In mining, metallurgy, electric power, chemical industry and other industries, the high-speed flowing medium in flue gas pipeline often contains a large amount of dust and hard particles. These "invisible killers", like sandpaper, continuously scour the inner wall of the expansion joint, resulting in the wear of the guide tube and the failure of the bellows. So, how to make the expansion joint wear-resistant? This paper will systematically analyze the four core technical schemes of wear-resistant treatment of expansion joints for you.
1. Challenges of high-speed dust-containing conditions to expansion joints
In the flue gas system of coal-fired power plants, cement plants, iron and steel smelting and other industries, the medium flow rate in the pipeline is high, the dust content is large, and the erosion and wear of the expansion joint are extremely serious. Take the dust removal pipeline of iron and steel plant as an example. Due to the serious corrosion of dust to the pipe wall and the fast wind speed in the pipe, a new corrugated expansion joint will often be damaged after only 3-4 months' service life。
The core of the problem of how to make the expansion joint wear-resistant lies in how to protect the key structures inside the expansion joint-especially the guide tube-from the direct scour of high-speed dusty air flow. At present, there are four main technical paths in the industry: ceramic lining technology, surface surfacing technology, special wear-resistant coating/lining technology and structural optimization design.
2. Scheme 1: Ceramic lining technology-making "hard" with "hard"
Ceramic materials have extremely high hardness and wear resistance, so it is one of the most direct and effective means to solve the abrasion problem by applying it to the inner wall of expansion joint.
1. Wear-resistant ceramic sheet/tube patch
Technical principle: Paste or inlay wear-resistant ceramic sheets (such as alumina ceramics and silicon carbide ceramics) on the inner wall of the guide tube of the expansion joint, and use the high hardness of ceramics (Mohs hardness ≥9) to resist material erosion.
Practice: A ceramic-lined compensator is provided with a ceramic protective layer on the inner wall of a flow guide tube, which can be a wear-resistant ceramic sheet, a wear-resistant ceramic tube or a self-propagating ceramic layer. This technology solves the problem that the traditional metal guide tube is easily worn and failed under the action of high-speed gas-solid two-phase medium。
2. Chemically sintered integrally formed ceramic layer
Technical principle: Chemical sintering technology is used to "seed" ceramic materials on the surface of metal substrate to form a dense ceramic layer, which is seamless compared with traditional patches.
Technical advantages: The integrally formed wear-resistant metal bellows expansion joint, the inner wall of the connecting pipe and the inner wall of the guide pipe are integrally formed by chemical sintering method and close to the ceramic layer. Because the ceramic layer is integral and has a smooth surface, local wear caused by gaps between the patches is avoided, and the wear resistance is further improved。
3. Ceramic liner sintering molding
Technical principle: Independently sintered molded ceramic liner, installed inside the expansion joint through special structure.
Process characteristics: The wear-resistant ceramic expansion joint is made of ceramic liner by sintering ceramic matrix composite material, which has high sintering density, which helps to improve the wear resistance, corrosion resistance and weather resistance of the expansion joint. The ceramic liner pipe and the end pipe are separated by rubber sleeves to avoid rigid contact rupture due to different thermal expansion and contraction properties。
3. Option 2: Surface Surfacing Technology-Balance between Cost and Efficiency
Technical principle: Wear-resistant alloy layer is welded on the inner wall of the expansion joint pipe to resist wear by increasing the hardness and thickness of the metal surface.
Applicable scenario: It is especially suitable for the transformation of metal expansion joints that require both high temperature resistance and wear resistance.
4. Scheme 4: Structural Optimization Design-Reducing Scour from the Source
In addition to materials and coatings, reasonable structural design is also an important means to realize the wear resistance of expansion joints.
1. Design of guide tube (lining tube)
The guide tube is the first line of defense to protect the bellows, which directly withstands the medium erosion. Key points of wear resistance design include:
- Extended design: Both ends of the guide tube are appropriately extended, and the coverage is wider
- Free end design: One end of the guide tube is fixed and the other end is free, allowing thermal expansion displacement
- Clearance control: Keep an appropriate clearance (5-10mm) between the guide tube and the bellows
Patent verification: The wear-resistant titanium alloy expansion joint is provided with a guide pipe in the inner cavity of the bellows, the left end is welded and fixed to the left connecting pipe, the right end is set as a free end and extends into the inner cavity of the right connecting pipe, and ceramic fiber filler is filled between the bellows and the guide pipe。
2. Annular spacer design
An annular spacer is arranged at the gap between the guide pipe and the connecting pipe, which can effectively prevent fine particles from entering the cavity of the bellows and prevent dust accumulation and wear inside the bellows。
5. How to choose the most suitable wear-resistant scheme?
The answer to how to make the expansion joint wear-resistant depends on the specific working conditions. The following table is available for selection reference:
| Operating condition | Recommended Protocol | Core Strengths |
|---|---|---|
| High temperature (> 400℃) + dusty | Ceramic liner/ceramic liner | High temperature resistance, high hardness and long life |
| Medium temperature (80-400℃) + abrasive dust | Garlock ABRA-SHIELD ™ | 50% better wear resistance than EPDM |
| Low temperature ( | Rubber expansion joint (type ERV-BR) | Seamless integral molding, high wear resistance |
| Metal Expansion Joint Retrofit/Repair | Inner wall surfacing wear-resistant layer | 3-4 times longer life |
| Extreme high temperature and high pressure + dust | Titanium alloy expansion joint + ceramic fiber filler | High temperature, high pressure and wear resistance |
| Gas-solid two-phase flow (high-speed dust) | Composite scheme of guide tube + ceramic coating | Dual protection to reduce scouring from the root |
INDUSTRY DEVELOPMENT TRENDS
With the development of industrial media in the direction of "high temperature, high pressure, high wear and strong corrosion", the wear-resistant technology of expansion joints shows three trends: composite material, structural integration and intelligent monitoring:
- Composite materials: Single metal has been difficult to meet the requirements, and materials such as ceramic titanium alloy and special rubber are more and more used in composite applications
- Structural integration: Technologies such as chemically sintered ceramic layers and one-piece molded rubber liners eliminate gaps and weak spots
- Condition monitoring: Some high-end expansion joints began to integrate online monitoring function to feedback the inner wall wear status in real time