Flange Gaskets

Fiber or Rubber Gasket Material

One of the most important properties in a gasket material is compressibility, and this leads many gasket buyers to think they need rubber. In many cases though there is an alternative: fiber gasket material. “Fiber gaskets” is a broad heading as there are many different types. Here we’ll explain what “fiber” means, how it differs from rubber and other rubber-like elastomeric materials, and when you might want to use it.

What is a Fiber Gasket?

Fiber gasket material is made through a process similar to papermaking. Strands of fiber are spread out and impregnated with a resin material. This dries to form sheets that are easily cut to shape.

Many different type fibers are used to produce gaskets with differing strength, compressibility and temperature ratings. These range from vegetable fiber and cellulose to more exotic materials like aramid, (a strong, heat resistant synthetic fiber.)

When additional compressibility is needed cork or a rubber binder (often NBR) is added. Alternatively, cellulose fiber material can be vulcanized to make a paper-like material that’s both hard and lightweight. When this has electrical insulating properties it’s known as “fish paper.”

Possibly the oldest type of gasket still in use is the vegetable fiber or “Detroiter” gasket. This is made from vegetable fibers impregnated with a glue-glycerine compound. It remains a popular choice in some applications.

Fiber Gasket Properties and Applications

Fiber material makes gaskets with high tensile strength, (so they’ll resist internal pressure,) and an upper temperature limit of 250 – 350°F. They have excellent resistance to chemicals, particularly oils, so are used in many industrial situations, especially chemical and petroleum product manufacturing.

The Contrast with Rubber

While true rubber is a natural product, the rubber used in gaskets is almost always a synthetic version. Synthetic rubbers function over a wider temperature range and are less vulnerable to damage by UV light. Commonly used materials are nitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), neoprene and EPDM. Available in a range of thicknesses and grades of hardness, these have generally good compressibility but are vulnerable to the effects of petroleum oils.

Hennig Gasket & Seals manufactures custom gasket from a large variety of fiber gasket material.  Contact us today for a fast quote.

Flange Gaskets: Full-Face or Ring

When sealing raised or flat face flanges there are two choices of gasket shape: full-face gasket and ring-type. Each has advantages, so before ordering you should know which will suit your application best. You should also understand the measurements your gasket supplier needs before cutting material.

Flange Basics

ASME standards describe several designs, but the most common are the raised face and the flat face. The difference between them is that the raised face flange has a raised region surrounding the pipe bore. The bolt holes are outside of this. The flat face flange has no such step.

The Ring-Type Gasket

This is positioned inside of the flange bolts and around the pipe bore. In a raised face design it sits on that surface. This design:

  • Requires less material and less cutting.
  • Can be installed without completely dissembling the joint, (making it a “drop in” gasket.)
  • Is harder to clamp in position.

When specifying a ring type gasket only three measurements are needed: ID (which corresponds to the pipe bore,) OD (which is the same is the OD of the raised face,) and gasket thickness.

The Full-Face Gasket

Like the ring-type gasket, this seals on raised flange faces, but has an OD the same as the flange. That means it needs holes for the securing bolts to pass through, and these help locate it on the flange, making alignment easier. Extending out to the flange OD has the added benefit of filling the gap between bolting surfaces, which stops dirt getting in. However, the joint must be completely dissembled for installation.

Specifying a full-face gasket requires these measurements:

  • ID (same as the pipe bore.)
  • OD (same as the flange OD.)
  • Bolt circle diameter (the diameter on which all the bolt hole centers are located.)
  • Number of bolt holes (and spacing if they’re not be regular – which would be very unusual.)
  • Gasket thickness.

Finding The Bolt Circle Diameter

While ID and OD can be measured with calipers or even a tape, this dimension is harder to determine.

  1. Pick two holes diametrically opposite. One we’ll call left hole, the other will be right hole.
  2. Measure from the outer edge of left hole, (the side nearest the flange OD) to the inner edge of right hole, (the side nearest the bore.) That dimension is the bolt circle diameter.
  3. As a check, measure a second pair of bolt holes and make sure the distance is the same. Remember the rule: outer edge to inner edge!


Full-face and ring gaskets will do an equally good job of sealing the joint. The difference really boils down to installation preferences and priorities.

