The reliability of a flange joint is determined not just by the quality of the industrial flanges themselves, but by the integrity of the sealing components: the gasket and the bolting hardware. The flange serves as the anchor, but the gasket provides the seal, and the bolts provide the compressive force.
This guide provides a systematic approach to selecting the correct gaskets and bolting materials, ensuring a tight, long-lasting, and compliant connection for all flange types.
1. Gasket Selection: The Key to a Leak-Proof Seal
The gasket must be capable of deforming to fill the microscopic imperfections on the flange faces and maintain that seal under the system’s operational pressure and temperature.
Step 1A: Determine Gasket Type (Non-Metallic vs. Metallic)
The choice depends heavily on the severity of the service:
| Gasket Type | Material and Structure | Ideal Application |
| Non-Metallic | Soft materials like rubber, compressed non-asbestos fiber (CNAF), or PTFE. | Low pressure (e.g., DIN flange PN10/PN16), low temperature, and utility service. |
| Semi-Metallic | Spiral-wound gaskets (SWG) using steel windings and a flexible filler. | Versatile; suitable for high pressure (e.g., ASME flange Class 300) and varying temperatures. Most common industrial choice. |
| Metallic (Ring Type Joint - RTJ) | Solid, soft metal rings (e.g., soft iron, SS316). | Extremely high pressure and high temperature (e.g., Class 900+), often used with Weld Neck Flange designs. |
Step 1B: Ensure Chemical Compatibility
The gasket material must be chemically inert to the process fluid. For instance, PTFE is excellent for highly corrosive chemicals, while certain elastomers are required for potable water systems.
Step 1C: Match Flange Face
Ensure the gasket is compatible with the flange types face:
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Full Face Gaskets: Used with Flat Face (FF) flanges.
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Ring Gaskets: Used with Raised Face (RF) flanges, sitting only within the raised area.
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RTJ Gaskets: Only used with flanges machined with the special RTJ groove.
2. Bolting Selection: Providing the Compressive Force
Bolts and nuts (often referred to as 'studs and nuts') must be strong enough to compress the gasket to its seating stress without yielding, both during initial tightening and throughout the service life.
Step 2A: Material Selection
Bolting material must be selected based on the flange material and the operating temperature:
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Low Temperature: ASTM A320 (e.g., Grade L7) is required for cryogenic or low-temperature applications.
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High Temperature: ASTM A193 (e.g., Grade B7 or B16) is the standard for high-temperature service and high-pressure ratings.
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Corrosion Resistance: For use with stainless steel flange in corrosive service, alloy bolting (e.g., ASTM A193 B8/B8M) is necessary to prevent galvanic corrosion between the flange and the bolts.
Step 2B: Lubrication and Torque Control
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Lubrication: Proper thread lubrication (e.g., molybdenum disulfide anti-seize) is critical. It reduces friction, allowing the calculated torque to translate accurately into the required bolt tension.
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Torque Sequence: Follow a standardized, often cross-pattern, bolting sequence (e.g., ASME PCC-1) to ensure the bolt load is applied evenly across the flange face, preventing gasket blowout or flange warpage.
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Related Guide: The importance of this control is highlighted in:
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3. Dimensional Coordination
The bolting hardware must adhere to the dimensions specified in the Flange Dimension & Weight Chart. The length of the stud bolts must be correct to allow for a few threads to protrude past the nut on both sides after tightening.
A successful flange joint is a balanced assembly where the gasket, bolt material, and applied torque are precisely matched to the pressure rating and material of the industrial flange itself.
Deepen Your Flange Knowledge
Mastering bolting and sealing is the final step toward joint integrity. Explore these related technical guides:
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Data Reference: Get the required bolt dimensions and weights for your design:
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Specialized Sealing: Understand why some systems require metal-to-metal seals:
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Core Flange Resource: Return to our complete overview of all flange types and pipe fittings:
Need assistance with specialized gasket material selection or complex bolt torque calculations? Contact us for Sealing Engineering Support.
