Studies on Effects of SMAW Variables on Corrosion Resistance of Austenitic Alloy

Welded Joints in Hydrochloric Acid (HCl) Medium
A. U. Iwuoha1 and I. A. Ezenugu2
1Department of Mechanical Engineering
2Department of Electrical and Electronic Engineering
1&2Imo State University, Owerri, Nigeria.
E-mail: nmatoha@yahoo.com
ABSTRACT: This paper studied the effects of Shielded Metal Arc Welding (SMAW)
variables (welding current, welding speed, electrode diameter and electrode coating type) on
corrosion behaviour of austenitic alloy (stainless steel [SS]) welded joints in hydrochloric
acid medium. A grade of AISI 300 series SS specimens in the cast state were welded with
different welding variables and the specimens subjected to corrosion studies in electrolyte of
1 molar solution of hydrochloric acid (HCl) freely ventilated at 30oC. The study adopted
electrode potential (critical corrosion potential) measurements with zinc rod reference
electrode as the index. The zinc rod potentials were converted to Saturated Calomel
Electrode (SCE) potential values. The critical corrosion potential dropped as the electrode
diameter increased. One possibility for this is that the “extended” welding time brought
about by large diameter electrodes created convenient window for microstructural change
and sensitization of base metal Heat Affected Zone (HAZ); in this state, weld decay cannot be
ruled out. The reducing reactions caused by release of hydrogen in rutile coated electrodes
compromised the metallurgical homogeneity of the weld with respect to the base metal; this
lowered the critical corrosion potential of welded joints produced with this type of electrode.
Higher welding current matched with workpiece thickness and geometry produced joints that
were more resistant to corrosion in HCl medium.