Metal-wound gasket

Metal spiral-wound gaskets are widely used industrial sealing components, constructed by alternately layering pre-formed V-shaped or W-shaped metal strips with various non-metallic flexible filler materials—such as flexible graphite and polytetrafluoroethylene—and then spirally winding the assembly. This unique composite structure endows the gasket with the high strength and excellent resilience of metal, combined with the softness and tight packing characteristic of non-metallic fillers, enabling it to provide reliable sealing of process media (gases or liquids) at flanged connections under extreme service conditions characterized by high temperature, high pressure, and cyclic fluctuations in both temperature and pressure.

Physicochemical Properties

The physicochemical properties of metal-wound gaskets are determined by the material combination of their “metal strip” and “filling strip,” thereby offering a high degree of design flexibility.
· Wide temperature range and high-pressure resistance: By selecting different filling materials, it can accommodate a broad temperature span from cryogenic to ultra-high temperatures; its helically wound metallic structure provides exceptional mechanical strength, enabling it to withstand very high system pressures.
· Excellent chemical stability: Whether the sealing element is made of metallic materials (such as stainless steel, Monel, or titanium) or non-metallic fillers (such as graphite or PTFE), it can be selected based on the corrosive properties of the process fluid, ensuring resistance to a wide range of chemical media, including acids, bases, solvents, and steam.
· Excellent compression and rebound characteristics: its structure generates radial clamping force during operation and, in response to fluctuations in operating conditions, compensates through the elastic deformation of the metal bellows—this constitutes the physical basis for achieving reliable sealing.

Application areas (application scenarios)

Metal spiral-wound gaskets are the core sealing components for flanged connections in pipelines, valves, pumps, heat exchangers, and pressure vessels across heavy industries such as petrochemicals, power generation, and metallurgy, and are particularly well suited to the following critical applications:
· Sealing under severe service conditions: Primarily used in piping systems subjected to high temperature and high pressure, frequent thermal cycling, or significant pressure fluctuations—conditions that place extremely stringent demands on the stability and reliability of the seal.
· Non-ideal flange conditions: For flanged connections with minor damage to the sealing surface, insufficient machining accuracy, or poor structural rigidity, the flexible gasket layer provides superior compensation and conformability.
· Critical industrial equipment: Widely used in key sealing points of refineries, chemical plants, power stations, nuclear power plants, and other facilities, these components are essential for ensuring continuous and safe production.

Advantages of this product compared with other products

Compared with single-material gaskets and other composite gaskets, its core advantage lies in its “rigid-flexible” structural design:
· Outstanding dynamic sealing performance: this is its most prominent advantage. The metal strip imparts exceptional spring-like resilience, enabling automatic compensation for flange-face separation caused by temperature and pressure fluctuations as well as bolt-stress relaxation, thereby maintaining long-lasting and effective sealing. In contrast, all-metal gaskets are prone to stress relaxation, while all-nonmetal gaskets lack sufficient resilience.
· Enhanced service-condition adaptability: Compared with pure rubber or pure PTFE gaskets, it exhibits a qualitative improvement in temperature and pressure resistance; compared with pure graphite gaskets, it offers superior mechanical strength as well as greater resistance to erosion and blow-out; and compared with metal flat gaskets that require substantial preloading, it places a lighter load on flange surfaces and bolts.
· Flexible customizability: The modular “metal-plus-fill” configuration allows for precise adaptation to a wide range of specialized service conditions—ranging from highly corrosive environments to ultra-high temperatures—by simply varying the materials, thereby extending the application scope far beyond that of single-material gaskets.

Precautions for Use

Proper installation is critical to ensuring gasket sealing performance and extending the service life of both the gasket and the flange:
1. Pre-installation preparations: The flange sealing surfaces must be carefully inspected and cleaned to ensure they are free of scratches, rust, dirt, or residues from old gaskets. At the same time, verify that the new gasket is intact, with no loose particles or deformation.
2. Standard installation procedures: Ensure that the gasket is precisely centered and positioned at the flange center. When tightening the bolts, follow the “cross-pattern, diagonal sequence, multiple passes, and gradual, even tightening” method to ensure uniform load distribution around the entire perimeter of the gasket, thereby preventing leakage or damage caused by uneven, one-sided compression.
3. Reuse is strictly prohibited: Metal spiral-wound gaskets are single-use sealing elements. After initial installation, compression, and exposure to service conditions, their internal structure undergoes plastic deformation and stress redistribution, rendering their sealing performance unreliable; therefore, the gasket must be replaced with a new one after removal.

Selection Guide

Correct selection requires systematically following the following logical sequence:

Step 1: Confirm the basic operating parameters. This is the foundation for equipment selection and requires clear definition of the medium’s chemical composition, corrosion characteristics, as well as the system’s maximum operating temperature, maximum operating pressure, and the range of possible pressure fluctuations.
Step 2: Identify the type of flange sealing face. This is critical in determining the gasket design. Flat or raised-face flanges typically use gaskets with an outer ring or with both inner and outer rings; female-and-groove flanges use gaskets with an inner ring; and tongue-and-groove flanges use standard-type gaskets. An incorrect selection can result in improper gasket positioning or failure of the seal.
Step 3: Select the appropriate material combination. This is crucial for ensuring gasket life and sealing performance.
· Metal belt material: Select based on the corrosivity of the process medium and the operating temperature. Commonly used materials are 304 or 316 stainless steel; for highly corrosive media or high-temperature applications, special alloys should be considered.
· Packing material: Select based on temperature and chemical compatibility. Flexible graphite is suitable for most high-temperature, non-strongly oxidizing environments; polytetrafluoroethylene (PTFE) is used in highly corrosive and low-temperature environments; for special high-temperature oxidizing environments, mica or ceramic fiber may be considered.
· Inner and outer ring materials: Primarily serve to provide reinforcement and positioning; typically the same as the metal belt material, though carbon steel may be used in non-corrosive applications.
Step 4: Focus on manufacturing quality and suppliers. Select reputable suppliers and inspect the physical product: the non-metallic filler strip should protrude slightly and evenly above the metal strip; the winding must be tight, uniform, and free of unraveling; and the inner and outer rings must fit well with the wound assembly, with no burrs.

Summary and Trends

In summary, metal-jacketed gaskets, with their outstanding resilience and compensation capabilities as well as broad material compatibility, have become the classic solution for addressing challenging flange-sealing problems under demanding, dynamic operating conditions. In modern industrial applications, they are often the first choice for piping systems subject to frequent temperature and pressure fluctuations.

It is worth noting that, in certain high-pressure stationary flange applications where absolute static sealing reliability is required, new types of gaskets—such as metal-toothed gaskets and corrugated-metal composite gaskets—are increasingly being adopted due to their lower leakage rates. However, under service conditions involving significant thermal cycling, the dynamic compensation advantages of metal-jacketed gaskets remain difficult to fully replace.