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Galvanized Pipe Failure

All piping systems have an inherent lifespan which may or may not be influenced by certain actions by the building property owners and engineers.  For HVAC systems and specifically for condenser or cooling tower water supplied to the refrigeration chillers, chemical inhibitors can be maintained to reduce corrosion activity to tolerable levels.  Boilers, steam systems, and hot water heating systems are also chemically protected.  For fire protection systems, chemical control is available but generally not provided, with the deterioration of the system wholly dependent upon pipe quality, thickness, the frequency of testing required and the volume of new fresh water introduced.

For plumbing systems, material selection becomes the critical issue since no chemical corrosion inhibitor can be introduced to potable drinking water.  Sanitary waste lines are typically constructed using extra heavy cast iron or ductile iron pipe offering a lifespan of between 75 and 100 years.  Supply piping for domestic cold water and hot water systems are today typically constructed using copper tube, having realized the shortened life and greater corrosion vulnerability of other materials such as galvanized steel.

Brass, which produces similarly long service life to cast iron, is generally too expensive in terms of material cost and installation.  The use of plastics, such as PVC, HDPE, or FRP reinforced plastic pipe, is generally unapproved for such service and inappropriate too most high rise buildings where high pressures of up to 200 PSI may exist.  This leaves copper pipe as the predominant and virtually only option for domestic cold water and hot water service today.

• Prior Mistakes Remain

Earliest water delivery systems were constructed of cast iron and even soft lead.  In prior decades and back to the early 1900’s, however, galvanized steel was widely installed for domestic cold water service given the assumption that the internal galvanizing finish would eliminate any corrosion impact and provide very extended service life.  Such assumption is fundamentally mistaken, however, since untreated water has a well documented corrosion impact against galvanized pipe to produce failures within approximately 40-60 years – this depending upon the quality of the galvanizing finish and the aggressiveness of the local water supply.  For older buildings in the New York City area, for example, most original galvanized steel pipe has been replaced as a result of widespread failure.

Still today, galvanized steel pipe is being recommended and installed for domestic cold and hot water service following this same mistaken assumption.  Stated by the American Galvanizing Association, “Constant exposure to temperatures below 390° F (200° C) is a perfectly acceptable environment for hot-dip galvanized steel.  Good performance can also be obtained when hot-dip galvanized steel is exposed to temperatures above 390° F (200° C) on an intermittent basis.”

Well, not quite.  In reality, domestic hot water temperatures are more than sufficient to dramatically accelerate the deterioration of any galvanized piping system.  Even the less frequent and lower temperature waste discharge from showers, bathtubs, kitchen sinks, washing machines, and clothes washers are sufficient to advance the deterioration of the galvanized steel run-out piping which typically connects drain and appliance outlets back to the main cast iron risers.  We have overwhelmingly documented such deterioration in dozens of past ultrasonic investigations.

Of further concern, the generally lower quality of today’s galvanized steel piping products has resulted in failures of domestic cold water piping systems in as little as 6 years, and of domestic hot water systems in as little as 2 years.  Advanced failures of dry fire protection systems within 2-5 years is widely recognized within the industry – with again the lower quality of both domestic and foreign produced galvanized steel piping cited.  This stands in contrast to our examination of galvanized steel fire sprinkler piping from 1907 in San Francisco, and domestic cold water lines in Chicago still measuring at new ASTM specifications.

Although galvanized steel pipe has been extensively used at the domestic cold water supply risers at building properties across the United States and elsewhere, brass pipe has been traditionally installed for the hot water side simply due to the knowledge that galvanized steel pipe cannot and should not be installed for any hot water system.  This is why galvanized steel pipe is not found at any steam or steam condensate piping systems.  Although significantly lower temperatures exist for domestic hot water service at around 120°F to 140°F, it is still sufficient enough to cause the deterioration of the zinc finish followed by advanced pipe failure.

