Abstract: Flanges can be divided into equipment flanges, pipeline flanges and nozzle flanges for equipment and pipeline connections according to the disciplines they correspond to in engineering. This paper briefly explains the design features of these three types of flanges, and introduces the preferred checking methods for equipment and piping disciplines. Different calculation results were obtained from adopting different checking methods under external load preferred by each discipline through a representative engineering example. On this basis, the paper further elaborates the calculation principles, respective characteristics, and existing problems of equivalent pressure method, NC3658.3, ASME Section Ⅷ and EN1591. Finally, combining with the comparison and analysis of the calculation results, suggestions for the selection of appropriate checking methods for small-diameter nozzle flanges under external load are made.

Key words: flange check, equivalent pressure method, EN1591, NC3658.3