In wet desulfurization systems, flue gas expansion joint water leakage is one of the most common and troublesome equipment failures. Whether it is a non-metal skin expansion joint or a metal expansion joint, once leakage occurs, it can cause ground pollution and pungent acid mist, and in the worst case, it will force the unit to reduce the load or even shut down for treatment。 This paper will systematically explain how to deal with the leakage of flue gas expansion joint from the leakage mechanism, cause analysis to the treatment plan, and help the operation and maintenance personnel to quickly locate the fault and take effective measures.
1. The harm and urgency of water leakage of flue gas expansion joint
Flue gas expansion joint water leakage is not a simple "water seepage" problem. The flue gas temperature after desulfurization usually drops to 45-55℃ and contains a large amount of saturated water vapor and corrosive media such as SO₂, SO₃, Cl⁻¹。 When leakage occurs in the expansion joint:
- Corrosive acid water spillage: Leaked condensate can have a pH as low as 2-3, causing severe corrosion to equipment platforms, steel structures and ground.
- Environmental risks: Pungent acid fog and visible "waterfall" water leakage can easily lead to environmental complaints.
- Equipment interlocking damage: Acid water penetrates into the interlayer of the skin of the expansion joint or the bolt hole, which will accelerate the corrosion failure of the fixture and lead to the expansion of leakage。
- Potential safety hazards: Treatment of leakage points in high-temperature flue areas, there are risks of scald, poisoning and limited space operation。
Therefore, once signs of flue gas expansion joint leakage are found, the cause must be analyzed immediately and targeted measures must be taken.
2. Three root causes of expansion joint leakage
1. Structural design defect: groove water accumulation effect
This is the core cause of non-metallic expansion joint water leakage. When the non-metallic expansion joint is installed with the skin, an annular groove will naturally be formed between the pressure plate and the skin。 When the unit is running, the condensed acid water in the wet flue gas accumulates in this groove and cannot be discharged naturally. Under long-term immersion, acid water causes leakage through the following paths:
- Slowly penetrates the skin fabric layer and corrodes the internal insulating cotton
- Infiltrating through gaps in platen bolts, corroding screws resulting in loosening or breaking
- Acid water flows out from the broken bolt hole or the damaged skin, forming a "small waterfall" phenomenon
Typical performance: Leakage starts after 1-2 years of operation, and leaks again in a short time after replacing the new skin.
2. Improper material selection
In order to reduce the cost, some manufacturers choose non-corrosion-resistant silicone rubber as the skin lining layer. Silicone rubber is rapidly aging and brittle in acidic environment, resulting in acid water contacting the platen bolt directly after the inner layer is damaged。 In addition, the 316L stainless steel expansion joint has an average lifetime of no more than two years in wet flue gas with high Cl⁻¹ concentration。
3. Installation and maintenance defects
- The bolts are not repeatedly tightened: the non-metallic expansion joint pressure plate is 4-6 meters long. After one-time tightening, the distal bolts will loosen due to skin compression deformation。
- Missing or worn deflectors: Causes dusty smoke to directly scour the bellows or skin inner layer.
- Too fast start-stop speed: drastic temperature changes make the expansion joint subject to alternating stress, accelerating fatigue cracking。
3. Quick diagnosis of water leakage types
| Water leakage phenomenon | Probable cause | Urgency |
|---|---|---|
| Water seepage on the skin surface, no obvious rupture | Grooved water penetrating fabric layer | Medium, need to plan processing |
| Dripping water at pressure plate bolts | Bolt loosening or corrosion fracture | High, need to be fastened or replaced |
| Skin obviously damaged, acid water spray | Mechanical damage or high temperature breakdown | Emergency, need to be shut down |
| Metal expansion joint weld leakage | Stress corrosion cracking | High, need repair welding or replacement |
| Flange face leakage | Broken glass flakes, corroded bolt holes | High, needs to be repaired overall |
IV. Rapid repair and radical cure plan
Scheme 1: Temporary leak plugging treatment
For non-emergency flue gas expansion joint water leakage, polymer sealing material can be used for temporary plugging:
- Clean up dust accumulation and loose anti-corrosion layers around leakage areas
- Welding repair of corroded and perforated metal framework
- Use highly elastic tung oil gel or special plugging cement to fill grooves and cracks
- The surface is sealed with flexible glass flakes for corrosion protection
This protocol can be implemented without shutdown or short shutdown conditions and can be maintained for 6-12 months after treatment.
Option 2: Radical repair-groove filling technique
To fundamentally solve the flue gas expansion joint water leakage, it is necessary to eliminate the groove water accumulation this root source. The mature process scheme is as follows：
- Shutdown cleaning: remove the dust accumulated around the expansion joint and cut the original damaged skin
- Skeleton repair: Clean up floating dust of metal frame and weld reinforcement of corroded parts
- Bottom layer anti-corrosion: brush highly elastic tung oil gel on the bottom of the groove
- Fill the sealing layer: fill in high-temperature and corrosion-resistant closed-cell foamed butyl rubber filler (compression ratio 7:1), and compact in layers
- Surface sealing: The groove is completely smoothed with highly elastic tung oil gel, and the thickness is controlled at about 5mm
- Perimeter strengthening: Flexible glass flakes are used to prevent corrosion at the joints around the expansion joints, with a thickness ≥3mm
Key advantages: After filling the groove, acid water cannot accumulate, which fundamentally eliminates the penetration path, and the filling material is elastic, which does not affect the normal expansion and contraction function of the expansion joint.
V. Preventive maintenance recommendations
- Regular tightening of bolts: Re-tighten the non-metallic expansion joint pressure plate bolts every time the machine is shut down for maintenance
- Check water accumulation in grooves: Check the expansion joint for abnormal water seepage through temperature measurement or observation hole during operation
- Control start-stop rate: avoid sharp temperature change and reduce thermal stress shock of expansion joint
- Establish a ledger: record the time, location and treatment method of each leak, and provide a basis for subsequent selection