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Water Jetting
General Discussion
Water Jetting
High- and medium-pressure water blast systems are used for paint stripping surfaces with low-volume water streams at pressures ranging from 3,000 to 15,000 psi (medium-pressure operations), and greater than 25,000 psi (ultra high-pressure operations).
These systems remove paint by spraying a stream of high-pressure water at the surface of the part. The advantages of this process include a readily available medium (water), an easily treatable waste stream, and an absence of fume and hazardous waste production. Medium-pressure systems may be augmented. For example, sodium bicarbonate may be added to the water stream, or environmentally compliant chemicals may be applied to painted surfaces prior to water blasting. Ultra high-pressure systems typically use pure water streams. With both medium- and high-pressure water systems, specialized nozzles can be used to achieve varying effects. A relatively gentle, layer-by-layer process 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.
The capital costs for ultra high- and medium-pressure water processes vary considerably depending on the process and its application. Capital costs for medium-pressure systems range from $40,000 to $70,000, and capital costs for ultra high-pressure systems range from $100,000 to $1,000,000.
Water jetting provides for a clean surface that is ready to paint. In addition this process produces a surface that complies with SSPC-12/NACE No. 5 specifications. The US Navy has allowed use of this process for removal and installation of non-skid deck coverings on Navy ships.
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