Pressure Vessel Design: 17 Facts You Should Know

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Primary and secondary stresses in pressure vessels | Pressure vessel stress analysis | Pressure vessel design procedure:


The first step in designing a vessel is the purpose of application and specifications that function the container characteristics. The environment and nature of liquid and gases are another important factors.
The parameters involves in the designing:

  • The temperature and pressure (maximum safety).
  • Factor of safety.
  • The capacity to contain the volume.
  • Corrosion allowance
  • Design temperature.


Spherical vessel:


M=\\frac{3}{2}PV\\frac{\\rho }{\\sigma }
where,
M = mass, (kg)
P = pressure difference (the gauge pressure), (Pa)
V = volume,
\\rho = The density of the vessel material, (kg/m3)
\\sigma = The maximum working stress that material can tolerate. (Pa)

Cylindrical vessel with hemispherical ends:


M=2\\pi R^{2}(R+W)P\\frac{\\rho }{\\sigma }
where,
R=radius
W=middle cylinder width
overall width=(W+2R)
Stress in thin-walled pressure vessels:
\\sigma _{\\Theta }=\\sigma long=\\frac{Pr}{2t}
stress in longitudinal axis

p is internal gauge pressure,
r is the sphere’s inner radius,
The thickness of the sphere wall is denoted by t.

Pressure vessel equations for stress | Pressure vessel equations | Pressure vessel formula | longitudinal stress pressure vessel:

\\sigma _{\\Theta }=\\frac{Pr}{t}
\\sigma long=\\frac{Pr}{2t}
sigma = stress in the longitudinal direction, p is internal gauge pressure, and sigma = stress in the longitudinal direction
r is the sphere’s inner radius,
The thickness of the sphere wall is denoted by t.

pressure vessel design
pressure vessel design
Image credit: Cdang, Reservoir cylindrique sous pression contrainte, CC BY-SA 3.0

Mechanical design of pressure vessel | Pressure vessel design | pressure vessel calculations | how to design pressure vessel | pressure vessel dimensions

create outline of the design:
Design and create the requirements of the vessel using the dimensions.
Include dimensions such as shape, diameter, length, pressure, temperature, and construction material.
Find out mechanical strength:
Find out mechanical calculations using the software.
Software gives both 2D or 3D drawings:
pressure vessel design drawing:

Design standards:
The purpose of application of vessel.
Operating pressure and temperature
Materials for fabrication
Vessel head type
Orientation: Horizontal or vertical
Dimensions
Openings and connections
Requirements for heating and cooling
Surface finish
External factors
Design stresses are adjusted using safety factors applied to material properties, including:
Yield strength (design temp)
Ultimate tensile strength (room temperature)
Creep strength (design temp)

Gasket design for pressure vessel:

A gasket is designed in such way that the flanges should be able to create the specific amount of compressive load on the surface of the vessel. It created an seal with no pressure. The gasket should be attached to the flange surfaces and be compressed to reduce the internal voids and spaces.


Design of a noncircular pressure vessel:

Because of the geometry of the cylindrical shape, most pressure vessel and pipe flanges have a circular cross section. However, there are some pressure vessels or pressure ducts where a rectangular or other non-circular shape is required, whether for space or process reasons.


Water pressure vessel design:

hydrostatic test
Water pressure vessel design
Image credit: Peter Southwood, Hydrostatic test, CC BY-SA 4.0


Hydrostatic testing uses water for the test.
It is a method that comprises pipeline systems, gas cylinders, boilers, and pressure vessel. These components are tested to check the strength and any kind of leakage from the system.
Hydro tests are quite required for the repair and replacements of the equipment that will operate under the desired conditions.
Hydrostatic test is the type of pressure test that can work by using the water and filling water in the components that removes the air contained within the system. and it pressurizes system with up to 1.5 times the design pressure.

How to calculate static head in pressure vessel:


Pressure vessel end cap design(heads):
Design pressure of vessel includes:
Static head= Pressure resulting from weight of liquid
Acting on internal of the pressure.
Higher liquid height results in higher pressure.
Static fluid pressure is independent of the liquid’s form, total mass, or surface area.
pressure= weight/area=mg/A

Pressure vessel skirt design:


Generally skirt support is provided to the tall columns.
The vertical orientation of the container is supported by the skirt support in pressure vessels. The benefit of using skirt supports is that it reduces the amount of stress at the supports.
Skirt is a cylindrical shell column with a diameter equal to or greater than the vessel’s outside diameter.
The skirt is welded to the vessel’s bottom and sits over the bearing plate.
The bearing plate is located on top of the concrete foundation system.

