At 20 ksi, the surface was primarily bright brass with scattered patches of deep purple oxide. There was no significant thinning of the tube wall at any cleaning pressure. No wall loss due to hydrolaser cleaning was seen in the brass tubes. Only at 20 ksi were some of the protruding surface features removed, leaving an overall smoother surface without reducing the minimum wall thickness. Scattered patches of the iron-rich deposit remained after the 10 ksi process, certainly a smaller amount than remains after cleaning by scrapers.
Corrosion prevention is the main reason for cleaning the heat exchanger.
The violet oxide layer beneath the deposits serves to protect the base metal and there is no benefit in removing it. The thickness of the oxide layer was virtually unchanged by the 10 ksi hydrolasing, indicating that cleaning at 10 ksi effectively removed the silt and slime. If the Metallurgy Lab can be of further assistance, please call. In addition, several pit-like indications were machined using a drill. None of the Partially through wad defects deformed or leaked during the fisted exposures.