Coating thickness is one of the most fundamental parameters in any pipeline coating specification, yet it is also one of the most frequently debated. Too thin and the coating provides inadequate protection; too thick and costs increase without proportional performance benefit. Arriving at the right thickness specification requires understanding the relationship between film build, physical properties, and service environment.
Minimum Thickness Requirements by Service Environment
For buried onshore pipelines in moderate soil conditions, industry consensus supports minimum polyurea dry film thickness (DFT) of 40–60 mils (1.0–1.5 mm) for mainline sections. For aggressive soils, soil stress environments, or locations with mechanical damage risk, specifications of 80–125 mils (2.0–3.2 mm) are common. Rock ditch and directional drilling applications may specify 125–250 mils (3.2–6.4 mm) of polyurea or a hybrid polyurea/HDPE system.
The Relationship Between Thickness and Holiday Risk
Thinner coatings are more vulnerable to holiday formation during application and installation. Statistical analysis of holiday testing data across hundreds of projects shows that holiday frequency decreases exponentially as DFT increases above 20 mils — with 40-mil coatings showing approximately 80% fewer holidays per linear foot than 20-mil coatings applied under identical conditions.
Measurement and Verification
Dry film thickness is measured using magnetic pull-off gauges (Type 1) or electronic digital gauges (Type 2) per SSPC-PA 2. For thick-film polyurea applications, multiple gauge readings per pipe joint — typically five readings per joint with specific acceptance criteria for individual readings and averages — are required to ensure specification compliance. Download our DFT measurement procedure template to standardize thickness measurement across your projects.