Raw Materials for Spiral Wound Gasket

In the critical world of industrial sealing, where pressure, temperature, and chemical resistance define success or failure, the Raw Materials for Spiral Wound Gasket are the unsung heroes. The performance, longevity, and reliability of the entire gasket hinge on the precise selection and quality of its constituent materials. At Kaxite Sealing, with decades of engineering expertise, we understand that a spiral wound gasket is only as good as the raw materials from which it is crafted. This comprehensive guide delves into the core materials, their properties, and the technical specifications that define premium sealing solutions for demanding applications across oil & gas, chemical processing, power generation, and beyond.

The Core Anatomy of a Spiral Wound Gasket

A spiral wound gasket is a mechanically robust seal created by winding a pre-formed metal strip and a filler material in a V-shaped spiral around a metal centering ring. This combination creates a resilient, spring-like structure that compensates for flange irregularities, bolt stress relaxation, and thermal cycling. The choice of raw materials for each component is paramount.

Detailed Breakdown of Raw Materials and Their Properties

1. Metal Windings: The Structural Backbone

The metal winding provides the gasket's mechanical strength, spring-back, and structural integrity. The selection is based on corrosion resistance, temperature capability, and strength.

• 304/304L Stainless Steel: The most common choice. Excellent general corrosion resistance. 304L has lower carbon for improved weldability and resistance to sensitization.
• 316/316L Stainless Steel: Superior corrosion resistance, especially against chlorides and acids, due to added molybdenum. The standard for chemical service.
• 321 Stainless Steel: Stabilized with titanium for superior resistance to intergranular corrosion at high temperatures (800°F - 1500°F).
• 347 Stainless Steel: Stabilized with niobium, offering similar high-temperature performance to 321 with excellent corrosion resistance.
• Alloy 20 (Carpenter 20): Excellent resistance to sulfuric acid and other aggressive chemicals. Contains nickel, chromium, and molybdenum.
• Monel 400/Alloy 400: A nickel-copper alloy with outstanding resistance to seawater, hydrofluoric acid, and alkaline solutions.
• Inconel 600/625: Nickel-chromium alloys for extreme temperatures and oxidizing atmospheres. Excellent strength and corrosion resistance.
• Titanium: Exceptional strength-to-weight ratio and superb corrosion resistance in chlorides, oxidizing acids, and seawater.
• Copper, Aluminum, Mild Steel: Used for specific, less aggressive services where cost or thermal conductivity is a factor.

2. Filler Materials: The Sealing Element

The filler material is wound concurrently with the metal strip, providing the primary seal by filling microscopic flange imperfections. It must be chemically compatible with the medium and capable of withstanding process temperatures.

• Expanded Graphite (Flexible Graphite): The most widely used modern filler. Superior chemical resistance (except strong oxidizers), excellent thermal conductivity, and resilient sealing from cryogenic to 450°C (842°F) in non-oxidizing atmospheres. Kaxite Sealing uses high-purity, low-chloride grades.
• PTFE (Polytetrafluoroethylene): Offers near-universal chemical resistance and a wide temperature range (-200°C to 260°C / -328°F to 500°F). Ideal for harsh chemical services. Available in white or filled grades.
• Ceramic (Mineral) Fiber: Used for extreme high-temperature applications, often up to 1000°C (1832°F) or higher. Provides excellent thermal resistance but less resilience.
• Mica (Phlogopite): A traditional high-temperature filler, resistant to steam and fire. Often used in power generation and turbine applications.
• Non-Asbestos Organic/Inorganic Fibers: Aramid, glass, or ceramic fibers bound with elastomers. Provide good general-purpose performance for moderate temperatures and pressures.

3. Centering/Guide Ring: Alignment and Compression Control

This outer ring holds the spiral wound element, centers it between flanges, and provides a compression stop to prevent over-stressing the winding.

• Materials: Typically carbon steel (for low cost, painted for corrosion protection) or stainless steel (304, 316) to match the winding material and service environment. Aluminum or other metals are used for specific needs.
• Function: Prevents inward buckling of the spiral wound element and ensures proper positioning during installation.

Kaxite Sealing Standard Material Combination Specifications

The table below outlines common standard combinations offered by Kaxite Sealing. Custom combinations are available for specialized applications.

