19 June 2001
Figure 5-19 Underwater Steel structures Checklist
___ Start the inspection at the splash/tidal zones and at depth of about 60 cm
(24 inches) below mean low water (MLW). This is where most mechanical
and corrosion damage is found.
___ Clean all marine growth from a 30-cm (12 inch) square section of pile
(clean a larger area if inspecting sheeting) and visually inspect for rust,
scale and holes.
___ If the structure has a cathodic protection system, check the cleared area
with an underwater voltmeter to determine its effectiveness. Acceptable
levels of cathodic protection are between -0.80 to -0.90 volts when
compared to a silver/silver chloride reference cell.
___ Sound the surface with a hammer to detect any scaled steel or hollow
areas. Inspect holes in steel sheeting for loss of backfill material through
the opening and subsidence of adjacent ground surface.
___ Visually inspect the structure and sound with a hammer where there is
minimal marine growth.
___ At the bottom, record the water depth, using a wrist depth gauge, on a
Plexiglas slate with a grease pencil.
___ Record other visual observations, such as coating condition (peeling,
blistering, erosion). Closely inspect splices for loss of weld materials and
looseness of splices.
___ Record the condition of cathodic protection equipment (broken or corroded
conduits, loose wires, consumed or lost anodes).
___ Record the extent and type of corrosion, structural damage, or any other
significant observations, using calipers and scales to determine thickness
of steel flanges, webs and plates.
___ Return to the surface and immediately record the observation data in the
___ If more sophisticated means are required to evaluate the condition of steel
piling, ultrasonic inspection is available for more complete thickness
measurements. These measurements must be made in areas clear of all
marine growth and scale. Using ultrasonic equipment in areas with
corrosion pitting can give erroneous thickness measurements. Magnetic
particle inspection may be used, particularly on welded connections, to
detect cracks and small defects.