The influence of ultrasound vibration on the pitting corrosion of AISI 316 stainless steel

Abstract
Abstract
The influence of ultrasound vibration on pitting corrosion suppression of AISI 316 stainless steel was investigated using galvanostatic polarization and weight-loss techniques in Cl-containing solutions at 20 and 50 C. SEM surface analysis was performed after anodic treatment. Both galvanostatic polarization and weight-loss revealed efficient pitting corrosion suppression when US vibration (28 kHz) is applied to a stainless steel. The pitting resistance basis in increased in 100 mV and the weight of dissolved metal in 4-6 times lower under the US influence.



Introduction

Pitting corrosion causes main corrosion problems mainly for stainless steels. The nature of pitting corrosion is the penetration of the wall of the equipment without significant metal losses. Another problem of pitting corrosion is that the location of pits can not be predicted with high accuracy, so there is always uncertainty were corrosion will occur.
In recent years the influence of ultrasound on stainless steel was intensively investigated. Many works are directed on evaluation the destructive influence of US cavitation. Cavitation was found to cause defects formation and accelerate surface degradation. However, some works indicate that cavitation can increases surface hardness.
In work Wang 2008 a weak US was applied to a SUS304 stainless steel when pitting corrosion or crevice corrosion was induced by a polarization method in a sodium chloride solu­tion. The growth behavior of corrosion was investigated and the influence of US was discussed. The pitting corrosion and the crevice corrosion of SUS304 stainless steels can be largely suppressed by the application of an ultrasound. The reason is attributed to the decrease of the enrichment of hydrogen
and chloride ions in the pits or in the crevice by removing the corrosion product and stirring the liquid there. Despite positive results being obtained in the work, in practical application it is not always possible to expand the cavitation field far from US horn. Cavitation field radius usually does no exceed 100-700 mm around horn LUQUEDECASTRO 2007, this limits the application of US cavitation. However, US vibration of a metal can expand on much higher distances. So, this work was aimed to study the pitting suppression with US vibration of a stainless steel plate. The US horn was attached to the stainless steel plate, not immersed in the water, to cause it's vibration on the US frequency.