Pitting Test

The "pitting potential" and the "repassivation potential" of 316L stainless steel are experimentally determined at -0.4 °C and 50°C in NaCl 3g/l. They are determined from the experimental polarisation curve.

Solution NaCl 3g/l in water
WORK Stainless steel disc EM/EDI/INOX AISI 316L:
(C<0.03%,Cr=17%,Ni=12%,Mo>2%)
on a rotating disc electrode at 500 rpm
(EDI101 with its CTV101 Speed control Unit)
REF Calomel electrode (XR100)
AUX Platinum wire (XM100)
A/D IN Temperature in °C (T201)
Digital Thermometer with analogue output
CP06 Thermostated cell, temperature maintained with bath flow circulation.

The polarisation curve is recorded at 5 mV/s from OCP toward anodic potentials up to 1.5 mA and after 10 seconds at this potential, the potential scan is reversed in cathodic direction.

1)Display: Type = Normal X = Potential Y1 = Current Y2 = A/D IN (Temperature in °C)
Overlay the two experimental pitting curves: Pitting-0.4°C008.CRV (red) Pitting 50°C008.CRV (blue) and use the "Axis" function to distinguish Y1 from Y2.

The "pitting potential" corresponds to the potential at which the current starts to increase on the anodic scan. The "repassivation potential" corresponds to the potential at which the current becomes negligible on the reverse (cathodic) scan. The more anodic the "pitting potential", the less subject to pitting the sample. A "repassivation potential" close to the "pitting potential" indicates that the sample is capable of reprotecting itself easily after pitting.

The sample under examination is much less sensitive to pitting corrosion at -0.4°C than at 50°C.