Installation errors result in premature gasket failures. As a best case scenario, that failure causes system downtime. System stoppages take place, and then there are revenue losses to worry about. This is a problematic situation, but it’s fixable. Things could be so much worse, though. For one thing, the leaking fluid could be combustible or toxic. In view of these issues, a proven methodology must be adopted when fitting gaskets.

Establish a Best Practices Approach

Even when fastening a light load in place, an installer will use an accepted bolt tensioning procedure. One fastener is tightened then its opposite number is tightened, and so on until the joined parts are uniformly anchored in place. Again, that’s how load-susceptible fittings are treated. Surely a high-performance flange gasket requires at least as much attention? To install that seal in a safe and secure manner, especially when it’s expected to contain high-pressures, a number of clearly defined steps must be executed. Metaphorically speaking, a gasket fitting and installation ladder functions as a procedurally administered guide, one whose rungs must be tended to with great care.

Climbing the Gasket Fitting Ladder

Following this metaphor, you begin with the first rung. A gasket installation is underway. Keeping that best practices outlook firmly in mind, the engineer inspects the flange faces. Are they clean? Has the system been de-energized and depressurized? Complying with all relevant health and safety guidelines, the installation area is made safe. Wearing a safety helmet, the installer gets to work. A wire brush comes out after the inspection phase has finished. Grime is covering one of the flanges, so this matter needs to be addressed before the job can go any further. Cleaned until the surface gleams, a second inspection checks for scratches and/or surface dents. Excessive pitting is another potential seal integrity troublemaker. By the way, the ASME PCC-1 codes and standards can be used to determine whether a sealing face discontinuity exceeds a predefined guideline maximum.

Flange parallelism comes next, with the installer lining up the sealing faces until they align perfectly. Spaced according to the aforementioned guidelines, the gasket is inserted next. It’s clean and free of tears, as proven by a final seal examination, so the gasket is inserted. From here, the next few minutes of the job are reserved for seal manipulation. On carefully centring the sealing ring and ensuring proper seating, a coating of anti-seize paste finalizes the face preparation work; now comes the accepted cross-bolt tightening pattern. All that’s left now is to apply the recommended fastening torque. Remember, a gasket cannot be over-compressed, nor can the bolts receive too much tensioning force.

Gasket installers run the risk of creating untenable situations when they install the wrong products on low-temperature fittings. At the very least, the wrong gasket material will harden and lose elasticity. It’ll experience creep and glass-transition brittleness. Upon stiffening, gaskets can’t compress, not without experiencing damage. As a worst case scenario, cracks propagate throughout seals because they can no longer deform when compressed. So, just to recap, low-temperature applications absolutely require low-temperature gaskets.

All About Subzero Gasket Hardening

Most pliable rubbers can handle light chills. However, few synthetic polymers have the wherewithal to hang loose when attacked by subzero conditions. Whether the cold is outside, perhaps on a pipeline that’s crossing the arctic tundra, or it is part of the flow conditions, as set up on a cryogenics facility, those lesser gasket materials experience compression set issues. Essentially, their tractable long-polymer chains come to a full stop because they can’t endure the ultra-low temperatures. When that happens, the potential energy stored inside a once pliable gasket turns against itself. The energy can no longer be contained by the stiffening sealing substance, so the material starts to crack and break down.

Worst Case Incidents: Cryogenics Leaks

If an inert liquid, a substance that’s normally a gas, leaks out of a freeze-damaged gasket, it’s not going to combust. That doesn’t mean it is safe, not at all. Taken down as low as -150°C, the escaping liquid is dangerous. A few seconds of exposure to that heavier-than-air substance would be enough to cause a nasty case of thermal burn. Skin and soft tissues literally freeze solid when such leaks occur. Then there’s the fact that the leak is probably evaporating. The frozen mist takes to the air and causes respiratory damage. And this is just an inert medium. What about cryogenically frozen hydrogen compounds and methane-based chemicals? As the cracks spread on an incorrectly specced gasket, these escaping fluids combust and explode. Heavier than air, these frozen mist clouds must be avoided at all costs.

