Guide to Spiral Wound Gasket Selection

In the industrial field, whether in petroleum, chemical, metallurgy, power, shipbuilding, or machinery industries, sealing of pipelines, valves, pressure vessels, and other equipment is crucial. As a high-performance sealing component, spiral wound gaskets are widely used in various flange connections due to their unique structure and excellent performance. However, faced with numerous spiral wound gasket products in the market, how does one choose a gasket suitable for their operating conditions? This article provides a detailed explanation of the key points for selecting spiral wound gaskets, helping you choose the most appropriate sealing component from many products.

Spiral wound gaskets are made by helically winding high-quality stainless steel (commonly SUS304 or SUS316) alternately with flexible filler materials such as graphite, PTFE, asbestos-free, or asbestos. They generally use a "V" or "W" shaped steel strip structure, with the start and end points spot-welded to form a structurally stable composite gasket. This unique structure allows spiral wound gaskets to possess both the strength and toughness of metal and the flexibility and chemical resistance of non-metallic materials.

The metal strip is one of the core components of a spiral wound gasket, and the choice of material critically affects the gasket's performance. Commonly used metal strip materials include SUS304 and SUS316. SUS304 stainless steel has good corrosion resistance and oxidation resistance, suitable for most industrial environments. SUS316 stainless steel further increases resistance to chloride ions, making it more suitable for media containing chlorides. When selecting metal strip materials, the specific operating conditions and the characteristics of the medium should be considered to ensure that the gasket can provide stable sealing over long-term use.

Non-metallic filler mainly serves sealing and cushioning functions. Common materials include graphite, PTFE, asbestos-free, or asbestos. Graphite has excellent high-temperature performance and chemical stability, maintaining stable sealing under high-temperature and high-pressure conditions. PTFE is renowned for its superior chemical resistance and low friction coefficient, suitable for sealing strongly corrosive media such as strong acids and strong alkalis. Asbestos-free materials are environmentally friendly fillers with good flexibility and sealing performance, harmless to humans and the environment. When selecting non-metallic filler, the medium's properties, temperature, and pressure should be considered comprehensively to ensure the filler can provide optimal sealing performance under specific operating conditions.

According to different operating conditions and flange sealing surface types, spiral wound gaskets can be divided into basic, inner ring, outer ring, and inner-outer ring types. Each type has unique structural features and applicable ranges.

The basic spiral wound gasket has the simplest structure, without inner or outer rings. It is typically used in medium- and low-pressure tongue-and-groove, flat, or raised face flanges. This type of gasket has good compressibility and recovery, multiple sealing layers, and a certain degree of self-tightening. It is not very sensitive to surface defects of the flange sealing surface, does not stick to the flange sealing surface, and can partially offset the effects of pressure, temperature changes, and mechanical vibrations. It can maintain excellent sealing performance under harsh conditions such as high temperature, low temperature, high vacuum, and cyclic impact or vibration. Because of its simple structure and low cost, the basic spiral wound gasket is widely used in medium- and low-pressure applications.

The inner ring spiral wound gasket adds an inner ring based on the basic type. The inner ring is usually made from the same material as the winding steel strip, meeting the corrosion resistance requirements of the pipeline medium and often superior to the pipeline or flange material. The inner ring primarily strengthens the structural stability of the gasket, preventing the spiral wound gasket from unwinding during use. This type allows the gasket to achieve maximum compression, and the surface precision requirement of the flange sealing surface is not high. It is especially suitable for situations with uneven load, loosening of joint force, cyclical temperature and pressure changes, or impact and vibration. It is generally used in medium- and low-pressure tongue-and-groove, flat, or raised face flanges.

The outer ring spiral wound gasket adds an outer ring based on the basic type. The outer ring mainly serves for alignment between the flange and gasket and to control the gasket's compression force. The outer ring is also called a centering ring. Internationally, it is usually made of galvanized or coated carbon steel or from the same material as the pipeline or flange. Due to the presence of the outer ring, the gasket is easy to center, making installation and removal convenient, and it allows control of the maximum compression. The outer ring spiral wound gasket has good compressibility and recovery, multiple sealing layers, and a certain self-tightening function. It is not very sensitive to flange surface defects, does not stick to the flange sealing surface, and can partially offset the effects of pressure, temperature changes, and mechanical vibrations. It can maintain excellent sealing performance under harsh conditions such as high temperature, low temperature, high vacuum, and cyclic impact or vibration. Outer ring spiral wound gaskets are generally used in medium- and low-pressure flat and raised face flanges.

