System – Domestic Water

• Overview

Historically, domestic water plumbing systems presented the least corrosion and failure problems, and have been generally regarded as trouble-free.  This expectation has changed over the last 25 years, however, due to lower quality piping products, more complex engineering design, changes in the water supply, and of course – age.  The characteristic blue-green green discoloration at sinks, water fountains, and other fixtures actually represents dissolved away copper pipe, and should always be recognized as the need for further investigation.

• Common Problems

With few exceptions such as for hospital, some manufacturing, and pharmaceutical research, most domestic water is carried through copper pipe.  Older building properties were commonly constructed using threaded galvanized steel pipe and even brass, and for extremely old buildings – a form of highest quality copper called TP, for threadless pipe.

While many failure issues at new copper pipe can be traced to various factors associated with water quality or more accurately its composition, it is still a fact that older pipe materials such as red brass and TP seem virtually immune.  Our investigation of extremely old buildings from the 1920s and earlier have documented red brass and TP in still near new condition, yet investigations of recently constructed properties where failures have occurred have identified widespread weakness.

For any building constructed using galvanized steel pipe, an ultrasonic investigation is likely to show large scale deterioration and the need for pipe replacement.  Older properties from the 1950s have simply reached the end of their useful service life, yet newer buildings are failing equally.  This is especially true in cities like Chicago, where galvanized steel pipe was improperly specified for use in domestic hot water systems.  Now well recognized after the damage has occurred, heat deteriorates the zinc protective finish to cause its accelerated failure.

An interesting dichotomy exists in that older galvanized steel pipe was of greatly superior quality allowing it to provide an extended service life, but with that long service interval now having expired.  At the same time, newer pipe, due to its far lower quality, will provide substantially lesser service even though it has been in operation a shorter period of time.  Our oldest investigation of galvanized steel pipe was to a lower Manhattan building circa 1896.  Only around 2015 did failures begin to occur, leading to an ultrasonic investigation showing the system as having reached the end of its useful service life after an astonishing 119 years in service.  Yet today, we are called in to investigate galvanized steel domestic water systems failing after only 5 years!  So many events of such spectacular improbability can only be explained as due to manufacturing differences, although many experts disagree.

While the mechanism of failure is always the same for galvanized steel pipe, loss of the zinc protective finish followed by aggressive pitting, copper pipe is far more vulnerable to many different failure mechanisms.

• Greatest Threats

For most building properties, an understanding of the water source is the first step necessary to ensuring long service life for any domestic water system.  As we have learned as result of over 1,050 ultrasonic piping investigations, various assumptions and beliefs relating to domestic water service have been established as fact, when a closer, more critical, and more scientific review has proven them wrong.

Various issues well documented to influence wall loss at any domestic water system are:

• • • • Water quality

A full water analysis is always beneficial in understanding potential risks caused by the chemical content and aggressiveness of the water supply. A Langelier Saturation Index calculation based upon all necessary parameters of the water should be close to 0.00 or neutral.

• • • • pH

Related to water quality, a low acidic pH always suggests that higher deterioration will occur.  A high pH, on the other hand, indicates a scaling condition having the capacity to construct pipe inside diameter over time.  Neutrap pH is therefore preferred.

• • • • Flow velocity

Copper pipe is a relatively soft metal, which makes it vulnerable to erosion and cavitation caused by a water velocity above a specific limit.  This problem is commonly revealed at the downstream side of an elbow where water naturally becomes more turbulent and especially at reducing fittings.  As water is forced into a smaller pipe diameter, its velocity is increased.  Cavitation also increases to produce severe etching at the outer radius of the elbow.

Any flow control devices introduce the potential to accelerate water velocity after its restrictive orifice, which in turn has been known to produce severe erosion type deterioration of the copper pipe immediately downstream.  The interest to provide infinite computer control over flow rates and water pressure has produced new erosion related problems unknown to standard gravity fed systems of decades ago.

• • • • Water volume

Water is a natural solvent depending upon various parameters, and therefore has a greater impact against most types of pipe, even plastic.  As contact between fresh water and the pipe surface increases, so does the ability of the water to have an impact – especially so where other negative factors such as temperature, low pH and soft water exist.  This translates to a higher level of deterioration at a main riser in comparison to a less used distribution or branch line.

• • • • Temperature

For galvanized steel pipe, it is easy to ultrasonically measure higher levels of deterioration were even moderate temperatures are involved.  As temperature increases, deterioration to the zinc protective finish rises dramatically.  Temperature has a lesser impact against copper pipe, although it still will accelerate its deterioration, as well as reduce is tensile strength.  As temperature increases, the impact of other factors such as water velocity and softness also increase.

At left we show 2 removed samples of 1-1/2 in. galvanized steel riser pipe from an approximate 43 year old Chicago residential property.  Domestic hot water on the left and domestic cold water on the right, and both originally side by side.  Severe deterioration has occurred to the hot water side, with the redish-brown deposits almost closing its inside diameter its original pipe wall oxidized to a much larger rust product.

The dramatic difference in condition is entirely temperature related, and even the less elevated temperatures from a sink or shower have been documented to have impacted the galvanized steel run-out pipe to the risers.  The deterioration of commonly installed galvanized steel sanitary waste and vent pipe is often overlooked in many older building renovations.

