In the flue duct system of power plant boiler, the expansion joint is the key component to absorb the thermal expansion displacement of the pipeline, and the upper tile support of the flue expansion joint of power plant is an important auxiliary structure to ensure the normal operation of the expansion joint and prevent the damage of the outer guard plate. Many power plant operation and maintenance personnel often find that the outer guard plate at the expansion joint is pulled apart, deformed or even fell off during inspection, which is often directly related to the unreasonable design or lack of upper tile support. This paper will deeply analyze the structural principle, selection key points and maintenance methods of upper tile support of flue expansion joint in power plant, which will provide practical reference for engineers and technicians.
1. What is the upper tile support of the flue expansion joint of the power plant?
The upper tile support of the expansion joint of the flue of the power plant is a support device mounted on the outer guard plate of the expansion joint area, which is mainly used to bear the weight of the outer guard plate and the heat insulation layer, and at the same time allow the expansion joint to move freely in multiple directions。
During the operation of power plant, the burner and boiler body will expand and move in three dimensions: front and back, left and right, and up and down with the temperature change. If the outer guard plate at the expansion joint is not properly supported, it will cause the outer guard plate to be pulled apart or even fall off. The upper tile support of the flue expansion joint of the power plant is designed to solve this problem-it can support the outer guard while meeting the requirement of free sliding in six directions。
A typical power plant flue expansion joint upper tile support structure includes two legs and a cross brace. The supporting legs are composed of vertical supporting rods and frames, respectively welded at both side ends of the expansion joint; Both ends of the cross brace are penetrated into the frame of the two legs, and can slide freely in the frame。
2. Core functions of upper tile supports of flue expansion joints in power plants
1. Multidirectional displacement compensation
Complex thermal displacement occurs in the flue of power plant during start-stop and load change. The unique feature of the upper tile support of the expansion joint of the flue of the power plant is that the horizontal brace can realize the free sliding of front and back, left and right and up and down in the frame, and fully absorb the expansion displacement in three directions。
2. Fixation and protection of outer guard plate
The outer guard is usually covered on the outside of the insulation layer for protection and aesthetics. Without reliable support, the outer guard is prone to being pulled and cracked by thermal displacement in the expansion joint area. The upper tile support provides a stable supporting foundation for the outer guard plate through the cooperation of the legs and the cross braces.
3. Insulation layer thickness matching
The length of the vertical support rod is designed according to the thermal insulation thickness of the outer protection plate of the expansion joint of the smoke duct, which is usually 30~40mm higher than the thermal insulation thickness, so as to ensure that the support device can effectively bear load without affecting the thermal insulation effect。
4. Improve overall structural strength
The frame structure made of square steel has high strength, which can effectively resist the vibration and wind load of the outer guard plate in operation, and prolong the service life of the outer guard plate。
3. Structural design key points of upper tile support of flue expansion joint in power plant
Correct design of upper tile support of flue expansion joint in power plant is the prerequisite to ensure its long-term reliable operation. Here are the key design parameters:
1. Structural design of outriggers
- Vertical support rod: Usually made of angle iron, the lower end is welded to one side end of the expansion joint, and the upper end is welded to the frame
- Frame: Made of square steel cut, the interior space needs to accommodate the free sliding of the cross brace
- Welding quality: The welding should meet the strength requirements to avoid cracking during operation
2. Cross brace design
- Material: Machined from square steel smaller than the cross section of the frame
- Length: Matches the width of the expansion joint to ensure smooth penetration of both ends into the frame
- Sliding clearance: Proper clearance between the cross brace and the frame should be reserved to ensure free sliding and avoid excessive sloshing
3. Size matching principle
- Length of vertical support rod: determined according to the insulation thickness, usually 30~40mm longer than the insulation thickness
- Cross brace length: Consistent with the width of the expansion joint
- Frame inner diameter: slightly larger than cross brace section, reserving sliding space
Installation and Maintenance Guide
