Let’s talk about the importance of potable water. Safe to drink, even for infants, clean water supplies keep nations hydrated. The livestock on farms, the vegetables in fields, the taps in your home, they’re all categorized as potable water. This life-sustaining fluid is conditioned, often recycled and filtered, and it’s rarely squandered. Accordingly, it’s imperative that a water-sealing gasket functions as intended, with plenty of leak proofing strength.

Qualities to Look For In Potable Water Gaskets

Consider the nature of the liquid that’s flowing in a utility pipe. To be perfectly honest, the conditioned water isn’t wholly natural, not anymore. Additives have been introduced into the water supply. There’s chlorine in the line, with its disinfecting properties acting as a germ killer. In some communities, they also add fluoride to drinkable water supplies. The chemical additive protects the general public from tooth decay. For that latter additive, there’s some debate over whether the chemicals work, but that’s a matter for those who study such issues. Back with a potable water line, gaskets are installed that won’t weaken when a chlorine-mixed water supply flows.

Leach-Immune Water Fitting Sealants

So far, so good, the chosen gaskets in a potable water supply line can’t be damaged by abrasive water additives. If there are chloramines or ammonia, fluoride or some orthophosphate compound in a hydration line that’s meant for human consumption, then the applied rubber, fibre, or plastic gasketing medium cannot be sensitive to such moderately abrasive chemicals. Next, there’s another issue that can cause consumer concern. Briefly, if the sealing medium contains a chemical base that can be “leached” out of the rubber by a fast-flowing stream or one that’s hot, then this substance is clearly unworkable. To be clear, safe water supplies adhere to the AS/NZ4020 national standards, the NSF/ANSI 61 regulations, and Australia’s own WaterMark certification scheme. All of these rules are rigidly observed by pipe installers and gasket manufacturers.

Unstable elastomers with leach-sensitive plasticizers are clearly not utilizable in water lines or their fittings, not when those chemicals could prove hazardous to someone’s health. Having clarified that point, a few gasket labels are needed to close out this post. EPDM seals are chloramine resistant and hydrolytically stable. Durlon 7910, a branded gasket material, is another likely candidate. Nitriles and elastomers that satisfy the NSF/ANSI 61 standards also fall tidily into this category. Remember, people, livestock, crops, food preparation areas, and general potable water mains supplies all require leach-immune gaskets. To retain that key quality, they also must resist abrasive water supply additives, including chlorine and ammonia.

Anti-stick compounds coat gaskets so that maintenance techs can easily remove aging ring seals. If fibre or polymer reinforced gaskets didn’t include non-stick plating, how could a tech remove a used seal? Remember, when it was installed, torque-tensioned bolts crushed the material against two flange faces. Sure, that action does prevent pressurized fluids from creating a leakage pathway, but a cost is exacted after the fastener tightening work is done.

Anti-Stick Gasket Coatings Serve the Maintenance Sector

Upon watching someone tightening the bolts around a pair of flanges, it’s hard to believe this joint could be anything less than a permanent fitting. Masses of torque are pattern-tightened around the flanges. The gasket inserted between those faces is compressed until not one single drop or wisp of pressurized fluid can escape. Only, what if the pipe connection needs to be disassembled for some reason? Maybe a new generation of gaskets is taking over, or maybe the current seal is aging badly. If the flanges separate, after the bolts have been uncoupled, of course, then that obsolete material ring shouldn’t be impossible to remove. Even though it was compressed by unimaginable mechanical forces, an anti-stick coating should be in place so that an outmoded gasket can be removed without any kind of hassle whatsoever.

Employed as a Creep Relaxation Arbitrator

The case described in the above text is easy enough to picture. Surfaces and materials stick when they’re squeezed into a thinner shape for any length of time. How about the installation headaches encountered during a gasket’s installation, though? As the hard metals and tough fibres are crushed between two flange faces, they begin to spread. The squeezing mechanical force causes a gasket to thin and move outwards to the edge of the flanges. Usually, there’s nothing to worry about when this wholly expected spreading action occurs. However, static surfaces can “catch” or “seize up” when they spread over rough flange grains. When this happens, a gasket experiences strain. It distorts slightly and weakens. By coating gaskets in anti-stick coatings, they expand evenly under the crushing pressure. No creep distortion will take place when a gasket slips evenly under the compressive tightening pressure.

