Metal Spiral wound gaskets are widely recognized as high-performance sealing components in industrial pipeline systems and equipment flanges. Their unique composite structure and material combinations enable them to adapt to harsh working conditions such as high temperature, high pressure, and medium corrosion. Below is a detailed introduction from the perspectives of **material selection**, **structural design**, and **chemical properties**:
## 一、Material Selection of Metal Spiral wound gaskets
The performance of Metal Spiral wound gaskets depends largely on the rational matching of two core materials: the **metal winding strip** (providing structural support and strength) and the **filler material** (ensuring sealing performance). The selection of materials is determined by factors such as working temperature, pressure, medium type, and corrosion resistance requirements.
### 1. Metal Winding Strip Materials
The metal strip serves as the "skeleton" of the gasket, providing mechanical strength, temperature resistance, and corrosion resistance. Common materials include:
- **Carbon Steel (CS)**
- **Application scope**: Suitable for low-temperature (≤300℃) and non-corrosive media (such as air, water, and oil) in general industrial pipelines.
- **Advantages**: Low cost, high mechanical strength, and easy processing.
- **Limitations**: Poor corrosion resistance; prone to rust in humid or corrosive environments, making it unsuitable for acidic, alkaline, or salt-containing media.
- **Stainless Steel 304/304L**
- **Application scope**: Widely used in medium-temperature (≤600℃) and mild corrosive environments, such as food processing, pharmaceutical equipment, and water treatment pipelines.
- **Advantages**: Excellent corrosion resistance to atmospheric, water, and weak acids/alkalis; good oxidation resistance at high temperatures.
- **304L feature**: Lower carbon content than 304, reducing the risk of intergranular corrosion after welding or high-temperature use.
- **Stainless Steel 316/316L**
- **Application scope**: Ideal for strong corrosive media (such as seawater, chlorine-containing solutions, sulfuric acid, and phosphoric acid) and high-temperature environments (≤650℃), commonly used in chemical, marine, and petrochemical industries.
- **Advantages**: Added molybdenum element significantly improves resistance to pitting corrosion and crevice corrosion; better overall corrosion resistance than 304.
- **Special Alloys**
- **Inconel (e.g., 600/625)**: Resistant to high temperatures (≤1000℃) and strong corrosion (such as nitric acid, high-temperature molten salt), used in aerospace and high-temperature chemical reactors.
- **Hastelloy (e.g., C276)**: Excellent resistance to strong acids (hydrochloric acid, sulfuric acid) and chloride corrosion, suitable for extreme chemical environments.
- **Titanium (Ti)**: Lightweight, high strength, and resistant to seawater, chlorine, and most organic acids, but higher cost, used in high-end corrosion-resistant scenarios.
### 2. Filler Materials
The filler is wrapped in the metal strip, providing elasticity and sealing performance by filling flange surface irregularities. Common fillers include:
- **Non-Asbestos Fiber**
- **Composition**: Usually mixed with inorganic fibers (glass fiber, ceramic fiber) and organic binders, compliant with environmental standards (asbestos-free).
- **Performance**: Good temperature resistance (≤400℃), low cost, and suitable for general water, steam, and oil media.
- **Graphite**
- **Types**: Natural graphite or expanded graphite, often impregnated with resin or metal to enhance strength.
- **Advantages**: Excellent high-temperature resistance (pure graphite ≤600℃ in oxidizing environments, ≤1000℃ in reducing environments), good chemical inertness (resistant to most acids, alkalis, and organic solvents), and high compressibility.
- **Application**: Widely used in high-temperature, high-pressure pipelines and equipment in petrochemical, power, and metallurgical industries.
- **PTFE (Polytetrafluoroethylene)**
- **Advantages**: Corrosion resistance to almost all chemicals (except molten alkali metals and fluorine gas), low friction coefficient, and non-stick surface.
- **Limitations**: Poor temperature resistance (≤260℃), high cold flow tendency under long-term pressure.
- **Application**: Suitable for low-temperature, strong corrosive media (such as hydrofluoric acid, chlorine gas) in chemical and pharmaceutical industries.
- **Ceramic Fiber**
- **Performance**: Ultra-high temperature resistance (≤1200℃), good thermal insulation, but low elasticity and brittleness.
- **Application**: Used in high-temperature furnaces, boilers, and kiln flanges where extreme heat resistance is required.