How Flanges Influence Gasket Material Selection

If flange and enclosure door surfaces were perfectly smooth and perfectly aligned, gaskets wouldn’t be needed. In the real world though, uneven gaps are always present and must be sealed to prevent leaks or contamination. Sealing options range from inexpensive red rubber and buna N materials to advanced silicone rubber gaskets, and include materials as diverse as graphite, PTFE and paper.

When replacing gaskets it’s common to use the same material that’s just been removed. If joints never change, that approach is often adequate. But by considering the nature and design of the sealing surfaces or flanges, it may be possible to select a longer-lasting material.

Impact of flange material

Some flanges can’t take high clamping forces, especially as they age. Plastics tend to become brittle and some metals lose ductility as they age, particularly if put through repeated temperature cycles. This means a soft, easily compressed gasket material is needed.

Impact of flange geometry

Bolt patterns or the position of clamps and latches can distort the mating surfaces, leading to uneven gaps. For example, an enclosure door with a single central latch can leave large gaps at the corners when closed. Also, a flange that’s been assembled and dissembled repeatedly for many years will start to distort, creating uneven gaps.

Flange alignment can change over time. After years of service it’s possible that piping will have moved, with the result that flange faces are no longer parallel. Again, the result is an uneven gap. Another problem is surface imperfections resulting from careless gasket removal.

These problems demand thicker gasket material that provides more compression. But thicker material needs higher loads to compress down in the joint, and those loads can lead to more distortion in the flanges.

Things change

Flanges and mating surfaces change over time and products that performed well, perhaps red rubber or buna N gaskets, may no longer be up to the job. When replacing gaskets, consider the condition of the sealing surfaces or flanges. A different material may last longer in the joint.


HVAC Sealing Material Primer

HVAC system seals and gaskets maintain efficiency by preventing the loss of heated and cooled air. Whether installing new ductwork, modifying an existing system, or just replacing worn out gaskets, it’s important to choose appropriate material. Many HVAC specialists consider neoprene gaskets the default choice, but it’s possible better performance could be achieved with EPDM or silicone gaskets.

HVAC Gasket Applications

Gaskets have three main roles in HVAC systems:

  • Sealing opening panels, flaps, and doors
  • Reducing transmission of motor or fan vibration
  • Allowing for thermal expansion and contraction


Almost every ducting system includes access doors and panels, along with dampers that close off airflow through “legs” of the system. To minimize closing forces, these need a soft material with good compressibility. Combined with appropriate thickness, such gaskets will also take up the dimensional variation and uneven edges inevitable in most systems.

Reducing Vibration Transmission

Fans and motors can cause a vibration in flat ducting that’s audible as a low hum. To avoid complaints from building tenants, incorporate gaskets at appropriate interfaces. The cellular structure absorbs the vibration and prevents it spreading throughout a system.

Expansion and Contraction

Metal ducting experiences significant dimensional changes in response to switching between warmed and cooled air. A gasket with good recovery takes up these changes while still maintaining a leak-tight seal.

Environmental Factors

Outdoor applications challenge HVAC gasket material as UV light degrades some materials, and moisture penetration must be avoided. Low temperatures and ozone might also be a concern in some applications.

HVAC Gasket Materials

Neoprene gaskets and those made from thermoplastic elastomers (TPE’s) generally perform when soft and resistant to compression set. EPDM gaskets work well outdoors as they stand up to sunlight and other weathering effects. Where air or gas temperatures are high silicone gaskets can be a good choice.

Closed cell materials may be preferable because air and moisture cannot pass through, although these are firmer, requiring higher closing forces.

Installation is simplified by using a pressure sensitive adhesive (PSA). This can be laminated on to the gasket material or can be applied in tape form.

Focus on the Cost of Sealing

Gaskets exist to seal joints or interfaces. They’re either keeping something in or keeping something from getting in, and if they do their job no one notices them. That’s probably why some gasket buyers find themselves under pressure to go with the cheapest. Only later do they find that a very expensive mistake.

Gasket failure is expensive

The consequences of a leaking joint range from the trivial to the fatal. At one end of the spectrum, if a pipe flange gasket lets a trace of toxic chemical into the environment the results can be unthinkable, and will probably incur the wrath of the EPA. Fines and clean-up costs could sink the most successful company. Or consider other less serious but still expensive examples. Water penetrating an electrical enclosure gasket could damage equipment inside, causing lengthy unplanned downtime. Failed boiler seals might shut down a heating system, sending employees home. Even when the impact is minor, a lot of time might be spent cleaning up, and a lot of product wasted.

