Failure investigation of a centrifuge duplex stainless steel basket

Starch is an essential ingredient for both food and non-food industrial sectors. One of the steps on the manufacturing process of starch is centrifugation by means of huge rotating baskets. In the present case, a basket of more than 2 m in diameter was made of duplex stainless steel. The minimum service life of this type of baskets is established in 15 years. However, after around 5 years in service, the automatic security system of the centrifugal process stopped the basket rotation. The component was then examined by dye penetrant and a through-wall crack with more than 50 cm of surface length. In order to determine the reason (or reasons) for such failure, an investigation was performed. This investigation included material analysis, mechanical testing, and fractographic studies. A high level of shrinkage porosity was detected and considered as the main responsible of crack nucleation. Also, the presence of nitrides contributed to a fast propagation of the crack front.