Mining draglines are large mining machines which have a booms of about 100 m in length. The booms are tubular structures made up of three large chords connected by smaller lacing tubes. There is a regular cracking phenomenon at the welds which means that the cracking must be remotely detected, exactly located and repaired. This paper describes the cracks which grow in the weld joints (called clusters) and the system by which the booms are protected from catastrophic collapse and the maintenance and repair techniques used to keep them in service.

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Thermal shock loading, such as that which occurs when a hot material is sprayed with cold water, produces a very high stress level near the exposed surface that eventually may lead to the development of cracks. Further growth of the cracks under repeated thermal shock is a very complex phenomenon due to the transient nature of the highly non‐linear thermal stresses and the strong influence of the environment. There are cases in industry where cracks created by thermal shocks have arrested and stopped, and others where the cracks have progressed. Understanding this difference in behaviour is very important to the operators of pressure plant. This paper describes an experimental examination of crack growth in pressure vessel steel specimens exposed to repeated thermal shock. A test‐rig that achieves large‐scale thermal shocks through the repeated water quenching of heated flat plate specimens is used. The effect of steady‐state loads on the growth is also analysed. Environmental effects due to the aqueous nature of the testing environment are found to be a major contributor to the crack growth kinetics.

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