A pressure vessel is a container that contains a gaseous/fluid mixture. They are used in industry to contain and transport pressurized fluids or gases, as well as for containing temperature-sensitive materials for distribution within buildings, etc.
Pressure vessels are used for a variety of different purposes, including pressure cooking, steam generation, and water heating. They can also be used to store liquids or gases under pressure.
- Pressure vessels are vessels, tanks, and pipelines that transport, store, or receive fluids.
- A pressure vessel is a container having a difference in pressure between the interior and outside. Except under rare circumstances, the inner pressure is normally greater than the outside pressure.
- In the case of steam boilers, the fluid within the vessel may change state, or it may mix with other chemicals in the case of a chemical reactor.
- High pressures, high temperatures, and, in certain situations, combustible fluids or extremely radioactive materials are all common features of pressure vessels. As a result of these dangers, it is critical that the design prevents any leakage.
- Furthermore, these containers must be properly built to withstand the operating temperature and pressure.
- It’s important to remember that a pressure vessel rupture has the potential to inflict serious bodily harm and property damage. In design of a pressure vessel, plant safety and integrity are essential considerations.
Parts of a Pressure Vessel:
components of a pressure vessel
The primary components of pressure vessels in general are as follows:
1-Shell: This is the most important component since it contains pressure. Pressure vessel shells are welded together in the form of separate plates to create a structure with a common rotating axis. The form of a shell might be cylindrical, spherical, or conical.
2-Heads (end closures): All pressure vessels must have heads at the ends (or another shell section). Curved heads are more common than flat heads. The reason for this is because curved designs are more durable and allow for smaller, lighter, and less costly heads than flatheads. Intermediate heads are heads that may be used both inside and outside of a vessel. These intermediate heads are distinct pressure vessel portions that allow for varied design situations.
3-Nozzle: A nozzle is a cylindrical component that enters the pressure vessel’s shell or head. They’re utilized to connect pipes for flow into or out of the vessel, connect instrument connections (level gauges, thermowells, pressure gauges), and provide access to the vessel’s interior through a manway or for direct attachment of other equipment items (e.g. heat exchangers).
4-Support (Saddle): The saddle is utilized to support all pressure vessel, earthquake, and wind loads. Depending on the size and direction of the pressure vessel, several kinds of supports are used. It is the section of the vessel that is not pressured.
Supports come in a variety of shapes and sizes.
Support for the saddle:
- Saddle support is used to support horizontal drums in two places.
- To avoid excessive local stress in the shell at the support point, it distributes across a vast region of the shell.
- The drum’s longitudinal thermal expansion is unaffected by one saddle support being fastened and the other being free.
Support for the legs
- Small vertical drums are often supported by legs soldered to the shell’s bottom part.
- Typically, the maximum ratio of support leg length to drum diameter is 2:1.
- To offer extra local strength and distribution, reinforcing pads are first welded to the shell.
- The number of legs required is determined by the size of the drum and the weight to be transported.
- Spherical pressurized storage tanks also include support legs.
- Wind or earthquake stresses are absorbed by cross bracing between the legs.
- Lungs may also support vertical pressure channels.
- Typically, lugs are only used on small and medium-diameter pressure vessels ( 1 to 10 ft )
- Moderate height-to-diameter ratios of 2:1 to 5:1 are also acceptable.
- To offer stability against overturning loads, the lugs are often fastened to horizontal structural components.
vertical pressure vessel in the leg
Skit Assistance:
- Skirts are often used to support tall vertical cylindrical pressure containers.
- A support skirt is a cylindrical shell part welded to the bottom head or the lower portion of the vessel shell ( for cylindrical vessels).
- The skirt is usually long enough to provide for adequate flexibility so that the shell’s radial thermal expansion does not result in severe thermal stresses at the skirt’s junction.
Pressure Vessels Have a Wide Range of Uses
- Compressed air receivers for industry
- Tanks for storing domestic hot water
- cylinders for diving (Scuba diving)
- Chambers for decompression
- Towers for distillation
- Autoclaves are a kind of autoclave that is used (In medical industry to sterilize)
- Petrochemical plants and oil refineries
- Vessels for nuclear reactors
- Reservoirs, both pneumatic and hydraulic
- Liquefied gas storage containers for ammonia, chlorine, propane, butane, and LPG.
Pressure Vessels ASME Codes
Pressure vessels are intended to function safely at a specified pressure and temperature, known as the “Design Pressure” and “Design Temperature” in technical terms. A vessel that is not constructed properly to manage high pressure poses a substantial safety risk. As a result, design codes such as the ASME Boiler and Pressure Vessel Code in North America, the EU’s Pressure Equipment Directive (PED), the Japanese Industrial Standard (JIS), CSA B51 in Canada, Australian Standards in Australia, and other international standards such as Lloyd’s, Germanischer Lloyd, Det Norske Veritas, Société Générale de Surveillance (SGS S.A.), Lloyd’s Register Energy Nederland (formerl) govern the design and certification
- It’s a set of regulations for designing, fabricating, and inspecting boilers and pressure vessels.
