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Changes in Appearance and Corrosion Protection of Polyurethane Pipeline Coatings During Weathering Exposure

Changes in Appearance and Corrosion Protection of Polyurethane Pipeline Coatings During Weathering Exposure
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Very thick polyurethane coatings are used to provide corrosion protection for water pipelines that must be placed below ground and then may be exposed to ground water. Occasionally there are construction delays and pipe sections remain above ground for extended periods before installation. Under these conditions, atmospheric conditions and exposure to solar UV light cause the coatings to lose gloss and become yellow. These changes can be very obvious and thus raise concerns that the corrosion protective qualities of the coating have also similarly diminished. 

Product Number: 51217-038-SG
Author: S.G. Croll, C. Gu, V. Upadhyay, B.D. Keil,
Publication Date: 2017
Industries: Pipelines, Tanks, and Underground Systems , Corrosion Monitoring and Control , Coatings
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$20.00
$20.00

Very thick polyurethane coatings are used to provide corrosion protection for water pipelines that must be placed below ground and then may be exposed to ground water. Occasionally there are construction delays and pipe sections remain above ground for extended periods before installation. Under these conditions, atmospheric conditions and exposure to solar UV light cause the coatings to lose gloss and become yellow. These changes can be very obvious and thus raise concerns that the corrosion protective qualities of the coating have also similarly diminished. Aromatic polyurethane coatings have been subjected to 6 months accelerated laboratory weathering as well as continuing natural weathering in Florida and Texas. The accelerated weathering caused very large, rapid changes in appearance but did not provoke any significant reduction in corrosion protection, as assessed by electrochemical impedance spectroscopy. Coating degradation was quantified with gloss, color, thickness loss (by weight change) and impedance. Coating thickness remains almost at its starting value which provides the corrosion protection, whereas the appearance changes are caused by changes in the outer surface of the coating. Thus, in such circumstances, for very thick coatings, appearance changes do not correlate with corrosion protection. It is well known that accelerated and natural weathering are difficult to correlate quantitatively, but natural exposure of only 6 months produced similarly obvious changes in appearance and small changes in corrosion protection.

Very thick polyurethane coatings are used to provide corrosion protection for water pipelines that must be placed below ground and then may be exposed to ground water. Occasionally there are construction delays and pipe sections remain above ground for extended periods before installation. Under these conditions, atmospheric conditions and exposure to solar UV light cause the coatings to lose gloss and become yellow. These changes can be very obvious and thus raise concerns that the corrosion protective qualities of the coating have also similarly diminished. Aromatic polyurethane coatings have been subjected to 6 months accelerated laboratory weathering as well as continuing natural weathering in Florida and Texas. The accelerated weathering caused very large, rapid changes in appearance but did not provoke any significant reduction in corrosion protection, as assessed by electrochemical impedance spectroscopy. Coating degradation was quantified with gloss, color, thickness loss (by weight change) and impedance. Coating thickness remains almost at its starting value which provides the corrosion protection, whereas the appearance changes are caused by changes in the outer surface of the coating. Thus, in such circumstances, for very thick coatings, appearance changes do not correlate with corrosion protection. It is well known that accelerated and natural weathering are difficult to correlate quantitatively, but natural exposure of only 6 months produced similarly obvious changes in appearance and small changes in corrosion protection.

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