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Water Jetting the Toughest Coatings
More and more professional blasters are turning to ultra-high pressure (UHP) blasting for challenging industrial cleaning and stripping projects. Water is not only cost-effective, it effectively and efficiently cleans the surface without damage to the existing profile and with very little impact on the environment.
UHP is ideal for the removal of heavy rust, scale, resins, chemical residues, and thick or abrasion resistant coatings – such as chlorinated rubber, coal-tar epoxies, polyurethanes, and glass-flake coatings. Water jetting cuts through both rust and coating by literally dis-bonding it from the surface. The waste is then rinsed away – resulting in a totally clean surface.
Ultra-High Pressure (UHP) Systems
The key component of all UHP systems is the pump which is expected to deliver pressures ranging from 6,000 psi (415 Bar) to 40,000 psi (2800 Bar). That coupled with power ratings up to 1,000 horsepower (735 kW) means these pumps need to be solidly constructed and durable. Depending on jobsite conditions, high pressure pumps can either be electric or diesel powered, as well as mounted on trailers, skids, or containers. For projects involving hazardous materials or environments, special models are also available.
Alongside the UHP pump, each unit requires special hoses and tool heads needed to clean the surface. Depending on the application, there are a variety of tools including internal pipe & tube cleaning tools, vacuum-attached crawlers, abrasive cutting systems, internal tank cleaning heads, floor & grate cleaners, and remote-controlled robotic cleaning systems.
An often-overlooked component of the Water Jetting approach is the PPE (protective apparel) needed by the operators. Most might consider jeans and a t-shirt enough for water blasting, but the truth is 40k psi will devastate flesh if they come in contact. For that reason, specially designed clothing, which has been rated to provide protection against UHP is necessary.
Benefits of Ultra High Pressure (UHP) for Surface Preparation?
- UHP water jetting is dustless which increases visibility, improves speed, reduces potential injury and environmental issues.
- UHP minimizes waste by not using any abrasive media, eliminating that expense as well as abrasive clean-up costs.
- By eliminating dust, UHP allows the continuation of other operations near the blasting site that might otherwise be delayed or compromised.
- UHP ensures no contaminants are added to the project surface whilst cleaning it.
- UHP water jetting removes soluble salts and other contaminants from the surface.
- The UHP stripping process does not create a new surface profile, but restores it back to its original profile.
With the right configuration of equipment, UHP water jetting can effectively:
- remove tough paints and thick coatings,
- wet abrasive blast,
- strip coatings from floors and grates,
- cut slag out of drain lines,
- remove deposits from pipes,
- clean interiors of tanks,
- cut steel plates,
- and scarify or demolish concrete.
Standards for blasting with HP & UHP
A set of four surface preparation standards for water jetting have been jointly produced by The Society for Protective Coatings (SSPC) and NACE International. The highest level standard is SSPC-SP WJ-1/NACE WJ-1, Waterjet Cleaning of Metals – Clean to Bare Substrate. SP WJ-1 contains requirements for cleaning metals to bare substrate using waterjet cleaning, including the required end condition of the surface and procedures and materials necessary to achieve the end condition.
The other three standards in this set are:
- SSPC-SP WJ-2/NACE WJ-2
- SSPC-SP WJ-3/NACE WJ-3
- and SSPC-SP WJ-4/NACE WJ-4
SSPC/NACE also produce a visual guide with reference photographs for steel surfaces prepared by waterjetting – SSPC-VIS 4/NACE VIS 7. This Shows previously coated and uncoated, rusted steel surfaces cleaned to WJ-1, WJ-2, WJ-3, and WJ-4 finishes as defined by the SSPC/NACE standards for waterjetting. Additional photos illustrate degrees of light, moderate, and heavy flash rusting after waterjetting.
