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.
Numerically based literacy is applied when selecting a gasket. An engineer runs a finger down a list, finds the results of the scan pleasing, and the decision is made. Interestingly, gasket parameters are also stored in graphical formats. On graphs, two axial lines cross. A curve intersects. It creates a picture of a seal’s mechanical characteristics. That, in a nutshell, is a technique that also applies to gasket compression curves.
Plotting the Two Key Datasets
This is a performance-illustrating tool. The curve clearly depicts how a specified gasket will react as it’s compressed between two flange faces. It shows material densifications as fastener loads are applied. As Y-axis load factors increase, the X-axis shows how well the seal handles the compressive energies. To measure the densification, the material crushing energies are translated into dimensions. Essentially, as a load bears down, the Y-axis measurements are recorded. Meanwhile, simultaneously recorded on the X-axis, a loss of gasket thickness is measured. At any point where those energies intersect, a mark is made on the graph. As those marks accumulate, a line is plotted through them until the gasket compression curve becomes readily apparent.
Why Is This Curve An Essential Performance Benchmarker?
Engineers create the curves as performance baselines. They show how the material stiffness of a seal reacts as it’s placed under a compressive load. The depth of the arc of the curve, how it flattens or straightens out at different clamping pressures, tells an important story. Admittedly, it takes a trained engineer to create this shape, but that information, once garnered, can be read by an installation professional. At any given point along the axial lines, that trained eye sees how a gasket deforms under pressure. On applying fastener force, on taking that turn energy higher than what’s suggested by the curve, a gasket could extrude out and create a number of leak pathways. Kept within the plotted curve limits, such overloading calamities become unlikely because the installer defers to the gasket’s material stiffness parameters, as described in the seal’s compression curve.
Unlike a static numerical seal parameter, gasket compression curves show a broad range of possible loading effects. As the loads increase or reduce, the installer sees how a gasket handles the different loads. Intended as a material stiffness-to-load factor interpreting guide, the compression curves show how different gaskets densify and compress. More than this, they demonstrate material deformability, extrusion dangers, and potential leakage pathways. Do always comply with a list of numerical behavioural parameters when selecting a gasket. Fortify this approach by knowing how the material will react to a given load.