Installation Considerations
- Welding sequence: First, welding two legs on both sides of the expansion joint respectively, and then penetrating the cross brace after cooling, so as to avoid sliding stuck caused by welding thermal deformation
- Position centering: Make sure the frames of both legs are at the same level, otherwise the cross brace will be blocked when sliding
- Anti-corrosion treatment: The environment of flue in power plant is complicated, so the surface of support should be coated with anti-corrosion, especially the wet flue should be paid more attention
- Coordinate with the insulation layer: Note that the support should not destroy the continuity of the insulation layer during installation, and the length of the vertical support rod should accurately match the insulation thickness
Key points of daily inspection
| Check Items | Normal state | Abnormal performance | Treatment measures |
|---|---|---|---|
| Sliding flexibility | The crossbrace can be moved freely within the frame | Stuck, stuck | Clean up foreign matter and apply high-temperature grease |
| welding point | No crack, no desoldering | Weld cracking | Repair welding and strengthening |
| Corrosion situation | Slight surface corrosion | Severe corrosion, cross-section weakening | Replacement or antiseptic treatment |
| Deformation condition | Structural integrity | Bending, twisting | Correction or replacement |
Common Troubles & Troubleshooting
Fault 1: Cross brace sliding stuck
- Cause: Frame deformation, foreign objects caught in, or insufficient thermal expansion gap
- Exclusion: Clean foreign objects, check the frame for deformation, and expand the sliding clearance if necessary
Fault 2: Cracked welding joints
- Cause: Vibration fatigue, poor welding quality, or displacement exceeding limit
- Excluded: Re-weld and add stiffeners
Fault 3: Supports fall off
- Cause: Welding failure between vertical support rod and expansion joint
- Exclude: Check whether the expansion joint body is deformed, and reweld after repair
V. Cooperative design with other expansion joint accessories
Power plant flue expansion joint upper tile support does not exist in isolation, it needs to work in tandem with the following components:
- Expansion joint body: Supports are welded on both sides of the expansion joint, and their strength should match that of the expansion joint
- Outer guard plate: The support member carries the weight of the outer guard plate, and there should be a reliable connection between the two
- Insulation layer: Supports need to pass through the insulation layer, and heat insulation gaskets should be provided to prevent heat bridge effect
- Flue supports: The design of the supports should be coordinated with the overall support system of the flue to avoid additional stress
It is worth noting that the flue in the high-temperature area of the power plant boiler may also need to be used with flexible hanging devices. For example, flexible round steel hanging coupling devices are often used to compensate for the shortage of radial displacement of expansion joints at the high temperature furnace smoke extraction outlets of boilers。 The upper tile supports of flue expansion joints of power plants and these hanging devices together constitute a complete displacement compensation system.
VI. SUMMARY
The upper tile support of the flue expansion joint of power plant is the key structural component to ensure the long-term stable operation of the outer guard plate of the flue expansion joint area. Through the unique "leg + slidable horizontal brace" design, it can support the weight of the outer guard plate and the insulation layer, and realize the free displacement compensation in six directions of front and rear, left and right, up and down, effectively avoiding the problem of the outer guard plate being pulled or falling off。
Summary of core points:
- Structural principle: It is composed of vertical support rod, frame and slidable cross brace. The cross brace can realize multi-directional free sliding in the frame
- Key design: The length of the vertical support rod should match the heat insulation thickness (usually exceeding 30~40mm), and proper sliding clearance should be reserved between the cross brace and the frame
- Installation requirements: The welding should be firm and the position should be centered to avoid the welding thermal deformation affecting the sliding performance
- Maintenance Focus: Regularly check sliding flexibility, welding joint status and corrosion, and deal with jamming and cracking problems in time
- Systematic thinking: Cooperative design with expansion joint body, outer guard plate, heat insulation layer and hanging device can exert the best effect
For power plant technicians, during the design or overhaul of flue expansion joints, do not ignore the function of tile supports on flue expansion joints of power plants. An upper tile support with reasonable design and standard installation can significantly prolong the service life of the outer guard plate, reduce the operation and maintenance cost, and ensure the safe and stable operation of the flue system.