In the operation and maintenance of boiler flue gas system, how to disassemble and assemble boiler flue gas expansion joint is a practical problem that maintenance personnel often face. Whether it is the aging replacement of non-metallic skin or the overall replacement after corrosion failure of metal expansion joint, the standardized disassembly and assembly process is directly related to construction safety, maintenance quality and service life of equipment after operation. This article will systematically explain how to disassemble and assemble the boiler flue gas expansion joint from the preparation work, disassembly steps, installation points to acceptance criteria, and provide an operable technical guide for on-site maintenance personnel.
Preparation before disassembly and assembly
1. Confirmation of operating conditions
Before disassembling and assembling the boiler flue gas expansion joint, the following conditions must be confirmed:
- System isolation: The boiler has been stopped, the flue has been cut off, and the upstream and downstream equipment has been installed with blind plates or plug-in plates
- Temperature drops to ambient temperature: It is strictly prohibited to work under high temperature to prevent scalding and thermal stress deformation
- Internal gas replacement: The flue gas has been evacuated, the oxygen content has reached the standard (≥19.5%) after testing, and there are no toxic and harmful gas residues
- Work ticket handling: has obtained limited space work ticket, hot fire ticket (if welding is required), high altitude work ticket, etc
2. Preparation of tools and materials
Prepare the corresponding tool according to the expansion joint type:
| Tool Category | Metal expansion joint | Non-metallic expansion joint |
|---|---|---|
| Disassembly and assembly tool | Wrenches, sockets, cutters, jacks | Electric wrenches, screwdrivers, platen crowbars |
| Hoisting equipment | Hand-pulled hoist, lifting belt, lifting lug | Hand-pulled hoist, hoisting belt |
| Measurement tool | Tape measure, level ruler, vernier caliper | Tape measure, level ruler |
| Replacement of spare parts | New Bellows Assembly | New skin, insulating cotton, bolts |
3. Inspection of new spare parts
The new expansion joint or skin must be unboxed prior to installation:
- Check whether the model, specification and pressure level are consistent with the design
- Check the appearance for transportation damage and deformation
- Verify that the flow direction is clearly identified
- Check whether bolts, gaskets and other accessories are complete
2. Disassembly steps
1. Record the original state
Before disassembly, the following information should be recorded to provide a reference for installation:
- Distance between expansion joint and fixed bracket and guide bracket
- Is there a pre-bias or cold tight value
- Flow direction marking direction on expansion joint body
- Take a photo to preserve the original installation status
2. Remove constraints
- Remove the connecting bolts at both ends of the expansion joint (flange connection) or cut the weld (welded connection)
- For non-metallic expansion joints, use an electric wrench to remove the pressure plate bolts in turn
- Note: If the expansion joint has a transport rod and has not been removed before, it should be removed together
3. Hoisting and disassembly
The key link of how to disassemble and assemble the boiler flue gas expansion joint is the hoisting operation:
- Set a lifting point above the expansion joint, and hang the hand-pulled hoist
- Tie the hoisting belt to the expansion joint frame or lugs, not to the bellows or skin
- Lift slowly until the sling is stressed, and continue lifting after confirming the balance
- After removing the last connection, remove the old expansion joint from the flue
4. Clean up the interface
- Remove old gaskets, rust and debris from pipe flanges
- Polish the welded interface to expose a metallic gloss
- Clean up the dust accumulation at the installation position of the expansion joint
3. Installation steps
1. Frame repair (non-metallic expansion joint)
For non-metallic expansion joints with skin replacement, the metal frame should be repaired before installing the new skin:
- Check the frame for corrosion and deformation
- Polishing and removing rust on the corroded part
- Apply anti-corrosion coating (glass flake cement, thickness ≥2mm)
- Replace damaged platen bolts
2. Expansion joint in place
- Lift new expansion joint to installation position
- Adjust the direction according to the recorded direction mark to ensure that the small end of the guide tube is facing the direction of flue gas flow
- After initial placement, check the levelness with a level ruler, deviation ≤3‰
3. Connection and Fixation
Flanged connection:
- Place new sealing gasket (high temperature resistant asbestos pad or PTFE pad)
- Insert bolts, manually screw nuts
- Evenly tighten 2-3 times in diagonal order, and the final torque is according to the design requirements
Welding connections:
- Fixed by spot welding, corrected position and then fully welded
- When welding, jump welding method is adopted to control the interlayer temperature and prevent overheating deformation
- Clean the weld slag after welding and check the appearance of the weld
4. Non-metallic expansion joint skin installation (if applicable)
For the case of only replacing the skin, the installation steps of how to disassemble and assemble the boiler flue gas expansion joint are as follows:
- Lay new insulating cotton (aluminum silicate fiber cotton) in the frame, the thickness is as original
- Lay the new skin on the frame to ensure even margin all around
- Install platen, insert bolts
- Repeated tightening by "diagonal tightening and fractional tightening", torque 50-80N·m
5. Drain hole setting
For horizontally installed expansion joints, drainage holes (DN25-DN65) shall be provided at the lowest point of the frame, and dust-proof nets shall be installed.
