Gasket Material Compatibility Chart for Chemicals

May 22, 2017

Selecting the right material for a gasket is never easy. Temperature and pressure must be considered, and so too must the nature of the fluid being sealed. Some combinations of fluid and gasket material are just incompatible. Choose wrongly and the gasket will fail prematurely. When purchasing gasket material, mention the intended purpose. That way a material specialist can tell you if there’s a better alternative.  View our rubber sheet gasket material compatibility chart for chemicals.

Learning More About Material Compatibility

Some of the most frequently used gasket materials are neoprene, nitrile rubber, EPDM, silicone and Viton®. (Technically, this last one is a DuPont tradename for fluoroelastomer or FKM as it’s known in the ASTM standards.) Each has strengths and weaknesses in terms of chemical compatibility. “Rubber Gaskets & Seals” on our website provides a summary of what chemicals various gasket materials do and do not work with.

The other way to approach material selection is from the perspective of the chemical. Unfortunately that means identifying every possible chemical, which makes for a very long list. For some commonly used fluids the lists below highlight good and bad combinations. But don’t rely solely on these – always ask advice!

Good Material Compatibility Pairings for Chemicals

  • Acetone (a form of ketone): EPDM
  • Aldehydes (found in many food ingredients): SBR
  • Ammonia: Good choices are neoprene and EDPM gasket material
  • Animal fats: Nitrile, Viton®
  • Automatic transmission fluid: Nitrile rubber (NBR) and Viton®
  • Brake fluid: EPDM and styrene-butadiene rubber (SBR)
  • Ethylene glycol (antifreeze): nitrile rubber, Viton®, EPDM and neoprene work well
  • Fuels and oils: Nitrile rubber (NBR), Viton®
  • Ozone: EPDM, silicone, Viton®

Bad Gasket Material Pairings for Chemicals

  • Acetone (a form of ketone): Avoid contact with nitrile rubber, neoprene, silicone and Viton®
  • Aldehydes (found in many food ingredients): Nitrile
  • Ammonia: Poor with SBR and Viton®
  • Animal fats: SBR
  • Automatic transmission fluid: Avoid EPDM, SBR and Silicone
  • Brake fluid: Viton®
  • Fuels and oils: EPDM, SBR, Silicone
  • Ozone: Nitrile and SBR

Seek Advice for Material Compatibility with Chemicals

These lists give only a superficial overview of a complex subject. The only sure way of selecting the correct gasket material for any given chemical is to seek guidance from a material specialist. At Hennig Gasket, if we don’t know we’ll find out.  Contact us Today.

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Gaskets for Low Temperature Applications

May 08, 2017

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.

Gasket Material
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How Do You Recognize a Quality Gasket

Apr 24, 2017

Gaskets themselves are inexpensive but often expensive to replace. A high-quality gasket fits well and prevents leaks or ingress of contaminants until the next scheduled maintenance, and preferably longer. An inferior product could leak prematurely, forcing an expensive unplanned shutdown That’s why it pays to buy good custom-cut gaskets, but how do you differentiate between one that’s high quality and one that isn’t?

Was the Gasket Protected During Shipping?

Look at the packaging the gasket came in. If that’s bent, folded or compressed there’s a good chance the gasket material has taken some kind of compression set. Does it look like it was exposed to sunlight? UV light will shorten the life of an SBR or nitrile gasket, although neoprene and silicone gaskets are less sensitive.

Cleanliness

Did the manufacturer take the time to clean both sides of debris from the cutting process? Small particles stuck between the flanges could create a leak path.

Gasket Material

Look to see that the gasket manufacturer has used the material you expected, (if that was something you specified,) and not a cheaper lookalike.

Gasket Edge Quality

This is determined by the cutting process used and the condition of the tooling and equipment. While the OD surface of a flange gasket is primarily just aesthetics, (unless it has to fit in a groove or channel,) a shoddy appearance reflects poorly on the installer.

Internal edges are more functionally important. Check for strings of material not quite cut through as these could get into the material flow. Likewise any cutouts, (like a bitemark,) can create a cavity that causes turbulence, creates noise and reduces flow velocity.

