Pressure Equipment Design by Analysis

Pressure equipment such as vessels, flanges, valves and tees are safety critical and can have complex stress distributions. Pressure vessel codes such as ASME VIII Division 2 and BS EN 13445 incorporate 'Design by Analysis' methodologies which can be implemented using finite element analysis (FEA), and which offer an alternative to traditional design rules. 'Design by Analysis' enables the designer to accurately assess the component against each failure mode, as stresses and structural behaviour can be predicted. By contrast, traditional design rules often incorporate conservatism to compensate for the fact that design rules do not accurately predict the entire stress distribution within the vessel, and do not address all modes of failure, such as fatigue and fracture.

Implementing the 'Design by Analysis' methodologies using FEA in line with industry standards allows for a more efficient design, while not compromising on safety. It also enables an accurate determination of the margin of safety for each failure mode. As a consequence, 'Design by Analysis' is used in the following areas:

  • Design of vessels and components having dimensions outside of those covered by traditional design rules
  • Optimisation of designs in order to reduce material and manufacturing costs
  • Fitness for purpose assessments where manufacturing tolerances have been exceeded
  • Assessment of complex loadings such as temperature distributions
  • Nozzle external load capacity evaluation
  • Fatigue assessments
  • Detailed buckling assessments

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Pressure Vessel Head and Nozzle Stress Distribution

Non Linear Limit Load Analysis of Tee Section