Abstract

Modern design philosophies for offshore cranes require the structural components to be designed for the dynamic loadings experienced in the offshore environment. If these predicted impact loads are applied to the relevant winch load-paths, then the components in those load-paths can be appropriately designed. Specifications do not at present, require the operator to predict at the enquiry stage, the service duty and load spectrums for the crane. When these ore specified by the operator, the designer is able to apply appropriate Stress levels to the components to attain the required crane life.

Introduction

During the last 7 to 8 years, over 90 reported incidents concerning offshore cranes have occurred. Approximately 10% of these incidents involved injuries, half of which were fatal. Much has been achieved by societies, authorities and manufacturers, since the first generation of offshore cranes was commissioned. Specifications and regulations are now more appropriate far the unique conditions in which these cranes operate. Although directed at the onerous operational conditions experienced in the North Sea, the philosophies expressed here apply to oil cranes operating between supply vessels and platforms.

Examples of Failures

Some known examples of failures of cranes in offshore use are as follows:

  • Boom collapse;

  • Boom pendant failure;

  • Slew ring failure;

  • Winch drum breakage;

  • Winch gear failure;

  • Brake failure.

Reasons for Failures/Accidents

  • Driver error;

  • Overloading (lack of overload protection);

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