A short Presentation on Basics of Pressure Vessels

A short Presentation on Basics of Pressure Vessels [With PDF]

What is a Pressure Vessel

A pressure vessel is a closed leak-tight container (normally cylindrical or spherical) designed to hold fluids (i.e, gases or liquids) at a pressure substantially different (higher or lower) from the ambient pressure. They are usually made from carbon steel or stainless steel and assembled from plates by welding method. However, other materials like Aluminium, copper, non-metals, etc also find usage as pressure vessel material in some specific situations. Fig. 1 shows a typical pressure vessel used in THE oil & gas industry.

What are the Types of Pressure Vessels?

Based on their installation they are classified into the following two groups.

  1. Vertical pressure vessel
  2. Horizontal Pressure Vessel

Various methods are used to support pressure vessels, like

  • Lug Support
  • Ring Support
  • Skirt Support
  • Leg Support
  • Saddle Support

Types of end attached to the vessels are

  • Dish ends
  • Conical ends
  • Flat Ends

Fig. 2 shows the general configuration of a pressure vessel.

A typical pressure vessel for a process plant
Fig. 1: A typical pressure vessel for a process plant

Design Inputs of Pressure Vessel

While designing pressure vessel following inputs are required

  • Internal Pressure / External Pressure
  • Design temperature
  • Material of constructions
  • Type of support
  • Type of loading (wind load/seismic loading/snow loading)

Pressure Vessel Design Formula

The basic formula for designing the cylindrical shell is

σ = PD/2t

Therefore,           t = PD/2σ

Where,

  •                 t = thickness of the shell
  •                 P = internal pressure
  •                 D = diameter of the shell
  •                 σ = tensile stress
General Configuration of a typical pressure Vessel
Fig. 2: General Configuration of a typical pressure Vessel

This basic formula is modified in international design codes.

For ASME Sec VIII, the thickness of the cylinder is calculated by the following formula (Fig. 3)

Formula for calculation of pressure vessel shell thickness
Fig. 3: Formula for calculation of pressure vessel shell thickness

Where,

  • t = thickness of the shell
  • P = internal pressure
  • R = radius of cylinder
  • S = tensile stress
  • E = joint efficiency

Refer ASME Sec VIII Div 1 for design formulas for all sections of the vessel/cylinder.

Type of Pressure Vessels:

Based on supporting types they are of following types

  • Vessel Supported on Lug Support (Fig. 4)
  • Vessel Supported on Skirt(Fig. 4)
  • Vessel Supported on Leg(Fig. 4)
  • Vessel Supported on Saddle(Fig. 5)
Various types of supports for pressure vessel
Fig. 4: Various types of supports for pressure vessel
Pressure Vessel Supported on Saddle
Fig. 5: Pressure Vessel Supported on Saddle

Pressure Vessel Parts

  • Shell, head
  • Nozzles
  • Flanges
  • Gaskets
  • Internals
  • Platforms & ladders

Design codes used for Pressure Vessel

  • EN 13445: The current European Standard, harmonized with the Pressure Equipment Directive (97/23/EC). Extensively used in Europe.
  • ASME Code Section VIII, in addition, supported by Sections II (materials), V (NDT/NDE) and IX (welding). Published by the American Society of Mechanical Engineers.
  • ASME Code Section VIII Division 1: US standard, design by the formula. Almost exclusively used in North America, widely used worldwide.
  • ASME Code Section VIII Division 2: Alternative Rules, design by analysis.
  • ASME Code Section VIII Division 3: Alternative Rules for Construction of High-Pressure Vessel
  • BS 5500: Former British Standard, replaced in the UK by EN 13445 but retained under the name PD 5500 for the design and construction of export equipment.
  • AD Merkblätter: German standard, harmonized with the Pressure Equipment Directive.
  • EN 286 (Parts 1 to 4): European standard for simple pressure vessels (air tanks), harmonized with Council Directive 87/404/EEC.
  • BS 4994: Specification for design and construction of vessels and tanks in reinforced plastics.
  • IS 2825-1969 (RE1977) : code unfired Pressure vessels

Internals used in Pressure Vessel:

Internals are used to separate the liquid from a mixture of liquid & vapour. Refer Fig. 6

Pressure Vessel Internals.
Fig. 6: Pressure Vessel Internals.

Example of Pressure Vessel

Fig. 7 shows a few of the various types of pressure vessels that are normally used in plants.

  • Separator
  • Scrubber
  • Distillation Column
  • Shell & Tube Heat Exchanger
  • Reactors
Figure showing various types of pressure vessels.
Fig. 7: Figure showing various types of pressure vessels.

Material of Construction most widely used

  • Carbon steel and Cladding Plates
  • Stainless Steel
  • Duplex Stainless steel
  • Fibre Glass Reinforced Plastic

Applications of Pressure Vessel

Pressure Vessels are most widely used in the following sectors

  • Refinery and Petro-chemical
  • Fertilizer
  • Oil and Gas
  • Chemical

Few more Resources for you..

Brief Explanation of Major Pressure Vessel Parts
A Presentation on VESSEL CLIPS or VESSEL CLEATS
10 points to keep in mind while using project specific pressure vessel nozzle load tables during stress analysis
Understanding Pressure and Temperature in the context of Pressure Vessel Design
A Video tutorial on “Comprehensive Design Code Coverage for Pressure Vessel and Heat Exchanger Design” by Bentley Institute

Reference

https://faculty.washington.edu/vkumar/me356/pv_rules.pdf

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