In the operation and maintenance of flue gas pipeline system, how to deal with the gap of flue gas expansion joint is a practical problem that technicians often face. Whether it is the platen joint of non-metallic expansion joint, the flange joint surface of metal expansion joint, or the skin overlap joint, improper treatment of any gap can lead to air leakage, water leakage, accelerated corrosion and even system shutdown. This paper will systematically explain how to deal with the gap of flue gas expansion joint from the gap type diagnosis, sealing scheme selection to construction steps, and provide an operable technical guide for on-site maintenance personnel.
1. Type and risk level of expansion joint gap
The type, location and leak severity of the flue expansion joint gap must be accurately judged before any treatment is performed.
1. By location
| Gap Type | Common Location | Leakage media |
|---|---|---|
| platen joint | Nonmetallic expansion joint skin and frame connection | Flue gas, condensate acid |
| Skin overlap seam | Non-metallic expansion joint skin splicing (large expansion joint) | Flue gas, condensate acid |
| Flange joint | Joint of expansion joint and pipe flange | Flue gas |
| Metal bellows weld | Metal expansion joint bellows longitudinal seam or annular seam | Flue gas |
| Drainage hole pipe root seam | Drainage short pipe and frame connection | Condensing acid solution |
2. Classification by leak severity
| grade | Phenomenon | Urgency | Recommendation Processing Method |
|---|---|---|---|
| Level 1 | Minor air/water percolation, no visible drip | Plannable processing | Surface sealant filling |
| Secondary | Obvious air leakage (feel windy) or dripping | Higher | Sealant + reinforcing layer injected after seam cleaning |
| three-level | Jet-like leakage, system parameter fluctuation | Emergency | Integral disassembly and reseal after shutdown |
2. Scenario 1: Joint treatment of non-metallic expansion joint pressure plate
Platen joints are the most common leakage points for non-metallic expansion joints. How to deal with the gap of flue gas expansion joint The core of this scenario is to eliminate the gap between the platen and the skin.
Causes of problems
- The pressure plate bolt is not tightened repeatedly according to the specification, and the bolt is loose after the skin is compressed
- No sealing gasket between skin and platen or ageing of sealant
- Platen deformation or insufficient cutting size of skin
Material Preparation
- High temperature resistant sealant (silicone type, temperature resistance ≥250℃)
- Fluorinated rubber sealing strip (thickness 3-5mm, width matched with pressure plate)
- Electric wrench, torque wrench
- Stainless steel spacer (for clearance compensation)
Operation Procedures
- Remove old seals: Loosen platen bolts, remove platen, and remove old sealant and aged strip
- Clean the base surface: Use a wire brush or sandpaper to clean the skin surface and the contact surface of the pressure plate to remove dust and oil
- Place new sealing strip: Continuously lay fluororubber sealing strip on the skin along the pressing plate position, and miter joint at 45°
- Apply sealant: Evenly apply high temperature resistant sealant on the surface of the sealing strip and the contact surface of the pressure plate
- Install platen: Place platen, insert bolts, manually screw in nuts
- Fractional tightening: adopt the method of "diagonal tightening and fractional tightening", the first torque is 30N·m, the second time is 50N·m, and the third time is 80N·m
- Check the seal: check for leaks after restoring the system
Precautionary measures
- Tighten bolts once in 1 month and once in 3 months after operation
- Check the sealing status of pressure plate joints every time the machine is shut down for maintenance
3. Scenario 2: Skin overlap seam treatment
The skin of large non-metallic expansion joints (width> 2 meters) is usually made of multiple pieces, and overlap joints are the weak links.
Causes of problems
- Insufficient overlap width (
- The overlap is not glued or the adhesive is aging
- Heat shrinkage of the skin causes the lap to pull apart
Material Preparation
- Skin patch of the same material (width 150-200mm)
- Fluororubber glue (two components)
- Rolling tool
Operation Procedures
- Clean the lap area: Use solvent (acetone or alcohol) to clean the 50mm area on both sides of the lap joint
- Apply glue: Evenly apply fluororubber glue on both sides of the overlap seam, and let it dry until it is not stick to your hands (about 10-15 minutes)
- Fit: Press the skin overlap and exhaust the air from center to edge with a rolling tool
- Reinforcement covering: Cover a layer of reinforcing sheet of the same material with a width of 100mm above the overlap seam, and apply the same glue to fit
- Curing: 24 hours at room temperature
- Inspection: Airtightness inspection after curing
Precautions
- Construction ambient temperature should be ≥10℃, humidity ≤85%
- The overlapping direction should be consistent with the flow direction of smoke gas (the rear piece presses the front piece to prevent smoke gas from washing the opening)
4. Scenario 3: Treatment of gap on flange joint surface
The gap treatment of flange connection is a scenario with high technical requirements in how to deal with the gap of flue gas expansion joint.