• • • • Water softening

A significant misunderstanding within the building management industry is to produce heavily softened water absent of any minerals whatsoever, when in fact certain critical minerals or other natural elements are required for the longevity of a copper piping system.  Heavily softened water is often identified as the leading cause of widespread copper pipe failure, as well as to the advanced failure of galvanized steel.  Water softening units are often sold or specified competitively based upon their reduction in total dissolved solids – ignoring the fact that some level of dissolved mineral and other components are critically important to the lifespan of the pipe itself.

• • • • Reverse osmosis

Less common, running RO water through copper or galvanized steel pipe has a similar deleterious effect.

• • • • Physical failure / Workmanship
        

The common use of brazing or silver solder for copper pipe long ago has now been superseded by the use of solder.  For various reasons, failures at soldered pipe connections have been increasing; those complete pipe separation failures always producing the most catastrophic and expensive failures.

Partially explaining some failures, the quality of workmanship has greatly suffered in recent years, with frequent inquiries to ultrasonically inspect copper pipe due to incomplete soldered joints having voids.  Questions have also been raised regarding the suitability and strength of some pipe solders and fluxes.  While defects due to incomplete soldering are hidden, poor quality workmanship abounds, pipe is angled into fittings due to barely 1/8 in. insertion, evidence of overheating or underheating, no lines plumb, or square, or level.  Like most other facets of construction, craftmanship seems long gone

New pressed-on type connections are replacing soldering as a joining method, and at the same time raise concerns due to the increased turbulence imparted to the water by their hex shape, and to the very well documented association between turbulence, cavitation, and advanced copper pipe wall loss.

Other physical vulnerabilities include the installation of steel plugs into copper fittings, welding galvanized steel pipe, the installation of brass valves to galvanized steel pipe, and the fabrication of any pipe line using multiple pipe materials.

• • • • Suspended solids

Although generally less of an issue for most domestic water supplies, the presence of any suspended particulates always increases the potential for corrosion to occur.  Microbiological growths, although they should be absent, can also accelerate the deterioration of any domestic water system.

• • • • Internal iron oxide deposits

Rust generated from upstream sources such as carbon steel or galvanized steel mains, PRV stations, hot water heater tubes, etc. have the potential to migrate into the copper lines and settle to produce microfine pinholes as a result of galvanic interaction.  Any observation of pinholes occurring in a straight line dead center along the bottom of a horizontal copper line is a strong indication to a cause originating upstream.

In the photo at left, a carbon steel gate valve to a 4 in. copper domestic cold water main has severely deteriorated and released a large volume of iron oxide into the copper pipe.  Although a “copper” piping system, this iron oxide has migrated downstream into much smaller distribution and branch lines where it then deposits to initiate galvanically induced pitting of the copper pipe.

A significant yet unknown and unseen problem for most copper piping systems is due to the deterioration of various steel fittings installed elsewhere.

• • • • Galvanic activity

Steel pipe hangers at a copper line can introduce galvanic activity at their contact point leading to an advanced but localized failure  Inappropriate grounding practices have also been identified as the source of higher and more widespread deterioration.  Computer related power distribution units inside data centers have been known to shed excess voltage to ground – thereby impacting the copper domestic water lines possibly within that ground path.

• • • • Dezincification

This is a very common issue related exclusively to older yellow brass domestic water pipe given the natural affinity of water to acquire zinc.  Over time, softer water leeches away the zinc from the brass alloy to produce a more porous form of copper.  The problem is generally associated with yellow brass due to its higher zinc content, and has also been related to the failure of brass valves and other fittings manufactured having a high zinc content.  Higher temperatures on the hot water side generally accelerate the process.

Any brass pipe carrying relatively soft surface water will experience dezincification after approximately 80 years of service, which is a common problem to older New York City properties.  For the generally lower quality valves and other brass fittings manufactured today having a higher zinc content, failures have been documented in under 10 years.  Dezincification as well as other forms of corrosion are well defined throughout this Internet site.

• Testing Focus

Given the extended layout of most domestic water piping throughout any property, it is useful to identify a potential issue or weakness prior to it revealing itself in the form of a pipe failure.  Except for threaded galvanized steel failures and copper pipe separations where improperly installed, most domestic water piping failures are in the form of an original pinhole – thereby indicating the need for repairs.  Areas of interest for any domestic water piping investigation are:

• • • Galvanized steel pipe
    • Downstream of any flow control devices
    • Heavily softened water
    • At dissimilar metal connections
    • Discharge elbows at high velocity pumps
    • Older steel domestic water storage tanks

Ultrasonic testing is easily performed on copper pipe although not all modes of failure or deterioration can be detected.  Using even the highest frequency UT probes, it is often difficult to identify the micro fine pitting or fracturing of copper pipe.  Yet, an ultrasonic investigation will raise a red flag if wall loss is significantly higher than normal.

Any failed section or component of any domestic water piping system should be kept in close to its original form and submit it for metallurgical analysis. Far too often, the pipe failure and a definitive answer to why it failed is sold for scrap – thereby leaving the original question unanswered.

Corrview maintains multiple galleries related to this issue in addition to other corrosion related issues. To visit a gallery, please click the related issue you would like to see:

Erosion

Internal Rust Deposits

Dezincification

Galvanic Activity

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