Applications – Residential

• Systems Overview

Keeping a residential building in shape not only protects an investment, but it also keeps tenants happy.  Ultimately a building depends upon the reliability of plumbing, HVAC, and fire suppression systems to ensure tenant comfort.  Plumbing systems handle domestic cold water, domestic hot water, vent and sanitary waste requirements.   Just as important to the comfort of building tenants is the HVAC system which provides building wide heating and cooling.

While plumbing and HVAC systems provide comfort to building tenants, the fire sprinkler system is actually the most important, and provides life safety to building occupants.

• Common Vulnerabilities

Due to their complex design and extensive piping layout, well known vulnerabilities are defined below:

• • • Domestic Water

Potential vulnerability exists at any domestic water systems simply due to extensive layout of pipe throughout.  Unlike other building properties which may share two or three common riser stacks, residential buildings will often have a set of individual risers to serve each apartment.   This threat increases as building properties age and as corrosion activity progresses, and is greatly dependent upon its material and method of construction.  While domestic water systems are typically constructed of copper pipe today, galvanized steel has been widely installed in the past, and remains in many older building properties.  This pipe, which is commonly threaded, now represents a very significant threat to most older residential buildings – especially when used for domestic hot water service.  The advanced failure of domestic hot water systems constructed of galvanized steel is an extremely common problem in Chicago and some other American cities.

Yellow brass pipe, also commonly used decades ago, suffers from “dezincification” or the loss of zinc over time.  Having a service life of approximately 80 years, most of the yellow brass pipe in older buildings is reaching the end of its useful service life.   On the other hand, threadless pipe, or TP, a high quality form of copper no longer manufactured, has been shown to last almost indefinitely.

• • • Vent and Waste

While the vent and waste piping is not under pressure similar to the domestic water, it has its own specific vulnerabilities, especially for residential buildings having a substantial number of riser stacks.  Smaller diameter vent and waste run-out lines are typically constructed using threaded galvanized steel pipe having a similar vulnerability to water supply lines and typically are the first to fail.  First indication of a corrosion issue is typically in the form of pinhole leaks at the threads.

The larger diameter waste and vent mains are typically made of  cast iron – extra heavy bell and spigot for older properties but thinner no-hub for newer construction.  Unlike the more predictable failure of other piping materials, the failure of cast iron pipe, due to its inherent characteristics, is typically in the form of a split or fracture rather than a pinhole leak.  Extra heavy cast iron bell and spigot pipe has an estimated service life of approximately 80 years, and often more.  Newer waste systems – far less.

• • • HVAC

HVAC systems are very specific to each building property and can consist of chill water, condenser water, heat pump, dual temperature, condensate, hot water heating, steam, and steam condensate.  Heating and cooling systems serving the common spaces of the building may be fed from a large centralized refrigeration machines, which typically involves larger diameter piping.  While the units which provide comfort to individual units are usually fed from perimeter risers where substantially smaller diameter pipe introduces a much greater weakness.  The pipe location, small size, generally poor insulation, and threaded construction all adding together to produce significant threat which increases over time.  These riser may operate as a separate 4 pipe system, or more commonly as a 2 pipe dual temperature system providing heat in the winter and cooling during the summer.  Chill water and dual temperature systems typically show low internal corrosion, but can suffer much greater external wall loss due to insulation failure and moisture condensation.  This is especially common for the perimeter risers which are closest to the building envelope where high humility and air movement is common.

For high rise residential buildings, this threat is increased as the distribution of its smaller diameter perimeter piping will be much more extensive and operate under higher pressures.  Although typically zoned in order to control pressures, the failure of any threaded pipe section is often catastrophic, and will produce far more damage than a pinhole leak at a large diameter main riser.  Should any leak occur, water damage would likely cascade down the height of the building affecting multiple floors until it is able to be isolated.  This is a very common problem faced by building owners throughout the United States.  Equally important to the operation of the perimeter HVAC system is the condensate line.  Most commonly, issues are identified when the condensate drain has been installed using galvanized steel rather than copper.

