ABSTRACT
Welding is the process to join two or more similar or dissimilar metal with the application of heat and sometime pressure. Gas Tungsten Arc Welding (GTAW) is commonly known as Tungsten Inert Gas Welding (TIG Welding). Corrosion of metal is an ubiquitous phenomenon that occurs in various forms. Atmospheric or uniform, galvanic, crevice, pitting, and microbial corrosion are most familiar forms of corrosion. The service life of engineering structures is affected by the quality and strength of the welded joints. The effects of corrosion affects the quality of the welded joints and the general structure. The offshore structures are exposed to the various environments, and it is well known that the corrosion rate and the corrosion mechanism under each environment, marine atmosphere, splash zone, tidal zone, underwater zone and bottom zone, are different. The aim of this study is to model the environmental effects of corrosion on tungsten inert gas weld joints of a mild steel pipe using response surface methodology.
Mild steel pipe was cut into dimension 40mm in length, 12mm diameter and 3mm thick with a power hacksaw, grinded and cleaned before the welding process. The experimental matrix was made of twenty (20) runs, generated by the design expert software adopting the central composite design. The response was measured, which is the rate of corrosion and then modelled using the response surface methodology.
The result obtained in this study shows that the current has a very strong influence on the rate of corrosion. Based on the findings, it is summarized that the corrosion rate is minimum when a welding voltage of V = 18V, current = 120A and gas flow rate = 13lit/min. The response surface methodology employs certain statistical tools which are Anova, goodness of fit, coefficient of determination and noise to signal ratio which determines the adequacy and significance of the model developed. The result from this study shows that the model has a very good variance inflation factor and p-value < 0.05. The model posseses favourable coefficient of correlation (R)value for the rate of corrosion
