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Chloride ion corrosion, often found in marine environments, is a significant environmental factor that contributes the corrosion of steel and other metals. In addition to marine environments, this ion is found in humid conditions, where water from humid air contaminated with soluble chloride salts has been condensed. Chloride corrosion is typically referred to as ‘pitting corrosion’ as it is usually extremely localized and can lead to small pinholes in the metal. When steel is used as reinforcement to concrete, chloride corrosion may also occur. In fact, exposure of reinforced concrete to chloride ions is the primary cause of premature corrosion of the steel reinforcement. The alkaline environment of concrete (pH of 12 or 13) will typically provide steel with corrosion protection. This is because a thin oxide layer or passivating layer, forms around the steel, preventing metal atoms from dissolving. However, when the passive oxide layer is completely destroyed (pH falls below 9.5) in cases where the alkalinity of the concrete is reduced or the chloride concentration in the concrete increases to a certain level, corrosion is imminent. In this case, reinforced concrete at a methanol plant was exposed to chloride ions, significantly corroding the internal steel reinforcement.
reinforced-concrete-protective-oxide-layer
Steel reinforcement is usually protected by a passivating layer due to the alkalinity of concrete. This layer becomes jeopardized when concrete is exposed to a high concentration of chloride. Photo courtesy of Portland Cement Association.

 

The cooling tower of this methanol production facility had experienced significant corrosion over the years. Due to its marine location, the plant faced constant exposure to marine air and moisture, in addition to circulating salt water throughout the cooling tower. A third party engineering firm was brought in to determine the extent of the penetration of salt water into the concrete. Initial findings showed the pH of the concrete to be 10.8, making corrosion vulnerability of the steel a certainty. As the reinforcing steel began to corrode, the bond between steel and concrete also began to fail, causing the concrete to crack and threatening the design capacity of the entire structure.
Chloride ion corrosion of reinforced concrete column
The corroded steel reinforcement and spalled concrete on columns and the walls of this methanol plant threatened its structural integrity.

 

HJ3’s CarbonSeal carbon fiber repair system was recommended to bring the cooling tower up to its design capacity and prevent further corrosion and degradation. The repair was executed in two phases. The first phase was to repair the highest priority area, which was the exterior supporting wall on the west side of the structure. The second phase included the reinforcement of supporting concrete columns along the north and south walls. In each case, spalling concrete was chipped off and removed with a high pressure water jet. Any and all exposed steel rebar was cleaned to near white metal and protected with a zinc rich primer coating. The concrete was patched back to a uniform surface, primed, the CarbonSeal high modulus paste was applied and saturated CarbonSeal fabric applied. The CarbonSeal system was then protected with a chemical-resistant top coat.
Reinforced concrete wall strengthening
HJ3’s CarbonSeal carbon fiber repair system was wrapped around the columns and walls of the plant.
HJ3’s CarbonSeal system was able to strengthen the reinforced concrete walls and columns of this methanol production plant within two phases that fell in accordance with the plant’s planned outages. These repairs were done in time despite rainy and wet conditions, where the concrete had to be dry prior to the installation of HJ3’s CarbonSeal system. Following HJ3’s repair, there was also an earthquake, to which the CarbonSeal system stood up un-phased and maintained the structural integrity of the cooling tower. The HJ3 CarbonSeal repair will provide the plant with the long-term solution it desired, at a significant cost savings over the alternative of can be performed quickly, and will not corrode for no future maintenance on a repaired section. If you have chloride ion corrosion on your steel or concrete infrastructure and would like to learn more about HJ3’s CarbonSeal industrial repair systems, contact our project managers today at hj3pm@hj3.com.
HJ3's CarbonSeal concrete wall repair system
The CarbonSeal chemical-resistant top coat was applied to the CarbonSeal carbon fiber, protecting the system.