh temperature axial expansion joint、Universal corrugated expansion jointWait, we have them all in the information of our website. Just look at the product photos.

The fault performance is nothing more than those: smoke leakage (smoke is visible to the naked eye), abnormal noise (crunching or howling), deformation (bellows bulging or depressed), and loose tie rod (nut dropped and tie rod swayed). Here's a quick judgment table:

• Smoke leak + abnormal noise→ The high probability is fatigue crack of metal bellows, or aging perforation of non-metallic bands.
• Deformation + tie rod skew→ It may be that the thermal displacement of the pipeline exceeds the limit, and the expansion joint is hard-pulled.
• Surface intact but smoke leakage→ Check whether the guide tube falls off, and the smoke rushes directly to the bellows.

Find out the type and fault, and the following scheme can prescribe the right medicine.

2. How to temporarily plug leakage without stopping production in an emergency

Can't afford to stop the production line? Then plug it first. In two steps:

Small cracks or minor leaks: If there is only trachoma as large as a needle hole on the metal bellows, or there is a little leakage on the edge of the non-metal expansion joint, you can make a temporary bandage with high-temperature resistant silicone cloth and stainless steel clamps. Note: Be sure to clean the ash around the leakage point before bandaging, otherwise it will not stick firmly. In addition, if the flue gas temperature exceeds 300℃, silicone cloth can't hold it, so it has to be tied with ceramic fiber blanket + iron wire.

Local breakage of non-metallic expansion joint: Find a non-metal ring belt of the same material (our website hasNon-metallic expansion joint (fabric fiber expansion joint)Stock material), cut into a patch larger than the hole, glue it with high-temperature-resistant glue, and fix it with stainless steel bars and bolts on the outside. Note: The patch should cover the hole at least 50mm, otherwise it will crack again after a convulsion.

⚠ ️Safety reminders: High-temperature smoke burns are no joke! The front and rear baffle doors of the flue must be closed in place before starting. For example, if you haveDouble-sealed single-axis circular baffle doorOrFlue gas baffle doorConfirm that the sealing surface is completely closed, and it is best to hang a lock again to prevent others from misoperating. If installedElectric plug-in insulation doorOrManual plug-in insulation doorAlso shut down first, so that there is no pressure in the flue.

3. Select a reasonable repair or replacement scheme according to the type of fault

Temporary plugging is a delay, and it has to be changed. Say in a few scenarios:

① Fatigue crack of metal bellows: Direct replacement. When selecting, you should match the original design parameters-caliber, wave number, material (304 or 316L), pressure level, and don't buy it blindly. Of our websiteCorrugated expansion joint for power station industryAndMetal Corrugated Expansion Joints in Cement IndustryAll have standard models, just report to customer service according to the original nameplate.

② Aging and damage of non-metallic band: You can change only the ring belt, or you can change the whole beltNon-metallic expansion joint (fabric fiber expansion joint)。 Partial replacement saves money, but it should be noted that the thermal expansion coefficients of the old and new bands may be different, so it is recommended that the whole replacement is more worry-free.

③ Deformation and failure of tie rod or nut: Check firstHow to adjust the tie rod nut of expansion joint(Refer to Article 12 of our Q&A). If the tie rod is already bent, then replace it with a new one directly. The nut slipped? Change the high-strength nut, tighten it and apply anti-loosening glue.

④ The guide tube falls off: Re-weld, or replace with a new guide. The function of the guide tube is to block the high-speed flue gas from directly washing the bellows (Article 7 of our question and answer is very clear), so be sure to align with the center when welding, and don't weld off.

In addition, if the corrosion is serious (such as acid dew point corrosion in desulfurization flue), it is recommended to upgrade the material directly: usePTFE-lined hoseOrPTFE compensator, much stronger corrosion resistance.

