Low Temperature Elastomers

Jul 31, 2017

Low temperatures play havoc with elastomeric gasket materials, as NASA will testify. (Details of how seal failure caused the Challenger disaster are available on the NASA website.) The issue is that at low temperatures gasket materials like nitrile rubber and neoprene become stiffer and less able to fill gaps. The TR10 number, derived from ASTM D1392, shows the temperature at which this stiffening effects sealing performance. The problem for people buying gasket material is knowing how low temperatures can go and which low temperature elastomer is best.

Global Low Temperature

Military Standard MIL_HDBK_310_1851 “Global Climatic Data For Developing Military Products”, tells equipment developers what conditions to design for. This notes that the lowest temperature ever recorded is -68°C (-90°F), in the USSR. Statistically, the lowest temperature to be expected in the coldest regions of the world is -69°C (-92°F).

Low Temperatures in the USA

Weather.com tells us the lowest temperature experienced in the U.S. is -62°C (-80°F), in Prospect Creek Alaska. Closer to home, the lowest in the contiguous 48 is -57°C (-70°F), measured at Rogers Pass, Montana. For those in the Midwest, record lows in Illinois, Indiana and Ohio are in the -34°C (-30°F) range, while Michigan, Wisconsin, and Iowa have records ranging from -43°C to -48°C (-45°F to -55°F).

Of course, this is without the effects of wind chill. Air flowing over surfaces takes heat away, making the temperature appear lower than it actually is. And the harder the wind blows, the greater the cooling effect.

Implications for Gasket Material Selection

When selecting gasket material for outdoor applications it’s essential to determine the lowest possible temperature. Not doing so risks leaks during periods of extreme cold, which is never a good time to be replacing a failed gasket!

Most nitrile rubber, EPDM and neoprene gasket materials work down to around -46°C (-50°F). HNBR is limited to around -40°C (-40°F) while silicone will endure temperatures down to around -59°C (-75°F). (values vary for individual material grades.)

If a gasket might be exposed to low temperatures material should be selected to suit. Specialists at Hennig Gasket will be happy to advise.

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What is TR-10 (temperature of retraction) for Gasket Material?

Jul 17, 2017

Elastomeric gaskets, like those made from nitrile rubber and neoprene, work because they are flexible. Compressed in a flange, the material fills the gap between joint faces, regardless of how each side moves. When a joint gets cold the gap often grows wider, and the gasket material is expected to recover enough to maintain a good seal.

When elastomers become very cold they lose this ability. When choosing gasket material for an application that could see low temperatures it’s important to check it has sufficient low temperature flexibility. This is indicated by their TR10 number.

Low-temperature Behavior

Nitrile rubber and neoprene gaskets are flexible because they are made from entangled chains of molecules that move over one another. When temperatures drop, contraction limits the movement of these molecules and the material gets stiffer. Eventually, there’s no room for any movement and the material becomes brittle.

The “freezing” temperature of an elastomer is termed it’s Glass Transition Temperature (Tg). Strictly speaking, freezing happens over a range, and the brittle point is several degrees lower than the Tg. What matters for gaskets though is when the material loses any ability to recover.

The Temperature of Retraction

ASTM D1392 advises that “..retraction rate is believed to correlate with low-temperature flexibility of … rubbers.” Retraction is measured by first stretching and then freezing an elastomer. It’s then gradually warmed up, and as the molecular chains regain some freedom to move it starts to shrink back.

This recovery is measured against temperature and indicates when the elastomer transitions into rubber-like behavior. Experience shows this happens when it recovers by around 10% of it’s elongated length. The point at which this happens is the temperature of 10% retraction or TR10.

Gasket Material for Low-temperature Applications

If an elastomeric gasket will get cold, two things are needed: the lowest anticipated temperature, and the TR10 value for the candidate materials. If TR10 is not available use Tg as a substitute. For reliable in-service performance, ensure these values are lower than the worst conditions the gasket will experience.