Fit

Check for dimensional accuracy before stripping down the joint or opening the flange! A quality gasket will be cut to exactly the sizes you asked, (within the limits of what the cutting process can do.)

Cutting Corners Never Pays

A poor quality gasket might cost a little less, but if the joint leaks and needs repair it can be a costly decision. That’s why you should know how to recognize a quality gasket.

Contact Hennig Gasket & Seals when you require high-quality custom cut gaskets.

Gaskets & Seals
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Steam Gasket & Material

Apr 24, 2017

Heating, sterilization, humidification and power generation are a few of the ways steam is used in industry and commerce. Steam systems combine heat with pressure so any leak in pipework is potentially dangerous. This is especially true when using steam that’s superheated, and therefore not visible to the naked eye. To reduce the risk of leaks, material for steam system gaskets should always be selected with regard to the specific requirements of the equipment being worked on.

Steam Gasket Requirements

Steam is water vapor at or above 212°F (100°C). In steam systems, it’s under pressure and usually at higher temperatures. The temperatures and pressures used vary by system and these need determining before selecting a steam gasket.

Superheated steam is steam at temperatures above the saturated steam curve for that particular pressure. Temperatures of 500°F (260°C) or more are possible, creating special requirements for gasket materials. Here we’ll address materials suitable for gaskets in conventional saturated steam systems.

Steam Gasket Material

Many common gasket materials don’t handle steam well. Neoprene and silicone are two examples. Nitrile rubber or NBR is another material seldom recommended, mainly because depending on formulation its upper temperature limit is around 300°F (150°C)

One good steam gasket material choice is Ethylene Propylene Rubber (EPDM.) EPDM gaskets will handle steam at temperatures up to 395°F (200°C) and also provide good resistance to dilute acids and alkalies, alcohol, ketones and automotive brake fluids.

Styrene-butadiene rubber (SBR) gaskets are another good choice. While lacking the upper temperature limit of EPDM – 340°F (170°C) is about their limit – they do hold up well to steam. Particularly in cloth-inserted grades SBR gaskets resist both pressure and high compression loads.

Select for the Specific Application

Steam systems can be difficult to gasket because temperatures and pressures vary between systems. When seeking material for steam system gaskets always determine the properties of the system to be sealed. Don’t use a gasket purchased for one system in another that may have different characteristics. As always, material specialists at Hennig are available to answer any questions.  Contact us today.

Flange Gaskets
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What is Neoprene

Apr 10, 2017

Possibly the most widely used (and certainly the type we’re asked for most), neoprene gaskets are a good choice in many applications. However, they do have some limitations. It’s easier to understand when and when not to use neoprene gaskets if you know something about the material. Here we’ll answer: What is Neoprene? What makes neoprene so useful in many gasket applications? And when you should look for something else.

Rubber-Like Elastomer

In the 1930’s and ‘40’s scientists cooked up several types of artificial rubber. Styrene-butadiene rubber (SBR) and nitrile-butadiene rubber (NBR) are two of the best known. A third was neoprene. Like NBR and SBR, it’s mainly carbon and hydrogen, but has chlorine added to each molecule. That makes its chemical name chloroprene, or polychloroprene once polymerized. The ASTM D1418 designation for neoprene, which was DuPont’s tradename, is CR. The ASTM D2000 type and class is BC and BE, depending on the specific grade.

Useful Properties of Neoprene

The first ASTM D2000 letter tells us the upper-temperature limit of neoprene is 212°F (100°C). The lower temperature limit is around -30°F (-34°C), although neoprene becomes stiffer before getting that cold. The second letter indicates that it is prone to swelling when exposed to oils.

Neoprene does, however, resist attack by mineral and vegetable oils. It’s also resistant to ozone and weather aging, making it useful in outdoor applications.

It takes relatively little force to deform, which helps make neoprene gaskets versatile. Shore A durometer numbers are typically 50 – 70, meaning it’s quite soft. (Learn more about Shore and Durometers in, “Understanding Gasket Material Hardness” and “Measuring Gasket Material Hardness.”)

