In the industrial sector, whether in petroleum, chemical, energy, or pharmaceutical industries, the sealing of pipeline systems and equipment connections is of paramount importance. Gaskets, as materials or material combinations clamped between two independent connecting components (primarily flanges), play a critical role in maintaining a seal and preventing media leakage. This article will delve into gasket selection, performance requirements, and practical application considerations, helping readers better understand and utilize this essential component.
A gasket sealing system typically consists of connecting components (such as flanges), the gasket itself, and fasteners (such as bolts and nuts). The primary role of a gasket is to seal the mating surfaces throughout its intended service life, ensuring that the sealed medium does not leak or corrode and that it can withstand the effects of temperature and pressure. The performance of a gasket depends not only on its inherent properties but also on the system's stiffness and deformation, the roughness and flatness of the mating surfaces, and the magnitude and uniformity of the bolt preload.
As the core component of a sealing system, a gasket's performance directly determines the effectiveness of the seal. Only by meeting a series of key performance requirements can a gasket reliably function under various complex operating conditions, ensuring the safe operation of pipeline systems and equipment.
A gasket should have a reasonable service life at both the maximum and minimum operating temperatures. Different gasket materials have vastly different maximum operating temperatures. In addition to short-term tolerance, continuous operating temperature must also be considered. For example, natural rubber gaskets are suitable for lower temperature ranges, while metallic gaskets can withstand higher temperatures. A critical quality indicator is the gasket's creep relaxation performance at a given temperature. Most gasket materials experience increased creep at elevated temperatures, which can affect sealing performance.
Gaskets must resist chemical corrosion from the sealed medium, making this a primary consideration in selection. For non-metallic or composite gaskets, the chemical resistance of the non-metallic material can be referenced from manufacturer-provided tables. Metals in direct contact with the medium should have corrosion resistance equal to or greater than the flange material. For instance, in highly acidic environments, acid-resistant materials such as PTFE or Hastelloy gaskets should be chosen.
A gasket must withstand the maximum pressure, which may be the test pressure, typically 1.25–1.5 times the normal operating pressure. For non-metallic gaskets, the maximum pressure is also related to the highest operating temperature, requiring consideration of the maximum PxT value (pressure * temperature). For example, high-pressure steam pipelines require gaskets that can handle both high pressure and high temperature, such as metallic ring gaskets.
Gasket thickness depends on its type, material, diameter, sealing surface condition, and the medium. When flange roughness and flatness are within acceptable limits, thinner gaskets are preferred as they better resist stress relaxation, reduce leakage due to smaller contact areas with the medium, and have higher blow-out resistance. Gasket dimensions should comply with relevant standards to ensure effective sealing.
After understanding performance requirements, the next step is to explore the basis for gasket selection. Selecting a gasket is a systematic process requiring the consideration of multiple factors to ensure optimal sealing performance in practical applications.
Gasket selection depends on flange material, sealing surface type, roughness, and bolt specifications. For example, non-metallic flanges require gaskets with lower preload requirements to avoid crushing the flange during tightening. Different flange types correspond to specific gasket types: Raised Face (RF) flanges pair with gaskets with inner and outer rings, Tongue & Groove (TG) flanges with basic spiral wound gaskets, and Male-Female (MFM) flanges with gaskets featuring only an inner ring.
Confirm the type (gas, liquid, steam, corrosive liquids, etc.), concentration, purity, and presence of particulates. Different media demand different chemical resistance from gaskets; for example, strong acids require acid-resistant gaskets, while plain water imposes minimal requirements. Operating pressure, instantaneous maximum pressure, long-term operating temperature, and extreme temperature fluctuations must also be considered to ensure sealing performance under actual conditions.
Selected gaskets should comply with relevant industry standards, such as GB/T 9126 (petrochemical), HG/T 20606 (chemical), and ASME B16.20 (international). For flammable, explosive, toxic, or hazardous media, gaskets must pass sealing and safety certification tests to prevent risks.
Gasket selection is a complex process requiring careful consideration of multiple factors to ensure optimal sealing under specific conditions.
Suitable for water, air, and low-pressure steam. Recommended non-metallic gaskets include natural rubber (good elasticity, low cost), hydrogenated nitrile rubber (better oil resistance than natural rubber), and asbestos rubber (increasingly restricted; non-asbestos alternatives recommended). These gaskets are easy to install but should not exceed the upper temperature limit to avoid aging or hardening.
