Surface Preparation and Cleaning Applications
Domain focus
Surface Preparation and Cleaning Applications tests whether you can match waterjetting standards, nozzle type, standoff, and pressure/flow to the specified result - and recognize the standard that defines acceptance.
Core rules
- Waterjetting cleanliness is defined by SSPC-SP 12/NACE No. 5, with visual grades WJ-1 (clean to bare substrate), WJ-2 (very thorough cleaning), WJ-3 (thorough cleaning), and WJ-4 (light cleaning).
- Flash rust after waterjetting is graded L (light), M (moderate), or H (heavy). The coating specification states which grade is acceptable and how soon coating must follow.
- Nozzle pattern: 0° straight jet for cutting and concrete removal; 15–25° fan for coating and scale removal; 40° for delicate surfaces and rinsing.
- Standoff and overlap matter: jet energy falls with distance, and roughly 50% overlap prevents striping. Higher pressure is not automatically better - flow, dwell time, and angle do the cleaning.
- Contain and treat runoff; blast water may carry paint, metals, and salts.
Worked example
A tank interior is specified WJ-3 with moderate flash rust allowed. Choose a 25° fan nozzle, about 8–10 in standoff, 10,000 psi, and 50% overlap, then verify with the specified comparator and check flash rust before coating. Choosing WJ-1 would waste time and raise flash rust risk without being required.
Traps
Equating WJ-3 with abrasive-blast SSPC-SP 10; assuming WJ-4 removes tight coating; ignoring flash rust grading; and raising pressure instead of adjusting standoff or overlap.