The Direct Route to Design by Analysis, as laid down in EN 13445-3 Annex B, is a major step forward towards a more rational, informative design process for unfired pressure vessel components.

This approach provides much insight into the behaviour of the components and, especially, into the safety margins against individual failure modes.

This approach offers advantages with respect to design improvements, and also with respect to in-service inspections, in-service inspection procedures, and the specification of in-service inspection intervals, including risk-based inspection approaches.

The presently existing restriction to unfired pressure vessels made of sufficiently ductile steels is not really restricting the present standard encompasses the majority of unfired pressure vessel and the extension to other sufficiently ductile materials is straightforward.

The presently existing restriction to unfired pressure vessels operating below the creep regime will cease to exist in the near future the draft of the design checks for unfired pressure vessels operating in the creep regime has already passed the first enquiry stage.

There may exist theoretically more attractive, more rational approaches, based on total probabilistic concepts, on the concept of reliability of structures [123], but these have still a long way to go to gain general acceptance in the pressure vessel industry, with its variety of designs and phenomena. Moreover, the partial safety factor concept, used in the Direct Route to Design by Analysis, is flexible and open enough for incorporation of some of these (improved) probabilistic concepts the concept of reliability may serve the framework...