The traditional method of proving a pressure vessel or heat exchanger design is to carry out mechanical design calculations in accordance with procedures in established design codes. While the so-called design-by-rule approach is sufficient in the majority of cases there are sometimes features of the design or aspects of the process operation which, because they are not covered by the available rules, necessitate the use of design-by-analysis methods to demonstrate code compliance.
Typical applications of the design-by-analysis method are as follows:
- Design of large diameter circular and rectangular openings
- Design of nozzle openings situated in the knuckle region of dished ends
- Assessment of temperature gradients at shell-skirt junctions
- Analysis of nozzle loads on air cooler header boxes
- Analysis of special flange designs
- Assessment of design details vulnerable to temperature differentials set up under severe thermal cycling conditions
Finite element stress and thermal analysis is carried out using CREO/Simulate and ANSYS MECHANICAL finite element programs. Structural analysis capabilities include static linear and non-linear stress analysis, forced vibration and modal analysis and fracture mechanics. Thermal analysis capabilities allow complex transient or steady state temperature distributions to be evaluated for subsequent thermal stress analysis. All finite element analysis work is undertaken by FCL staff with qualifications and experience consistent with NAFEMS (National Agency for Finite Element Methods and Standards) Personnel Accreditation guidelines.
It is FCL’s view that the value of design-by-analysis work depends not only on the accuracy of the analysis but also on the interpretation of results and the manner in which the findings of the work are reported. FCL’s knowledge in this area is invaluable, both in minimising the need for client involvement and in achieving timely approval from third parties.
It is anticipated that the use of design-by-analysis methods in pressure vessel and heat exchanger design will continue to grow with development of the underlying European and US design codes. FCL, with the in-depth knowledge of these codes at its disposal, aims to maintain its position as one of the UK’s leading suppliers of design-by-analysis services to the pressurised equipment industry.