Photo Gallery E5: Structural Tank Supports
Unlike internal pipe corrosion, external corrosion, whether occurring to the pipe itself, pipe supports and bracing, structural steel, or any other steel component of the building property is generally due to a lack of maintenance. Internal pipe corrosion is always present, and can be estimated either through ultrasonic investigation or suggested through the observation of other indicators such as rust deposits, failed mechanical seals, lost heat transfer efficiency, etc. External corrosion activity is not only far more obvious, but it is also far easier to avoid or correct.
Often, structural corrosion will produce a secondary impact against other critical building components. For most, long term corrosion initially results in small pinhole leaks. Much older riveted tanks experience leaks at the rivets and overlapped seams before pinholes at the wall. Similar to piping, older tanks had a much heavier wall thickness allowing them to survive longer. Common to all square or rectangular tanks is the advanced deterioration of internal I-beam supports and cross bracing, as opposed to those tanks supported at the exterior wall. Bowed side walls of any tank strongly suggests heavy internal corrosion and a far more serious threat than a weeping pinhole.
When 38 years of corrosion activity between the base of a 30,000 gallon domestic cold water storage tank and the steel I-beam supports raised it 1 in. higher due to the expansive property of rust, the impact to the tank was still unobserved. Sufficient wall thickness existed at the thick tank bottom. For the 8 in. schedule 40 outlet lines from both cells, however, 38 years of corrosion and weakness, now further stressed with one end anchored in the concrete slab, and the other to the tank wall 1 in. higher, snapped it clean off at an elbow to produce a catastrophic flood.
The current availability of outstanding paints, coatings, tapes, epoxies, and other protective measures means the virtual elimination of this problem if addressed properly and in a timely fashon. Once significant damage occurs, however, it is not easily corrected.
