Structural / Mobility
Technical Paper

Design against brittle fracture for unfired pressure vessels in European standard EN13445

Niobium Bearing Structural Steels

There have been large uncertainties concerning the risk for brittle failure in welded high strength and duplex stainless steels, since both specific design rules as well as proper materials data have been lacking. This has been of major concern particularly in safety classed components like pressure vessels. To solve this problem, new methods have been developed to allow for an economic and safe design against brittle failure. These are based on principles of fracture mechanics derived in European research during the last 15 years. The new design principles have been implemented in the European pressure vessel code EN 13445, because in the present version of EN-13445 from 2002 (the first published version) there are some severe limitations concerning the use of high strength steels. In fact, steels with yield strength above 460 MPa cannot be used without performing detailed fracture mechanics analysis and duplex stainless are not allowed in gauges above 30 mm, which excludes many modern high strength steels with good toughness properties. The new method quantifies how the thickness, the strength, impact toughness and heat treatment influence the risk for brittle failure. In the derivation, the influence of the residual stresses has been taken into account as well. Starting from a specified maximum crack size that depends on the component thickness, the minimum safe design temperature has been derived. Together with the charpy toughness to fracture toughness correlations a practical design methodology for end users has been developed. The method has been validated by large scale tests. The presentation will introduce into the European Standardisation activities and provide details how new and modern steels can be introduced into standards by means of combining research results, modern material mechanics methods and existing experience. (AU)
Technical Paper (PDF 583.07 KB)