There are two primary reasons for adding a non-stick gasket coating. The finish performs as a creep relaxation compensation mechanism. As the flange fasteners tighten, a fitted gasket expands evenly. Essentially, that ring remains circularly shaped, even when it’s exposed to great compressive energies. Secondly, anti-stick finishes allow maintenance services to do their jobs without any gasket-sticking impediment getting in their way. The old gasket slips free. Otherwise, sticking stubbornly to the flanges, this work might just require the services of an abrasive tool, one that could possibly damage the flange faces.

Constant seating stress gaskets function as flange-interface fulcrums. That’s a difficult term to interpret, especially for non-engineering types. Picture a gasket with a uniform carrier ring. This incompressible metal annulus absorbs the bulk of sealing stress as a ring of pattern-tightened bolts pulls two flange faces together. Cleverly placed at a stress-neutral location on the gasket face, the annular acts as a ring-shaped pivot zone, one that evens out any and all mounting stress.

Following Flange Face Trajectories

It’s a simple enough movement, isn’t it? Two flanges come together, bolts tighten, and a gasket compresses. A perfect seal is produced. Only, that’s not really what happens in real-world gasketing applications. When those two faces meet, they actually deform slightly, right at the outer edges of the flanges. They bend slightly as they compress a gasket. With more strain pushing the outer surfaces, the inner section of the joint experiences a reduction in seating uniformity. It’s like the seating load is splitting into pressure bands. Out at the furthest edges, the load is highest. Moving inwards, though, the seating load drops off precariously.

Constant Seating Stress Compensation

Granted, this effect is imperceptible when measured on a pipe and gasket joint that uses small diameter flanges. What, however, if the flanges are wide and flat? Flange deformation is the cost here. By fitting constant seating stress gaskets, we counter this seal undermining effect. The steel annular, the centrally positioned ring, which protrudes a few key millimetres outwards, performs as a seating compensation feature. Of course, the ring isn’t meant to function as a pliable seal. This is a rigid section of incompressible metal. To complete the gasket, the annular needs one or more additional rings, which are typically fabricated out of PTFE or some other similarly high-functioning gasketing rubber. At any rate, once the flange sections on a stress-susceptible pipe joint do tighten, this artificial fulcrum is right there, centrally positioned as a stress-mitigating fulcrum, and those flanges won’t deform.

Different issues crop up when flange forces aren’t uniformly distributed. Creep relaxation problems and flange compressibility effects climb dangerously high because of the uneven loading. On-site technicians can see the consequences. They’ll see that the flange edges are pulled tighter towards one another. There’s no way the gasket between those faces can be uniformly compressed. On taking the joint apart, more signs of uneven compression are spotted on the gasket and the flanges. If these sealing defects are confirmed, the fitter really should replace the seal with a constant seating stress gasket, one that uses a steel annular as a load balancing fulcrum.

Polyurethane is a remarkable material. Used in gaskets, the infinitely adaptable polymer takes advantage of its resilient molecular structure to create a whole range of industry-leading products. Adhesive substrates and industry foams have drafted in many different urethane enhanced products. Similarly beguiled by the polymer’s application resistive properties, the gasketing sector hasn’t been slow in adopting a whole smorgasbord of polyurethane derived gasketing products.

Polyurethane Gaskets Exhibit Superior Mechanical Strength

Before talking about chemical resistance and heat indefatigability, let’s see if polyurethane gaskets have any physically relevant strong points. Mechanically tough, the flexible plastic deforms but doesn’t abrade easily. It’s a compressible substance, but gaskets made out of PU (PolyUrethane) have a gift for regaining their shape after flange loads are removed. Cut and nick resistant, crack and tear impervious, too, gaskets made out of this polymer are designed to be application robust. And yet, somehow, through the art of chemical reprocessing, the plastics and foams that PU can be formed into are highly adaptable. A gasket can be rigid and as durable as a comparable metal ring. Alternatively, the sealing product can be formulated so that it exhibits a high elasticity coefficient.

