Hydrogen Disbonding of Stainless Clad Steels by Cathodic Current

Abstract

Hydrogen disbonding of stainless clad steels was examined by "in-situ detection method", which is composed of ultrasonic wave inspection and cathodic hydrogen charging.
Disbonding cracks occurred in the hard martensitic layers in the interface region between high alloy and carbon steel.
Ni and Cr in the high alloy diffuse into the carbon steel, and C in the carbon steel migrates into the intermediate phase to cause the martensitic transformation.
The susceptibility to hydrogen disbonding is affected by the hardness of this layer.
The hardness of the martensitic layer is increased with increasing the carbon content in the carbon steel, which leads to the raised susceptibility to the hydrogen disbonding.
The concentration of hydrogen in the carbon steel under cathodic protection was measured by electrochemical hydrogen permeation method.
The concentration of hydrogen is less than 0.01 mass-ppm under usual cathodic protecting condition.
On the other hand, the threshold concentration of the hydrogen disbonding is more than 0.1 mass-ppm.
So it is thought that there is no possibility of the hydrogen disbonding under the cathodic protection.