July 25, 2018
A chemical leak in a pressure vessel is one of the worst-case scenarios that designers think about day and night. Even a pinhole leak is a danger here, an inconceivable risk factor. In an effort to know-thy-enemy, studies have been conducted into the common causes of those caustic leaks. Why do they occur? Is there an engineering design strategy that will unequivocally address the issue? Let's find out.
Pressure vessels are designed to contain rated fluid stresses. If the tank geometry and weld seams are held to the rated design limits, leaks are unlikely. On the other hand, if the unit is exposed to higher fluid stresses, the possibility of a chemical leak looms large. Weld seams and sheet metal tolerances become dangerously stressed when overpressure incidents are tolerated. That's a bad enough practice in a hot water device, but it's so much worse if the under-pressure medium is a corrosive chemical.
The next pressure vessel has been fabricated in accordance with the latest engineering codes, yet a leak has still developed. Let's head back to the laboratory and model the incident. The wall thickness is adequate and the seams are perfectly applied, so why is a steady trickle of caustic liquid pooling on the ground? Well, perhaps the alloy seams aren't fully reinforced. Perhaps the alloy walls are not stress-fracture free. Aggressive compounds just need the tiniest chink in a vessel's armour plating to begin their corrosive efforts.
The wrong gasket material has been sourced. Now the leak is entirely bypassing the pressure vessel. Even though the storage unit has been built to handle all conceivable chemical incidents, the fittings and extraneous parts around the tank are letting the whole show down. It's like using a steel door on a walk-in safe when the adjacent walls are made of soft plaster. The hardened door isn't going to fail, but the same can't be said for those soft walls. If the pressure vessel is robustly fabricated and designed to handle all chemical loads, then its fittings must adhere to that same code-ratified convention.
Inside chemically active pressure vessels, dynamic events are taking place. There are catalysts and reactants at work. Heat-activated state changes convert gases to liquids, and vice versa. The fluid effervesces, it boils at low temperatures and reacts dynamically to new processing elements. Even environment changes can influence matters. Water gets into an open maintenance hatch, then it combines with traces of caustic soda. Before we know it, a leak has developed. Vessel expansion, chemical corrosiveness and more, these common causes must be addressed so that those hazardous chemicals can be kept in check.
Fusion - Weld Engineering Pty Ltd
ABN 98 068 987619
1865 Frankston Flinders Road,
Hastings, VIC 3915
Ph: (03) 5909 8218
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