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.
Once upon a time, so the story goes, asbestos gaskets were commonly in-use because they provided exceptional thermal strength. The fibrous, silicate-based mineral obviously still exhibits superior heat-resistance fortitude, but asbestos is now recognized as an environmentally hazardous material, too. Known for some time now, the tiny fibres cause life-threatening lung diseases. No matter, a whole range of non-asbestos gasket materials are now available.
Compressed Non-Asbestos Gasket Solutions
It’s the compressed fibres that needed replacing during the whole asbestos removal crisis. And it was a crisis, with entire businesses popping up to withdraw the needle-like fibres from countless applications overnight. Sure, those fibres endangered gasket workers, but asbestos was also used as a structural insulant and fire-break, so older buildings used the fibres, too. Anyway, back to gasket applications, this fibre is undeniably dangerous, but it’s also inexpensive and rated to withstand enormous amounts of thermal energy. To replace the material, a whole new range of compressible synthetic fibres have evolved. They include Aramid, carbon fibre, and expanded graphite substitutes.
Equipped With Enhanced Friability Ratings
If a compressed fibreglass gasket is exposed to massive amounts of flange face stress, the synthetic fibre strands will crack and crumble. Under duress, perhaps because of a high bolt torque setting, the gasket fails because it disintegrates when compressed. Let’s leave fibreglass for those tasks that don’t need a lot of flange pressure, then. For high-pressure fluid loads, for liquids and gasses that are super-heated, a tougher synthetic fibre type is selected to overcome such sealing limitations. Designed to handle compressibility extremes and high-temperature fluid streams, the synthetics targeted here are purpose-designed to tolerate such energy extremes. Whether made out of Aramid or carbon, fibreglass or some brand-marketed seal variant, the fibres must be capable of being torque-tightened. Furthermore, the required level of compressibility cannot compromise the chosen fibre’s mechanical integrity.
Although the most physically essential part of a non-asbestos materials’ build, these fibres are only present in heat resistant gaskets in low percentages. Filling out the rest of the blend’s mix, an elastomeric compound provides additional seal resiliency. The non-asbestos gasket materials, be they made out of fibrous aramid or graphite, are blended with a binder, which adds more compressible strength to the product. Already capable of tolerating high temperatures and higher pressures, the right binder also incorporates a healthy measure of chemical resistance.
Again, due to their toxic properties, asbestos gaskets have fallen from grace, but that’s not a problem, not when there’s a whole range of compressible synthetic fibres and binders to fill the hole left by this formerly popular heatproof gasketing mineral.
Aggressive chemicals can “burn” though ill-suited gasketing materials. Solvents, strong acids, caustic alkalis, all of these substances are capable of causing corrosive fallout. As an unsuitable seal material erodes, the corrosive chemicals then leak and pool. Depending on the nature of this caustic chemical leak, it could then vapourize and take flight. Clearly, on contemplating the terrible consequences of a corrosive gasket leak, engineers must always demand suitable gasket materials.
Chemically Suitable and Compatible Gasket Types
If high pressures stress a seal, then a mechanically capable seal is tightened by a ring of bolts that’ll handle a quoted load factor. With high or low temperatures, expandable seals cope with known thermal variances. Moving onto chemical fluid loads, design problems are compounded by strange material oxidizing and catalyzing energies. Chemistry, the study of atomically scaled material reactance, is a harder field to quantify. As such, specific gasket materials should match given compound formulas. Otherwise, perhaps if an acid-resisting gasket were to be used to contain an alkaline fluid, then it couldn’t be counted on to function. Even if the alkaline substance was diluted, the flange or fitting might fail because it’s protected by a mismatched gasket. Again, because this point deserves emphasis, specific chemical bases must be matched against particular seal material types.
Selecting The Right Gasket Material Type
For concentrated acids and alkalis, a high-quality EPDM (Ethylene Propylene Diene Monomer) will provide plenty of protection. Fluoroelastomers are also designed to handle such corrosive energies. After all, Nitric and Sulphuric acids are but two of a vast range of differently formulated acids on the market. Moving over to fluids that erode seals but are otherwise ordinarily non-corrosive, fuels and oily substances are held back by Buna-N, which is more commonly known as Nitrile Rubber. Other seal rubbers seem to collapse and age when attacked by fuels, but Nitrile gaskets hold firm. Finally, considering the vast number of corrosive compounds flowing around today’s chemical facilities, PTFE (PolyTetraFluoroEthylene) gaskets are generally used as all-round sealing products, for they’re often classed as broad-spectrum chemical resistance seals.