Flange Gaskets
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Weather Resistant Gasket Material Selection

Jul 03, 2017

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.

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The Importance of Testing Gasket Material

Jun 19, 2017

One cause of leaking joints is fluid-gasket incompatibility. Some materials swell and others become brittle. Elasticity and recovery decline faster than expected and fluid finds a way out. Temperature and pressure accelerate this material breakdown and hasten premature failure.  Testing gasket material for performance becomes a very important exercise.

Your Situation May Be Unique

The published information about which gasket materials to use and avoid with various fluids is always only a guide. The range of fluids to seal is virtually unlimited, and environmental factors vary. The only way to be completely sure any given gasket material will perform satisfactorily is to put it in the application.

Sample Testing

Gasket replacement is often costly, so while there’s no better test than to see how it performs in-service this isn’t a practical approach. The alternative is to expose samples of the gasket material or materials being considered to conditions like those in the application.

The simplest approach is to immerse pieces of the candidate materials in the fluid. Retain a control sample to allow quick comparisons to the initial material condition. Recover a test piece periodically to check for deterioration, or set up multiple samples for a range of test durations. Overall test duration should be as long as possible to replicate the in-service conditions.

If equipment is available, heat or cool the material to the temperature expected. Obviously, temperature cycling is hard to replicate, as are clamping loads. If the gasket material will be used outdoors, and particularly if it’s likely to see sunlight, place one or more samples outside.

Evaluation

Ideally, you would measure thickness to assess swelling, and look at compression under load and recovery. Often though, visual examination and feel are enough to gauge if the material is going to survive in the application.

Ask Hennig

Testing gasket material still doesn’t guarantee a long life, but it does reduce the probability of premature failure. Compared to the trouble of replacing a leaking gasket the effort is often worthwhile. Hennig Gasket is always happy to supply gasket material samples for evaluation. If you’d like to run your own tests, contact us today.

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Gasket Leak Detection and Repair (LDAR) Protocols

Jun 05, 2017

Leaking volatile organic compounds, (VOCs) can cause breathing difficulties for people living or working near the source. Some VOCs, known as volatile hazardous air pollutants (VHAPs,) may even cause cancer or birth defects.

According to the EPA, valves are the largest source of leaks. They account for some 60% of the 70,000 tons of VOCs that escape each year. Next up are flanged connections, responsible for around 30% of “fugitive” emissions. Valves generally leak around the stem or gland. For flanged connections gaskets play an important role leak prevention.

Create a Formal Program

No business wants to be associated with problems like these. That’s why a leak detection and repair (LDAR) program is so important. LDAR is required under 25 different Federal standards, but even if a business doesn’t come under one or more of these, a program still provides benefits.

Leaks are lost product, and that’s wasted money. Leaks tend to get worse over time too, so early detection can prevent a larger problem in the future. Relying on informal, ad hoc inspections is no way to monitor equipment condition. Instead, use a LDAR program to formalize the process.

LDAR Basics

The EPA publication, “Leak Detection and Repair: A Best Practices Guide” explains how to run an effective program. The five key steps of this are:

  • Identify components that need testing for leaks – valves and anything that uses a gasket to seal fluids.
  • Define “leak” in terms of a ppm level. (The EPA suggests using a tighter level than required by applicable standards.)
  • Implement a monitoring program – “Method 21” is a formal process documented in the EPA booklet referenced above.
  • Repair leaks. The EPA recognizes that not all leaks can be fixed immediately but expects prompt action. Either keep gaskets on-hand or find a reliable supplier who can make-to-order and has short lead times.
  • Keep records

Choose Quality

Replacing gaskets can be expensive, but neglecting them could cost more. Buy quality gaskets from an established supplier and install them with care. That way they’ll last longer and you’ll have fewer problems.  Hennig Gasket & Seals has been in the business of manufacturing custom cut gaskets and seals for over 100 years.  Contact us today.

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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.

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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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