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Corrosion’s Greater Impact To Chill Water Pipe

Pipe corrosion represents the 2nd greatest threat to any building property next only to fire. Different levels of threat exist for different piping systems – a roof level pinhole leak at a condenser water line representing a far lesser threat than a chill water pipe separation over high voltage electrical switchgear. Failures resulting from the corrosion of piping systems are easily capable of producing millions of dollars in equipment and water damage for most building properties, are cited at $1 million dollars of lost trading revenue per minute for a financial institution’s data center, and has caused the loss of human life where rust corrosion product itself has stopped water flow through a fire sprinkler system.

• Corrosion Is A Natural And Unstoppable Force Of Nature
  

Simply stated, corrosion is the natural reversion of certain metals back into their original elements over time. It can be slowed and greatly reduced by certain precautionary measures such as the addition of chemical corrosion inhibitors or applied coatings, but not stopped or eliminated.

The mild carbon steel pipe traditionally installed for all HVAC and chill water piping systems, ASTM A53, is especially vulnerable to corrosion, and must be carefully maintained and monitored to reduce corrosion’s impact. Various forms of chemical inhibitors are injected into the system to reduce internal corrosion by various mechanisms. Biocides used to control bacteria are also applied and play an important role. The effectiveness of such efforts vary widely depending upon chemical type, concentrations maintained, and other methods under the instruction of a corrosion control specialist; typically a third-party to the building property.

In addition to water quality, metal quality, microbiological elements, chemical treatment and other factors influencing the corrosion of steel pipe directly; piping design, operation, maintenance, and other issues also play a role.

• The Cost Of Corrosion Is Immense

A study by the National Association of Corrosion Engineers, NACE, has estimated that the cost of corrosion in terms of pipe and material replacement as well as damage and loss of service is approximately $276 billion dollars annually. This represents approximately 3.1% of America’s Gross Domestic Product. For perspective, the total damages caused by hurricanes, tornadoes, floods, fires, and blizzards over past decades has averaged $1.7 billion dollars to Americans annually. Read more about ‘The Corrosion Threat’

The United States military cites corrosion as their second greatest threat next to warfare.

Yet, this massive $276 billion dollar economic loss is typically hidden and insidious, widely dispersed across hundreds of thousands of isolated events, silent in nature, and does not receive the media attention typical for hurricanes, tornadoes, and other natural disasters. Some failures, however, do gain media attention.

In June of 2017, the failure of a small threaded pipe section released sufficient water to produce catastrophic flood damage and force the evacuation of the Manchester, MA VA Medical Center:

Yet, thousands of additional examples occur each year without such headlines. Unless catastrophic in nature, most corrosion problems receive no attention outside the area of their immediate impact.

• Corrosion’s Greater Impact Against Chill Water Pipe

Of the various forms of piping failures which can occur, full pipe separations at the threads, as was the case at the Manchester VA Hospital above, traditionally produce the greatest damage. This is due to the following issues:

• • • Carbon steel pipe of 3 in. and smaller is typically threaded rather than welded or clamped.
    • Standard schedule 40 grade pipe is traditionally specified for chill water and dual temperature service rather than a heavier material such as schedule 80.
    • Pipe wall thickness reduces as pipe diameter decreases.
    • Chill water pipe serving HVAC needs of a hotel, condominium, or other residential type of buildings is usually in the form of multiple small diameter pipe risers capable of providing individualized comfort control, and thereby introduces substantially greater opportunities for failure to occur.
    • Threading schedule 40 pipe removes approximately 50% or more of its original pipe wall – thereby creating an immediate weakness due to lowest wall thickness at every joint.
    • The installation of threaded isolation valves, typically manufactured of brass, introduces an additional threat due to galvanic corrosion caused by dissimilar metal contact.
    • Chill water pipe suffers a dual corrosion attack to both its interior and exterior surfaces.
    • Fiberglass insulation provided to chill water risers was typically insufficient in terms of its thickness and effectiveness to prevent moisture migration to the cold pipe surface.
    • Far more effective materials such as hard shell closed cell foamglass, the standard for protecting chill water pipe in more humid environments such as Houston and Miami, were never used for New York properties.
    • While termed a “moisture barrier,” the foil/paper sealing tape commonly applied to chill water insulation is inadequate, and will inevitably fail – thereby causing external corrosion.
    • Corrosion Under Insulation (CUI), is common to virtually any chill water system of any property, located anywhere throughout the United States.
    • The external threat to chill water pipe from insufficient and ineffective fiberglass protection was not recognized by design engineers nor piping installers at the time, and is still widely ignored as a potential problem today.
    • Insulation for chill water systems was typically specified based upon R value and the need to reduce the loss of its cooling capacity rather than the need to prevent moisture migration.
    • Another interest in the application of fiberglass insulation was to prevent sweating or condensation at the cold pipe surface capable of producing water related damage to nearby surfaces rather than damage to the pipe itself.
    • Installing chill water riser pipe within tenant or guest room spaces having a high value to their available surface area resulted in the interest to minimize insulation thickness.
    • Carbon steel chill water pipe is not painted or coated to protect it against corrosion prior to insulation under the mistaken assumption that the insulation alone is sufficient to protect the pipe. Most uninsulated pipe is painted for corrosion protection.
    • Additional steps to prevent moisture migration such as outer protective jackets, wraps, paints, coatings, or other steps were never specified for pipe installed out of sight behind building walls.
    • New building properties constructed today utilize the same ineffective fiberglass insulation and have not adapted their designs to address this common issue.
    • A search of our archives of over 1,012 piping investigations identifies 228 as primarily related to chill water piping problems, whether internal, external, or both.
    • A further search of our archives for dual temperature piping, which is essentially chill water pipe operating only during the summer cooling season, identifies 30 primary investigations.
    • Together, the issue of corrosion at chill water systems is a major problem facing all building properties throughout the United States, and is growing in both severity and frequency as those properties age.
    • The issue of external surface corrosion caused by insulation failure/inadequate insulation, which is only one of the two threats present at chill water riser piping systems, should not be unexpected to anyone working within the HVAC and corrosion related fields.

• Chemical Water Treatment Plays A Vital Role

For chill water piping systems, however, a potentially greater threat always exists from the outside surface depending upon its insulation and various factors relating to such.

Corrosion activity in any closed system, such as chill water, can be maintained at near 0.3 to 0.4 mils per year (MPY).

Corrosion rates identified in our reports are based upon actual measured wall thickness losses over time, and not corrosion coupon estimates of known inaccuracy. Corrosion coupon results define only the relative corrosivity of the liquid against a new metal specimen, and do not report or define the amount of corrosion loss occurring to the pipe wall itself.

© Copyright 2024 – William P. Duncan, CorrView International, LLC