- This creates and maintains design, building, and inspection standards that provide the highest level of safety and security for people and property.
- Section VIII of the ASME Boiler and Pressure Vessel Code (BPVC)
- Division 1 – Pressure Vessel Construction Rules
- Alternative Rules (Division 2)
- Alternative Rules for the Construction of High-Pressure Vessels (Division 3)
Materials for Pressure Vessels in General
The following materials are utilized in the building of pressure vessels:
- Steels
- Aluminum and copper are nonferrous metals.
- Titanium and zirconium are examples of metals.
- Plastic, composites, and concrete are examples of nonmetallic materials.
- Protective coatings, both metallic and nonmetallic
The following are some common properties of several materials:
- Carbon steel is strong and has a modest resistance to corrosion.
- Low-alloy steels: high-temperature strength
- Corrosion resistance of stainless steels
- Corrosion resistance of nickel alloys
- Seawater resistance of copper alloys
- Aluminum is a lightweight, low-temperature strong metal.
- Titanium: chemical resistance, seawater
- Refractories are materials that can withstand very high temperatures.
- Corrosion and chemicals are two non-metallic issues.
Factors Affecting Material Selection:
The following are some of the factors that influence material selection:
- Process fluids (for example, a material may be ideal for corrosive fluids, but it can melt when the operators’steam’ the equipment during cleaning)
- Temperature in use
- the working pressure
- Velocity of the fluid
- Product contamination
- Equipment should last as long as possible (May choose to incur shorter life and replace more often)
- Cost of building materials (base material + manufacturing expenses)
Types of Pressure Vessels – Pressure Vessel Classification
Based on the thickness of the wall:
1) Vessel with a Thin Wall 2) Vessel with a Thick Wall
Geometric Shapes-Based:
1) Vessels with a cylindrical shape 2) Vessels with a spherical shape 3) Vessels with a Rectangular Shape 4) Vessels with several functions
Based on the following installation methods:
1) Vessels that are vertical 2) Vessels that are horizontal
Using the Operating Temperature as a Guide:
1) Vessels with a low temperature (less than or equal to – 20° C) 2) Vessels with a normal temperature range (between – 20° C and 150° C) 3) Vessels with a Medium Temperature Range (150°C to 450°C) 4) Vessels with a high temperature (more than or equivalent to 450° C)
According to the Design Pressure:
a) Low-Pressure Vessels a) Low-Pressure Vessels b) (0.1 MPa to 1.6 MPa) 2) Vessels with a Medium Pressure (1.6 MPa to 10 MPa) 3) Vessels with a High Pressure (10 MPa to 100 MPa) 4) Vessels with Extremely High Pressures (More than 100 MPa)
Technological Processes-Based:
1) Vessel of Reaction 2) Vessel for Heat Exchanger 3) Vessel for Separation 4) Vessel for Storage Containers
Pressure Vessels: What’s the Difference Between Thin Shell and Thick Shell?
- Pressure vessels are categorised as thin shells or thick shells based on their size.
- A thin shell is defined as one with a wall thickness (t) of less than 1/10 to 1/15 of the diameter (d) of the shell. A thick shell, on the other hand, is defined as one with a wall thickness higher than 1/10 to 1/15 of the diameter of the shell.
- Boilers, tanks, and pipelines utilize thin shells, whereas high-pressure cylinders, tanks, and cannon barrels employ thick shells.
- Internal fluid pressure (p) and allowed stress (t) are two further criteria for classifying pressure vessels as thin shells or thick shells.
- A thin shell is one in which the internal fluid pressure (p) is less than 1/6 of the allowed stress. A thick shell, on the other hand, is defined as having an internal fluid pressure larger than 1/6 of the permissible stress.
End Closures: What They Are and How They Work
- End closures for cylindrical pressure vessels are formed heads.
End closures are divided into two categories:
1. Heads with a dome:
a) Hemispheric, b) Semi-ellipsoidal, and c) Torispheric
2. Conical shaped heads
Pressure Vessel Design:
Internal Pressure Causes Stresses in a Thin Cylindrical Shell
The following assumptions are used to analyze stresses created in a thin cylindrical shell: 1) The influence of the cylinder wall’s curvature is ignored. 2) The tensile stresses are evenly distributed over the wall portion. 3) The influence of the heads at the pressure vessel’s end restraining action is ignored.