Open condenser water systems suffer the highest levels of corrosion and represent the largest share of problems identified in our ultrasonic investigations.  While issues at the condenser water system have a lesser direct threat to tenants and water damage, it is critically important during the building cooling season, especially for buildings which operate year round in warm temperatures.  Specific areas such as any low / no flow locations, future connections, by-passes, exterior roof level pipe as well as and pipe which may be drained for freeze protection often exhibit highest levels of wall loss.  Any small diameter threaded pipe is as well a high priority test locations due to the greater possibility for failure.

Occasionally, older building properties are heated using steam radiators.  For the steam itself, we constantly identify the most favorable results of any piping system.  Less favorable results are commonly identified at the steam condensate counterpart, specifically at horizontal sections where condensate may remain.

• • • Fire Sprinkler

The functioning of a fire sprinkler system relies as much upon internal corrosion conditions of the piping as much as it does its prompt activation.  Highest oxygen content and greater water movement at the building inlet is a common source of fire pipe deterioration, followed by other locations which experience fresh water movement.  For residential buildings especially, constant renovations or changes in fire code means a reconfiguration of the fire protection system as well.  This requires frequent draining and filling, with each cycle then introducing fresh oxygenated water to drive the corrosion process.

A further vulnerability to all more recently installed fire sprinkler systems is movement toward  thinner materials such as Schedule 10 of 7 pipe, and even threaded thinwall schedule 10 pipe.  The use of galvanized steel pipe, which was once considered the answer to the entire fire pipe corrosion problem, can actually advance system failure due to its declining quality.  Combined, significantly greater threat exists to a piping system which was considered for almost a century as being immune to the corrosion.

• Pipe Related Issues

We consider pipe material quality as the most significant factor related to system longevity.  Our ultrasonic investigations have proven noticeable differences between the far superior quality of all pipe manufactured decades ago against what is available today, and we commonly identify better results at 60 year old examples of original pipe in comparison to pipe recently been installed into the very same system.  Retaining original pipe which is still in good condition throughout aging building properties is a significant benefit to building owners today.

In addition to a greater vulnerability to all forms of corrosion, most pipe is manufactured not to the wall thickness specified by ASTM, but to the minimum thickness allowed by ASTM, or typically 12.5% less.  This has a lesser impact against larger diameter welded pipe, and far great impact against both thinwall pipe as well as threaded pipe installations.

• Top Failure Locations

Domestic Water

• • • • • Galvanized steel pipe – hot water especially
        • Older yellow brass pipe
        • Dissimilar metal connections – especially brass to galvanized steel

Vent and Waste

• • • • • Small diameter run-out lines
        • Galvanized steel piping
        • Fracturing of cast-iron mains

HVAC

• • • • • Chill water – Perimeter risers / Small diameter pipe
        • Dual temperature – Perimeter risers / Small diameter pipe
        • Galvanized steel condensate
        • Condenser water – low/no flow areas, drained pipe, roof level pipe
        • Horizontal steam condensate

Fire Sprinkler

• • • • • Building inlet
        • Areas of greatest water movement
        • Thin-wall Schedule 10, 7, or 5

• Testing Priorities

With the specific vulnerabilities defined above, areas of priority for testing can be easily established.

• • • For domestic water systems, any galvanized steel pipe is always a high priority for testing, as well as at any connection points to a brass isolation valve.
    • Older yellow brass pipe suspected of weakness due to dezincification is best addressed through a metallurgical lab analysis.
    • Testing of the vent and waste system should include all piping from the smallest diameter lines to the largest diameter mains.
    • When evaluating the condition of HVAC systems, it is important to recognize that corrosion activity is generally common throughout the entire system, and therefore causes the greatest impact at smaller diameter lines.
    • For chill water or dual temperature systems, a two front corrosion impact typically exists requiring testing of all pipe sizes.
    • Chill water or dual temperature systems are most vulnerable at the perimeter risers – increasing the level of difficulty in their evaluation due to the need for entry into the perimeter columns.
    • Steam condensate  is a common problem area for many building properties, but provides less concerns for vertical runs.

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