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.