 All copper tubes for water service are treated, usually by sand (or other nonferrous medium) blasting or acid pickling, to remove any films produced during manufacture with the result that Type 1 pitting initiated by carbon films is now very rare.If water is left to stand in a tube for an extended period, the chemical characteristics of the water change as the mixed scale and corrosion products are deposited.In addition any loose scale that is not well adhered to the wall will not be flushed away and air dissolved in the water will form bubbles, producing air pockets.