Neoprene Limitations

Aromatic hydrocarbons like benzene and toluene will degrade neoprene, as will ketones and chlorine-based chemicals. While it has many uses, neoprene should not be used with food.

Neoprene Material Forms

Neoprene gaskets are typically cut from sheet material. A range of thicknesses and hardnesses are available. Neoprene can also be foamed and is available in both open and closed-cell forms. This has the advantages of lower density and greater compressibility. Hennig material specialists can provide more details.  Contact us for your custom neoprene gasket material needs.

Neoprene Gaskets
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The Role of Fiber Gaskets

Mar 27, 2017

While there are many new elastomeric sealing materials, it’s often prudent to follow the mantra, “What comes out of the joint goes back into the joint.” Especially in older processing and heating equipment that is often a fiber gasket. Many different materials can be used to provide the fibers, so the properties and applications of these gaskets vary enormously.

Back to Asbestos Gaskets

In 1899 an Austrian called Richard Klinger discovered a way of making effective soft gaskets by compressing asbestos fibers into sheet form. These sealed under low loads and resisted steam, oil, water and high temperatures and pressures. That made them ideal for use in boilers, heat exchangers and heating and hot water systems as well as oil refining and other process industries.

By the 1980’s the health hazards of asbestos were well-known and gasket manufacturers were substituting other materials with similar properties. Sticking with fibrous material in a binder meant they could use the existing manufacturing processes, one reason why fiber gaskets remain commonplace today.

Modern Fiber Gaskets

The main types of fiber gasket material are:

  • Cellulose
  • Cellulose with rubber
  • Cellulose with insulating fiber
  • Cellulose with synthetic fiber
  • Cellulose with vulcanized fiber
  • Vegetable fiber (Detroiter)

These are all available in a range of sheet thicknesses and die-cut readily. They are considered “soft” gaskets, meaning they are suitable for applications with relatively low clamping forces, such as Class 150 and 300 flanges.

Fiber Gasket Properties

Gasket properties are determined by both fiber and binder material. For example:

  • Vegetable fiber (Detroiter) gaskets – upper temperature limit of around 250°F (121°C), good resistance to oil, gasoline, water and steam. Generally inexpensive.
  • Cellulose fiber with rubber – upper temperature limit around 350°F (177°C), good resistance to oil, gasoline, water and steam.
  • Aramid fiber in NBR binder – upper limit on temperature can be up to 825°F (440°C), suitable for a wide range of industrial applications.

Fiber Gasket Identification

If you’ve removed a fiber gasket and aren’t sure what type it is, bring it in. Our materials experts should be able to help.

Fiber Gaskets
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Brewery Gaskets? We’ll Drink to That!

Mar 13, 2017

Most gaskets are used to seal fluids or for environmental protection. Every so often though we are asked for a gasket for a less common application. One interesting example is the silicone or EPDM gaskets used around manways in brewery tanks.

Equipment Cleaning

Brewing depends on fermentation, a natural process involving lots of enzymes and chemistry. If the equipment is less than perfectly clean bacteria may contaminate what will become beer.

To avoid this, breweries clean and sterilize rigorously. Every mash tun and fermentation tank, plus the pipework in between, is treated with steam, caustic cleaning solutions, or both. Larger tanks often need someone to go inside to do the cleaning, which is why they’re usually constructed with a “manway”.

Manway Gaskets

A “manway” is an entrance point big enough for a man to enter through. Usually circular or oval, if located at the bottom of the tank, they need to withstand the pressure and temperature of the liquid inside. Some are just cover plates bolted to a flange, but in brewery equipment, it’s far more common to have a hinged door that clamps shut.

Regardless of design, every manway needs a gasket to stop it leaking. Those used in breweries must tolerate cleaning chemicals and steam as well as process heat. To avoid the need for high clamping forces, they should be soft, and ideally will resist taking a compression set. They also have to be food-grade to avoid imparting any kind of taint or contamination.

Suitable Gasket Materials

For manways in brewery tanks food-grade silicone and EPDM gaskets are the most common choice. Both are elastomers, so while they are elastic and deform under even quite light loads, they do not compress. Silicone gaskets have the higher temperature limit, typically 400°F (204°C), and are resistant to fungal attack, but have poor tolerance to steam.

