Silicon carbide and tungsten carbide are the two most common materials for mechanical seals in industrial equipment. Silicon carbide excels in corrosion resistance and performs better in clean fluids, while tungsten carbide offers superior toughness and handles dirty conditions more effectively. The choice between them depends on your specific application requirements including fluid type, operating conditions, and budget constraints.
Material Properties
| Property | Silicon Carbide (SiC) | Tungsten Carbide (WC) |
|---|---|---|
| Hardness (Mohs) | 9 – 9.5 (extremely hard) | 8.5 – 9 (very hard) |
| Density (g/cm³) | ~3.1 (lightweight) | ~14.5 – 15.6 (very dense) |
| Thermal Conductivity | ~120–160 W/m·K (high) | ~85–110 W/m·K (moderate-high) |
| Thermal Expansion | ~4.0 × 10^−6/°C (low) | ~5.5 × 10^−6/°C (higher) |
| Compressive Strength | ~3900 MPa (very high) | ≥5000 MPa (extremely high) |
| Fracture Toughness | Lower – brittle (low impact strength) | Higher – tough (resists shock) |
| Chemical Inertness | Inert ceramic (excellent corrosion resistance) | Metal-bonded carbide (good, but binder can corrode) |
| Maximum Service Temp | ~¹1500–1800 °C (maintains strength at extreme heat) | ~¹1000 °C (binder limits upper use temperature) |
Wear Resistance
Both silicon carbide and tungsten carbide are prized for their excellent resistance to wear and abrasion. Their extreme hardness makes them far more wear-resistant than softer face materials like carbon or stainless steel.
However, silicon carbide’s superior hardness (Mohs ~9.5) gives it an edge in abrasive conditions – it outperforms tungsten carbide (Mohs ~8.5–9) in scratch resistance and wear durability. In slurry or sandy service, a SiC seal face tends to experience minimal abrasion. Tungsten carbide, while slightly softer, is still an “extremely hard” material (ranked just below diamond) and highly wear-resistant.
Where tungsten carbide often excels is in scenarios involving impact, bending, or particle impingement. Because WC is tougher and less brittle, it is less likely to chip or crack from transient mechanical shocks (e.g. cavitation, vibrating equipment, or occasional hard particles between faces). In abrasive slurry pumps, for example, large or irregular particles might cause brittle fracture in a SiC face, whereas a tungsten carbide face might survive the impact.
Corrosion Resistance
Silicon carbide is chemically inert: it does not react with most acids, alkalis, or solvents, and it forms a passivating silica layer at high temperatures, making it highly corrosion-resistant.
Tungsten carbide, by contrast, is a metal-carbide composite; its corrosion behavior depends largely on the binder metal. WC itself is relatively inert (it resists most chemicals except strong oxidizers like a hot HF/HNO₃ mixture), but common cobalt binders are prone to attack by acids and certain chemicals.
Chemical Compatibility
Silicon carbide’s broad chemical inertness means it is compatible with a very wide range of fluids – including strong acids (sulfuric, hydrochloric, nitric), caustic alkalis (sodium hydroxide), solvents, sour hydrocarbons (high H₂S content), sea water, and so on.
Tungsten carbide can handle many fluids as well, but with caveats. Neutral or mildly corrosive fluids (e.g. many oils, water with near-neutral pH, hydrocarbon mixtures, etc.) are generally fine for WC. However, strong acids, brines, and oxidizing chemicals tend to be problematic for WC.
Lubrication
Both SiC and WC perform best with at least a thin fluid film between faces, but SiC’s properties give it an advantage in poor lubrication conditions. SiC has a naturally low coefficient of friction and high thermal conductivity, so it runs cooler and with less friction if lubrication is marginal. In fact, silicon carbide can often be used in applications with low lubricity or even intermittent dry running.
High-Temperature Performance
Silicon carbide can withstand very high temperatures (material stability to ~1600–1800 °C), far beyond the limits of most seal deployments. In practical terms, SiC faces can operate at temperatures where many other components (elastomers, metal parts) would fail.
Tungsten carbide, while also a high-melting material (~2780 °C melting point), is constrained by its binder at elevated temperatures. Cobalt or nickel binders can begin to soften or lose strength at a few hundred degrees Celsius.
High-Pressure Performance
Tungsten carbide’s higher density and modulus contribute to withstanding high hydraulic pressures without cracking or deforming. WC’s denser, tougher structure enables it to endure extreme pressures better than SiC.
Silicon carbide, although very strong in compression, is more brittle and can fracture if the pressure-induced stresses result in tensile or flexural loads that exceed its fracture toughness. Additionally, WC can handle any pressure shocks or oscillations more safely – a sudden pressure spike is less likely to shatter a WC face than a SiC face.
Common Industrial Applications
- Oil & Gas (upstream drilling, fracking): Tungsten Carbide (shock and abrasion in mud, high pressure)
- Oil Refining / Petrochemical: Silicon Carbide (corrosive media, high temperature) in many services; WC for some high-pressure clean services
- Chemical Processing: Silicon Carbide (acids, solvents, corrosives)
- Mining & Slurry Pumps: Tungsten Carbide (extreme abrasion, impact)
- Water Treatment (aggressive or dirty water): Silicon Carbide (corrosion, sand abrasion); for clean water or mild service, WC also used
- Power Generation: Mix of WC (high-pressure feed pumps) and SiC (high-temp or aggressive water) depending on system
- Pharma/Food: Silicon Carbide (inert, hygienic)
Cost
Tungsten carbide seals often have a higher upfront cost. In scenarios where a SiC face might crack and necessitate replacement, a WC face might keep running, thereby extending the mean time between maintenance.
On the other hand, silicon carbide seals, being cheaper initially and extremely resistant to wear and chemical attack, can provide very long service life in their ideal conditions (with minimal maintenance).
