How Do Serrated Gaskets Work in High Pressure Flange Connections?

2026-07-07

1. How Do the Serrations Create a Positive Seal Under High Bolt Load?

In our factory, we have produced Serrated Gaskets for over 15 years. The working principle is simple yet effective. When you tighten the flange bolts, the raised concentric serrations on the gasket surface bite into the flange face. Unlike flat gaskets that rely solely on friction, Serrated Gaskets create a mechanical interference. The serrations penetrate the oxide layer and minor surface imperfections, forming a labyrinth seal. This multi barrier effect prevents fluid from escaping even at pressures up to 2,500 psi. Our Ningbo Kaxite Sealing Materials Co., Ltd. uses a proprietary profiling process that produces serrations with a specific angle and depth. For a standard 300 lb flange, the serrations are typically 0.5 mm high with a pitch of 1.2 mm. When you apply 200 Nm of torque on M24 bolts, the serrations embed about 0.05 mm into the flange material, which is enough to create a gas tight seal. This is why Serrated Gaskets are preferred in refineries and chemical plants where even a tiny leak can be catastrophic.

2. Why Is the Soft Material Layer Critical for Serrated Gasket Performance?

Many people think that the metal core alone provides the seal. In our factory, we have learned that the soft facing material, such as graphite or PTFE, is equally important. The serrated metal core provides mechanical bite, but the soft layer fills the microscopic valleys between the serrations and the flange. Our Serrated Gaskets are available with a graphite facing that can withstand 450°C, or a PTFE facing for corrosive chemicals. When compressed, the soft layer deforms into the spaces left by the serrations, creating a barrier that blocks both gas and liquid permeation. Our Kaxite tests every batch for compression recovery. We aim for a recovery rate of over 45 percent at 300°C. This ensures that if the flange pressure drops and then rises again, the gasket still seals. Without the soft layer, the metal serrations alone cannot stop capillary leakage along the grain boundaries of the flange. That is why all professional Serrated Gaskets include a facing material.

3. What Technical Parameters Define a Reliable Serrated Gasket for High Pressure?

Performance depends on precise geometry and material selection. Our factory manufactures Serrated Gaskets according to DIN 2697, ASME B16.20, and BS 3381. The table below lists the key parameters we control.

Parameter	Our standard value (serrated metal core)	Impact on high pressure sealing
Serration pitch (distance between peaks)	1.0 – 1.5 mm (depending on size)	Fine pitch creates more bite points
Serration height (from root to peak)	0.4 – 0.6 mm	Sufficient to penetrate hard flange surfaces
Serration angle (included angle)	90 degrees (standard)	Balances bite and reusability
Core thickness (steel base)	2.0 mm for DN 150 – 600	Provides rigidity under bolt load
Facing thickness (graphite or PTFE)	0.5 mm per side (minimum)	Compensates for flange surface roughness

Property – Facing type	Graphite faced Serrated Gasket	PTFE faced Serrated Gasket
Maximum temperature (continuous)	450°C (oxidizing) / 550°C (inert)	260°C
Pressure class rating	Class 150 to 2500	Class 150 to 600
Chemical resistance	Excellent for most acids and hydrocarbons	Excellent for strong acids and solvents
Creep relaxation at 300°C	≤ 12% after 100 hours	≤ 8% at 200°C
Typical leak rate (helium)	< 10⁻⁵ mbar·L/s	< 10⁻⁶ mbar·L/s

Our factory also measures the coefficient of friction between the Serrated Gasket and the flange. This determines how much torque translates into compression force. For lubricated bolts, we recommend a torque reduction factor of 0.9 to avoid over compression. Our Ningbo Kaxite Sealing Materials Co., Ltd. provides detailed installation sheets with every order.

