Abstract Résumé

In this paper, data will be given of test procedures for high-strength and extra-high-strength steels especially for applications in high-pressure equipment.

It will be argued in the paper that the specifications for impact tests in these applications should be based on the results of large-scale tests.

Dans cet article des renseignements sont donnés sur les procédés d'essais relatifs aux aciers de haute et très haute résistance spécialement orientés vers la construction d'appareils de haute pression.

On a également attiré l'attention sur le fait que, en vue de telles applications, les spécifications pour les essais de résilience doivent être basés sur des essais utilisant des échantillons de grande dimension.

INTRODUCTION

Not so many years ago the requirements for pressure vessels could still be met by the use of low strength steels. Fracture-safe design was mainly based on practical experience and a few simple mechanical tests. A great number of service failures had been analysed and translated into improved methods of design and steel specifications. In the past two decades this procedure has certainly led to a gradual decrease of service failures after the first explosion of brittle fractures during the World War II period. At the moment that we have learned to walk in this field without too much stumbling we are told by industry, however, that walking is too slow and that we should drive a car. The development of new chemical processes asks for pressure vessels of ever increasing size and operating pressure. To meet these modern more severe requirements new high strength steels of the normalized or quenched and tempered type have to be used. There is, however, insufficient experience with the new high strength steels to formulate specifications, which will guarantee the same degree of safety as the old specifications for the conventional steels. In solving this problem we are hampered by the lack of knowledge on the micro and macro aspects of fracture initiation and propagation.

There are nearly as many theories of fracture as there are actual service failures. Moreover, it seems to be a special hobby of scientific investigators in this field to devise their own tests for determining the ductile-brittle by Prof. Dr. Ir. C. A. VERBRAAK Metaalinstituut TNO and Technological University Twente Í Holland) transition in steel. There is a rich choice of divergent test methods and no general accepted order of merit for these various tests. Still each day many engineers have to take the responsibility for the choice of a specific steel for the fabrication of a large variety of equipment.

The national specifications might be either too severe or too vague according to the personal opinion of an individual engineer.

One consideration, however, is predominant for him: there should be no failure in practice, because this could mean the end of his career as an

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