Photo Gallery B5:   Internal Rust Deposits

Rust deposits are created in proportion to the amount of pipe metal lost.  At corrosion rates of 5 MPY or greater, substantial rust deposits can be produced, which in turn results in severe under deposit corrosion along with other operating problems.  While a large 12 in. diameter carbon steel condenser water piping system can easily tolerate a moderate to high corrosion rate of 5 MPY, the rust deposits created will migrate to lower flow smaller diameter lines where it has a far greater and more focused impact.  Common system features such as crossover lines, by-pass lines, full diameter headers, bottom futures, and other low-flow configurations then become the site of far greater corrosion loss.  Such deterioration is hidden from sight, unmeasurable except through ultrasound, and generally not known to exist.

A cross section of any heavily deteriorated pipe will often show large growths of rust termed “tuberculation.”  Removing such rust deposits will then produce visual evidence of deep pitting proportional to the height of the deposit itself.  Conversely, an ultrasonic measurement of deep wall loss defines tuberculation deposits, at the same time that their visual observation defines deep under deposit pitting.  Both exist simultaneously, and are proportional.

For most piping systems, once rust deposits accumulate to the volumes shown below, they are almost possible to remove.  Left to remain, the chemical inhibitors will provide little to no protection to the base steel and deep pitting will accelerate.  Although almost all chemical water treatment suppliers claim that their products are capable of penetrating through heavy rust deposits, our ultrasonic investigations, supported by conditions as shown below, have proven otherwise.

Unless dramatic steps are taken to remove all such rust deposits using high pressure water jetting or aggressive acid cleaning, corrosion and pitting activity will only accelerate.