Tip #11 - Hydroblasting standards
Hydroblasting is a technique for cleaning surfaces, which relies entirely on the energy of water striking a surface to achieve its cleaning effect. Abrasives are NOT used in hydroblasting systems. Consequently the problems caused by dust pollution and by the disposal of spent abrasives are eliminated. Two different hydroblasting operating pressures are commonly encountered.
- High pressure hydroblasting, operating at pressures above 680 bar (10.000 psi)
- Ultra high pressure hydroblasting, operating at pressures above 1.700 bar (25.000 psi)
This visual standard has been prepared by the use of ultra high pressure hydroblasting equipment. The standard however is applicable to surfaces produced by a whole range of hydroblasting pressures, providing the equipment used is capable of cleaning to the visual standard depicted.
The steel surfaces produced by hydroblasting do NOT look the same as those produced by dry abrasive blasting, or slurry blasting. This is because water on its own cannot cut, or deform steel like abrasives. Hydroblasted surfaces therefore tend to look dull, even before they “flash rust”. In addition Grade D steel, with active corrosion pitting, shows a mottled appearance after hydroblasting. Mottling occurs when the corrosion products are washed out of the pits, leaving a bright patch, and the surrounding areas are left a dull grey, brown to black colour. See note 5.10. This pattern is the reverse of that left by abrasive blasting, where anodic pits are often dark, due to corrosion products not being entirely removed, and the surrounding areas are bright. “Flash rusting”, i.e. light oxidation of the steel, which occurs as hydroblasted steel dries off, will quickly change this initial appearance.
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