WATER JETTING

The Society for Protective Coatings (SSPC) defines two overarching levels of surface preparation that use pressurized water: water cleaning and waterjetting.

Water Jetting
March 2016. USS Abraham Lincoln (CVN 72)
undergoing waterjetting during a
Refueling and Complex Overhaul (RCOH).

Water cleaning is typically used to remove loose material and debris as well as grease and soluble salts from surfaces in accordance with SSPC SP 1 Solvent Cleaning. The water pressure for this type of surface preparation ranges from 0 to 10,000 pounds per square inch (PSI). According to the waterjetting standard SSPC-SP WJ-1/NACE WJ-1, Clean to Bare Substrate, waterjetting is broken down into high-pressure waterjetting which ranges from 10,000 to 30,000 PSI and ultrahigh-pressure waterjetting (UHPWJ) which uses water pressure greater than 30,000 PSI. The U.S. Navy typically employs UHPWJ for coating removal.

Water cleaning is typically used to remove loose material and debris as well as grease and soluble salts from surfaces in accordance with SSPC SP 1 Solvent Cleaning. The water pressure for this type of surface preparation ranges from 0 to 10,000 pounds per square inch (PSI). According to the waterjetting standard SSPC-SP WJ-1/NACE WJ-1, Clean to Bare Substrate, waterjetting is broken down into high-pressure waterjetting which ranges from 10,000 to 30,000 PSI and ultrahigh-pressure waterjetting (UHPWJ) which uses water pressure greater than 30,000 PSI. The U.S. Navy typically employs UHPWJ for coating removal.

Ultrahigh-pressure systems typically use pure water streams. With waterjetting systems, specialized nozzles can be used to achieve varying effects. A relatively gentle, layer-by-layer process, colloquially known as selective stripping, may be used for removal of organic paints at a layer at a time versus the use of a different nozzle for the removal of metal flame spray coating and other tough, tightly adherent coatings.

The process water, paint, and residue are collected by an effluent-recovery system that filters the paint and residue. The recovery system removes leached ions (e.g., copper, cadmium, and lead), chlorides, sulfates, nitrates, and other contaminants from the water. The water is then passed through a coalescing tank for removal of oils and film, then through charcoal filters, micro-filters, and finally, a de-ionization system to ensure that the water being recycled is Grade A de-ionized water. The recovered de-ionized water is recycled back into the process.

Waterjetting provides a clean surface that is ready to paint. The appearance of a surface that has been waterjetted is different from an abrasive-blasted surface. One disadvantage of waterjetting is that it does not produce a surface profile, it only exposes the existing profile. Therefore, alternative surface preparation methods may have to be accomplished in order to obtain an adequate surface profile for a coating system. Waterjetted surfaces must comply with one of the following joint SSPC and NACE surface preparation standards:

  • SSPC-SP WJ-1/NACE WJ-1 – Clean to Bare Substrate
  • SSPC-SP WJ-2/NACE WJ-2 – Very Thorough Cleaning
  • SSPC-SP WJ-3/NACE WJ-3 – Thorough Cleaning
  • SSPC-SP WJ-4/NACE WJ-4 – Light Cleaning.

These standards may be obtained from SSPC or NACE International.

References

SSPC: The Society for Protective Coatings/NACE International. Joint Surface Preparation Standard. Waterjet Cleaning of Metals SSPC-SP WJ-1/NACE WJ-1 – Clean to Bare Substrate.

NAVSEA Surface Preparation Point of Contact

Mark W. Ingle
NAVSEA HQ, SEA 05P2
Phone: (202) 781-3665
Email: mark.w.ingle@navy.mil