What is a Spiral Wound Gasket? Applications, Types, and Specifications 2026

Imagine a high-pressure steam line in a refinery hitting 450°C. Suddenly, a standard flat gasket yields under the thermal cycle, leading to a catastrophic blowout that shuts down the entire unit. This is the exact pain point where the Spiral Wound Gasket becomes non-negotiable. Engineered for resilience, these semi-metallic seals “breathe” with the flange movement, ensuring your plant stays leak-free under the most punishing hydrostatic loads.

Engineering Construction of Spiral Wound Gasket Components

The Spiral Wound Gasket is not a single piece of material but a precision-engineered assembly designed to handle the mechanical stresses of high-pressure piping. Under the ASME B16.20 standard, the construction is divided into three distinct functional parts. Each component plays a critical role in maintaining seal integrity during thermal expansion and pressure surges.

Outer ring (Centering Ring)

The outer ring, typically made of carbon steel with a corrosion-resistant epoxy coating, serves as a centering device. It fits snugly within the bolt circle of the flange, ensuring the sealing element is perfectly aligned with the pipe bore. Beyond alignment, it acts as a compression stop, preventing the internal winding from being crushed by excessive bolt torque. In modern engineering, the outer ring is color-coded to identify the winding and filler materials at a glance.

Inner ring

Often overlooked but technically vital, the inner ring provides an additional compression stop and acts as a heat shield. Its primary engineering purpose is to prevent "buckling"—a phenomenon where the internal windings are pushed into the pipe bore due to high bolt loads or internal pressure. According to ASME B16.20, inner rings are mandatory for all PTFE-filled gaskets and for all gaskets in Class 900 and above to maintain structural stability.

Sealing element (Winding)

This is the "heart" of the Spiral Wound Gasket. It consists of a pre-formed V-shaped metallic strip (the winding) and a soft filler material (Graphite, PTFE, or Mica). The V-shape creates a spring-like effect, allowing the gasket to compress under load and "recover" or expand when the flange faces move due to thermal cycling. This dynamic sealing capability is what makes the spiral wound design superior to flat-sheet gaskets in critical service applications.

Mandatory Markings on a Spiral Wound Gasket (ASME B16.20)

For traceability and safety, every Spiral Wound Gasket must be etched with specific data on the outer ring. These markings are the "identity card" of the gasket, allowing inspectors to verify compatibility before installation. A standard marking includes:

• Manufacturer's Name or Trademark: Identification of the producer.
• Flange Size & Pressure Class: e.g., 4" 600# (Class 600).
• Winding Material: Often abbreviated (e.g., 316L for Stainless Steel).
• Filler Material: (e.g., FG for Flexible Graphite).
• Designation: ASME B16.20.

Material Selection for Spiral Wound Gasket Fillers and Metals

Selecting the right metallurgy and filler is a balance between temperature, pressure, and chemical compatibility. While 304 and 316L Stainless Steel are the industry workhorses, extreme environments require exotic alloys like Monel, Inconel, or Titanium. The filler material is equally critical; Flexible Graphite is the standard for high-temp steam, while PTFE is reserved for highly corrosive chemical environments where graphite may be attacked.

Standard Spiral Wound Gasket Color Coding Chart

To prevent catastrophic installation errors, the industry follows a strict visual identification system. The outer edge of the centering ring is painted with a specific color to identify the metal winding material, while the rim may feature stripes to identify the filler. For instance, a Spiral Wound Gasket with a Green rim and Gray stripe immediately tells a technician they are holding a 316L Stainless Steel gasket with Flexible Graphite filler, as per ASME B16.20 guidelines.

Classification of Spiral Wound Gasket Types (Style R, CG, CGI)

Choosing the correct "Style" is as important as the material. The four primary configurations define how the Spiral Wound Gasket interacts with the flange face and the internal fluid:

• Style R (Sealing Element Only): Used in tongue-and-groove or male-and-female flanges. It lacks rings and relies entirely on the flange recess for centering.
• Style CG (With Outer Ring): The most common type for raised-face flanges. The outer ring centers the gasket and acts as a compression limiter.
• Style CGI (With Inner & Outer Ring): The "Gold Standard" for high-pressure/temperature service. The inner ring protects the windings from heat and prevents inward buckling.

Dimensional Spiral Wound Gasket Specification and Tolerances

Dimensional accuracy is governed by ASME B16.20 for pipe sizes 1/2" to 60" and pressure classes 150 to 2500. A critical specification is the uncompressed thickness. While most people assume the gasket is flat, the sealing element is actually thicker than the rings to allow for proper compression.

Determining Correct Spiral Wound Gasket Thickness

Standard Spiral Wound Gasket thickness for the sealing element is 4.5 mm (0.175"), which compresses down to approximately 3.2 mm to 3.4 mm when fully seated. The metal rings (Inner/Outer) are typically manufactured to a thickness of 3.2 mm (0.125"). Maintaining this differential is what ensures the "spring-back" or recovery necessary to seal fluctuating loads.

Spiral Wound Gasket Pressure Rating and Temperature Limits

Pressure ratings are intrinsically linked to the flange class. A gasket marked for Class 1500 can withstand significantly higher hydrostatic loads than a Class 300 equivalent due to increased winding density. Temperature limits are defined by the filler: Flexible Graphite can handle up to 450°C in oxidizing atmospheres, whereas PTFE is limited to 260°C. For cryogenic service, these gaskets remain functional down to -196°C.