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.