Gasket replacement is expensive

There’s the time and materials to do the job and perhaps other expenses involved in accessing the gasket location, but these pale next to the cost of lost production. A single leaking pipe can bring an entire plant to a halt while a new gasket is installed. Planned replacement is always preferable to reacting to a leak, but either way takes equipment out of service for a period of time.

Lifetime reliability

The price of the gasket is a very small part of the cost of a sealing problem. Logically then, anything that extends the life of the gasket is worth doing.

There are many options for sealing a joint or interface. Gasket materials come with long lists of specifications. Interpreting these and selecting the optimal combination takes in-depth product knowledge and understanding. Gasket experts might find what they need in a catalog, but for most buyers the best option is to ask their supplier. They’ll be happy to explain the characteristics of each gasket material

Preparing Flanges for New Gaskets

Preparation is everything they say, and that’s certainly true for flanged pipe connections. As flanges are brought together and the bolts tightened, the flange gasket compresses and flows into surface irregularities. If those are too severe for the gasket material to fill, the joint will leak. Here’s some advice on flange preparation.

Step 1: Inspection

Examine both flange faces carefully for damage like cracks, dings, burrs and radial scoring. Scoring is the worst problem as this will almost certainly create a leak path. Also check for alignment and verify that the faces are flat and parallel. (It’s possible for flanges to warp if the bolts are tightened in the wrong sequence.) Some softer gaskets will tolerate flanges being slightly out of parallel, but this does depend on the material being used.

Also check bolts, nuts and washers for signs of damage or corrosion. If in doubt as to fitness for purpose, opt to replace.

Step 2: Clean the Mating Faces

It’s common for traces of the old gasket to remain on the flange surfaces. These can be removed with a wire brush or scraper. However, to avoid damaging the flange face, this must be made from a softer material. Brass is usually a good choice. Always brush in a circumferential direction and not radially.

Step 3: Preparation

Inspect the new gasket for damage and ensure that it’s the correct size for the joint. Don’t use any kind of sealant on the gasket or sealing faces unless specifically advised to do so by the gasket manufacturer.

Proper torque tightness is essential to deform the gasket and seal the joint. If there’s excessive friction bolts will seem to be at their torque limit when they’re not, resulting in leaks. This can be avoided by lubricating the threads and under the heads of the bolts. (Ensure the lubricant is compatible with expected service conditions.)

Do it once

Inspection and cleaning may seem time-consuming, but doing a job once is better than having to fix a leak. That’s why thorough preparation of flange surfaces is so important.  Contact Hennig Gasket & Seals for custom manufacturing of flange gaskets to your exact specifications.

Dealing with Expansion and Contraction of Flange Gaskets

A gasketed joint is rarely static. Changes in temperature can cause mating flanges to move apart or closer together, creating a variable gap that the gasket has to fill. That’s why understanding the influence of temperature helps when selecting the gasket material for flange gaskets.

Flanged joint dynamics

In service a gasket is compressed between two flanges. Sufficient load must then be applied to hold the joint closed, regardless of how conditions change.

Fluid moving through the pipe creates hydrostatic end thrust that opens up the joint. Internal pressure also creates side loading on the gasket, trying to extrude it out between the flanges. And changes in temperature result in expansion and contraction of both the piping and the fastening bolts.

Temperature influences

Temperature changes have two sources: the temperature of the fluid being transported, and the environment through which the pipe runs. In a continuous process media temperature may vary very little, but a pipe exposed to hot desert sun could experience a range of 80 deg F or more over a twelve hour period.

The influence of media temperature changes, (perhaps at start-up or shut-down,) will depend on the details of the pipework installation. However, most likely higher temps will act to close the gap between mating flanges.

Higher temperatures will make the flange bolts grow, so reducing the clamping force. Tightening to recommended torque levels creates some elongation that compensates for expansion, which is why proper jointing procedures should always be followed.

Of lesser importance, gasket materials and piping usually have different coefficients of thermal expansion. This may cause differential movement between flange and gasket which could, in marginal situations, open up a leak path.