Applicable to petroleum and chemical industrial pipelines. Recommended gaskets include semi-metallic types such as metal-jacketed gaskets (metal shell + non-metal core for good sealing and heat resistance) and spiral wound gaskets (metal and non-metal strips wound together for excellent compressibility and elasticity, a universal choice for medium pressure). The metal strip material (e.g., 304 or 316L stainless steel) should match the corrosion properties of the medium.
For high-pressure steam pipelines, hydrogenation reactors, and high-temperature heat exchangers. Full-metal gaskets are required, such as serrated metallic gaskets (compression sealing suitable for male-female flanges) and metallic ring gaskets (octagonal or oval, for tongue-and-groove flanges, extremely strong sealing but high surface finish required). Full-metal gaskets should match flange materials to avoid galvanic corrosion.
Chemical compatibility is critical for long-term gasket performance. If the gasket reacts with the medium (corrosion, expansion, degradation), sealing performance drops and the medium may be contaminated. Consider chemical properties (acidic, alkaline, oxidizing, reducing, solvent or oil content) when selecting a gasket. Manufacturers provide material-medium compatibility charts for reference. For special media, third-party tests or small-scale simulation tests (e.g., immersion tests) may be required. High-temperature and high-pressure conditions may trigger latent reactions even if compatible at room temperature.
Flange flatness, roughness, and damage directly affect gasket compression and fit. Different gaskets require specific surface roughness:
Non-metallic gaskets (rubber, non-asbestos): smooth surfaces, Ra ≤ 3.2 μm.
Semi-metallic gaskets (spiral wound): moderate roughness, Ra = 1.6–6.3 μm. Too smooth may cause sliding, too rough may damage sealing layer.
Full-metal gaskets (serrated, ring): high-precision surface, Ra ≤ 1.6 μm. Grinding may be required if uneven. Non-metallic gaskets can use fine sandpaper; full-metal gaskets require precision machining.
Proper assembly and maintenance are key to long-term gasket stability. Ensuring correct selection, installation, and maintenance maximizes performance, sealing integrity, and system safety.
Preload Control: Bolted flange connections require adequate bolt torque. Preload control is challenging due to varying gasket compression requirements. Special gaskets may need custom designs. Bolts should be tightened evenly to avoid local stress variations that affect sealing.
Regular Inspection and Replacement: Gasket condition should be checked regularly. Leakage requires immediate action. Even without visible leaks, long-term operating gaskets should be replaced periodically. Clean flange surfaces thoroughly, remove residue, inspect for damage, and repair if needed.
Coping with Temperature and Pressure Fluctuations: For large temperature swings, select gaskets with good thermal shock resistance, such as flexible graphite spiral wound gaskets. Avoid frequent extreme temperature changes. For pressure fluctuations, ensure the gasket maintains sealing at maximum pressure and does not leak when pressure drops. Material and type should account for these conditions.
Correct assembly ensures proper gasket function, while proper maintenance prolongs life and safeguards sealing performance.
Common causes include improper gasket selection, poor assembly, damaged flange surfaces, and uneven bolt preload. Solutions include checking compatibility, repairing flange surfaces, and adjusting bolt torque. In some cases, replace the gasket or add secondary sealing measures.
Long-term use may lead to aging and reduced performance due to temperature, chemical exposure, and mechanical stress. Select chemically resistant materials, minimize mechanical stress, and replace severely aged gaskets regularly.
Occurs under high-pressure or high-velocity fluid when gasket is expelled from the flange, causing seal failure. Prevent by selecting gaskets with high blow-out resistance, ensuring proper flange design, uniform bolt preload, and precision surface finish. Special measures may include thicker flanges, high-strength bolts, or specialized flange designs.
Gaskets are the core sealing components of pipelines and equipment connections, and their importance cannot be overstated. From material selection to dimensional design, flange compatibility, chemical resistance, assembly, and maintenance, each step affects sealing performance and system safety. Proper selection ensures stable performance under various temperature, pressure, and medium conditions; correct installation and periodic maintenance extend service life and prevent leaks, aging, or blowouts. In short, gaskets are not only the seal guardians of pipeline systems but also critical to safe and efficient industrial operation. Mastering gasket performance and application standards is vital for improving reliability and reducing operational risks.