Abstract
Erosion corrosion is an important consideration in the design of systems in which materials are exposed to nonuniform fluid flow. There have been inconsistent experiences with the relationship of seawater flow rates and wastage of copper alloys. This study specifically addresses corrosion of NiAl-bronze (Alloy C958) in flowing seawater at velocities of 25, 50, and 100 feet per second (fps). The testing described in this paper was conducted to determine the amount of weight loss, the characteristic pitting, and changes in surface roughness that will occur when NiAl-bronze (Alloy C958) is exposed to different seawater velocities under freely corroding and cathodically protected conditions.
Under freely corroding conditions, corrosion increased with increasing flow rates. Nonuniform corrosion occurred at the lowest flow rate (25 fps). The higher flow rates showed uniform corrosion evidenced by a smooth, polished appearance after exposure. Cathodic protection to -0.60 Volt versus silver-silver chloride essentially stopped corrosion of the coupons exposed to low and high flow rates (25 and 100 fps). The cathodically protected coupon exposed to 50 fps flowing seawater had significant nonuniform corrosion.
The results of this study suggested that turbulence intensity, in addition to bulk flow velocity, affected corrosion rates. The results showed significant pitting occurred under highly turbulent flow conditions. Further investigation is required to define the relationship between turbulence intensity and corrosion both under freely corroding conditions and with cathodic protection.