4. How Does the Serrated Gasket Maintain Load Over Thermal Cycles?

High pressure flanges often experience thermal cycling, which causes bolts to elongate and compress. A flat gasket might lose its seal under these conditions. Our Serrated Gaskets, however, retain spring back because the serrations act like small springs. When the flange cools and contracts, the serrated teeth push back against the flange face. This elastic recovery helps maintain gasket stress. Our factory has performed thermal cycle tests from 25°C to 400°C for 500 cycles. The Serrated Gasket maintained over 85 percent of its initial seal stress. We attribute this to the combination of a flexible graphite facing and a resilient stainless steel core. This characteristic is why many power plants use Serrated Gaskets in steam turbine connections. Without this load retention, the flange would require frequent retorquing, which is both unsafe and costly. Our design minimizes that need.

Frequently Asked Questions About Serrated Gaskets in High Pressure Flanges

Question 1: Can Serrated Gaskets be reused after flange disassembly?

Answer: While Serrated Gaskets are more robust than soft cut gaskets, we do not recommend reusing them in critical high pressure applications. The reason is that the serrations deform plastically during the initial compression, and the facing material also takes a set. Reusing a Serrated Gasket may result in uneven compression and potential leakage. Our factory has tested reused gaskets and found that the leak rate increases by an average of 40 percent on the second installation. However, for low pressure, non hazardous services such as cooling water, some plants do reuse them after careful inspection. If you must reuse, check for any loss of facing material, cracked serrations, or obvious flattening. Our Ningbo Kaxite Sealing Materials Co., Ltd. always recommends using a new Serrated Gasket for every critical flange opening to guarantee safety and performance. The cost of a new gasket is negligible compared to the risk of a leak.

Question 2: What flange surface finish is required for Serrated Gaskets to work properly?

Answer: The ideal surface finish for Serrated Gaskets is between Ra 3.2 µm and Ra 6.3 µm (125 to 250 microinches). This is a standard serrated finish produced by a lathe or grinding. If the flange surface is too smooth, say Ra 1.6 µm, the serrations may not bite enough, causing the gasket to slip during thermal expansion. If the surface is too rough, above Ra 12.5 µm, the soft facing material may not fill the deep valleys, leading to a path for leakage. Our factory recommends using a flange surface comparator to check the finish before installation. Many local pipe fitters in Texas and Alberta have adopted our recommended practice of applying a thin anti seize compound on the flange face, which helps the serrations bite without galling. We also advise against using spiral wound gaskets on the same flange as Serrated Gaskets because the required surface finishes differ. Stick to the recommended range and your Serrated Gasket will seal reliably.

Question 3: How does the serrated pattern differ from a corrugated or embossed design?

Answer: This is a common confusion. A Serrated Gasket has multiple concentric, sharp V shaped grooves cut into the metal core, usually with a consistent pitch and depth. A corrugated gasket has wider, rounded waves that are more like an undulation. The serrated design provides much higher contact stress per unit area because the tip is narrow. In our factory tests, a Serrated Gasket achieved a seal stress of 70 MPa at 100 Nm bolt torque, while a corrugated gasket only reached 45 MPa under the same condition. The embossed design is a hybrid where a pattern is stamped onto flat metal, but it lacks the precision of machined serrations. For high pressure flange connections, the machined Serrated Gasket is superior because it offers consistent bite and predictable compression. We supply both types, but for critical services like hydrogen or natural gas, our Ningbo Kaxite Sealing Materials Co., Ltd. always recommends the serrated version for maximum reliability.

Final Summary

Serrated Gaskets provide a unique combination of mechanical bite and soft facing seal that is ideal for high pressure flange connections. Their ability to withstand thermal cycling, resist creep, and maintain bolt load makes them the first choice for demanding industrial services. Our factory has refined the design and manufacturing process to ensure consistent quality. From material selection to final inspection, every Serrated Gasket we produce is tested for dimensional accuracy and sealability. Our Ningbo Kaxite Sealing Materials Co., Ltd. is your reliable partner for critical sealing solutions.

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