Gasket Material

Although the word “fiber” is often used to describe sheet gasket material, fiber gasket material is a very broad category. In this blog post we’ll explore what types of material count as “fiber” and when and why you might want to use them.  Hennig Gasket & Seals is gasket material suppliers of all types. 

Two Main Categories of Fiber Material

“Fiber” can refer to vegetable fiber gasket material, or to sheets composed of fibers bound in an elastomeric matrix. Each provides varying levels of the temperature and chemical resistance, strength, and conformability needed in a good gasket, but there are differences between them. What’s more, within each category there are many variations of composition.

In addition, “fiber” can also mean ceramic fiber or cellulose-based gasket material. Those are quite specialized and won’t be covered here, but if you’re interested in them the specialists at Hennig Gasket  can help.

Vegetable Fiber Gasket Material

This material is made by a similar process to papermaking. Plant material is crushed and pulped to leave a mass of fibers. These are spread and dried as sheets.

Vegetable fiber gasket material, often referred to as “Detroiter” material, is very thin and has good dielectric properties. It’s resistant to water, air and most fuel oils, as well as gasoline and benzine. Adding cork to the mix results in a thicker, more compressible material.

Compressed Fiber Gasket Material

This is made by mixing aramid fibers in an elastomer like NBR or SBR, then rolling it into sheet form. Aramid is a contraction of aromatic polyamide, which is a high-strength synthetic polymer. (One of the tradenames it goes by is Kevlar.)

In gasket applications aramid supplies strength and temperature resistance while the elastomeric binder provides compressibility. Manufacturers tailor the material to specific gasket applications through elastomer selection and by varying the amount of aramid used.

Compressed fiber gasket material offers strength, good compressibility, and creep-resistance. Chemical resistance depends on the type of elastomer incorporated. As gasket material suppliers of a wide range of compressed fiber gasket material from well-known manufacturers like Garlock, Klinger, UTEX, Flexitallic and JM Clipper, we have the material to accmodate your application needs.

Gaskets seal everything from pipe flanges to manways but there’s no single gasket material that can do everything. However, Thermoseal C4401, (also known as Klingersil C-4401,) comes close. Here’s a quick review of how to select gasket material and an introduction to this versatile choice.

Factors to Consider

For every sealing application, a first step is to work out what material to use. This entails considering the temperature, environment, media, and pressure that the gasket will experience. (The mnemonic “TEMP” might help you remember this list.) Once those are known a gasket material can be chosen.

TEMP Compatibility Challenges

All gasket materials have a limited temperature range. Environmental concerns relate to things like exposure to ozone, UV light, and water. The media is the fluid being sealed in the pipe or outside the enclosure or man-way. And the pressure is the force the gasket will be exposed to.

Of these factors, media may pose the biggest sealing challenge. Every gasket material resists attack by some chemicals but is susceptible to others. EPDM for example is acetone-resistant but vulnerable to many fuels and oils. (Those examples are taken from “Gasket Material Compatibility Chart for Chemicals”.)

Meet Thermoseal/Klingersil C-4401

Thermoseal C4401 is one of a family of compressed fiber-reinforced gasket materials produced by KLINGER Thermoseal. These are made by mixing fibers into a rubber-like binder and then rolling it into a sheet. The fibers provide strength while compressibility and recovery come from the binder.

In Thermoseal C4401 the binder is a nitrile rubber and the fibers are aramid. Aramid is a light and strong synthetic fiber that resists abrasion and solvents. Nitrile is a form of synthetic rubber with excellent elastic behavior and good oil resistance. When combined the result is a gasket material that withstands temperatures as high as 750 °F (399 °C), and withstands a long list of chemicals.

Ask About Thermoseal/Klingersil C-4401

If you’re unsure about the media you’re sealing or just looking for a universal gasket material, C4401 is an excellent choice. Specialists at Hennig Gasket & Seals will be happy to tell you more.

