2004 Volume 53 Issue 12 Pages 560-567
The corrosivity of freshwater on stainless steels is evaluated using the Mahalanobis-Taguchi System (MTS). At first, water quality parameters, such as pH, hardness and concentration of SO42-, Cl- are collected from a group of non-corrosive water of various regions (reference water). In MTS analysis, any unknown water can be judged whether it belongs to the group of the reference water or not according to its Mahalanobis distance (MD). MD of unknown water, a positive scalar value, is calculated from its water quality parameters and the inverse matrix of correlation matrix made from the reference water data.
In case that the MD of unknown water becomes less than about 3-4, the water is evaluated to belong the group of reference water, that is, non-corrosive. On the other hand, when the MD becomes larger than 3-4, the water is assumed not to belong to the reference water group and is corrosive.
In this study, interaction effects of water quality parameters are taken into consideration in MTS analyses. Parameters used in corrosivity evaluations are selected from six analytical variables (pH, conductivity, SO42-, Cl-, M-alkalinity and total hardness) and their interaction parameters that are calculated as products of any two of them. Present conclusions are (1) a number of misjudgments in corrosivity evaluation can be reduced remarkably by considering the interaction parameters of the reference water, (2) the corrosivity of unknown freshwater data that has been obtained can be correctly judged by using the proper set of 11 parameters, and (3) the parameters selected according to the lager the better type SN ratio aren't always optimal but are practically effective to some extent.