製油所であろうと、産業用フランジ接続に関しては, 化学プラント, 発電所, または海洋プラットフォーム - ジョイントの信頼性は、多くの場合 1 つの重要な要素に帰着します。: ガスケット応力. It’s the hidden force that determines whether your flange seals tightly or leaks under pressure.

この記事では, we’ll explore what gasket stress on flange actually means, why it’s essential for leak-free performance, how it’s calculated, and how to manage it properly during design and installation. Whether you’re a plant engineer, piping designer, or maintenance technician, understanding gasket stress is fundamental to flange joint integrity.

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What Is Gasket Stress?

Gasket stress, also known as gasket seating stress, is the compressive force applied per unit area of the gasket surface. It is generated by the preload in the flange bolts, which compress the gasket between two flange faces to create a seal.

Gasket stress is usually measured in units such as:

• MPa (megapascals)

• psi (pounds per square inch)

• N/mm² (newtons per square millimeter)

If the gasket stress is too low, the gasket may not seal properly, 漏れの原因となる. If the stress is too high, the gasket may be crushed or extruded, also leading to failure. これにより、 correctly controlled gasket stress essential to the performance of any bolted flange connection.

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Why Is Gasket Stress Important?

Gaskets don’t seal on their own. They require compression to fill surface imperfections on flange faces and to resist the internal pressure of the system. The primary roles of gasket stress include:

• Achieving initial sealing during bolt tightening

• Maintaining the seal during pressure and temperature fluctuations

• Withstanding internal pressure without being blown out

• Compensating for gasket relaxation or creep over time

Proper gasket stress ensures that the joint remains leak-free under both operating and transient conditions.

で SASA FLANGE, we understand that high-quality flanges are only as good as the gasket sealing they support. That’s why our flanges are designed and machined to ensure optimal gasket stress distribution in all applications.

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Components That Influence Gasket Stress

Several key factors affect the amount of gasket stress achieved in a flange joint:

1. Bolt Load (Preload)

The force generated by tightening bolts compresses the gasket. Bolt load must be sufficient to achieve the required gasket stress without exceeding material limits.

2. ガスケットの種類

Different gasket materials require different levels of stress:

• ソフトガスケット (PTFE, ゴム) need lower stress

• Spiral wound or corrugated metal gaskets need moderate stress

• リング型ジョイント (RTJ) and metallic gaskets require high stress

3. Gasket Seating Area

Smaller seating areas result in higher stress for the same bolt load. The contact width and geometry of the gasket are critical.

4. Flange Material and Rigidity

Flexible or thin flanges may deform, reducing effective stress on the gasket. Rigid flanges help maintain consistent compression.

5. Bolt Lubrication and Friction

High friction in threads or under bolt heads reduces the preload achieved for a given torque, thereby lowering gasket stress.

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Minimum and Maximum Gasket Stress

Every gasket material and type has:

• あ minimum seating stress – The stress needed to initiate the seal (often denoted as Y in ASME codes).

• あ maximum compressive stress – The limit beyond which the gasket material may fail or be crushed.

Typical Minimum Values:

• ソフトガスケット: 5 – 15 MPa

• うず巻形ガスケット: 20 – 50 MPa

• メタルガスケット: 70 – 200 MPa

Typical Maximum Values:

• Rubber gaskets: ~25 MPa

• PTFEガスケット: ~40 MPa

• 螺旋状の傷: ~150 MPa

• RTJガスケット: 300+ MPa

Exceeding these limits can cause leaks, blowouts, or damage to the gasket and flanges.

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How Is Gasket Stress Calculated?

The general formula for gasket stress is:

Gasket Stress (SG) = Bolt Load (F) / Gasket Contact Area (あ)

どこ:

• SG = Gasket stress (MPa or psi)

• F = Total bolt preload applied (N or lbf)

• あ = Effective gasket contact area (mm² or in²)

例えば, a gasket with a contact area of 2000 mm² compressed by 60,000 N of bolt force will have a stress of:

SG = 60,000 / 2000 = 30 MPa

This value is then compared to the required seating stress for the selected gasket type.

