19 June 2001
are required under a Level III inspection, a plan and sampling techniques must
be developed and tailored to the specific areas of concern.
Some types of corrosion, however, may not be detected by visual
inspections. For example, inside steel pipe piling, anaerobic bacterial corrosion
caused by sulfate-reducing bacteria (Figure 5-17) is difficult to detect by visual
inspection. Fatigue distress can be recognized by a series of small hairline
fractures perpendicular to the line of stress but these are difficult to locate by
visual inspection. This type of problem, however, is more prevalent to offshore
platforms with welded structural connections than to standard piers and wharves.
Cathodic protection systems need to be closely monitored both
visually and electrically for signs of loss of anodes, wear of anodes, disconnected
wires, damaged anode suspension systems, and low voltage.
Table 5-6 summarizes special sampling equipment, measurements
required, and ratings used in the inspection of steel structures.
Table 5-6. Inspection Equipment, Measurements, and Ratings of Steel
Special Sampling Equipment
Measurements, Ratings, or Samplings
Ultrasonic equipment for determining
Deformation of structural members
Cathodic protection potentials
Location and size of damaged areas
electronic potentials on cathodically
Depth of pits and extent of their
Samples of corrosion products or
Underwater Inspections. Use Figure 5-19 "Under Water Steel
Structures Checklist" to ensure that a thorough inspection of underwater steel
structures is done. An engineer should explain to the diver exactly what to look