Corrosion Under Insulation - Unique Solution

July 27, 2021

Corrosion continues to be a major challenge to all industries and remains one of the largest expenses to industry other than healthcare. (1) Even though there have been numerous papers published regarding the specific corrosion phenomenon of CUI (corrosion under insulation), there has not been much done to address the industry issue. CUI affects both carbon steel and stainless-steel materials. The latter becomes more susceptible as a plant ages and chlorides and other contaminants build up on the surface underneath the insulation.(2)

Based on a study initiated by NACE International, the global cost of corrosion is estimated to be US $2.5 trillion (2013), approximately 3.4% of global gross domestic product (GDP). It is estimated that US $375- $875 billion could be saved globally on an annual basis if available corrosion prevention measures were implemented.(3)

CUI is influenced by insulation, temperature, moisture, chloride content, and type of metal. Wet insulation is the root cause of most CUI issues for carbon steel, and wet insulation with high chlorides is typically the cause for stainless steel CUI.(2)(5)

Dr. Hira Ahluwalia of Material Selection Resources, Inc., published a paper in 2014 identifying fixed equipment as the most susceptible to CUI and suggesting that $0.35 of every maintenance dollar is spent on fixed equipment. He furthermore identified piping as responsible for 55% of fixed equipment costs, with CUI accounting for 40-60% of the piping maintenance cost, or $0.10 of every maintenance dollar.(5)

Multiple companies offer coatings for CUI prevention. These coatings must be applied to the metal surface prior to installing the insulation. Like any traditional coating, once the surface integrity is compromised, corrosion occurs and propagates underneath the coating, ultimately causing failure. Cortec® Corporation has two unique solutions: one that is painted onto the metal surface or the insulation and is good up to 1100 °F (600 °C), the other that may be injected into the insulation on an insulated surface at approximately every 20 feet (6 m) and is good up to 338 °F (170 °C). The Cortec® Vapor phase Corrosion Inhibitor (VpCI®) provides protection by displacing moisture (hydrophobic action) and neutralizing the surface charge (ionic bonding) as the inhibitor molecule is adsorbed onto the metal. The inhibitor molecule provides excellent corrosion protection when exposed to very corrosive elements such as halogens (chloride, fluorides, etc.), HCl, and H2SO4.

The following pictures represent how the VpCI® molecule travels through air and water to provide corrosion protection to metal surfaces even though they are covered with water.

In the preceding examples, VpCI® vapors are blown into the air space above the water and permeate the water, protecting the metal in the water and above the water.

VpCI® can also be added to the water to form a homogenous solution. The inhibitor molecule travels through the water to the metal. It also volatizes from the water to saturate the air space above the waterline and subsequently reaches the exposed metal.

The steel wool in the bottle to the left is an example of hydrophobic and ionic bonding as molecules are adsorbed onto the metal surface. With no free electrical charge on the metal surface to combine with corrosive elements, corrosion cells cannot initiate.

The same concepts apply to the Cortec® CorroLogic® inhibitors for CUI. In the case of the injectable inhibitor (CorroLogic® CUI Inhibitor), when liquid is injected into the insulation, the VpCI® molecule volatizes from the liquid and travels through the insulation, causing a one-molecule thick film to adsorb onto the metal surface. In the case of the coating (CorroLogic® CUI High-Temp Inhibitor), the VpCI® is applied in a liquid solution that carries the VpCI® molecules to the metal surface, where they adsorb prior to the application of insulation.

Studies by Dr. Behzad Bavarian, California State University, Northridge, have demonstrated the effectiveness of both the Cortec® CorroLogic ® CUI Inhibitor and Cortec® CorroLogic® CUI High-Temp Inhibitor to prevent CUI.

Conclusion
The testing conducted by Dr. Behzad Bavarian, California State University, Northridge, demonstrated that insulation impregnated with VpCI® liquid could reduce the corrosion rate by a factor of 30, while testing of the high temperature inhibitor typically applied by coating the pipe demonstrated a corrosion rate reduction by a factor of 15 when exposed to a boiling temperature and high chloride environment.(6)(7) Use of these inhibitors will reduce overall maintenance costs, equipment repair and replacement, and unplanned shutdowns due to CUI-induced failures.

References
1. Fast, Doug. “A Two-Step Solution to the High Cost of Corrosion Under Insulation.” Corrosionpedia.com, 26 July 2020 <https:// www.corrosionpedia.com/2/6495/corrosion-underinsulation-cui/a-two-step-solution-to-the-high-cost-ofcorrosion-under-insulation>.
2. Holden, James E., PE. “Impact of Aging Plants on Stainless Steel Components.” Stainless Steel World Americas, June 2022.
3. Koch, Gerhardus, et al. “International Measures of Prevention, Application, and Economics of Corrosion Technologies Study.” NACE International: Houston, TX, 1 Mar 2016 <http://impact.nace.org/documents/Nace-International-Report.pdf>.
4. Rudling, Peter, Alfred Strasser, and Friedrich Garzarolli. “Welding of Zirconium Alloys.” A.N.T. International, October 2007 <https://www.antinternational.com/docs/samples/FM/11/First_chapter_-_ZIRAT12_STR_Welding_of_zirc_alloys.pdf>.
5. Ahluwalia, Dr. Hira. “The Hidden Enemy: Corrosion Under Insulation.” Material Selection Resources, Inc., presentation on 14 Nov 2014.
6. Bavarian, Dr. Behzad. “Protection Effectiveness of Vapor Corrosion Inhibitor VpCI®-619 for Corrosion Under Insulation at Elevated Temperatures,” California State University, Northridge, and Cortec® Corporation, Feb. 2018 <https://www.cortecvci.com/Publications/Papers/CUI-report-on-VCI-619.pdf>.
7. Bavarian, Dr. Behzad, et al. “Protection of Corrosion under Insulation using Vapor Phase Corrosion Inhibitors, Corrologic VpCI-658.” California State University, Northridge, and Cortec® Corporation, April 2015 <https://www.cortecvci.com/Publications/Papers/Corrologic-VpCI-658-inhibitor-effects-on-CUI-final-report.pdf>.

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