Weather is hard on gasket material, thus identifying a weather resistant gasket material is important. Ultraviolet (UV) rays in sunlight attack bonds between carbon atoms in many rubbers. Ozone, (O3) often found in polluted industrial areas and around electrical enclosures, does the same. Temperature extremes, especially cold, affect material performance, as can moisture.

Open vs Closed-Cell Gasket Material

Open cells will absorb moisture. If temperatures drop to freezing the subsequent expansion could quickly destroy the material. Always choose closed cell material for a gasket that’s likely to get wet.

Materials to Avoid in Outdoor Applications

Inexpensive nitrile rubber/NBR, often selected for its good oil and solvent resistance, is not a good choice for weather resistant gasket material. The same goes for SBR. Nitrile gasket material is poor with both O3 and UV light, although water resistance is quite good. Its low-temperature limit is around -30F (-34C).

Better Weather Resistant Gasket Materials

Neoprene is a popular choice for gasket material but is not recommended for outdoor use. While it can handle a wide temperature range and offers moderate weather resistance, O3 resistance is poor.

Best Weather Resistant Gasket Materials

A little more expensive than Neoprene, EPDM is good for outdoor gasket applications not involving exposure to oils or solvents. EPDM provides a combination of good O3, UV, and general weather resistance.

Like EPDM, silicone gasket material resists attack by O3, UV, and general weather resistance, but also has excellent fungal and biological resistance. (Sometimes relevant in humid climates.) It has a wide temperature range but poor abrasion resistance is a limitation in applications with a significant joint movement or frequent opening. Silicone also suffers from high gas permeability and is not recommended for use with ketones, petroleum or chlorinated solvents.

For superior outdoor performance, fluorosilicone materials stand out. These have excellent resistance to O3, UV, and weather plus a very wide temperature range. They are also good with fuels. Their main limitations are poor abrasive performance and high price.

Gasket Material Selection Advice

Always consider the application environment when choosing weather resistant gasket material. Outdoor locations expose a gasket to UV light, weathering, and possibly O3. Extremely low temperatures can also be a problem. Hennig Gasket material specialists can provide further advice.

A common mistake when selecting gasket material is to consider only the upper temperature limit. Excessive temperatures can lead to gasket failure, but so too can low temperatures. The Challenger Space Shuttle disaster is perhaps the best known example of this.  Low temperature elastomers are worth looking at.

Gradual Transition

Metals are either solid or liquid with no fuzzy middle ground. Elastomeric materials like neoprene and SBR don’t have this clear melting/freezing point. They just become harder or softer. The dividing line is called the Glass Transition Temperature (Tg), but the difference in material behavior either side can be quite subtle. This makes it difficult for manufacturers of gasket materials to specify strict minimum temperatures. Instead, you’re more likely to see a range.

Elastomers and Low Temperatures

Low temperatures are a problem for elastomeric gasket materials, for two reasons:

1. The lower the temperature the more the elastomer resists deformation under load. That’s bad because the material needs to squash into the faces being sealed.
2. Low temperatures change compression set performance. A cold gasket material can take on a compression set and then leak as temperatures rise. (This is essentially what happened with the Challenger.)

Defining “Low”

In gasket terms, low temperatures are those which might be reached during winter in the upper Midwest. That means -20° to -40°F, which is far above the kind of cryogenic temperatures seen when processing and storing liquefied gases.

Gasket Material Selection

For very low temperatures, those down to -300°F, PTFE/Teflon gaskets are usually the material of choice. However, Teflon does tend to creep, making it unsuitable for some applications.

Silicone gaskets stay flexible at temperatures down to -80°F with some grades reaching -100°F. Nitrile rubber gaskets will typically work down to -80°F, although it’s important to check the material specs for details. Other elastomers harden before getting that cold, so always check material specifications.

Consider Both Temperature Extremes

Low temperatures can be as much of a problem for gasket materials as high temperatures. The loss of the Challenger serves as a reminder that gaskets may be exposed to temperatures below design limits.