## 二、Structural Design of Metal Spiral wound gaskets
The structural design directly affects the sealing effect, pressure resistance, and installation adaptability of the gasket. Common structural types include:
### 1. Basic Winding Structure
- **Winding Form**: The metal strip and filler are alternately wound in a spiral manner, forming a concentric circular cross-section with alternating peaks and valleys. This structure allows the gasket to deform elastically under flange pressure, ensuring tight contact with the flange surface.
- **Inner/Outer Rings**:
- **Inner Ring (Centering Ring)**: Made of the same material as the metal strip, it prevents the filler from being squeezed into the pipeline during installation, ensuring centering and improving pressure resistance. It is mandatory for high-pressure systems (Class 600 and above).
- **Outer Ring (Guide Ring)**: Guides the gasket during installation to avoid misalignment, protects the winding layer from damage, and limits excessive compression of the gasket.
### 2. Common Structural Types
Structural Type
Features
Application Scenarios
Basic Type (Without Rings)
Simple structure, low cost; suitable for low-pressure, non-critical flanges.
General water, air pipelines with low pressure (≤1.6MPa).
With Inner Ring
Enhanced pressure resistance, prevents filler extrusion.
Medium-pressure pipelines, valves, and heat exchangers.
With Inner & Outer Rings
Highest structural stability, precise positioning, and anti-compression.
High-pressure (≥6.4MPa), high-temperature equipment flanges (e.g., steam turbines, chemical reactors).
Oval/C-shaped Wound Gasket
Special cross-section design, better adaptability to uneven flanges.
Flanges with slight deformation or low surface finish.
### 3. Key Structural Parameters
- **Winding Density**: The number of spiral turns per unit length; higher density improves sealing stability but reduces elasticity.
- **Thickness**: Common thicknesses are 3mm, 4.5mm, 6mm, etc., selected based on flange groove depth and pressure requirements.
- **Surface Finish**: The metal surface is usually untreated or passivated to enhance corrosion resistance.
## 三、Chemical Properties of Metal Spiral wound gaskets
The chemical properties depend on the combination of metal strip and filler, determining their adaptability to different media:
### 1. Corrosion Resistance
- **Medium Compatibility**:
- Graphite-filled gaskets with 316L stainless steel strips show excellent resistance to organic acids, alkalis, and salt solutions, but are not suitable for strong oxidizing media (e.g., concentrated nitric acid) as graphite may oxidize.
- PTFE-filled gaskets with titanium strips are ideal for strong corrosive media such as hydrofluoric acid and chlorine gas, but PTFE may swell in some organic solvents (e.g., ketones).
- Inconel alloy strips with ceramic fiber fillers resist high-temperature molten salts and sulfur-containing gases, suitable for petrochemical high-temperature reactors.
- **Environmental Adaptability**:
- Stainless steel 304/316 gaskets are resistant to atmospheric corrosion and can be used in outdoor or humid environments.
- Carbon steel gaskets are prone to rust in humid conditions and require anti-corrosion coatings (e.g., zinc plating) for short-term use in non-corrosive media.
### 2. High-Temperature Resistance
- **Continuous Operating Temperature**:
- Non-asbestos-filled gaskets: ≤400℃;
- Graphite-filled gaskets: 304 strip ≤600℃, Inconel strip ≤1000℃;
- Ceramic fiber-filled gaskets: Inconel strip ≤1200℃.
- **Thermal Stability**: The metal strip maintains structural strength at high temperatures, while the filler (e.g., graphite) resists oxidation and decomposition, ensuring no hardening or cracking.
### 3. Pressure Resistance
- **Sealing Under Pressure**: The metal strip provides rigidity to resist flange pressure, while the filler deforms to fill gaps, enabling the gasket to adapt to high-pressure environments (up to Class 2500 or 42MPa for special designs).
- **Compression & Rebound**: The spiral structure allows elastic deformation under pressure, maintaining sealing performance even with slight flange displacement caused by temperature or pressure fluctuations.
### 4. Limitations in Chemical Performance
- **Sensitivity to Strong Oxidants**: Graphite fillers are easily oxidized in concentrated nitric acid or high-temperature oxygen environments, leading to performance degradation.
- **Cold Flow of PTFE**: PTFE fillers may exhibit cold flow under long-term high pressure, resulting in reduced sealing effect, requiring periodic re-tightening.
- **Galvanic Corrosion Risk**: Dissimilar metal contact (e.g., carbon steel flange with stainless steel gasket) in corrosive media may cause galvanic corrosion, requiring matching material selection.
