Use of SVET to evaluate corrosion resistance of heat tinted stainless steel welds and effect of post-weld cleaning

• The effect of heat tints on the corrosion resistance of a 2507 duplex stainless steel Tungsten Inert Gas (TIG) welded joint was assessed. The Scanning Vibrating Electrode Technique (SVET) was used to study oxide dissolution, initiation and propagation of corrosion on the weld at the open circuit potential (OCP) and at applied potentials. Small spot X-ray Photoelectron Spectroscopy (XPS) was used to investigate the composition and thickness of the heat tints. Both heat tinted and post-weld cleaned conditions were tested. Post-weld cleaning methods investigated were brushing, brushing plus polishing and brushing plus pickling paste. The results from the 2507 weld were also compared with results from a TIG 316L weld. SVET was shown to be an appropriate technique for characterising in-situ the activity of heat tints. It was seen that heat tints dissolve by electrochemical reactions that can be mapped with the SVET and correlated with the level of discoloration of the oxides, with the purple-brown oxide being the most active. The slow dissolution of the oxide gave a gradual decrease in current density over longer immersion times, leading to establishment of a passive state. The mechanical post-weld cleaning methods proved to be insufficient to remove the anodic activity in the heat tint. The most efficient process was brushing followed by pickling which resulted in a totally passive surface measured with SVET and a higher critical pitting temperature.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik -- Korrosionsteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering -- Corrosion Engineering (hsv//eng)

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