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.