Finite element analysis on grey cast iron assets: a case study on penstocks in the wastewater system

Abstract

Penstocks have been used in the water industry for flow control since the Victorian expansion and consolidation of clean water and wastewater networks. However, the Victorians were the first to use grey cast iron (GCI) castings to manufacture large scale penstocks. Most of these ageing assets are still in operation; however, engineering assessments are necessary to determine a structure’s fitness for service. Even today, penstocks in the sewer system tend to be made from GCI, due to ease of manufacturing, resistance to corrosion and cost. One characteristic property of GCI is the graphite flake structure in the material, contributing to its low toughness, inconsistency in material strength and brittle behaviour, despite exhibiting slight hardening properties. Finite element analysis (FEA) is a numerical method which allows the analysis of complex structures by splitting it into finite parts and solving them with a computer processor. Despite the versatility of FEA, appropriate considerations and assumptions are necessary due to the difficulty to obtain data from inspection and unique material behaviour of GCI. The article shows concerns for an analysis of GCI penstocks using FEA, which extends into the application of fracture mechanics approaches for defect assessments.