• The Chicago Area

One area of the United States which has been heavily impacted by this problem is in Chicago, and where the widespread use of galvanized steel pipe for both domestic cold water and hot water service has produced substantial failures requiring total pipe replacement.  We have documented this impact at buildings throughout Chicago, throughout the Chicago Public School system, and in many Chicago area high rise condominium and co-op properties.  Beginning with random leaks spaced apart by months or years, any detailed properly focused investigation will typically expose a widespread problem throughout the building.  Left to continue, the problem only accelerates in its severity until one or more major pipe failures result in heavy water damage to force some level of action.

Pipe failure is very rarely an isolated event as often assumed, and more likely the precursor to a much larger problem.  Once the zinc galvanized finish has failed, all corrosive potential then focuses its impact against more localized areas to produce deep and severe pitting.  Although various hopeful explanations may arise to suggest such failures being due to lesser issues such as pipe orientation or flow related corrosion, the problem is always due to the impact of heat against the galvanized zinc protective finish.

• A Thin Layer Of Protection

Galvanized steel pipe is carbon steel pipe with a thin hot dipped zinc finish to protect it against corrosion.  According to Wikipedia, “It is the process of coating iron, steel or aluminum with a thin zinc layer, by passing the metal through a molten bath of zinc at a temperature of around 860°F (460°C).  Depending upon its ASTM specification, the zinc protective finish is rated based upon ounces of zinc per square foot of material.  Specifications may define a thickness in microns, such as 85 um, or in terms of weight per square foot, such as 1.8 oz. of zinc per sq. ft. of total surface area.  Such specifications define that half of that weight of zinc is applied internally.

For cold water service, this protective coating is generally effective.  For the Chicago area where the lake based surface water supply is soft and non-aggressive, galvanized steel pipe can easily provide over 100 years of reliable cold water service.  Our prior inspections of older building properties in the Chicago area have produced results showing another 100 years of service available at the cold water galvanized piping; with virtually no wall loss in many examples.  For pipe where the galvanized finish is lacking to some degree, and where pipe quality is lower, deterioration will inevitably occur earlier.

Raising the temperature of galvanized pipe deteriorates the zinc finish; thereby causing a much more aggressive corrosion loss at the now unprotected carbon steel pipe.  Corrosion loss is directly proportional to water and pipe temperature, with greatest corrosion and pitting typically closest to the higher temperatures at the boiler or hot water heat exchanger.  For this reason, lower corrosion loss and less severe pitting is found at a domestic hot water return line.  While it is today well known to avoid the use of galvanized steel in steam and steam condensate systems, the lower temperatures of a domestic hot water system may have not been considered to be an equal threat to the zinc finish.  And according to some current authorities, no threat exists at such temperatures.

The use of galvanized steel for domestic cold water and domestic hot water systems is a widespread occurrence within the Chicago area likely due to a common but inappropriate design engineering specification being used and copied from one construction project to the next.  The final effects of heat 25-50 years later against zinc galvanized pipe were obviously not recognized when this piping specification was written and adopted.  Today, the results are clearly apparent.  For other cities such as New York, brass was typically used for domestic hot water service.

• Best Diagnostic Testing Method

Ultrasonic testing is the ideal method of evaluation to any suspected pipe corrosion problem.  It provides high-quality and accurate data across a wide sampling of points with minimum intrusion and inconvenience to building tenants, and if performed properly, will produce an unquestionable assessment of pipe condition.  It is typically possible to investigate 50 of more examples of pipe during a single day of investigation, with 2-3 days of field testing generally necessary at a typical 30 story condominium or co-op property.

Testing is recommended for all extremes of the property including each and every riser, and at representative lowest, middle, and highest floors within each zone.  If two or more zones exist, then each zone must be addressed as a separate entity.  Although the domestic hot water pipe may attract the most concern, any such ultrasonic investigation should address both hot and cold water services, as well as the hot water return if it exists.

