Abstract: Equipment for investigating crack propagation in thick steel plates of a material with applicability for pressure vessels comprises a test specimen in the form of a hollow cylinder of the material under investigation, a vertical spindle from which the hollow cylinder is suspended and which can be rotated at a speed of the order of thousands of revolutions per minute, damping means for damping against flexural resonance vibrations of the cylinder and spindle, a container for the cylinder and means for supplying hot air to the container via a port, means for applying through a port in the container, a jet of cold fluid on to a surface of the cylinder to apply thermal shock thereto the spindle being hollow to accommodate leads from instrumentation on the cylinder to a slip ring unit from which leads to control and recording equipment extend, the instrumentation serving to monitor crack propagation under the conditions of high speed revolution which induce a hoop stress in the material approaching its yield stren