Investigation into environmental stress cracking in processed food cans
File(s)
Author(s)
Smith., P. J.
Type
Thesis
Abstract
This study followed instances of filled can leakage in the late 1990s - 2000, affecting steel cans packed with high protein meats or fish. Such foods typically contain at least one anion promoting susceptibility, phosphate, and low levels of some promoters of hydrogen ingress into steel. Experiments utilised product brines from cans of tuna and red salmon, bulked and deep frozen. Tuna has some history of stress corrosion in steel cans but no cases were known for salmon. DC polarisation tests did not reveal conclusive evidence of passive conditions on the anodic polarisation curves. Slow strain rate tests including current measurement were conducted at the Open Circuit Potential, for three cold reduced 620MPa nominal yield strength steels of Al killed type, tested as notched specimens. Each steel showed loss of ductility at the notch region under high or low air (N2 flush) test conditions with either product. Discrete regions of environmental stress cracking were observed using SEM, for each steel type with salmon brine under high and low air conditions, with more limited evidence for tuna. Loss of ductility and environmental stress cracking were partial effects. The features observed were consistent with hydrogen cracking; analytical work revealed headspace hydrogen in the cans of each product type. Regression relationships for time to failure were derived combining the direct effect of mechanical work up to maximum load, and the inverse effect of the integrated current time parameter. FEA modelling for prediction of stresses was carried out for the notched tensile sample, a drawn redrawn fish can and an easy open end shell. The predictions permitted comparisons to be drawn between the different cases in the absence of corrosion. Further work e.g. by changing notch angles may help identify any threshold stress levels affecting this failure type.
Version
Open Access
Date Awarded
2010
Advisor
Hocking, Professor
Publisher Department
Department of Materials
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)