Hardcore corrosion? or Déjà Vu
Several years ago we were called on regarding a corrosion situation on some cooling towers at a nuclear power plant. The towers were concrete and the rebar was corroding and delaminating the concrete. We put together a proposal to decontaminate the concrete, repair the cracked and damaged areas and coat the concrete to stop further intrusion of chlorides. This quotation was for ~$800,000 each (total of 9).
They decided to put off making a decision while searching for more info...(the person in charge told us candidly that he would be moved in 12 to 18 months and he did not want that decision on his record...he also said the next person would be moved in 18 months with the same viewpoint)...the end result was 5 years later they are spending over 4 million each to replace these 9 cooling towers...and that does not include the removal and disposal cost of the old ones.
We run into similar scenarios constantly at everywhere from electronic plants to mining operations. If they can operate on a lower annual budget than their predecessor, they move up the ladder faster. I could go on with case after case, but the situation is the same...all many care about are doing as little as possible and covering their tails.
Corrosion in Space? or Déjà Vu
Although the question of whether corrosion of materials occurs in outer space is still being investigated by NASA, on a lesser scale the following case history relates the story of failure of the materials of construction of an observatory telescope dome used for inner space studies.
A telescope has a dome that consists of a variable opening aperture controlled by a mechanical mechanism, permitting viewing of the night sky through the thirty-year-old telescope inside the dome. The old German-designed and constructed dome is a cedar-framed structure internally, lined externally with a metallic copper sheathing. The structural supports for the entire telescope dome are made of carbon steel. The sliding aperture dome-cover is opened via a motor-driven cog-and-wheel mechanism, which is located around the lower circumference of the dome.
After thirty year’s service in the marine environment, the dome developed leaks internally during wet weather and an investigation of the cause of the water leakage problem was requested.
A detailed site inspection and examination of the metallic components of the telescope dome revealed the following features regarding the dome construction:
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The steel support structures, the dome opening mechanism, and other steel components of the observatory dome had undergone extensive general and galvanic corrosion during the service life. |
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The original design of the observatory dome had incorporated inadvertent contact between many dome steel structural members and the copper sheathing, which had established extensive galvanic corrosion cells inside and outside the dome. |
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Galvanic corrosion in the upper structural steelwork of the dome was serious and the corrosion damage had caused steel corrosion product oxide jacking at joints and fasteners, which permitted ingress of rainwater under the copper sheathing. |
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Galvanic corrosion of the steel components in the dome aperture opening mechanism at the bottom of the dome had resulted in severe corrosion damage to the steel, which had consequently been structurally weakened by the corrosion attack. |
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Because of infrequent maintenance to the external copper cladding on the dome and to the internal mechanical equipment over many the structural integrity of the telescope dome had been compromised. |
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Moisture ingress, which transported a marine aerosol into the dome internal compartments, had provided the electrolyte needed to support the galvanic corrosion mechanism observed between the copper and steel components inside the dome. |
Temporary remedial actions to alleviate the problem, included cleaning/painting accessible steel parts, application of grease and aerosol-applied corrosion inhibitors to the steel surfaces. Repairing the corrosion-damaged external copper cladding on the dome to minimize the corrosive actions of the weather was also a high priority. However, the long-term outlook for the telescope dome as it remains presently is not good. Extensive repairs and refurbishment are essential for the observatory dome’s survival in the near future, but funds have to be raised on a voluntary basis to achieve this aim.
If you want more details of this timeless case, please contact directly The Author.