*Temperature limits are approximate and depend on pressure, media, and continuous vs. cyclic service. Always consult Kaxite Sealing engineering data.

Critical Technical Parameters and Dimensions

Beyond material selection, precise engineering defines gasket performance. Kaxite Sealing gaskets are manufactured to ASME B16.20, API 601, and other international standards.

• Density (Plys per Inch): Controlled winding density (typically 3, 4, or 5 plys per inch) affects compressibility, recovery, and sealing force.
• Metal Strip Dimensions: Standard thicknesses range from 0.18mm to 0.25mm (0.007" to 0.010"). Width is precisely controlled for consistent V-shaped formation.
• Filler Thickness: Must be optimized in relation to the metal strip to ensure proper winding geometry and sealing performance.
• Gasket Width: The radial width of the spiral wound element is selected based on flange rating (Class 150, 300, 600, etc.) and inside/outside diameter.
• Inner & Outer Ring Identification: Kaxite Sealing gaskets often feature an inner ring for added blow-out resistance in high-pressure services and are clearly marked with material tags for traceability.

Raw Materials for Spiral Wound Gasket: Frequently Asked Questions (FAQ)

Q: What is the most important factor when selecting raw materials for a spiral wound gasket?
A: The single most critical factor is chemical compatibility between the process media and both the metal winding and the filler material. A material selection error here leads to rapid gasket degradation and failure. Always consult chemical resistance charts and, when in doubt, conduct compatibility tests or consult with Kaxite Sealing engineers for recommendations based on the exact service conditions.

Q: Why is Expanded Graphite so commonly used as a filler material?
A: Expanded Graphite offers an exceptional balance of properties: it is highly compressible and resilient (excellent recovery), seals effectively on relatively rough flange surfaces, has outstanding thermal conductivity, and resists a very broad range of chemicals (except strong oxidizers like nitric acid or saturated chlorine). Its wide temperature range makes it suitable for most common industrial applications.

Q: Can I use a 316 Stainless Steel gasket with Graphite filler for any chemical service?
A: No. While 316/Graphite is a versatile combination, it is not universal. The metal 316 is susceptible to corrosion from hydrochloric acid, sulfuric acid at certain concentrations and temperatures, and chlorides at elevated temperatures. The graphite filler is attacked by strong oxidizers. The selection must always be cross-referenced with the specific media, concentration, and temperature.

Q: What is the purpose of the inner ring on some spiral wound gaskets?
A: An inner ring, typically matching the winding metal, serves two key purposes. First, it prevents the spiral wound coil from buckling inward under high internal pressure, which could restrict flow or cause failure. Second, it provides a barrier that protects the filler material from direct exposure to erosive or high-velocity flow, extending gasket life. It is highly recommended for Class 600 and higher pressures and for erosive services.

Q: How does temperature affect the choice of raw materials?
A: Temperature impacts both metal and filler. Metals can lose strength or be subject to creep at high temperatures. Fillers have strict upper (and lower) temperature limits; for example, PTFE begins to soften above 260°C, while graphite can oxidize rapidly in air above 450°C. For very high temperatures, ceramic fiber filler with alloys like 347 or Inconel is necessary. Thermal cycling also demands materials with good fatigue resistance and recovery.

Q: My application involves thermal cycling. What material characteristics are vital?
A: For thermal cycling, the spring-back (recovery) of the gasket is paramount. The metal winding must maintain its elastic properties over the temperature range. Alloys like 321 and 347 are excellent for this. The filler must also maintain its integrity and not become brittle or degrade. Expanded Graphite generally performs well in cyclic service due to its resilience.

Q: What certifications or traceability does Kaxite Sealing provide for raw materials?
A: Kaxite Sealing is committed to full material traceability. We provide Mill Test Certificates (MTCs/CofC) for all metal winding and centering ring materials upon request. Our filler materials are sourced from reputable global suppliers with their own quality certifications. This documentation is crucial for quality assurance and compliance in regulated industries like oil & gas and nuclear power.

Q: Are there non-standard combinations available for unique challenges?
A: Absolutely. While the table above shows standard combinations, Kaxite Sealing specializes in engineering custom solutions. This can include special metal alloys (Hastelloy, Incoloy), proprietary filler blends, custom densities, or unique winding patterns to address specific challenges of extreme pressure, cryogenic temperature, ultra-high vacuum, or unique chemical cocktails.