Damaged gaskets, those that leak cold fluids, can cause serious harm to life and property. Even strong alloys can become brittle when suddenly exposed to low-temperature fluids. Also, on evaporating, a semi-chilled gaseous cloud represents an asphyxiation risk. Then there’s the possibility of a combustion hazard. Liquid hydrogen will obviously combust explosively. Although not exactly combustible, liquid oxygen will burn energetically when fueled by a spark. Finally, some liquefied gasses (including frozen ammonia) become toxic when released. At the end of the day, having assessed all of these destructive scenarios, gasket designers use freeze-resistant graphite, PTFE and Teflon materials to assure seal deformability.

Malleable metals and compressible elastomers are superior gasketing materials. They form powerful seals when extreme flanging forces are applied. However, that principal feature can sometimes go awry. It backfires on an application. Instead of demonstrating a talent for countering flange load, unchecked contraction and/or expansion energies interfere with a gasket’s operational functions.

Determining Ring Distorting Causes

Temperature extremes cause materials to expand or contract. If a great deal of thermal energy finds its way into a gasket’s material, that sealing substance will expand. At the other end of the temperature scale, the opposite issue takes hold. The icy fluid passing through the flanges chills the gasket, the material contracts, and a tiny void grows under the flange faces. Through that void, a leakage pathway could form. Likewise, in a heat-expanding seal, the perfectly aligned ring could shift until the gasket isn’t seated properly anymore. Worst-case scenario, a frozen and materially contracted gasket will crack because its once resilient structure becomes inelastic. Tortured by heat, the sealing material distorts and loses structural integrity. What a disconcerting, seal weakening state of affairs. Not to worry, there’s more than one way to handle this predicament.

Dealing With Gasket Deforming Energies

Straight to the point, don’t select a gasket elastomer or fibre that’s not designed to handle large temperature extremes. If, for example, the fluid stream contains pressurized steam or hot oil, select a ring that’s made of graphite. Formed into a foil jacket or a series of laminated rings, composite graphite gaskets are designed to handle high-temperature swings. Ceramic fibres and fluorosilicone seals are also designed to hold firm when high-temperature loads strike. Spiral-wound metal/ceramic fillers are another possibility, with low creep alloys delivering superior stability. Due to their expansion and contraction-neutral characteristics, alloy seals exhibit low distortion coefficients.

Located indoors or below ground, pipes aren’t exposed to UV (ultraviolet rays) or radiated heat. If a pipeline does run above ground, paint or a special coating will block the damaging rays. Better yet, in addition to a gasket material’s temperature resisting properties, that material should exhibit a satisfactorily high UV resistance feature. Take note, some chemical reagents can also impact sealing material integrity. In response to this possibility, select gaskets that are immune to chemical assault. By the way, environmental extremes can strike other parts of a pipeline. As the outside temperature soaks into a pipe, it conducts thermally along and through the rolled metal until it reaches the flange faces. If the externally generated heat, or cold, isn’t to overcome the flange clamping force, then a properly administered bolt jointing pattern must be followed.

In fluid processing applications, gasket blowouts are classed as worst-case scenario events. One moment everything is working flawlessly. Pumps are running and pressurized fluids are safely contained. A catastrophic second later, an entire flange pairing or pipe fitting has failed. Without any discernible warning whatsoever, the steam or chemical or fuel load is whistling out of the line as a highly energetic spout. A site disaster could be seconds away.

Assessing the Pressure-Fuelled Consequences

A steam leak, one that’s taken place on a pressurized line, can be so concentrated that it forms an invisible spout. If someone were to come in contact with that jet-like stream, the steam would cut through their skin like a cauterizing scalpel. As bad as this scenario is, it can become worse. A pressurized fuel leak will combust if a spark occurs nearby. With chemical leaks, this high-powered puncture will spread near and far while it poisons everything and everyone. And remember, this type of system breach occurs in seconds. There’s no time to come up with a leak prevention plan when high-pressure seals fail catastrophically. Knowing the disastrous potential, there’s a whole field of science dedicated to gasket blowout prevention.