Material selection impact

The ideal gasket possesses both good compressibility and good recovery or resilience, enabling it to maintain a seal as the gap between flanges changes and the compressive load varies. Natural rubber is one of the most effective materials, but is not always suitable.

The prudent approach is to discuss the application with the gasket vendor, being sure to make them aware of the various temperatures to which the joint will be exposed.  Contact Hennig Gasket & Seals today to discuss your flange gasket application.

How Hot is too Hot? Choosing the Right Gasket Material for a Non-Metallic Gasket

For non-metallic gasket applications, the operating temperature of the finished product is a major consideration. You need to know the temperature range (and other strengths and weaknesses) of potential materials so you can get the most durable custom gaskets and seals. Otherwise, they could prematurely harden, crack, deform and lose strength, elasticity and resilience, etc.

The following is a list of common non-metallic gasket materials, their properties and their most stable operating temperature ranges (in Fahrenheit). Understand that while there may be wiggle room on either end, it’s best to aim for somewhere in the middle of each particular material’s temperature range so that the gasket or seal performs optimally for the longest period of time before replacement is needed.

Nitrile: -30 to 250F (very resistant to oils, aromatic hydrocarbons, fuels and solvents).

Neoprene: -35 to 225F (resistant to weather, water, combustion and a long list of chemicals).

Polyurethane: -35 to 225F (resistant to oxygen, ozone, cracking, abrasion, cuts, grease and heavy loads; frequently used in machine mounts, electrical equipment wear pads and applications needing shock absorption).

Ethylene Propylene: -70 to 250F (resists severe weather conditions, acids, oxygen, alkalis, hot and cold water and ketones; not suitable for use with oils or fuels).

Fluorocarbon: -15 to 400F (its low friction and resistance to wear and tear make this a good material for gaskets that endure movement, a wide temperature variation and frequent reassembly).

Silicone: -65 to 450F (very resistant to hot, cold and oxygen, but poor resistance to oils and fuels; frequently used in food processing and medical applications).

Polytetrafluoroethylene: -238 to 574F (extremely wide temperature range, also stands up to harsh conditions of all sorts; frequently used in food processing, pharmaceutical, laboratory, semi-conductor, petrochemical and chemical and electrical applications).

Temperature range is, of course, just one aspect of a non-metallic gasket material that you will need to consider before project implementation; nevertheless, temperature tolerance is crucial. If you need custom gaskets and seals for your project, please call us at 1-800-747-7661 to discuss your needs with us.

Properties of Neoprene Gasket Material

Neoprene, which is also known as “polychloroprene,” is a type of synthetic rubber produced by the polymerization of chloroprene. Neoprene gasket material has become very common due to the fact that it resists the likes of ozone, sunlight, oxidation and many petroleum derivatives. Additionally, neoprene is characterized as being weather-, combustion-, water- and chemical-resistant. As you can see, it’s popular because it is resistant to many types of damages. What’s more, it’s also resistant to damage from twisting and flexing.

Here’s a closer look at the properties of neoprene so you can judge whether or not it’s a good material for your application:

  • Stretch and cushioning properties: Neoprene is elastic and form-fitting, able to conform to various sizes and shapes. It’s also cushioning, able to absorb shock.
  • Various grades available: From cloth inserted neoprene, which is reinforced with nylon for additional stability, to flame retardant neoprene, which passes a variety of flammability specifications, there are several grades available to suit any application. Other popular grades include commercial, FDA approved, diaphragm and high tensile strength.
  • General gauge thicknesses vary in size from 3/32-inch up to 2 inches.
  • Hardness ratings vary from 40 to 80.
  • Plate finish.
  • Neoprene can withstand temperatures ranging from -20 degrees F to 180 degrees F.
  • Tensile strength ranges from 900 to 1,000 PSI.
  • Elongation ranges from 350% to 400%.
  • Finally, widths are 36 inches, 48 inches or 72 inches.
  • Pressure sensitive adhesive, or PSA, are available upon request.
  • We fabricate neoprene gaskets through proven manufacturing processes that include waterjet cutting, flash cutting and die cutting.

One other neat feature about neoprene is that it’s impermeable, meaning that it can work as a tight barrier to prevent the escaping of gases or liquids.

For more information on the neoprene material and neoprene gaskets, and to speak with someone about placing an order, contact us today.