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Corrosion The Beginning

It would be impossible for a failure at a section of main condenser water riser to go unnoticed for more than a few minutes.  A blown off fitting at even a 1 in. medium pressure line would produce hundreds of gallons of water – causing it to be quickly located and addressed.  In contrast, much smaller leaks, depending upon their location and severity, can produce severe secondary problems that can easily avoid detection.  In certain instances, a smaller leak can actually create greater damage than one which is much larger.

A leak at a threaded connection, often the very first sign of a pipe corrosion condition, may exist for years prior to producing enough water to signal a problem.  Often located behind walls, in shaftways, under floors, and above ceilings, thread joint failures can slowly leak water into area surroundings to corrode other piping systems, metal supports, electrical services, and other equipment.  The extent of the damage is usually detected only once the leak extends past its immediate area and into the view of others.

Here, it is the small amount of water produced over an extended period of time that allows various forms of mold, many toxic in nature, to develop and thrive.  Once established, molds can have a severely negative impact on human health depending upon the nature of the species involved, its metabolic by-products, spores generated, its physical location, concentration, the volume and duration of an individual’s exposure to the mold or by-products, and the physiological susceptibility of those exposed.

Severe consequences can result from a mold condition – ranging from downtime and a costly remediation of the affected area – to health damage and civil and criminal lawsuits.  Some other facts and consequences of a mold infection include:

• Leak Location Important

Just what extent of damage occurs is often related to where the leak exists and how far the water travels.  A small leak at a vertical riser, and especially where the shaft is open to every floor, can produce extensive damage for hundreds of feet as the leak slowly descends the pipe.  In contrast, piping shaftways having a firestop at each floor will typically show signs at that floor as the water expands on that level only.

If the pipe is insulated, the insulation material will often collect the water to the point where it is completely waterlogged, thereby producing an exterior pipe corrosion problem along its entire outer surface.  Even a small to moderate leak at one location can saturate multiple floors of piping to produce an extensive degree of outer wall loss.  Given enough travel, it will evaporate along its path and still not produce a tell tale indication.

Leaking pipe at a vertical riser often deteriorates the steel pipe supports at the floors to the extent of making them virtually worthless.  This creates added stress on existing supports, and increases the threat of pipe separation – especially if the pipe is joined by a means other than welding.

An extremely common problem exists where a leak occurs over an electrical service panel or conduit.  Given the typically thin gauge of such enclosures, a few years of constant moisture is all that is necessary to produce a penetration through the metal – allowing water to contact the energized electrical components, and to eventually short the wiring.

Some common problems related to water leaks are presented below, and help to underscore the often unseen or unexpected threats which water can bring:

Electrical Threat An electrical service riser in this shaftway was installed immediately next to the condenser water riser.  In addition, the take-off from the riser to floor units ran parallel and above the electrical box and conduit. As a result of a moderate corrosion rate of 4 MPY over decades, and galvanic activity between the black steel pipe and brass valve, the schedule 40 pipe began leaking at the threads to corrode the junction box and cable below.

Common Pump Problem All pumps offer a catch basin below the seals to collect any water lost.  These basins are often piped into the lower trough and then routed to drain. Water then typically collects to initiate a corrosion problem between the pump base and stand.  Once rust develops, it will slowly expand and actually raise the pump upward, causing it to lose alignment and stressing the bearings and seals to produce greater leakage. This can be avoided by piping the seal basins directly to the drains.

Moldy Insulation Sometimes due to a leak, but often due to cold water condensation alone, moldy insulation will result if given the proper conditions. This problem is easily recognized by the dark discoloration of the insulation, but where concealed out of view, can grow into an extensive problem.  Combined with a movement of air to carry the mold spores, this water related problem has been the cause of many toxic outbreaks nationwide.

Hidden Pipe Leak A small pinhole leak at a threaded fitting 15 floors above ran down the pipe unnoticed until finally reaching this lowest floor apartment. This problem was first addressed by painting the walls over and over.  Given enough time, the leak caused extensive outer pipe damage and further failures along its 15 floor run.  Ultimately, some lengths of pipe were replaced as well as many walls.

Electrical Failure A small leak at a threaded elbow within a ceiling area allowed water to drain to its lower horizontal line.  Water collected at the insulated pipe, where it severely deteriorated the water line (shown above). Water dripping from the insulation onto a 480 volt electrical conduit below eventually corroded the line completely through in areas to create a new threat to other building services and potential for fire.

Deep Pitting A small leak at a threaded vent line onto this domestic hot water tank went unnoticed for many years, leaking onto the hard cast insulation along a major portion of the tank shell and then evaporating. When finally discovered, wall loss of over 0.250 in. was measured at the tank’s outer surface to leave a suspected wall thickness of 0.030 in. or less in some areas, and repair was recommended.  Failure at the above area occurred six months later and before repairs could be performed.

Exterior Corrosion A small leak at a weld for this low pressure domestic hot water tank was concealed by insulation for years.  This produced severe pitting in this localized area of approximately 0.225 in. deep. Sufficient wall thickness existed at this head to provide additional service life.  The head was cleaned of all rust product and a repair patch welded over the entire area.	Condensation An unknown condensation of moisture at the very bottom of this refrigeration machine evaporator produced severe and localized corrosion.  After 15 years, corrosion produced pinholes through this relatively thin 0.125 in. steel shell. More severe wall loss was produced between the bottom of the evaporator shell and metal base support, requiring removal and repair.

Insulation Mold Poorly insulated chill water pipe having frequent gaps at the seams, and in the presence of a high humidity environment, produced extensive mold throughout the entire system. UT testing showed surprisingly little corrosive effect against the exterior pipe wall, but overwhelming health threat due to widespread mold.	A Huge Threat Due to ideal conditions for mold to grow as well as poor quality, or poorly installed insulation placed on this large diameter chill water pipe, an outbreak of mold spread. Mold outbreaks cannot only damage and reduce the remaining service life of the pipe, but can as well be linked to many serious health problems.

• A Combination Of Factors

In most cases, secondary corrosion problems only exist where the wrong combination of factors occur – either because they are overlooked, or occur in a hidden environment and out of view.  A minor drip allowed to continue might not mean anything in an open area of a floor drain, but will produce significant damage within an enclosed space.

A pipe with wet insulation may not be any threat at the roof level cooling tower, but where it exists in a dark damp environment such as a fan room, raises the potential to grow and distribute mold spores throughout the entire facility.  Prompt attention to maintenance is always recommended.

© Copyright 2023 – William P. Duncan, CorrView International, LLC