Q. Effect on the corrosion rate of carbon steel?
The velocity of the acid has a significant effect on the corrosion rate of carbon steel. The recommended velocity range for piping systems is 1 to 3 ft/s (0.3 to 0.9 m/s). Surface irregularities causing turbulence or increased velocities may also result in accelerated localized corrosion.
Temperature dependence of sulphuric acid corrosion on carbon steel may call for an awareness of acid piping and vessel systems which are intended for outside service where solar heating may increase metal temperatures above the iso-corrosion curve.
Hydrogen grooving is another form of localized corrosion and tends to occur on vertical or inclined surfaces. As corrosion occurs, hydrogen evolves and can combine to form tiny bubbles. As these bubbles rise, following preferential paths, they rub against and disrupt the soft sulphate protective film thus exposing the carbon steel to further corrosion and forming characteristic grooves.