An alternative method to determine critical pitting temperature of stainless steels in ferric chloride solution

Abstract

The conventional test in FeCl 3 solution for determining the critical pitting temperature (CPT) of iron-base alloys is a time-consuming procedure. An alternative, electrochemical variant of the test has been used in which welded and non-welded duplex stainless steels are coupled in the solution via a zero resistance ammeter (ZRA). The current flowing between the two specimens increases abruptly when pitting starts as the solution is heated up above the CPT, giving a rapid measure of the CPT as well as other basic information. This technique was applied to determine the CPT of two duplex stainless steels of different compositions. The values determined by both methods resulted in good agreement. The time saving and the accuracy in distinguishing metastable from stable pitting of the electrochemical method was an advantage over the traditional immersion test. The effects of different heat inputs and surface finishes on the CPT of duplex stainless steel welds were investigated using the ZRA technique. A brief theory of the CPT is presented as a basis for future experimentation.