Chemical leaks are viewed as nightmare incidents by every gasketing engineer. They create their own leakage pathways, eat through that weakness path, then they pool innocuously on the ground. Worst case scenario, that leak could spread to a combustible fluid containment unit, or it could evaporate and become airborne. Respiratory damage becomes a real concern when this happens. One more time, to prevent such hazardous incidents from ever occurring, a specific gasket type and material family must be selected to suit a chosen compound base. Choose one of the above material families, but do remember that chemical reactions can further alter a compound’s formula, in which case yet another gasket material would be needed to compensate for the state change.
Past posts have highlighted flange face problems and incautiously selected gasket materials. And rightfully so, for such errors can cause and all sorts of sealing issues. However, there’s also the question of installation correctitude, which requires a whole books-worth of procedural smarts to ensure flange-to-flange jointing integrity. From bolt ring tightening patterns to gasket selection knowledge and flange face conformity, all of these factors must correspond with one another.
Explaining Gasket Sealing Parallelism
By referring to joint “Parallelism,” we’re saying that every stage of a joint must absolutely stay on task. If an approved bolt tightening pattern is applied just-so, then the right sealing ring for the job must support that tightening force. If that’s not the case, no matter how uniformly the flange faces anchor together, gasketing integrity cannot be confirmed. Again, for a gasket to demonstrate an application-mandated measure of sealing strength, all procedurally implemented steps must receive equal consideration.
Charting the Installation Stages
First on the installation parallelism chart, the gasketing ring is selected. A material base is picked out that will contain a quoted internal pressure and temperature range. High temperatures are the norm here, but cryogenics facilities require seals that won’t freeze and crack when hit by subzero temperatures. Next, the compressive load, as applied by the flanges and ring of bolts, will also impact a gasket’s size and shape. Selected so that it slips neatly in place, it also needs to be thick enough to handle the compressive pressures that’ll bear down as the flange bolts tighten. Finally, installers must know the chemical content of a piped fluid before a corrosion-resistant gasket can be selected.
Getting Involved with Sealing Procedures
Having been finished with the material selection stage, the installation work moves onto the bolt-tightening work. Brushes and sealing compounds pair with bolt lubricants and surface contact cleaners to prepare the flanges. Not to be overlooked, much time is spent aligning the gasket so that it seats properly and permits passage of all flange bolts. A calibrated torque wrench is at last lifted, then the bolts are tightened, not in a plain old sequential manner either. No, a tightening pattern is utilized, one that suits the job at hand.
To contain nigh-on incalculable fluid loads and great temperature extremes, every stage of this assignment must be carried out very carefully indeed. After selecting the gasket, a seal that has its own demanding list of product parameters, there’s all the alignment work to be done. The ring must be seated properly, and it can’t be blighted by a manufacturing flaw. Lastly, with bolt lubricants and sealing compounds in place, a hydraulic tensioner is used to pattern-fasten the bolts so that the flange faces apply uniform compressive force all around the gasket ring.
Harsh climates can damage sensitive machinery. Following on from that claim, extreme weather conditions cause damage to tough-as-nails industrial materials. And, since pipelines travel across vast open spaces, often while attacked by the most severe elemental forces, then they’re an easy target for this effect. Hot or cold, wet or dry, climate extremes can compromise a pipe, at least that’s the case if a pipe has a weak spot.
Gasket Stress: Extreme Weather Impact
Concerning that weak spot, gaskets can hardly be called fragile. They’re made of tough engineering plastics, dense fibres and durable metals. Still, think about weather-driven performance fluctuations. A hot sun directs radiated thermal energy straight at a flange. It reacts like a heat sink and absorbs the energy. Okay, the gasket material can handle the heat, but now the sun sinks. A cold night drops hard, the compressible seal contracts, and then the sun comes up again. Cyclical forces expand and contract the gasket. If this material can’t tolerate these transient energies, it’ll fail. Not right away, but the seal will eventually become inflexible, to the point that it cracks.
