What Affect the Sealing Performance of Your Gaskets?

Sealing gaskets are essential sealing components in mechanical equipment and piping systems, playing a crucial role in preventing medium leakage and ensuring the safe operation of the entire system. Widely used at flange connections across industries such as petrochemical, power generation, shipbuilding, municipal water supply, and food processing, the sealing performance of gaskets directly influences system safety, reliability, and economic efficiency.

However, gasket sealing effectiveness depends not only on the gasket material itself but also on a combination of factors including installation procedures, flange surface quality, operating pressure, temperature variations, medium properties, and equipment vibration. Understanding these factors is vital for correct gasket selection, proper installation, and maintenance, which in turn extends equipment life and reduces leakage risks.

This article systematically analyzes the key factors impacting gasket performance, beginning with the gasket's mechanical principles, and covering flange sealing surface characteristics, material properties, temperature effects, installation and maintenance, and the nature of the working fluid.

The fundamental role of a sealing gasket is to deform and fill the microscopic unevenness and gaps between flange faces, thereby creating a barrier that prevents medium leakage. Typically placed between flanges, the gasket compresses under bolt preload, filling surface scratches, grooves, and pores to block fluid flow.

Upon loading, gaskets experience two types of deformation:

Elastic deformation: The gasket undergoes reversible strain, allowing it to adapt to slight flange surface movements and maintain sealing pressure.

Plastic deformation: The material undergoes permanent shape change, completely filling gaps for a tight seal.

An ideal gasket material balances elasticity and plasticity, ensuring reliable sealing while avoiding excessive compression that could cause damage.

The gasket bears compressive loads transmitted from flange bolts. While theoretically the pressure should distribute evenly, flange deformation, uneven bolt tension, and heterogeneous gasket material properties often cause localized stress concentrations, potentially leading to sealing failure in those areas.

Additionally, internal medium pressure acts outward on the gasket sealing surface. The gasket must therefore withstand both bolt compressive forces and internal medium pressure to prevent the seal from being forced open and leaking.

Common gasket damage includes cracks, indentations, excessive deformation, wear, and chemical corrosion. Causes include:

Excessive compression causing brittleness or cracking.

Shear stress leading to surface scratches or fractures.

Thermal cycling inducing fatigue and degradation.

Corrosive media altering chemical composition and weakening strength.

Mechanical vibration loosening bolts and compromising the seal.

Understanding these stress and damage mechanisms is foundational for selecting suitable materials and designing effective installation procedures.

The quality of the flange sealing surface directly affects gasket performance. Even high-quality gasket materials cannot compensate for rough, uneven, or damaged flange surfaces.

Common flange sealing surface types include:

Flat surface: Suitable for soft gaskets; requires strict flatness.

Ring groove surface: Designed for metal gaskets that fit into grooves for mechanical sealing.

Raised face surface: Projects slightly to concentrate bolt pressure and enhance metal gasket sealing.

Proper surface design ensures uniform gasket loading and prevents sliding or shifting.

Surface roughness influences seal tightness:

Metal gaskets typically require a roughness of Ra3.2–Ra6.3; too rough can damage the gasket, too smooth prevents micro-engagement.

Soft gaskets tolerate higher roughness, usually Ra12.5–Ra25.

Sealing surfaces must be clean, burr-free, and free of mechanical scratches to avoid seal failure.

Flange flatness and perpendicularity relative to the flange axis impact the uniformity of bolt preload. Warped or tilted surfaces cause localized high pressure, potentially crushing the gasket or causing leaks.

Typical standards require flange flatness within 0.1 mm and perpendicularity within 0.2% of flange thickness.

Gasket materials vary widely and are chosen based on operating environment and medium. Common materials include graphite, PTFE (polytetrafluoroethylene), rubber, metals (stainless steel, copper, aluminum alloys), and composites, each with distinct advantages and limitations.

Key factors when selecting gasket materials:

Medium characteristics (corrosiveness, viscosity, temperature, pressure)

Operating temperature range

Sealing pressure demands (high-pressure systems require stronger materials)

Mechanical properties (elasticity, toughness, compressive strength, fatigue resistance)

Chemical stability (corrosion resistance, aging resistance)

Graphite gaskets: High temperature resistance (over 500°C), corrosion resistance, good elasticity; suitable for high-temp and high-pressure applications but mechanically fragile.

