The use and operational experience of forged high-pressure monobloc vessels is reviewed. It is noted that such vessels fall mainly into two categories: firstly those like stirred autoclaves for use in the continuous polyethylene process which are subjected to at the most two or three thousand cycles of pressure in a lifetime; and secondly, those such as isostatic compaction vessels which may be subjected to more than a hundred thousand cycles of pressure. It is concluded that the design procedures for one category are not sufficient for the other. Review of the performance of polyethylene autoclaves suggest that the design procedures which are based on well-established fundamental principles are more than adequate to ensure a safe design. With isostatic compaction vessels there is the added requirement to design against fatigue, and in particular to ensure adequate strength in the transition region between the threaded portion of the bore required for the screwed plug and the main bore, as it is mainly in this region that calamitous failures have been initiated. Some thoughts on some of the requirements for a code of practice for forged high-pressure vessels are put forward.

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