PRESSURE VESSELS
WHAT IS A PRESSURE VESSEL?
Pressure vessels are containers designed to hold fluids or gasses under high pressure. They can be found in a variety of situations, including industrial boilers and scuba tanks. Pressure vessels are heavily regulated and must meet stringent safety regulations to withstand the tremendous pressures they are subjected to.
In addition to steel, pressure vessels can be manufactured of aluminum or composite materials. Pressure vessels can be spherical or cylindrical in shape, and their sizes range from small tanks that one person can carry to large industrial vessels that stand several floors tall. Regardless of size or shape, all pressure vessels have the same goal: to properly confine their contents under high pressures.
DIFFERENT TYPES OF PRESSURE VESSELS
Pressure vessels are classified into many sorts based on their structure and function. Pressure vessels are classified into the following types:
Different types of pressure vessels Storage vessels are classified based on their purpose. Storage vessels are pressure containers for liquids, vapors, and gases. It is feasible to reuse vessels for subsequent procedures or to store finished products such as compressed natural gas (CNG) and liquid nitrogen.
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Heat exchangers:
Heat exchangers help to transfer heat between two or more fluids. The bioprocessing, food, pharmaceutical, and energy industries use them the most. Heat exchanger equipment is developed based on the thermal and flow properties of the fluids engaged in heat exchange, as well as the thermal properties of the conductive partition (indirect contact heat exchangers). The temperature difference between hot and cold fluids, as well as their internal pressure, cause stress on heat exchanger materials.
Boilers:
Boilers are machines that employ various forms of energy to generate heat. With this heat, liquids are transformed into vapor. A boiler is often made of metal vessels that transfer heat from a source to a fluid. Steam from the boiler is used for a variety of applications. The boiler accelerates the steam so it can turn the turbine blades. The boiler must be strong to withstand the pressure and heat. Most materials weaken as they become hotter.
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Process Vessels:
Process vessels are large containers used to carry out industrial processes such as mixing and stirring, decanting, distilling and separating chemicals, and chemical reactions. The pressure within a process vessel varies according to the operation and the substances utilized.
DIFFERENT TYPES OF PRESSURE VESSELS ACCORDING TO THEIR GEOMETRY:
Spherical Pressure Vessels:
Spherical pressure vessels are useful for keeping liquids under high pressure. They are strong and resistant to shatter, but they are difficult and expensive to manufacture. The pressure is distributed equally over the sphere, thus there are no weak places. Spheres take up less area than other shapes. If the two vessels are the same size, spherical ones will consume less material. Spherical vessels have a lower surface area, making them less prone to transfer heat.
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Cylindrical Pressure Vessels:
Cylindrical pressure vessels comprise a cylindrical shell and one or more heads. The cylindrical shell serves as the main body of the pressure vessel. The heads are end caps that cover the vessel's contents and might have a flat or rounded appearance. It alleviates the cylindrical container's weakness.
Cylindrical pressure vessels are among the most popular due to their numerous applications. They are less expensive to manufacture than spherical vessels, but not as sturdy. To resist similar quantities of pressure, cylindrical pressure vessels must have thicker walls than spherical vessels.
WHAT ARE THE DIFFERENT VESSEL ORIENTATIONS?
A cylindrical vessel can have a horizontal or vertical axis, depending on its use.
Vertical Vessel Orientation
Suitable for compact floor spaces and vessels with low volumes.
To efficiently mix fluids in mixing tanks.
A high gas-to-liquid ratio allows for easier removal of components during liquid-liquid separation.
Horizontal vessel orientation in heat exchangers allows for easier cleaning.
In settling tanks and flash drums to reduce entrainment
WHAT ARE THE CRITERIA FOR SELECTING MATERIALS FOR PRESSURE VESSELS?
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Can fulfill the strength criteria - The materials used to construct the pressure vessel must be durable enough to last its service life. It comprises being able to tolerate specified internal and external pressures, as well as structural stresses.
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Corrosion resistance is critical for pressure vessels because they must function well under extreme conditions.
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Return on investment - When calculating the lifespan of a pressure vessel, materials, fabrication, and maintenance expenses must all be considered.
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Ease of fabrication and maintenance - Metal sheets must be machinable and weldable in order to form the pressure vessel geometry. This method will make it easier to install the vessel's internal components.
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Availability - Pressure vessel material sizes must be readily available near the producer.
WHAT ARE THE MOST OFTEN USED MATERIALS FOR PRESSURE VESSELS?
The most common materials used to make pressure vessels are:
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Carbon steel
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Stainless Steel
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Hastelloy alloys are composed of nickel.
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Aluminum
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Titanium
WHAT IS THE DIFFERENCE BETWEEN QUALITY TESTING AND INSPECTION OF PRESSURE VESSELS?
The following are the testing procedures used to assure the pressure vessel's reliability and safety factor.
Visual Testing:
A certified inspector inspects pressure vessels at least every five years. They will inspect the vessel's inside and exterior for cracks, deformation, blistering, fluid leaking, corrosion, and any other damage that has occurred.
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Ultrasonic Testing:
This equipment detects surface or subsurface faults and measures the wall thickness of a pressure vessel using high-frequency sound waves. The material absorbs ultrasonic sound waves and converts them into electrical signals using a transducer. If any defects exist, the reflected waves will be affected.
Radiographic Testing:
A radiographic test uses x-rays or gamma rays to provide an image of what is under a pressure vessel's surface. Discontinuities, perforations, and density changes will affect how waves reflect. The film will be exposed after that.
This approach delivers consistent results, thus it is extensively utilized. However, radiation exposure is costly and necessitates specific training.
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Magnetic Particle Testing:
The gadget detects surface defects in ferromagnetic materials using magnetic current. The inspector passes a magnetic current across the pressure vessel using two probes. If the material is defect-free, the flux passes through it smoothly. However, if there are cracks or other anomalies, some of the magnetic flux will leak out of the surrounding material. These flaws will become more obvious if ferromagnetic particles—whether in liquid suspension or powdered form—are placed to the hull's exterior.
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Liquid Penetrant Testing:
An inspector sprays a small amount of liquid known as a penetrant to an area with welded seams or plates that may have faults. Once the penetrant has settled after spraying, the excess is scraped off the surface before applying developer, disclosing any penetrant that has seeped into gaps.
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Pressure Testing:
Pressure testing is done using either hydrostatic or pneumatic methods, with the former using water as a medium and the latter using air or nitrogen. The process begins by removing all air from the vessel before filling it with test fluid until 1.5 times the design pressure for hydrostatic testing and 1.2-1.5 times the design pressures for pneumatic tests are obtained, therefore internalizing said pressure. Because of the safety dangers created by the potential energy levels in pneumatic testing, industry experts choose hydrostatic testing.