EPDM gaskets have a lower upper-temperature limit, (250°F – 121°C) but are resistant to steam, ozone, acids, and alkalis. For this reason, these are the type of gasket used in many brewery tank manways.

Manway Gaskets
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Hennig Gasket & Seals – Part of Chicago

Feb 27, 2017

Hennig Gasket has been in business close to a century, and there’s still a Hennig at the helm. The business was started by Otto Hennig in 1920 before passing to James Hennig. He ran it for forty years until his retirement in 1987, and now it’s run by third and fourth generations of the family.

A lot has changed in that time. When Otto Hennig started the business the automobile was in its ascendancy, electricity was spreading across the country, and demand for gaskets for heating systems and manufacturing operations was growing. Of course, Chicago endured a few challenges in that period, but who knows, maybe cork or fiber gaskets made by Hennig found their way in to some of the bootlegger’s stills!

Some things haven’t changed though. We still make traditional cork and fiber gaskets, die cutting them from sheet, or if we don’t have the tooling, using an oscillating knife or even just hand cutting. If you’re maintaining or restoring aging equipment that used gaskets like these we can supply replicas of the originals. Alternatively, you may prefer upgrading to one of the many modern gasket materials that manufacturers have developed.

One example of material changes is the rise and fall of asbestos gaskets. Once essential in high temperature applications like boilers, (and perhaps stills,) these have been replaced by a range of non-asbestos gasket materials like Garlock BLUE GARD®. (This incorporates aramid fibers in a nitrile, neoprene or SBR binder.)

Neoprene and SBR gasket materials have themselves been around a long time, (just like Hennig Gasket & Seals!) but today there many newer alternatives. Elastomers like EPDM and FKM are proving valuable in many applications, especially for sealing against corrosive and high temperature fluids.

The best way of learning about gasket material properties is by speaking with an expert. At Hennig we’ve accumulated a wealth of knowledge and experience. And if you’re in the Lower West Side neighborhood of Chicago, call in. Just look for the brick mill-style building at 2350 West Cullerton.

Gaskets & Seals
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Understanding Gasket Tolerances

Feb 13, 2017

Like everything manufactured, gaskets have tolerances on their key features. These are dictated by a combination of material characteristics and manufacturing process. It’s important to understand these tolerances if your new gasket is going to fit.

Key Features

Unless a gasket goes in a channel the outer dimensions aren’t usually critical. What does matter though are the bolt hole positions, bolt hole diameter, and the inner shape, (because the gasket should not intrude into the flow.)

Gasket Material Thickness

Tolerances are dependant on the type of material and industry standards.  RMA commercial gauge sheet rubber tolerance chart shows typical tolerances. 

Manufacturing Process Tolerances

Here at Hennig, gasket material is cut in four ways: die cutting, oscillating knife (flash cutting,) water jet and by hand. Die cutting, used for quantity orders, is probably the least accurate yet also the most repeatable. The oscillating knife and water jet machines provide excellent accuracy, and as they cut one gasket at time repeatability is about the same. Hand cutting is the least accurate.

Here’s some more detail on each process:

  • Die cutting. Accuracy, defined as conformance to design, is set by the precision to which the steel rule is set into the mounting block. A laser-cut block can usually hold +/- 0.015” (+/-0.381mm) although this tolerance increases with the size of the tool. Larger tools are less precise. Softer, thicker material deforms more during cutting and a convex edge profile may result. Die-cut gaskets are very consistent, with the first piece identical to the last, (until the blade starts to wear.)
  • Water jet cutting. Accuracy is set by the precision of the gantry and table motion. In general, this is around +/-0.007”.
  • Oscillating knife. Machine repeatability is claimed as 0.010mm but in practice +/-0.003” (+/-0.076mm) is more typical. Softer and thicker materials can show greater variation.

Consider Tolerances When Ordering

Critical gasket dimensions influence the choice of cutting methods. In such cases, it’s important to let us know about these at the quotation stage.

Flange Gaskets
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The Role of Gaskets in Minimizing Fugitive Emissions

Jan 30, 2017

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.
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