The term ‘Pressure Vessel’ refers to a piece of equipment designed to hold or contain processed fluids (liquids or gas) at a pressure more than the atmospheric pressure, either internally or externally.
They are also known as Process Containing Equipment; because they contain processed fluids and Static Equipment; since they function without any rotating parts. Pressure Vessels help in the storage and transport of highly compressed gases with ease. Pressure vessels can be as small and ambulant as a ‘flame lighter’ to as big and bulky as those used in the petrochemical industry, weighing more than 1500 tons!
Structure of a Pressure Vessel and the Manufacturing Process
A Pressure Vessel can broadly be divided into 5 parts:
- Shell: It is the outer steel body of the vessel; it can be either cylindrical or spherical.
- Head: The upper ends and lower ends represent the head of the vessel. They enclose the cylindrical surface.
- Nozzles: These are small valves that connect the equipment with transportation pipes. They are also helpful in regulating the flow of compressed gas.
- Skirt/Legs: These pillar-like structures support the vessel’s body. Skirts support big, heavy vessels, and legs are attached to comparatively smaller, lighter vessels.
- Internal: The internals of a pressure vessel are authentic to the vessel manufacturer. It is something that the manufacturers do not disclose.
The manufacture of pressure vessels necessitates the use of specialized skills and a thorough understanding of the underlying science. Moreover, a vessel manufacturer must take plenty of precautions to ensure the safety of process equipment manufacturers, therefore providing a safe working environment.
The layout of the Manufacturing Process
- The process starts with bending steel plates, the main component of a Pressure Vessel.
- The steel plates are then bent to get cylindrical curvatures, carried out under the supervision of process equipment manufacturers.
- The next step in the process is to smoothen the internal surface of the curvature to prevent any possible injury.
- The surplus part of the sheet is cut off using automated machines under the guidance of process equipment manufacturers. After this step, the vessel is ready to be assembled.
- All the parts of the pressure vessel are assembled and welded together. External parts are assembled, and the vessel’s body is painted.
- The end product is now sent for a quality check under the supervision of a vessel manufacturer. For this, a rubber diaphragm is put inside the vessel and inflated. Then, the pressure holding capacity of the vessel is checked by an automated machine.
- Once the vessel passes the quality check adhering to the international standards, it is ready to be delivered to the customer.
The manufacturing of the pressure vessels must adhere to Section VIII of ASME’s Boiler and Pressure Vessel Code (BPVC). This international code sets the minimum requirement for a safe and reliable vessel manufacturing operation.
Section VIII has 3 sub-divisions:
Division I – It includes vessels with a capacity ranging from 15 PSI to 3000 PSI.
Division II – It includes vessels with a capacity above 600 PSI.
Division III – It includes vessels with capacities above 10,000 PSI.