Introducing the Blowout Prevention Factors

When designing high-pressure system gaskets, a series of pressure regulating parameters are addressed. There’s the fastening framework, which creates invisible beams of clamping force. Those beams also penetrate the seal to draw the opposing flange in tight. Tightened in a pattern, all potential axial and radial forces stay counterbalanced. Next, stopping leakage pathways from forming, ones that’ll make themselves known with explosive intensity, flange gasket materials exhibit great mechanical resilience. Obdurate as steel, the inwardly pressed sealing substance also provides a measure of outward pressing energy. It’s this compressibility, plus the material’s innate elasticity, that works in conjunction with the fasteners’ clamping force to create a reliable seal.

Statistically gathered and analysed, these factors are plugged into engineering equations and gasket blowout simulations. The different seals are tested to destruction within virtual computer spaces. Even then, the job’s not done. The next stage involves placing the seals within controlled test scenarios, where they’re then exposed to substantial amounts of mechanical stress. Again and again, blowout science procedures test different gasket families to destruction. Above and beyond such design precautions, there are yet more measures. One redundant safety system layer is layered upon the next. In all likelihood, those measures will never be used. All the same, they exist, and they’re continually maintained to ensure proper operation, should that worst case scenario ever happen. Finally, Blowout Prevention (BOP) valves are installed to offload those catastrophic pressures.

Helium cylinders are used in ordinary applications. For instance, florists use helium to fill their balloons. Far and above such mundane practices, the lighter-than-air gas has become an industry-essential substance. And that’s where the problems begin, for helium molecules have a talent for penetrating high-quality seals. Consequently, if a pipe or fitting seal is to thwart this gaseous escape artist, a low permeability gasket material must be sourced.

Low-Permeability Gasketing Candidates

By looking at the periodic table, a gasket designer sees that helium has an atomic number of two. Hydrogen is located at the number one spot, but that fluidic material is highly combustible. Taking that information into account, helium is hard to seal. It leaks past the smallest gaps and through materials that are porous. A good candidate as a low-porosity gasketing rubber would be nitrile. Nitrile seals are made out of dense elastomeric polymers, which won’t readily leak. EPDM (Ethylene Propylene Diene Terpolymer) can’t be penetrated easily, either. If EPDM or Nitrile gaskets don’t suit a specific application, then there are a range of capable fluoroelastomers that will. Best in this class, Viton gaskets stop helium leaks. They also perform well when fitted in applications that oppose different temperature extremes.

Application-Specific Material Impact

That latter issue forces gasket designers to alter their selected sealing materials. Case in point, a helium coolant supply cryogenically chills a bank of hot-running computer servers. The inert gas performs exceptionally well, but the installed gasket cracks because of the icy cold temperatures in use here. Nitrile is the initially chosen material. The elastomer is dense and very nearly leakproof, but it’s not cryogenically suitable. Crossing out the first choice gasket material, the designer opts instead for an equally non-permeable fluoroelastomer.

Introducing A Few Helium Gasketing Examples

Inert by nature, helium is used as a shielding gas. In arc welding applications, the gas stops weld pools from oxidizing. In electronics, the gas super cools hot circuits. Superconducting magnets also use this feature, so a helium supply will likely accompany the high voltage power lines that thread their way towards an MRI machine in a hospital. Of course, there’s the lighter than air floral balloons, too. Scaling up that usage area, large volumes of the gas allow massive blimps and weather balloons to take flight.

Of some concern, this super-light gas is running out. The two-atom molecules climb so high, so far above the Earth’s atmosphere that they escape into space. That means there’s a second reason for sourcing superior helium containment materials. The nitrile and EPDM rings are indeed expected to contain the gas, but they’re also expected to stop this increasingly rare gaseous medium from escaping the bounds of this planet’s atmosphere.