Define Cleaning for Underwater Inspection of Bridge?

Before any structure can be inspected, it is necessary to expose the surface material of the structure. Wherever there is marine growth or incrustation on the surface of the structure, cleaning of the same, may be in a limited area, will be required.

The best approach is to restrict cleaning to small zones, which are:

- Structurally critical areas

- Areas known to frequently deteriorate for that specific structural configuration

- Areas randomly selected to statistically lower the probability of overlooking damage

Bridge Inspector's Training Manual of FHWA, USA recommends a 15 to 30 cm bands or squares depending on the size and shape of the structure. Highest priority should be placed on locations near the low water line and connecting elements. If feasible, location at the mud line, and midway between the mud line and low water line should also be included. For large elements, squares around the perimeter should be chosen at effective intervals.

Light cleaning can be done with a diver's knife or with hand held tools such as a chipping hammer or a scraper. Cleaning of thick, hard growth will require pneumatic or hydraulic powered chippers, grinders and brushes. Tough cleaning jobs on concrete and steel may require high- pressure blaster.