Pressure vessel skirt support design:

  1. The vessel’s dead weight.
  2. The vessel’s operating weight.
  3. Lateral loads
  4. Wind load
  5. Seismic load

Skirts are the supports that are used in the vertical pressure vessels. They don’t take load from the pressure of the fluid inside the container.
Weight of the vessel and fluid inside and the environmental loads altogether are considered for the designing of the skirt support.
Skirts gives the less expensive design for the support of the taller pressure vessels.
W+Fw+Ew= Total load.

Design of a jacketed pressure vessel:

A jacketed vessel is a container designed to control the temperature of its contents by encircling the vessel with a cooling or heating “jacket” through which a cooling or heating fluid is circulated.
A jacket is an exterior cavity that provides for a consistent heat exchange between the fluid moving inside it and the vessel’s walls.
Liner-less composite pressure vessels (CPVs), also known as type 5 (type V) tanks in some sectors, are the most efficient composite pressure vessels (burst pressure x volume/weight).

Vacuum pressure vessel design:

vacuum pressure vessel design uses a design pressure which is in accordance with the full vacuum of the vessel state that the internal pressure is vacuum and external pressure becomes 100kpa that is atmospheric pressure.


Pressure vessel fatigue calculations:

Fatigue life of material is determined first. The fatigue of material is determined by testing many samples to check the failure of the material.
At each stress level, the number of cycles should be able to be calculated. Test samples are highly polished round bars that are as close to identical as manufacturing can make them. A test bar is rotated with a load applied so that a fiber at the bar’s surface is in tension and then in compression as the bar rotates, resulting in a complete stress reversal as shown.

There are several stress cycles, each with a different stress magnitude and number of cycles. Fatigue damage from each stress cycle adds up, so the total effect of all stress cycles must be calculated. The rule of Miner:

Pressure vessel shapes:


Although pressure vessels can potentially be any form, the majority are made up of portions of spheres, cylinders, and cones.
A popular design is a cylinder with end caps called as heads. The most frequent head forms are hemispherical or dished.

Design of a vertical pressure vessel support:


They have a better pressure distribution, making them more secure.
They use less energy because gravity allows their contents to flow easily and effortlessly.
They require less ground space for their inhabitation.

Area compensation method in pressure vessel:


Nozzle reinforcement is the method of the area compensation.
This method is used when there is opening in the cut section of the pressure vessel.

An area is removed from the shell and the head. The removed area should be equal to area added and it should reinforce by an equal amount of area near the opening.


composite pressure vessel analysis:


The objective of the analysis of the composite pressure vessel system is that It should increase the storage capacity of the system to the specific level. Hence, using the steel vessel, detailed analysis of the vessel design should be performed according to the multi axial stresses those are resulted from the tank design system in the transition region of cylinder and head.

Minimum wall thickness for pressure vessel:


1/16 inches is the minimum wall thickness is used for the pressure vessels.
pressure vessel volume formula:

where,
V= volume,
r= radius of the internal surface
a= area of the vessel
I= moment of inertia.

Pressure vessel principal stresses:


There are two principal stresses in the pressure vessel.
Hoop stress
longitudinal stress
This shows that the stress along the surface of the vessel should have resultant that balances the internal pressure.

FAQ/short notes:


What is the purpose of a pressure vessel:


Gases and liquids are held at high pressures within pressure vessels.
Pressure vessels are used in boilers, reservoirs, highly pressurized pneumatic cylinders, and industrial uses, among other things.


How do pressure vessels work:


It works at higher pressure or increasing pressures. It reaches the pressure that makes the application function work such that it holds the gases or the liquids in the storage tanks.
It provides the pressure through the valves or through the heat transfer.


What are the types of pressure vessels:

Pressure vessel types depends on the design of the vessels for the functionality of the applications in the industries. Mainly pressure vessels can be divided into the types according to their purpose for the applications. According to above factors mainly pressure vessels have three types:


Storage vessels:

These tanks are mainly useful for the industrial applications. These typically used in horizontal or vertical manner. It stores liquids and gases such as oil, chlorine and natural gases. It can be available in any size ranges. It is available in variable shapes like cylindrical or spherical for their vertical or horizontal manners. The material used in for the manufacture of the the type of product is carbon steel considering the external environment.
Such vessels need careful construction as the internal substances can be bad without proper maintenance.
Process vessels:

Process vessels are designed as per the requirements of the application while construction to reach the required specifications. Various processes can be performed in pressure vessels.
Pressure vessels can be used in conjunction with other products depending on the application. So the manufacturing material required for such vessel components can be of unique material or multiple different materials.
These pressure requires following important factors:
Proper designing
Proper material selection depending on the properties that reaches the applications requirements.
Careful and proper construction as per the specification.


What is the distinction between an autoclave and a pressure vessel:


An autoclave is a type of pressure vessel.
The main difference between the both is that the autoclaves are the type of pressure vessels that uses high pressure and high temperatures, the body should be capable of sustaining such high temperatures and pressures.

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