Constant strain stress corrosion tests, at 50 or 100% yield stress, were conducted on welded nickel steel samples exposed to a mixed nitrate solution for various times. Where grain boundaries intersected the specimen surfaces selective attack was invariably observed, even for relatively short exposure times. Average growth rates for the early stages of cracking showed considerable variability, by about an order of magnitude, for a given test time and point to the importance of replicate tests if appropriate data are to be collected.