• Common Evidence Of The Problem

A corrosion problem at a domestic water galvanized piping system will reveal itself in one of three ways:

• A leak or larger failure of the piping
• Loss of water pressure or water flow during peak periods of use
• Rust sediment clogging at faucet strainers, mixing valves, and toilets

Typically, it is a pipe leak that first exposes the problem.  The first few piping failures are usually attributed to other issues rather than system wide weakness; with multiple failures often required to prompt formal investigation.  Since the internal rust deposits constricting the pipe are actually the remnant of the original steel pipe wall, the greater such deposits the weaker the pipe and therefore the greater the threat to the system’s condition.  Internal rust deposits and wall loss are synonymous and proportional to each other – meaning that identification of one condition defines a relative presence of the other.

We provide some examples of this condition in the photographs below, and also offer a larger photo gallery of problems related to domestic hot water and domestic cold water piping in our Internet photo gallery entitled, Common Piping Problems.  All examples of pipe were from domestic hot water piping systems in the Chicago area, and illustrate various aspects of the problem.

Domestic Hot Water

Expansion Joint One of the first locations to fail at a domestic hot water system.  Movement of the mechanical joint, as designed, places additional stress on pipe already weakened by corrosion.	Internal Conditions Threat of failure is not the only concern raised.  Rust deposits are the end result of this corrosion condition, with the deposit itself the remnant of the original pipe wall.

Misinterpretation Galvanized pipe failure is often blamed upon some form of external influence, such as the nearby storage of chemicals, or cleaners.  In fact, dissolved rust and other elements leak through the failure point to evaporate on the surface; often producing this error in interpretation.	Early Indication The first stage of galvanized pipe corrosion problem whereby deep pitting will focus at one area to produce through wall penetration.  Small leaks will often evaporate away the hotter water and escape notice until a larger failure occurs.  Conditions capable of producing the above leak have far greater impact against its threaded ends.

Flow Restriction Most pipe corrosion problems are discovered due to a failure and flood.  A less frequent indication, however, has to do with restricted flow and pressures due to the high volume of less dense iron oxide deposits created as galvanized steel pipe deteriorates.	Run-Out Threat A very common point of failure exists at the smallest threaded piping immediately closest to the riser.  This is due to significantly less wall thickness of smaller diameter pipe which is subject to similar deterioration caused by higher water temperatures.

• Caution Necessary

As America’s building infrastructure ages, various inherent limitations to how they were constructed come into focus.  Fundamental to every building property are certain unavoidable physical service life limitations for every piping system – whether its fire, heating, cooling, waste, or domestic water.  Most building piping systems, except dry fire, are capable of providing greater than 75 years of reliable service, which is comforting to know for operators of recently constructed buildings.  With many high rise residences now at 50+ years of age, such once far removed threats become greater concerns to consider.

Add to that realization of age based deterioration any form of material defect or incompatibility, such as the use of low quality foreign produced schedule 10 pipe in a dry parking garage fire sprinkler system, or the above discussed installation of galvanized steel pipe into a domestic hot water system, and that expectation of relatively long pipe service life may be cut down to less than half, or lower.

• Limited Repair Options

At the point that a galvanized steel domestic hot water problem is discovered, most damage has likely already occurred.  There are no corrective actions that can be taken to reduce an existing threat other than reducing the water temperature in order to potentially reduce the heat’s impact just slightly.  Commonly proposed alternatives to line the pipe with various epoxy coatings are questionable in their effectiveness due to the need to sand blast away all traces of iron oxide deposit down to SP-10 white metal finish in an extended and complex piping system already heavily constricted with rust and having deeply pitted and weakened pipe walls.  Greatest threat of failure is always at the threads, of course, with 50% or more of the pipe cut away at each connection point.

Pipe replacement using copper is therefore the only reliable choice – requiring extensive intrusion into private residences at major expense and inconvenience.  With a typical high rise condominium property having 16 or more sets of risers over 30 or more floors, the challenge of replacing approximately 2 or more miles of domestic water pipe is a staggering challenge to any engineering firm, and to the unfortunate residents that need to survive through it.

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