When an internal pressure is applied to a thin cylindrical shell, it is likely to fail in one of two ways:
1) It may fail lengthwise (i.e. circumferentially), separating the cylinder into two troughs, as shown in Fig. 2) It may fail longitudinally (i.e. longitudinally), breaking the cylinder into two cylindrical shells, as shown in Fig.
As a result, the wall of a cylindrical shell exposed to internal pressure must endure the following two kinds of tensile stresses:
(a) Circumferential or hoop stress, and (b) circumferential or hoop stress
Longitudinal stress is the second kind of stress.
pressure vessel design
Hoop Stress or Circumferential Stress
= pd / 2t = pd / 2t = pd / 2t = p
Where p = Internal pressure intensity, d = Internal diameter of the cylindrical shell, l = Length of the cylindrical shell, t = Thickness of the cylindrical shell, and hoop stress = Circumferential or hoop stress for the cylindrical shell’s material
Longitudinal Stress is a kind of stress that occurs across a period of time.
= pd / 4t = pd / 4t = pd / 4t = p
Thick Cylindrical Shells Under Pressure From Within
- A thick cylinder is one with a ratio of less than 10 to 15 between the inner diameter (d) and the wall thickness (t) of the cylinder.
- Thick cylinders include hydraulic cylinders, high-pressure pipelines, and cannon barrels.
- In narrow cylinders, the radial stress (r) is ignored, however in thick cylinders, it has a substantial significance.
- Thick cylinders may be built using a variety of formulae. The choice of equation is determined by two factors: cylinder material (brittle or ductile) and cylinder end condition (open or closed).
- The following equations are often employed in the construction of thick cylindrical shells:
1. Lame’s formula,-
Lame’s equation is used to estimate the wall thickness when the cylinder material is fragile, such as cast iron or cast steel. It is based on the maximum principal stress hypothesis of failure, which equates maximum principal stress to the material’s permitted stress.
2. The equation of Birnie, –
The maximum stress theory of failure cannot be used to predict the allowed stresses in ductile open-end cylinders (such as pump cylinders, rams, cannon barrels, and so on) composed of ductile material (i.e. low carbon steel, brass, bronze, and aluminum alloys). The maximum-strain theory is used in these situations. Failure happens when the strain exceeds a limiting threshold, according to this idea.
3. The equation of Clavarino and
This equation is based on the maximum-strain theory of failure, although it is only applicable to ductile closed-end cylinders (or cylinders with heads).
4. The equation of Barlow.
For high-pressure oil and gas pipelines, this equation is often utilized.
Methods of construction
Riveted
- Before reliable gas and electrical welding, the standard method of construction for iron or steel boilers, compressed air receivers, and other pressure vessels was riveted sheets that had been rolled and forged into shape, then riveted together, often using butt straps along the joints, and caulked along the riveted seams by deforming the edges of the overlap with a blunt chisel.
- When the rivets were hot riveted, they contracted as they cooled, resulting in a tighter union.
Seamless
Seamless metal pressure vessel manufacturing techniques are usually utilized for relatively small diameter cylinders when large quantities will be manufactured, since the apparatus and tooling demand a considerable capital investment. The techniques are well-suited to high-pressure gas transit and storage applications, and they consistently provide high-quality results.
Backward extrusion is a method of forcing material to flow backwards along the mandrel between the mandrel and the die.
Aluminum extrusion (cold):
Seamless aluminum cylinders may be made via cold backward extrusion of aluminum billets, which involves pressing the walls and base first, then trimming the top edge of the cylinder walls, and then press forming the shoulder and neck.
Drawn:
Seamless cylinders may also be cold drawn in two or three steps from steel plate discs to a cylindrical cup shape.
Welded
Formed plates welded together are often used to construct large and low-pressure tanks. In pressure containers with human occupants, weld quality is crucial to safety.
Thorat, Sachin
Sachin is a Mechanical Engineering B-TECH graduate from a reputable Engineering institute. He is now employed as a designer in the sheet metal sector. He is also passionate in Product Design, Animation, and Project Design. He also enjoys writing articles about mechanical engineering and uses his original project ideas, design, models, and videos to inspire other mechanical engineering students.
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Pressure vessels are one of the most important inventions in modern day. They are used for a variety of purposes and types. This article will go over the different types of pressure vessels, their uses, and how to make your own pressure vessel. Reference: types of pressure vessels pdf.
Frequently Asked Questions
What are pressure vessels?
A: Pressure vessels are containers in which gases and liquids under pressure can be stored.
What are the types of pressure vessels?
A: There are four major types of pressure vessels that can be used in a boiler. These include, but arent limited to, superheaters, high-pressure boilers (HPB), economizers and feedwater heaters.
What is purpose of pressure vessel?
A: All pressure vessels are made of a double wall construction and have at least one air space between the two walls. The purpose is to create an atmospheric or working pressure inside the vessel that resists fluid flow.
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