Chemical Pressure Vessels

Chemical pressure vessels are tanks built to keep gases or liquids at pressures far above or below normal air pressure. Plants that produce chemicals or refine oil rely on those tanks every day - if a tank fails while it holds a pressurized substance, the result is fire, explosion or poisoning. The walls of the vessel come from thick plate or slab - carbon steel, stainless steel or an alloy. Each wall must survive the highest pressure the plant expects and an extra margin. Engineers fix a ceiling for pressure, a ceiling for temperature, a corrosion allowance plus a safety factor. After the shell and heads are welded, inspectors flood the tank with water for a hydro test or with air for a pneumatic test - check every seam with ultrasound or X-rays to be sure no crack is present. Many shells are long cylinders with ends shaped like half spheres or squashed hemispheres - this geometry carries the load with the least metal. A relief valve a pressure gauge but also interlock switches sit on top to open or shut the plant if pressure creeps too high. The law requires that each vessel follow the ASME Boiler besides Pressure Vessel Code and carry an official stamp. Scheduled inspection as well as repair keep the vessel fit for years of service.