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.