4. Key steps in construction operation-do it without making mistakes

Okay, the plan is settled, start changing. In order:

1. Mark original position before removal: Use a marker to draw a reticle on the flange and pipe, or punch a hole in the bolt hole. Why? Aligning these marks when installing new expansion joints can save a lot of effort.
2. Pay attention to the release of pre-tightening force when removing bolts: First loosen the two diagonal bolts, let the stress release slowly, and then remove the rest of the bolts. Don't dismantle it all at once, it will easily deform the flange.
3. Precautions for hoisting old expansion joints: Find a suitable hanging point. Most expansion joints are not heavy, so just use a hoist. But likeLarge diameter thick wall expansion jointOrExternal pressure single axial expansion jointThis kind of big guy, you have to use a forklift or crane. The hoisting belt should cover the trough, not the bellows.
4. New expansion joint installation: Notice the direction of the arrow!The direction of the arrow of the expansion joint refers to the direction of the medium flow(Article 10 of our question and answer), if the deflector is installed backwards, it will take a ride and accelerate wear. The direction of the guide tube is also consistent with the direction of the smoke, so don't turn it backwards.
5. Adjustment of tie rod nut: Refer to Article 12 of Q&A. Simply put, the nut should not be screwed to the end during installation, leaving the amount of pre-tension or pre-compression. How to calculate the amount of pre-stretch? Look at the cold tightness value on the design drawings. If there is no drawing, generally take half of the thermal displacement of the pipeline. For example, if the thermal displacement is 40mm, you will adjust the tie rod nut to the position of pre-stretching 20mm.

Check the flange surface before installing the flange. Is there any raised welding nodules or rust on it? Sand flat with an angle grinder. Don't pry the bolt hole hard, you can use a jack to jack it. Don't wear hard with stress, and when the time comes, the smoke leaks to you to doubt your life.

V. Inspection and trial operation after completion of repair

Finished installation does not mean finished, it has to be accepted. Inspect the appearance first: see if there is any leakage in the weld? Are the bolts tightened by torque? Are the tie rod nuts in place?

Then test for pressure or leak. Low-pressure flue gas pipelines (such as atmospheric flue) can be hit with wind pressure: use compressed air to hit 0.1-0.2MPa, and spray soapy water to see if there are bubbles. High-pressure pipelines (such as the main steam pipeline of power stations) must be tested under hydraulic pressure according to the specifications, and the pressure should be 1.5 times the design pressure, and the pressure should be kept for 30 minutes. Note: Drain the water clean after the hydraulic test to prevent freezing in winter.

Monitoring after the final drive. Record the data once a day from the first to seventh day of driving:Temperature, displacement, vibration values。 If you find abnormal displacement (such as the expansion joint being straightened) or excessive vibration, stop the machine quickly for inspection. In addition, if you have the matching on siteElectric plug-in insulation doorOrRound Flap Door (Double Seal)Remember to do the linkage test: close the baffle door, and then start the fan to see if there is any air leak. Use a plastic bag to cover the outlet of the baffle door. If the bag bulges and the seal is not tight, the baffle door has to be repaired after the expansion joint problem is eliminated.

6. Preventive maintenance-how to make the next maintenance come later

Sweat more in peacetime and bleed less in wartime. Look at three points in daily inspection:

• Non-metallic expansion joint: Is there any aging cracking? Shine it with a flashlight, and record the location if you find a tortoise crack.
• Guide tube for metal bellows: Worn or not? Take a mirror and stick it in. If it is more than half the wall thickness, it will be ready to be replaced.
• tie rod: Is there any rust? Are the nuts loose? Screw the loose nut once a month.

Clean up dust accumulations regularly. Especially the cement industry andDesulfurization flue gas baffle doorArea, ash and gypsum slurry are prone to clumping and jamming the displacement of the expansion joint. Blow with a high-pressure water gun or compressed air, don't use a hard shovel.

Stop the furnace for inspection at least once a year. Focus onRectangular expansion jointAndHigh temperature axial expansion jointSurface cracks can be inspected by penetration testing (PT).

Finally, establish a repair file. Each time what model of expansion joint is changed, the date of installation is recorded. Next time it breaks again, check the files to know what specifications to buy, and you don't have to go to the site to measure the size again. Is that the truth?