A pressure vessel is broadly defined as a container that has built to hold liquids, gases, and vapors at or above ambient pressure. The containers design to handle internal pressure but can also design and modified to handle external pressure.
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Significance of ASME Codes:
ASME (American Society of Mechanical Engineers) defines a pressure vessel as any container that serves the function of containing either internal or external pressure. The pressure may be from any external source or by applying heat directly or indirectly.
The pressure vessels may be horizontal or vertical in design. Depending on the application, pressure vessels divide into various types, such as:
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Storage vessel that can store fluids under high pressure, such as storage tanks
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Process vessels where different processes may occur, such as mixing two ingredients or breaking down and combining a product such as heat exchangers, distillation towers, and separators.
Boilers and other pressure vessels have to withstand incredible pressure and stress. Pressure vessels classify into two main groups that fire and unfired pressure vessels. The primary focus of the custom pressure vessel manufacturer is ensuring all the safety measures follow.
Fired vessels include boilers, while the unfired ones from the name suggest are those vessels that are not connected to any steam generation or anything that has a flame. Some of the popular pressure vessels used in many plants and factories include:
- Filter vessel.
- Air dryer.
- Air receiver.
- Liquid/Gas separators.
- Gas scrubbers.
- Heat exchangers.
There are many industry rules and regulations that pressure vessel manufacturers must follow, and companies should counter-check when buying or using particular pressure vessels. The containers design according to specific temperatures and pressures.
Due to application, the design of each pressure vessel is unique and depends on the operating limits. Operating above the largest pressure may result in an unfortunate accident and cause injuries to the workers.
The ASME Code and Parts of Pressure Vessels:
The development of pressure vessels involves different processes such as design, materials, fabrication, and inspection. The different standards that pressure vessel manufacturer must follow are
ASME (American Society of Mechanical Engineers) Boiler and Pressure Code Section VIII Div. 1.
European Pressure Vessel Directive.
CSA B51 Pressure vessel and Pressure of Piping Code.
The ASME Code Section VIII Div. 1 provides all the essential details that custom pressure vessel manufacturers must follow to design, fabricate, inspect, test, and certify the pressure vessels that may operate at internal or external pressure that exceeds 15 PSIG (Pounds per square in gauge).
The ASME code is a benchmark and used in 100 other countries apart from the US (United States). The ASME code is a comprehensive 700-page guideline that mentions every aspect in detail, from rules and formulas to design and manufacture pressure vessels.
The Common Parts of a Pressure Vessel are:
Shell:
The shell can weld or seamless pipe but mostly a rolled plate formed in a cylindrical shape. The rolled plate is the industry standard for most vessels having a large diameter. The plate place in a roller and specific ASME codes follow to weld the plates together in a cylindrical shape.
Heads:
The heads use to close off the vessel and contain the fluids. The different types of heads used in the factories and plants are hemispherical heads, elliptical heads, and flatheads.
The heads curve to provide more sturdiness and strength to the design, and they are less expensive than flatheads. The heads make through the ‘dishing’ and ‘flanging’ process. The dishing process involves the use of a hydraulic press to rotate the plate.
Flanging is the process where a straight section of the plate requires that can match with the cylindrical shell and allow a solid weld between the head and the shell.
Nozzles:
The fluids transfer in and out of the vessel through the nozzles. Several ASME codes are depending on the nozzle that requires and used. The codes cover the pressure, temperature rating, chemical composition, and material selection. The nozzles come in specific tolerances, markings, and dimensions.
Support:
The saddles at the bottom of the vessel provide the necessary support as the pressure vessel is incredibly heavy when filled with liquid or gas. Apart from saddles, there are also brackets, legs, and skirts that provide load-bearing capabilities.
Apart from the load of the liquids or compressed gases, the design of the support can also customize to withstand seismic, wind, and snow loads. Other types of support clips include attachment clips, platforms, lifting plugs, brackets, and davit assemblies.
The Purpose of Pressure Vessels:
The main purpose of pressure vessels is to help for use in the compress air system. The typical pressure of the vessel was kept at 8 to 10 bar (g). Many plants and factories worldwide use 6 to 8 or 6 to 10 bars, and it calls the service or working air.
The pressure vessels are mostly cylindrical without any sharp or pointed edges to prevent any stress. A round or cylindrical shape ensures no points in the vessel where the pressure is higher than another area or point.
At the top of some pressure vessel designs, two large pipes are used to transfer compressed air from the vessel. The two smaller pipes use as ‘appendages’ that are pressure gauges meant to determine the tank’s pressure.
There is also a differential pressure switch that signals the compressor when to turn on or off. The compressor shuts off when 8 to 10 bar is reached but will turn back when the pressure is reached or falls from 6 bar. A fusible plug may also mount on the top of the tank.
The big round hole in the pressure vessel known as a ‘manway’ can open for inspection and cleaning purposes. But before any action is taken, it is better to open the hole and wait and not just enter the vessel as chances are they may be little or no oxygen present and cause breathing issues.
Conclusion:
Following industry-standard codes is not easy as the codes revise each year but pressure vessel manufacturers have extensive experience in designing, fabricating and delivering safe and functional pressure vessels. Apart from the design and development of pressure vessels, repair, maintenance, and consultation services are also provided.