PTFE gaskets: Excellent chemical resistance, temperature range from -100°C to +260°C; low strength and prone to deformation, best for low-pressure systems.

Rubber gaskets: Good elasticity and sealing at low temperatures and pressures; poor high-temperature and chemical resistance.

Metal gaskets (e.g., stainless steel, copper): High strength and resistance to temperature and corrosion; limited elasticity, often combined with soft materials for sealing.

Composite gaskets: Combine advantages of multiple materials, offering elasticity and strength for harsh conditions.

Sealing depends on deformation capabilities:

Elastic deformation maintains sealing force by recovering shape.

Plastic deformation permanently fills sealing gaps.

A proper elastic-to-plastic deformation ratio ensures sealing effectiveness without damage.

Gaskets often operate under varying temperature conditions where thermal expansion and fatigue can degrade sealing.

Different thermal expansion coefficients of flanges, bolts, and gasket materials cause dimensional and stress changes:

Compression force may decrease as temperature rises, reducing seal pressure.

Mismatched expansions between flange and gasket can deform flanges and create leakage paths.

Repeated thermal cycles cause material fatigue, leading to cracking and embrittlement, especially in soft gaskets that harden or deteriorate under heat.

At low temperatures, soft gaskets can become brittle and lose elasticity. Uneven cooling of flanges and bolts may reduce bolt preload, risking leaks.

Use materials rated for high or low temperatures.

Ensure uniform flange and bolt temperature to avoid localized stresses.

Employ high-performance composite gaskets to resist thermal fatigue.

Design allowances for thermal expansion to reduce stress concentration.

Proper installation quality is critical for long-term sealing. Correct procedures and maintenance ensure sustained gasket performance.

Thoroughly clean sealing surfaces, removing old gasket remnants, oil, dirt, and damage.

Verify flange dimensions and flatness meet design requirements.

Select gasket material, thickness, and size suited to operating conditions.

Tighten bolts symmetrically in a cross pattern to avoid uneven stress and flange warping.

Apply preload according to gasket material and operating conditions to prevent damage or leaks.

Use torque wrenches to ensure accurate bolt tension and reduce human error.

Bolts may loosen due to vibration or thermal cycling, decreasing sealing force.

Use anti-loosening devices such as spring washers or thread adhesives.

Regularly inspect and retighten bolts as needed.

Periodically check gasket condition; replace if signs of aging, deformation, or corrosion appear.

Protect sealing surfaces from scratches and corrosion.

Increase inspection frequency in vibrating or high-temperature environments.

Since gaskets contact the working medium directly, its properties significantly affect sealing and gasket life.

Corrosive media (acids, alkalis, salts) degrade gasket materials, causing leaks; corrosion-resistant materials (PTFE, graphite, metal alloys) are necessary.

Steam and high-temperature gases require high-strength, heat-resistant gaskets.

Fluid viscosity influences sealing difficulty; high-viscosity liquids flow slowly, easing sealing, while gases and low-viscosity liquids pose higher leakage risk.

Liquid wettability affects capillary penetration. Porous or micro-cracked gaskets allow fluid ingress causing leakage. Dense materials provide better sealing.

Rising temperatures typically lower liquid viscosity, facilitating sealing, but increase gas viscosity and flow pressure. Temperature impacts on sealing layers are complex and require holistic analysis.

Sealing gaskets are critical components of mechanical sealing systems whose performance is influenced by numerous interrelated factors. Proper material selection, strict control of flange sealing surface quality, scientific installation practices, and regular maintenance are essential to ensure effective sealing and equipment safety. Achieving uniform gasket loading with suitable material properties guarantees reliable sealing of flange gaps. Flange sealing surfaces must meet design standards for shape, roughness, flatness, and perpendicularity. Gasket materials should be chosen based on medium characteristics, temperature, pressure, and operating conditions, balancing corrosion resistance and mechanical strength. Thermal expansion, fatigue, and aging caused by temperature changes should be mitigated through appropriate materials and design. During installation, bolt preload must be uniform and stable to avoid loosening and stress relaxation. The medium's properties, including wettability and corrosiveness, must be fully considered. Regular inspection and maintenance prevent leaks and extend gasket service life. By deeply understanding these factors and aligning with actual working conditions, engineers and maintenance personnel can significantly improve sealing system stability and safety, minimizing operational failures and economic losses.