Technical Bulletin # P-05


Total Piping Corrosion Protection During Winter Lay-Up
Or Extended Drain Down



THE PROBLEM:

     Increased corrosion losses occurring during winter drain down or extended periods of system inactivity are well known to occur. Our years of ultrasonic pipe testing have, beyond any doubt, documented corrosion rates of between 2 and 10 times that of piping which has been continuously filled with water. Due to wet and untreated conditions in the presence of abundant oxygen, roof level failures generally precede problems at basement or mid level piping by decades. See Technical Bulletin # C-05 about increased corrosion activity during winter drain down or lay-up.

     This problem is well illustrated by the below wall thickness data taken from the same 45 year old, 18 in. Extra Strong condenser water piping at a New York City property. At the left, the basement piping shows a low corrosion rate, and an average remaining wall thickness far above the 0.375 in. pipe which would be installed in new installations today. Remaining service is virtually limitless.

     Shown on the right, where the roof level pipe has remained drained for 5 months each winter over 45 years, we find significantly higher corrosion activity, and limited service life remaining. Lowest measured thickness points reduce its life even further.


Filled Pipe - Basement

Drained Pipe - Roof


     In comparing the original pipe wall thickness value to current and minimum permitted values, a dramatic difference is again shown in the bar graphs below.


Filled Pipe - Basement

Drained Pipe - Roof


     While most water treatment contractors will recommend raising the chemical corrosion inhibitor concentration just prior to winter drain down, in reality, such actions provide little, if any, added protection. Higher concentrations of standard water treatment chemicals are still limited by their ability to penetrate existing corrosion deposits, and typically lose their effectiveness over extended periods of time.

     Our ultrasonic pipe testing has documented that even the more effective and previously long employed chromate chemicals failed under extended drain down conditions. In the above example, the NYC building property was heavily treated with chromate corrosion inhibitors for over 30 years until they were banned, yet shows a significantly higher wall loss at the roof level not likely occurring only since 1985.


THE SOLUTION:

     While not available through most commercial water treatment contractors, extremely effective corrosion inhibitors for winter or extended lay-up exist through some specialty suppliers. The most effective category of corrosion control agent, known as a Vapor Corrosion Inhibitor (VCI), is sprayed, fogged, or otherwise introduced into the empty pipe in the form of a lightweight fine powder. The pipe is then temporarily closed off with plastic or a plug in order to retain the VCI vapor.



     VCI products protect metal surfaces with a thin, monomolecular barrier film which re-heals and self-replenishes itself. Its basic method of operation is shown in the below chemical schematic, and protects the anodic and cathodic areas of the metal in both the water and gaseous phases.



     Once in place, the VCI powder produces a penetrating gas which virtually stops corrosion for a period of up to two years. In actual use, VCI's produce almost total cessation of the corrosion process, as shown in a comparison of mild steel coupons below. The VCI produced gas also penetrates existing iron oxide deposits to provide protection to even heavily corroded systems.

     VCI corrosion inhibitors offer significant benefits in solving the winter lay-up problem, and will greatly extend the service life of such piping systems. While most commonly used for piping, VCI protection is also ideal for chillers, tanks, vessels and other HVAC related equipment which may be removed from service temporarily. Some of the many benefits provided are:

     In addition to the protection of piping during winter lay-up, various other forms of VCI products exist to solve the most difficult corrosion problems. Specialized VCI based chemical treatment programs are available to control the worst control corrosion problems. Please contact ECI for further information.



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