4.1 The test method determines the potential independent
critical pitting temperature (CPT) by way of a potentiostatic
technique using a temperature scan and a specimen holder that
is designed to eliminate the occurrence of crevice corrosion
(see Fig. 1). The specimen is exposed, either entirely or in part,
depending on test cell configuration to a 1M NaCl solution,
initially at 0°C. After an initial temperature stabilization
period, the solution is heated at a rate of 1°C/min. About 60 s
before the temperature scan is commenced, the specimen is
anodically polarized to a potential above the pitting potential
range. This potential is held constant during the whole temperature
scan. A potential of 700 mV versus SCE (25°C) has
been found suitable for most stainless steels. The current is
monitored during the temperature scan, and the CPT is defined
as the temperature at which the current increases rapidly, which
for practical reasons is defined as the temperature at which the
current density exceeds 100 μA/cm2 for 60 s. Pitting on the
specimen is confirmed visually after the test.