Our members regularly submit technical questions through the Ask the Expert portal. Here we’ve compiled the most frequently asked questions from professionals new to the pipeline coating industry, along with answers from our Technical Advisory Panel.
Q: What’s the difference between polyurea, polyurethane, and polyaspartic coatings?
A: All three are isocyanate-based coating systems, but they differ in their resin chemistry and resultant properties. Polyurea uses amine-terminated resins and cures very rapidly (seconds to minutes) regardless of humidity. Polyurethane uses hydroxyl-terminated resins and is moisture-sensitive, with longer cure times. Polyaspartic is a subclass of polyurea using aspartic acid ester amines, offering slower cure times (minutes to hours) for better open-time control and improved UV stability. For pipeline coatings, pure polyurea and polyaspartic hybrids are the most common choices.
Q: Why does my polyurea coating have pinholes after application?
A: Pinholes in freshly applied polyurea are almost always caused by solvent or moisture outgassing from the substrate. If the substrate contains moisture or residual solvent from a primer, rapid polyurea gel time traps the gas as pinholes. Solutions include allowing adequate primer flash-off time, confirming substrate moisture content with a moisture meter, applying a thin mist coat before the full build coat, or switching to a slower-gel formulation that allows outgassing before the film skins.
Q: How do I choose between NACE SP 10 and NACE SP 6 for my polyurea application?
A: The choice of blast standard depends on the coating system’s requirements and the service environment. Spray polyurea coatings for buried pipeline service typically require Near-White Metal Blast (NACE SP 10) to maximize adhesion and CP compatibility. For above-grade maintenance applications with less severe service conditions, Commercial Blast (NACE SP 6) may be acceptable with the appropriate primer system. Always follow the coating manufacturer’s technical data sheet requirements as the minimum standard.
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