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Maintaining Aged Infrastructure with Difficult-to-Coat Features

Maintaining Aged Infrastructure with Difficult-to-Coat Features
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Maintaining aged infrastructure can be challenging, especially when structures were designed with difficult-to-coat features, such as riveted construction, back-to-back plates, or skip welds. According to NACE SP0178 - Design, Fabrication, and Surface Finish Practices for Tanks and Vessels to be Lined for Immersion Service, these construction methods are not recommended for immersion service. 

Product Number: 51217-073-SG
Author: Allen Skaja, Richard Pepin, David Tordonato, Bobbi Jo Merten,
Publication Date: 2017
Industries: Pipelines, Tanks, and Underground Systems , Coatings and Linings , Coatings
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$20.00
$20.00

Maintaining aged infrastructure can be challenging, especially when structures were designed with difficult-to-coat features, such as riveted construction, back-to-back plates, or skip welds. According to NACE SP0178 - Design, Fabrication, and Surface Finish Practices for Tanks and Vessels to be Lined for Immersion Service, these construction methods are not recommended for immersion service. However, existing structures must be periodically recoated. This begs the question; what are the proper procedures for a successful recoat of these structures? The difficult-to-coat features were once protected using lead-based paints, solution vinyl resins, and coal tar enamel coating systems. Sometimes special mastic materials were used that contained asbestos and other reinforcing ingredients. Today’s coating systems are typically highly crosslinked polymers such as epoxies and polyurethanes. The standard practice within SSPC PA Guide 11 is to brush apply stripe coats to work the coating into crevices prior to spray application. In the case where the gap is too large for a coating to bridge, 100% solids epoxy mastic fillers are used to fill the void. All rivets and overlapping plates have crevices, which when coated can eventually result in cracks in the coating eventual corrosion. Potential causes of this damage are coating shrinkage stress and joint movement. The older coating systems protected these areas for 40-50 years before cracking. In contrast several of Reclamation’s recent recoating jobs experienced failures of these features within months, despite following application procedures. This paper reviews common practices for coating the infrastructure features described above, case history using modern coatings, specification language, and workmanship of contractors.

Maintaining aged infrastructure can be challenging, especially when structures were designed with difficult-to-coat features, such as riveted construction, back-to-back plates, or skip welds. According to NACE SP0178 - Design, Fabrication, and Surface Finish Practices for Tanks and Vessels to be Lined for Immersion Service, these construction methods are not recommended for immersion service. However, existing structures must be periodically recoated. This begs the question; what are the proper procedures for a successful recoat of these structures? The difficult-to-coat features were once protected using lead-based paints, solution vinyl resins, and coal tar enamel coating systems. Sometimes special mastic materials were used that contained asbestos and other reinforcing ingredients. Today’s coating systems are typically highly crosslinked polymers such as epoxies and polyurethanes. The standard practice within SSPC PA Guide 11 is to brush apply stripe coats to work the coating into crevices prior to spray application. In the case where the gap is too large for a coating to bridge, 100% solids epoxy mastic fillers are used to fill the void. All rivets and overlapping plates have crevices, which when coated can eventually result in cracks in the coating eventual corrosion. Potential causes of this damage are coating shrinkage stress and joint movement. The older coating systems protected these areas for 40-50 years before cracking. In contrast several of Reclamation’s recent recoating jobs experienced failures of these features within months, despite following application procedures. This paper reviews common practices for coating the infrastructure features described above, case history using modern coatings, specification language, and workmanship of contractors.

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