ABSTRACT

Catastrophic hose failures are potentially damaging to equipment and lethal to operators working in the immediate areas.

This paper is a summary of detailed investigative work, carried out at intervals over fifteen years, into causes of failures on a large number of quite different hoses. These ranged from small bore, power hydraulic, through medium bore, gas compensating, mud vibrator, rotary, choke and kill to large bore, oil conveying. Whilst each examination was carried out in isolation, patterns or modes of failures were noted crossing boundaries of hose type, size and use. AS a consequence, fundamental reasons were identified and have been used to predict most likely modes of failure in new designs of hoses or hoses presented for examination. The modes of failure which have been identified across this wide range of hoses have related to choice of materials, basic constructions, flexibility, end termination variations, service conditions etc. and were identified through laboratory and field investigations.

Some simple non-destructive checks are suggested for in-situ monitoring of hose deterioration in service.

1. INTRODUCTlON

Rapra Technology Limited, originally set up as The Rubber and Plastics Research Association of GB in 1911, has been involved over a considerable number of years in the consideration, examination and evaluation of hoses of all types. Over the past fifteen years the number of hoses examined, for one reason or another, has increased considerably. Some were in a "just-manufactured" condition; some were damaged, leaking gas, oil, mud or chemicals; some had failed catastrophically causing damage and injury and some had been involved in combustible gas explosions.

These hoses have ranged in size from 6 mm (¼") to 600 mm (25") and over working pressure ranges between 2 Bar g (30 psi) to 1000 Bar g (15000 psi). All of the examinations were treated as individual cases but, over the years, patterns or modes of failure appeared which covered not only one type of hose and use but all types and almost all uses. As a consequence each examination was treated as part of a continuing study so that fundamental modes of failure could be identified, made known, recognised, and dealt with at a design, manufacturing or service stage. In this way, separate industries, using hoses in very different service conditions, could benefit and not feel isolated within their own industry. As an added benefit, one objective of this continuing study was the possible identification of non-destructive in-service monitoring of hoses in service and suggested length of service for some types of hose as a consequence.

This paper outlines and summarises the investigative work on some 200 hoses to come to firm conclusions on fundamental modes of failure and proposed nondestructive monitoring of hoses In service.

2. HOSE DESIGN

Before plunging into the problems of hose failures, it is important to understand some elements of basic hose design and the function of the various hose components. From an understanding of those points, the reason for some hose failures may then seem that much more logical.

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