Abstract
The design of thick-walled monobloc cylinders to resist fatigue is of great importance in the chemical industry. There has frequently been the tendency when raising operating pressure to increase the strength of the material employed without realizing the dangers arising from a consequent reduction of fracture toughness. There is a real danger in the short-term fatigue region that the fatigue life may be reduced by increasing the strength of the material excessively and that the mode of fracture will be far more dangerous. Several examples of such fractures have been noted in the literature and experienced by one of the authors.
The paper describes experimental work carried out on thick-walled cylinders with a cross-bore made of En 25 steel heat-treated to various strengths from an ultimate of 60 tonf/in2 to well over 100 tonf/in2. These cylinders were tested under repeated internal pressure in a modified version of the testing machine developed by Austin and Crossland. Tension and hardness data are presented and it is hoped that fracture toughness data will also be available and that an attempt will be made to correlate fracture toughness data with the fracture of the cylinders. Fracture toughness testing is discussed.
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