Contact Hennig Gasket & Seals for your low temperature elastomer needs.

Fugitive emissions are a serious matter for chemical plants and petrochemical facilities. First, the EPA is focused on reducing unplanned releases of VOC’s into the atmosphere, and second, it’s a cost-saving opportunity. Studies blame valves for the bulk of these emissions, but flanged joints and their associated gaskets play a part too.

Hunting Fugitives

Defined as “… unanticipated or spurious emissions from any part of the process plant,” in 2014 the Fluid Sealing Association estimated fugitive emissions amounted to some 300,000 tons annually. Furthermore, it’s thought a high proportion are hydrocarbon gasses like methane believed to be environmentally harmful.

Plants handling such chemicals are expected to implement Leak Detection And Repair (LDAR) protocols, preferably on a monthly basis. “Sniffing” technology is the method most commonly employed, although IR camera technology is increasingly available.

Prevention First

Should a LDAR survey reveal a leak the next step is usually to shutdown the affected equipment for valve repair or gasket replacement. Unplanned shutdowns are disruptive and expensive, making it essential to avoid such events. While leak-free performance can never be guaranteed, buying different types of quality gasket materials and following good sealing disciplines will reduce the likelihood of problems.

Three Principles to Follow

• Select material appropriate to the media, pressure and temperature. Nitrile gasket material for instance is generally compatible with hydrocarbons like gasoline but should not be taken above 250°F. A neoprene gasket will perform better against ammonia, alcohols and mild acids while high temperature applications may need a fluorocarbon or PTFE gasket. In particularly arduous conditions a spiral wound gasket might be needed.
• Analyze the joint to determine material thickness and hardness needed. The general rule for gasket materials is “as thin and soft as possible.” The goal is always to ensure the gasket compresses sufficiently to seal the gap when the joint is bolted up. High bolt loads risk deforming the flange, potentially causing leaks.
• Follow good gasket replacement disciplines. Clean flanges thoroughly and verify mating surfaces are undamaged. Tighten bolts following the recommended sequence to avoid uneven compression and the risk of gasket extrusion.

Previous blog posts emphasized the importance of assessing the peak temperatures anticipated in a gasketed joint. Left unsaid has been why this matters. It’s probably obvious that polyurethane, nitrile and silicone gaskets all have a temperature at which they melt. More important, all will likely fail under prolonged exposure to temperatures near their melting point, due to a phenomenon called “creep.”.

Viscoelastic materials

Most gasket materials are viscoelastic. The “viscous” part means they have a propensity to flow slowly, like a thick gel and “elastic” refers to their ability to stretch and return to their original dimensions. However, elasticity has its limits. If the material is stretched too far it can’t return to its original size or shape, resulting in permanent “plastic deformation.”

Place a viscoelastic gasket material like polyurethane under load and it becomes thinner while simultaneously spreading outwards. This is “creep.” Releasing the load lets the material recover, but only to the extent that it has not been deformed plastically.

Creep relaxation

In a gasketed joint the material is compressed, either by the stretch of the flange bolts as they are tightened or by other retaining clamps. When first placed under load it starts to creep, but as the gasket thins the load lessens until the creep stops. This is termed creep relaxation. With good design this happens before the gasket reaches a point where the joint starts to leak.

Higher temperatures

Creep is related to temperature. When a polymer like polyurethane or styrene butadiene rubber gets warmer the molecular chains slide more readily. As a result it takes less force to produce a given movement. As the temperature approaches the melting point of the material, the force needed to produce a given movement falls quickly. To take one example, this means that at temperatures over 200 F (93 C) a nitrile gasket starts shows considerable creep.

Consider the material properties

Always select gasket material with the knowledge of the maximum temperatures expected. The more safety margin can be incorporated the less creep will be experienced, leading to a longer lasting gasket.