Abstract
Pressure vessels containing agitators supported by a nozzle on the vessel top cover are commonly used in a variety of industrial applications such as electric car battery material plants, metal refining plants, plastic recycling plants, food processing facilities, petrochemical plants and in the pharmaceutical industry.
The loads and moments induced by the agitator on both the top cover and the supporting nozzle are often cyclic in nature and it is common that these be ignored or only partially evaluated during the design of the vessel, especially when there may be time constraints or lack of resources. This can result in a shorter operating life for the agitator or its drive mechanism than originally expected, which could further lead to vibrational issues and subsequent fatigue failures in the top cover or the nozzle.
A correctly designed top cover and nozzle support for an agitator should be strong enough to withstand the sustained cyclic loads and contain features so it is acceptable for the cyclic conditions to allow the safe use of the equipment for the entirety of its intended design life.
The purpose of this paper is to firstly explain some of the recommended features that should be taken into account during the design and fabrication of agitator-mounted vessels and then to investigate a simple approach to estimate the fatigue damage on the nozzle. The suggested method will then be further examined against FEA results to ascertain its validity. British PD 5500 fatigue design rules will be considered for the evaluation.