6. Transportation Tie Rod Handling
After installation, the transport protection tie rod must be removed (the positioning limit tie rod must not be removed) so that the expansion joint can be expanded and contracted freely.
Inspection and acceptance after installation
1. Dimensional review
- Check that the expansion joint installation length is consistent with the design
- Verify that the distance between the expansion joint and the adjacent bracket meets the requirements of the drawing
2. Sealability Check
- Perform airtightness test after system restoration
- Apply soapy water or use a leak detector around the expansion joint
- No bubble or alarm signal is qualified
3. Bolt retightening
The pressure plate bolts need to be tightened once one month and three months after the non-metallic expansion joint is put into operation, because the skin compression will cause the bolts to loosen.
4. Data Archiving
Deposit the following data into the device ledger:
- Replacement Date
- New expansion joint models, specifications, manufacturers
- Installation Photos
- Acceptance Record
Safety Precautions
1. Height work protection
- Working height exceeding 2 meters must wear a safety belt and hang it at a reliable anchor point
- Set up a stable work platform or use a lift truck
2. Hoisting safety
- It is strictly prohibited to stand under hanging objects
- The hoisting belt shall not be tied to the bellows or skin
- Check that the lifting point is firm before lifting
3. Limited space operations
- Gas detection before entering flue (oxygen, CO, H₂S)
- Set up special supervision to keep communications open
4. Welding safety
- Clean up surrounding flammable materials
- Equipped with fire extinguishing equipment
- Protect bellows or skin during welding to prevent damage from welding slag splashing
VI. Frequently Asked Problems and Handling
| Question | Probable cause | Treatment method |
|---|---|---|
| New expansion joint won't be in place | Misalignment or deformation of pipe flange | Adjust pipe supports, or machine transition stub |
| Leaks immediately after installation | Gasket not straightened or bolt not tightened | Readjust the gasket and tighten the bolts evenly |
| Frequent loosening of bolts | Failed to tighten multiple times as specified | Regularly tighten and add spring washers after commissioning |
| Abnormal deformation of expansion joint | Transport tie rod not removed | Inspect and remove transport tie rods |
sum up
Mastering how to disassemble and assemble the boiler flue gas expansion joint is the basic skill of boiler flue gas system maintenance. The standardized disassembly and assembly process shall follow the principle of "preparation before disassembly, recording the original state, cleaning the interface, standardized installation and strict acceptance":
- Spare: System isolation, complete tool spare parts, new parts inspection qualified
- Disassembly: record the original state, release the constraint, safely hoist, and clean up the interface
- Installation: frame repair, direction confirmation, even tightening, drainage holes set
- Inspection: Dimensional review, airtightness test, bolt re-tightening, data filing
One standard disassembly and assembly operation can ensure that the new expansion joint reaches the designed service life. If you still have questions about the disassembly process or need professional technical guidance, it is recommended to entrust a qualified maintenance team to implement it to ensure the construction quality and operation safety.