Effect of Velocity on Corrosion of Steel under Water¹

Abstract

In run 63, 125 grams of glyceride were heated in a stream of pure nitrogen in a 500-cc. Pyrex flask. The glyceride was brought up to 293°C. in 15 minutes and held at this temperature, ±2°, for the duration of the run.

Effects of Velocity on Corrosion by Water

“…Figure 2 shows that the corrosion rate began to increase again at velocities higher than 3 feet per second. The same effect was observed in other experiments (22, 48) and has been attributed to erosion, at these velocities, beginning to strip away protective; films. This phenomenon is called erosion corrosion, and it can lead to severe attack at high velocities.…”

“…A number of investigators (8,22,47,48) have found that at higher velocities the corrosion rate may decrease again. The data of Roetheli and Brown (47) are reproduced in Figure 2.…”

“…The condition of the metal surface is another factor affecting the inflection point. This was studied by Russell, Chapell, and White (48). They pointed out that the test results showing passivity at high velocity were obtained by starting with clean specimens.…”

A Study of Corrosion Control with Sodium Hexametaphosphate

“…Speller and Kendall (6), under radically different conditions of experimentation, found that the corrosion rate of steel pipe with Pittsburgh tap water flowing through it increased with increasing velocity, with no indication of a decrease in corrosion over the entire range covered by either of the previous investigators. Russell, Chappell and White (7) showed that freshly cleaned iron gave results similar to those obtained by Friend, i.e., the corrosion rate first rose with increasing water velocities, and then, when the velocity had become high enough to supply oxygen in excess to the whole surface, fell again. Roetheli and Brown (8) concluded from results of experimentation that "A maximum rate of corrosion is obtained as velocitv is increased because of the combined 'effect of two opposing Oxygen Depletion: Maximum oxygen depletion values were found at low rates of flow, decreasing to a minimum with increasing rates of flow (Fig.…”

Preventing Internal Corrosion of Pipe Lines

“…In general, everything else being equal, the higher the gasoline flow velocity in a pipe line, the greater the corrosion rate. This follows because, if rust is present, part of the steel surface is screened by the rust from oxygen carried by the gasoline, and the supply of oxygen to the unscreened part of the surface promotes attack in accordance with the principles of differential aeration (15).…”