Materials That Can Handle Weather Extremes
Desert weather is bad, for that’s where cycling forces are at their worst. Arctic environments aren’t much better, though. What’s needed here, in both situations, is a weather-adaptable gasket family. The chosen material won’t crack when it’s chilled, nor will it harden when attacked by UV radiation. Lastly, neither ozone nor cyclical heating and cooling can cause the material to weaken. Whatever the occasion, it sounds like this is a job for a fluoroelastomer seal. Viton, a branded fluoroelastomer, can withstand high and low-temperature extremes, plus the material altering properties of both Ultraviolet rays and ozone gas. If this harsh-environment candidate doesn’t suit a specified application, a polyurethane gasket will provide an almost as capable set of weather negating features.
Essentially, thermal fluctuations are the biggest threats, but there’s also ultraviolet radiation, icy rain and ozone, too. Impressively capable, even when set upon by harsh weather conditions, Viton stays elastic when the temperature drops as low as -30°C. Better yet, especially for desert-installed seals, the synthetic rubber can tolerate 260°C of blistering heat. If Viton or polyurethane isn’t viable options, gasket designers are rarely stuck. EPDM (Ethylene Propylene Diene Monomer) rubber is yet another option. As a weather-resistant gasket material, this material makes for an outstanding cold weather candidate. Silicone is the last member of this weather beating quartet, but the story doesn’t end here, not when there are composites available that combine the best features of all of these synthetic rubbers.
A ring of bolted fasteners typically encircles a pair of flange faces. Ideally, the bolts are tightened in a pattern so that they deliver a fixed amount of torque. In this way, a pipe joint or system fitting maintains a leak-free coupling. Even if the fluid flowing through a coupling is highly pressurized, the properly tightened ring of fasteners holds firm, at least that’s the general assumption.
Rejecting Flange-Fitted Conjectures
Engineers never make assumptions. Apart from anything else, bolts suffer from torque loss hardships. Even a mere 24 hours after the tightening force has been applied, bolts and nuts will relax a little. And that’s the first pertinent causative factor, the fact that bolts don’t hold their shape. They stretch a little because heat-treated metals are tempered and malleable. If that weren’t the case, hardened fasteners would be so brittle, so frangible, that they’d fracture. To compensate for alloy malleability issues, installation technicians return to gasket fitting sites and re-torque relaxing bolts.
Concerning Gasket Creep Challenges
Less compression-capable sealing materials have trouble conforming to extreme flanging pressures. As the torque applied to a joint surpasses a gasket material’s compressibility limitations, it flattens out and loses its shape. This time around, instead of the bolts stretching, it’s the gap between those anchored fasteners that diminishes. At any rate, the effect is much the same. With that flange and gasket space contracting, torque loss problems blossom. Offsetting such challenges, gasket materials are creep tested and assigned relaxation resistance ratings. Take note, creep relaxation performance can also be influenced by in-system and environmental temperature fluctuations.
Avoiding Installation Mistakes
Wrongly applied tightening patterns complicate matters. Worsened when a technician doesn’t use a second or third re-torquing pass, bolted flanges suffer from seating stress on one side of the gasket while the opposing side presents as a low-compression sealing area. Left like this, a gasket blowout becomes a distinct possibility. Referring back to creep relaxation performance issues, thicker gaskets and more elastomeric materials are particularly sensitive to seating stress hazards. Incidentally, as another point of installation concern, pipe parallelism is a known torque loss troublemaker. If flange faces aren’t parallel, aren’t closely aligned, then a coupling’s positional characteristics will inevitably suffer.
Words like “creep” and “relaxation” become especially relevant when talking about torque loss difficulties. Subsequently, leakage and blowout conditions become high probability events. Let’s add compressibility and plasticity to the list of engineering terms. Compressibility, the way a gasket thins when it’s torque-tightened, is a factor that’s influenced by the selected gasket material and the thickness of that seal, among other things. On the other hand, plasticity problems ensue when malleable fastener metals stretch and deform.