1. Importance of pressure plugging of flue expansion joint

In continuous production systems such as power plants, chemical industry and metallurgy, flue expansion joints are subjected to high-temperature flue gas erosion, alternating thermal stress and corrosive media for a long time, so it is difficult to completely avoid failures such as bellows cracking and weld leakage. Once a leakage occurs, the traditional treatment method needs to be repaired after shutting down the furnace and cooling, resulting in millions or even tens of millions of production losses. The pressure plugging technology of flue expansion joint is an emergency maintenance technology that can quickly plug the leakage point under the condition of not stopping the machine and not reducing the load. It can eliminate leakage hazards within a few hours, avoid unplanned shutdowns, and ensure production continuity and environmental protection emission standards. Because the medium in the flue is mostly high-temperature flue gas (up to 500-680℃) and contains corrosive components such as SO₂, the operating environment of pressure plugging is harsh and the technical requirements are extremely high. This paper will systematically expound the complete scheme of pressure plugging technology from technical principle, construction method to safe operation.

2. Overview and scope of application of pressure plugging technology

2.1 Technical Principles

The core principle of pressure plugging technology of flue expansion joint is: under the condition of non-stop, with temperature and pressure, a new sealing structure is established outside the leakage point by using special sealing materials and fixtures, so that the leakage medium is confined in the sealed cavity, so as to achieve the purpose of leakage stop. This technology does not change the original equipment structure, does not involve hot operation, and is especially suitable for flammable and explosive environment.

2.2 Scope of application

The pressure plugging technology of flue expansion joint can be applied to the following working conditions:

For flue expansion joint, the typical working conditions are: temperature 150-680℃, pressure-5kPa ~25kPa, which is completely within the applicable range of pressure plugging technology.

3. Leakage type diagnosis and scheme selection

3.1 Common Leak Types

Before implementing the pressure plugging technology of flue expansion joint, the leakage type must be accurately judged:

3.2 Methods for rapid diagnosis in the field

To carry out pressure plugging technology of flue expansion joint under high temperature and complex working conditions, it is first necessary to quickly lock the leakage point:

• Visual inspection: Observe the direction and pattern of smoke emission
• Infrared thermography: abnormal temperature near the leakage point, showing obvious hot spots
• Listening positioning: High pressure leakage accompanied by sharp howling sound

4. Main construction methods of leakage plugging with pressure

4.1 Injection sealing method

Injection seal is one of the most widely used techniques for pressure plugging of flue expansion joints. The principle is that a special fixture is installed on the periphery of the leakage point to form a sealed cavity, and then the sealed injection agent is injected into the cavity through the injection hole, and a new sealing structure is formed after the injection agent is solidified.

Construction steps:

1. Design and machine the fixture according to the shape of the expansion joint and the leakage location
2. Install the fixture on the periphery of the leakage point, and be careful to avoid hinges and other affecting the structure
3. Connect high-pressure injection gun to inject sealed injection sequentially
4. Check the sealing effect after the injection is cured

4.2 Fully enclosed jacket plugging method

For the circumferential crack of high temperature SO₂ flue expansion joint, a fully enclosed jacket plugging structure can be adopted. The main points of this approach are:

1. Welding annular ribs on pipes on both sides of leakage expansion joints
2. The fan-shaped cover plate is arranged along the circumferential direction of the expansion joint to form a sealed space with the annular rib plate
3. The expansion joint is completely sealed so that the smoke can not escape

This method is convenient for on-site construction without shutdown, and is especially suitable for the repair process of SO₂ high-temperature smoke pipe leakage.

4.3 Steel strip binding method

For leaks with small cracks (length ≤50mm, width ≤2mm), the steel strip binding method can be used:

1. Cover cracks with high temperature resistant sealing gaskets
2. Tie and fasten with stainless steel strip along the circumferential direction of the expansion joint
3. Install semi-circular sleeves on the outside of the gasket if necessary

This method has fast construction speed and is suitable for temporary plugging in emergency situations.

4.4 On-line plugging of non-metallic expansion joints

For the leakage of non-metallic expansion joints in desulfurization system, there is also a mature online treatment scheme for pressure plugging technology of flue expansion joints:

1. Clean up dirt and residue around the leakage area
2. Apply high-temperature and corrosion-resistant adhesives (such as high-temperature-resistant steel plate acid-resistant water-blocking adhesives)
3. With instantaneous curing agent, the material can be cured quickly
4. For large damage, it can be covered with reinforcing cloth and applied twice

Special attention should be paid to the fact that the leakage of non-metallic expansion joints is often related to acid accumulation in grooves and screw corrosion. After online plugging, a planned shutdown should be arranged as soon as possible for complete replacement.

5. Key points of safe operation

5.1 Personal Protection

The working environment of flue expansion joint pressure plugging technology is mostly high temperature, toxic and limited space, so the following protective measures must be strictly implemented:

• Wear heat-insulating clothing, ear protectors, and high-temperature gloves
• Wear a positive pressure air respirator
• Set up full-time guardians to keep communication open
• Perform risk identification and JSA analysis prior to operation

5.2 Job Management

• Apply for thermal work tickets and restricted space work tickets before operation (if involved)
• Confirm composition of leaked media and assess toxicity and explosion risk
• Set up a safe working platform to prevent falling from height
• Equipped with fire extinguishing equipment and prepared for emergencies

5.3 Quality Control

• The fixture size should accurately match the actual situation on site
• The sealed injection shall be used in accordance with the temperature range specified in the product instructions
• After leak plugging is completed, 24-hour tracking and monitoring shall be carried out to confirm that there is no secondary leakage

VI. Treatment suggestions after temporary blocking

It should be emphasized that the pressure plugging technology of flue expansion joint is essentially an emergency maintenance means, which cannot replace permanent repair. After successful closure:

1. Include the leakage situation in the equipment defect management ledger, and indicate the leakage location, treatment method and current status
2. Operation personnel check at least once per shift to record the development of leakage
3. Develop a planned shutdown replacement or overhaul plan to avoid turning into a larger accident
4. A planned shutdown shall be scheduled for permanent repair within 3 months after the plugging

VII. Common problems and countermeasures

VIII. Summary

The pressure plugging technology of flue expansion joint is a mature emergency maintenance means, and its core can be summarized as follows: "clamp for injection sealing, jacket wrapping is completely closed, steel strip bundling is quickly treated, and non-metal adhesive is used". In actual operation, the most suitable plugging method should be selected according to the leakage location, crack shape, medium temperature and pressure-injection sealing or steel strip bundling is recommended for bellows cracks, full enclosure jacket structure is suitable for circumferential cracks, and non-metallic expansion joints are plugged by adhesive coating. In terms of safety, the pressure plugging operation in high-temperature flue gas environment must strictly implement the requirements of personal protection and operation management, wear heat insulation clothing and positive pressure respirator, and apply for corresponding operation tickets. It should be emphasized that leak plugging under pressure is a temporary emergency measure rather than a permanent repair plan. After successful plugging, it should be included in the equipment defect ledger, a planned replacement plan for furnace shutdown should be formulated, and the permanent repair should be completed within 3 months. By standardizing and implementing the pressure plugging technology of flue expansion joint, the leakage risk can be effectively controlled and the huge economic loss caused by unplanned shutdown can be avoided under the premise of ensuring the safety of personnel.