Illustrating Harsh Application Examples

So, polyurethane gaskets are physically tough. Even high tensile steel is tough, but it can corrode when attacked by oxidizing fluids. No worries, PU seals are chemically tough, too. They also retain their sealing properties when the temperature drops low or climbs high. A -60°C to 149°C span of nominal effectiveness is typically attached to a gasket made out of die-cut polyurethane. Chemically, the polymer functions unaffected when assailed by corrosive chemical streams, oils, hydraulic fluids, and solvents. Therefore, expect to see PU gaskets used heavily in chemical processing and oil refining facilities. However, these pressure and temperature-capable plastics do not do well against alcohols. If the gaskets are used on the crude oil side of a refinery, they wouldn’t then be employed as after-fractionalization gaskets, not in pipes and fittings that contained alcohol-like fractions.

To overcome application generalization issues, tailored polyurethane families have become available. All the same, a more focused study should be conducted before a series of polyurethane gaskets are installed. For example, PU seals are designed to handle most acidic bases and solvents, but that doesn’t mean the gasketing material will function as a universally acid proof plastic. At the end of the day, polyurethane gaskets slot into an industry opening, one that exists between flexible rubber gaskets and metal strengthened rings. They can be every bit as resilient as that metal, as pliable as the rubber, just by adding an additive or polymer-tailoring operation.

Polytetrafluoroethylene, which is also known by abbreviation aficionados as PTFE, is a versatile gasket material. It’s a fluoroelastomer, a synthetic compound that’s available in many forms. On switching over to ePTFE (Expanded PTFE), the carbon-fluorine compound gains new mechanical properties. Classed as a popular sealing material because of a talent for resisting chemical attacks, ePTFE adds greater material conformability and creep resistance to an already impressive set of features.

What is ePTFE?

It’s a synthetic plastic that incorporates all of the features of PTFE while also adding a new set of mechanically improved attributes. That means expanded PTFE operates across a wide range of service temperatures and can shrug off caustic fluid attacks, as imposed by some of mankind’s harshest chemical mediums. On top of that, the plastic is more rubber-like, more conformable and seal-pliable. It goes without saying, but let’s say it anyway; these are the physical attributes that attract the gasketing industry. Resistant to high pressures, high and low temperatures, and material eroding chemicals, PTFE is a desirable gasket medium. Expanded PTFE, on the other hand, retains all of the above features, then it adds mechanical flexibility to an already attractive package.

Expanded PTFE: Uses and Applications

First and foremost, the conformable plastic finds itself die-cut into rings and seated against large flange faces. Heavy-duty bolts and nuts are tightened in special patterns so that installer-imposed compressive forces surround a seal and pipe cavity. The point being, ePTFE can endure the highest imaginable compressive energies, yet gaskets made from this flexible fluoroelastomer seal won’t crack under the pressure. Creep and blowout impervious, too, the gaskets can contain high-pressure fluid streams. Because of these features, expect to find ePTFE gaskets used in the kind of applications that employ continual thermal cycling. In oil refineries and chemical processing plants, in cryogenics facilities and heat exchanger usage areas, the seals cope with high-to-low temperature transients. Low-to-high thermal variances are similarly tolerated.

If that last sentence doesn’t quite make sense, imagine an active equipment line. Pressure vessels are storing a caustic medium in here. That substance is hot and being held at high pressure. Now, many gasket materials can tolerate one or two of those energetic threats. ePTFE can tolerate all of these threats. Even pressed down hard by two flange faces, the expanded PTFE holds firm. Better yet, though, if the system using the gaskets executes some kind of a phase change, one that changes the processing temperature or storage pressure, then the gaskets won’t suffer. Free of creep, strong and reliable, the fluoroelastomer withstands application and process transients.