Pressure Vessel stress calculator

Use this code to calculate the stresses in cylindrical pressure vessels. A calculator class, Vessel, and a GUI class, PV_GUI, are provided.

Purpose

The calculator is intended for use with relatively simple pressure housings, without fittings, welds, or variations in material. For more complex vessels, the calculator may be used as a first step for the overall stress levels, to be followed by specific analysis of stress concentrations.

Theory

Given the dimensions of the pressure vessel, the material strength, and the applied pressure, the von Mises stresses in the wall are calculated. A safety factor is determined using both the maximum von Mises stress and the average stress between the inner and outer wall surface. The average stress is limited to a smaller proportion of the maximum allowable stress, which requires that vessels with thinner walls have larger margins of safety.

The allowable stress value should be chosen to represent the worst-case material strength while in use. By default, the tensile yield stress should be appropriate. If the service temperature is significantly higher than room temperature, the allowable stress should be reduced to compensate for any loss of strength in the material. Similarly, if the tensile strength and compressive strength are significantly different, choose the strength value corresponding to the load case (i.e. tensile for internal pressure, compressive for external pressure).

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Getting Started

Prerequisites

• No requirements outside the Python Standard Library

Installation

You can install this package from this repo by using pip:

cd pressurevessels
pip install -e pressurevessels

Note the -e flag, which installs in editable mode and allows you to modify the source at will after installing.

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Usage

For direct use of the Vessel class, you can import the module:

from pressurevessels import Vessel

and create a Vessel instance:

v = Vessel(pExt, pInt, OD, ID, allowable_stress)

After creating a Vessel instance, the following calculated properties are available:

• Vessel.averagestress : The average of the inner and outer von Mises stresses

• Vessel.maxstress : The maximum von Mises stress

• Vessel.maxInternal : The maximum allowable internal pressure, such that the minimum safety factor is 1.0

• Vessel.maxExternal : The maximum allowable external pressure, such that the minimum safety factor is 1.0

• Vessel.SF : The safety factor for the vessel, considering both the maximum stress and the average stress.

Alternatively, the results can be printed by printing the Vessel instance:

>>> vessel = Vessel(15, 0, 1.695, 1.460, 120)
>>> vessel
pExt: 15
pInt: 0
OD: 1.695
ID: 1.46
allowable_stress: 120

Minimizing Wall Thickness

After creating a Vessel instance, the wall thickness can be minimized to reach a safety factor of 1.00, by modifying either the OD or ID.

• Vessel.minimize_OD : keeping the ID constant, set the OD to the smallest value that results in a safety factor of 1.00
• Vessel.maximize_ID : keeping the OD constant, set the ID to the largest value that results in a safety factor of 1.00

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Using the GUI window

To use the GUI from tkinter, you can execute the module with python -m pressurevessels

The GUI window resembles the following:

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Roadmap

• Unit conversions (US and SI)

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

License

MIT