Causes of problems
- Uneven flange surface or corrosion pits
- Sealing gasket aging, compression permanent deformation
- Uneven or insufficient bolt preload
- Flange deflection caused by thermal displacement of pipe
Material Preparation
- High temperature resistant gasket (flexible graphite composite gasket or PTFE coated gasket)
- Stainless steel bolts and washers
- torque wrench
- Flange separator (if necessary)
Operation Procedures
- Remove the old gasket: Loosen the flange bolt, use the flange separator to push the flange open, and remove the old gasket
- Clean the flange surface: Use an angle grinder with a hundred impeller to polish the flange sealing surface to remove the residue and rust of the old gasket
- Check flatness: Use a straight ruler to check flatness of flange surface. If the deviation is> 0.5mm, it should be repaired or replaced
- Place new gasket: Place new sealing gasket centered on the flange face, ensuring that the bolt holes are aligned
- Fastening bolts: Evenly tighten 3 times in diagonal order, and the final torque is as designed (usually 80-120N·m)
- Hot re-tightening: After the system heats up to the working temperature, re-tighten the bolts once again
Suggestions for gasket selection
| Medium temperature | Recommended spacer | Description |
|---|---|---|
| ≤200℃ | Flexible graphite composite pad | Temperature resistance, corrosion resistance and good resilience |
| 200-400℃ | Stainless steel clad graphite pad | Reliable sealing at high temperatures |
| Flue gas is corrosive | Polytetrafluoroethylene coating pad | Excellent acid resistance |
V. Scenario 4: Treatment of welding gap of metal corrugated pipe
Cracks or pinholes appear in the weld of metal expansion joint bellows, which is a serious fault.
Causes of problems
- Weld defects (unfused, pores)
- Stress corrosion cracking
- Fatigue crack
Material Preparation
- Angle grinder
- Welding wire of the same material (e.g. ER316L, ER2209)
- Argon arc welding machine
- Permeation detection agent
Operation Procedures
- Crack Localization: Determine the precise location and length of cracks by penetration detection
- Grinding and clearing: Use an angle grinder to grind a V-shaped groove along the crack and penetrate the crack deeply
- Welding repair: Adopt argon arc welding, low current, fast welding, control the interlayer temperature ≤150℃
- Grinding and dressing: Grinding the weld seam flush with the base metal
- Permeation re-inspection: perform permeation inspection again to confirm that there are no defects
- Passivation treatment: the weld area is passivated by pickling
IMPORTANT
- Stress corrosion cracks are often more than one, so the detection range should be expanded
- The corrugated pipe with multiple cracks or repeated cracks should be replaced as a whole and should not be repaired repeatedly
VI. Emergency temporary blocking (handling without stopping)
In an emergency situation where the machine cannot be stopped, the following emergency plan can be used to deal with the leakage of the flue gas expansion joint gap.
Material Preparation
- High temperature resistant leak plugging glue stick (instant curing type)
- Stainless steel belt or throat hoop
- Acid-resistant rubber sheet (thickness 3-5mm)
Operation Procedures
- Quick Surface Cleaning: Use a wire brush to remove floating dust and rust around gaps
- Glue stick sealing: After kneading and softening the leak-plugging glue stick, press it firmly on the gap
- Rubber mat covering: Cover acid-resistant rubber sheet over the cement
- Clamp fastening: Clamp the rubber plate to the expansion joint with stainless steel belt or throat hoop
Precautions
- Only suitable for low pressure (≤5kPa) small leakage
- Temporary measures are valid for 1-4 weeks
- Must be permanently repaired at the latest scheduled downtime
VII. Preventive maintenance suggestions
After the clearance treatment of flue gas expansion joint is completed, the following measures can be taken to effectively prevent re-leakage:
- Regular tightening of the bolts: Tighten the non-metallic expansion joint once in 1 month and once in 3 months after it is put into operation, and then check it quarterly
- Patrol inspection: Visually inspect the gaps every week for discoloration and leakage traces
- Aging inspection of sealant: check whether the sealant is cracked or powdered every year, and reapply it in time
- Gasket Replacement Cycle: Flange gaskets are recommended to be replaced every 2-3 years
- Ledger record: Record the time, location, method and effect of each gap treatment
sum up
How to deal with the gap of flue gas expansion joint needs to choose the most suitable scheme according to the type, location and leakage severity of the gap:
| scene | Core Methods | Key takeaways |
|---|---|---|
| platen joint | Replacement of sealing strip + gluing + fractional fastening | Tighten bolts multiple times after commissioning |
| Skin overlap seam | Cleaning + gluing + reinforcing covering | The overlap direction is consistent with the airflow |
| Flange joint | Replacement spacer + even fastening | Thermal re-tightening cannot be omitted |
| Weld crack | Grinding repair welding + penetration detection | Multiple cracks should be replaced as a whole |
| Emergency plugging | Plugging glue stick + clamp fastening | Permanent repair during scheduled downtime |
The core of gap treatment lies in "thorough clearing, material matching, uniform fastening and regular review". One standard gap treatment ensures that the expansion joint restores its sealing performance. If you are facing complex gap leakage problems, it is recommended to entrust a professional maintenance team to deal with it to ensure the construction quality and system safety.