The inner-outer ring spiral wound gasket is currently the most widely used type of sealing gasket and has the best resilience among semi-metallic gaskets. It is made by alternately winding "V" or "W" shaped thin steel strips with various fillers. By changing the combination of materials, it can resist chemical corrosion from different media. Metal inner and outer rings are used to strengthen the body and achieve accurate positioning, controlling maximum compression and preventing the basic body from unwinding. The outer ring makes installation more convenient. Generally, it is used in medium- and low-pressure flat and raised face flanges. Inner-outer ring spiral wound gaskets can withstand high temperatures, high pressures, and adapt to ultra-low temperature or vacuum conditions. The surface precision requirement of the flange sealing surface is not high, and installation and removal are convenient.

Compression, recovery, and sealing performance are three important performance indicators, directly determining the gasket's sealing effect and service life.

Compression refers to the degree to which the gasket thickness decreases when subjected to external force. Generally, under the premise of meeting compression requirements, a higher compression value is better. This is because higher compression allows the gasket to better fill small irregularities on the flange sealing surface, improving sealing performance. However, excessive compression may cause over-deformation during use, affecting structural stability and sealing performance.

Recovery refers to the extent to which the gasket can return to its original thickness after being compressed. Higher recovery indicates better elasticity, allowing the gasket to better accommodate minor flange deformations and pressure changes, maintaining good sealing performance. Generally, under the premise of meeting recovery standards, higher recovery is better. Gaskets with high recovery can automatically adjust sealing pressure under temperature, pressure changes, or mechanical vibrations, extending sealing life.

Sealing performance is one of the most important indicators of gasket quality. High-quality spiral wound gaskets should have excellent sealing performance, effectively preventing medium leakage under various operating conditions. Sealing performance depends not only on the gasket’s material and structure but also closely on surface quality and manufacturing precision. When selecting a spiral wound gasket, priority should be given to products with good sealing, moderate compression, and as high recovery as possible.

When selecting a spiral wound gasket, multiple factors must be considered, including operating conditions, flange sealing surface type, gasket performance indicators, surface quality, and manufacturing precision. The following are some specific selection points:

Different operating conditions impose different performance requirements. For example, in high-temperature and high-pressure conditions, gaskets resistant to high temperature and high pressure should be selected. In corrosive media, gaskets with good corrosion resistance should be selected. Temperature and pressure ranges, chemical properties of the medium, and flange material and surface type must also be considered to ensure the gasket meets the operating requirements in actual use.

Flange sealing surface type also significantly affects gasket selection. Common flange sealing surfaces include tongue-and-groove, flat, and raised face. For tongue-and-groove flanges, basic or inner ring spiral wound gaskets are generally selected. For flat flanges, outer ring or inner-outer ring spiral wound gaskets are suitable. For raised face flanges, basic, inner ring, outer ring, and inner-outer ring spiral wound gaskets can all be used, but the most suitable type should be determined according to specific operating conditions and sealing requirements.

When selecting spiral wound gaskets, products from manufacturers with a complete and effectively implemented quality management system should be prioritized. It is best to select products from companies holding special equipment (pressure pipeline component) manufacturing licenses and valid type test reports. These companies generally have strict quality control systems and advanced production processes, ensuring that product quality and performance meet standards.

Under the premise of meeting operating conditions, products with moderate compression and as high recovery as possible should be selected. At the same time, ensure the gasket has good sealing performance, maintaining stable sealing under various harsh conditions. In the selection process, performance indicators can be checked by reviewing product manuals, consulting manufacturers, or conducting performance tests to make the right choice.

When purchasing spiral wound gaskets, carefully check the surface quality and manufacturing precision. Inspect whether the gasket body surface has scratches, voids, unevenness, or rust; whether the non-metallic strip is uniform and slightly raised above the metal strip; whether spot weld spacing is even; and whether the reinforcing ring surfaces are free of burrs, unevenness, or rust. Although these details may seem minor, they directly affect the gasket's sealing performance and service life.

As a high-performance sealing component, spiral wound gaskets are widely used in the industrial field. Their unique structure and excellent performance allow them to maintain stable sealing under various harsh conditions. When selecting spiral wound gaskets, multiple factors should be comprehensively considered, including operating conditions, flange sealing surface type, gasket performance indicators, surface quality, and manufacturing precision, to ensure the most suitable product is chosen.