Design engineers often use specialized tools such as:

• ASME Section VIII Division 1 または 2 calculations

• EN 1591-1 analysis

• Flange design software (例えば, Caesar II, PV Elite)

• 有限要素解析 (FEA)

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Gasket Stress During Operation

It’s important to remember that gasket stress is dynamic, not static. After initial bolt-up, gasket stress can change due to:

• Internal pressure pushing back on the gasket

• Thermal expansion or contraction of flanges and bolts

• Gasket relaxation or creep 時間とともに

• Bolt relaxation or embedment in the flange face

Engineers must account for both initial seating stress そして operating stress, which is the net compression after internal pressure is applied.

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Flange Face Types and Their Impact on Gasket Stress

Different flange face finishes and types also affect gasket behavior and stress distribution:

• 盛り上がった顔 (RF) – Most common; concentrates load in a small area, increasing gasket stress.

• 平面 (FF) – Used for low-pressure, soft gasket applications.

• リング型ジョイント (RTJ) – Requires very high gasket stress; precision-machined grooves are critical.

• タング・アンド・グルーブ / Male-Female – Improve gasket alignment and sealing performance.

SASA FLANGE supplies all these flange face types and ensures that machining tolerances and surface finishes align with gasket requirements.

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Consequences of Incorrect Gasket Stress

Failure to achieve or maintain proper gasket stress can lead to:

• Leaks – The most immediate and common result.

• Gasket Blowout – Especially under high pressure or vibration.

• Flange Face Damage – From over-compression or incorrect gasket selection.

• Frequent Maintenance – Due to loosening bolts or gasket creep.

• Safety Risks – Especially in systems handling flammable or toxic fluids.

These risks highlight the importance of proper design, torque control, and flange manufacturing.

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Best Practices to Ensure Proper Gasket Stress

To get gasket stress right, follow these proven best practices:

1. Select the Right Gasket
   Match the gasket type and material to the pressure, 温度, and chemical environment.

2. Calculate Required Bolt Loads
   Use industry standards or software to determine preload and required torque.

3. Use Lubricated, Calibrated Bolts
   Friction can reduce preload by up to 50% if unaccounted for.

4. Tighten Bolts in the Correct Sequence
   Always use a star-pattern tightening method in multiple stages to achieve even compression.

5. Verify Bolt Tension
   Consider ultrasonic tension measurement or hydraulic bolt tensioners for critical joints.

6. Avoid Reusing Gaskets
   Most gaskets are designed for single-use only.

7. Inspect Flange Faces
   Ensure flatness, 表面仕上げ, and cleanliness before assembly.

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Real-World Example: Gasket Stress Failure in Refinery Heat Exchanger

In a Southeast Asian refinery, a newly installed heat exchanger suffered a serious flange leak during commissioning. The team discovered that:

• Spiral wound gaskets were used

• Flanges were slightly misaligned

• Bolt torque was uneven and under-specified

Gasket stress was below minimum values, allowing internal pressure to cause blowout. After recalculating bolt loads and reassembling with proper torque, the leak was eliminated—emphasizing the importance of understanding and managing gasket stress.

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結論

Gasket stress on flange is not just a technical calculation—it’s the foundation of reliable flange joint sealing. Too little stress, and the gasket won’t seal. Too much, and the gasket may be damaged or extruded. Achieving the correct gasket stress requires careful planning, 精度, and adherence to industry standards.

By selecting the right gasket, calculating accurate bolt loads, and using proper installation techniques, you can create joints that remain tight and safe over the entire lifecycle of your piping system.

で SASA FLANGE, we are committed to providing flange products that ensure proper gasket seating and sealing performance. Our flanges are precision-machined and quality-checked to support gasket integrity under all conditions.