Underwater Inspection and Evaluation
“A Critical Component” for Preventative Maintenance, Operation and Relicensing
William J. Castle, P.E.
W.J. Castle, P.E. & Associates,
P.C. 693 Main Street, Building B, Suite 1
Lumberton, New Jersey 08048 USA
For the information to be useful, documentation must be clear and concise and in accordance with generally understood terminology. Inspection forms should be filled out as the inspection progresses, and reports should be completed soon after the inspection has been finished. Standard forms and report formats facilitate the documentation procedure and are essential for comparing the results of the present inspection with past and future inspections.
When appropriate, visual inspection should be documented with still photography and closed-circuit television. Still photography provides the necessary high definition required for detailed analysis, while video, although having a less sharp image, provides a continuous view of the inspection. All photographs should be numbered and labeled with a brief description of the subject. A slate or other designation identifying the subject should appear in the photograph. When color photography is used, a color chart should be attached to the slate to indicate color distortions. Videotapes should be provided with a title and lead-in describing what is on the tape. The description should include the method of inspection used, the nature and size being inspected, and any other pertinent information.
The method a diver uses to communicate his findings depends on diving conditions. As a minimum, the entire inspection can be recorded on audio tape for a more accurate inspection. The tapes can then be transcribed back in the office for a complete history of the inspection.
A. 35MM Photography
Still photography can be of great value since they can help an inspector communicate his findings. Photographs of defects are useful in preparing repair plans, can be used as part of the repair bid documents, and may assist in obtaining funding for repair work.
Certain conditions will limit or prevent use of photography. Dark water may require the use of a clearwater box.
Underwater video, either black and white or color, can provide documentation for an entire inspection or for selected areas. Video systems with a surface system also provide good documentation at low cost.
A monitor on the surface is usually necessary even if an inexperienced or unqualified inspector is performing the diving work. This allows an engineer on the surface to see the same area as the diver and to view what the diver is describing.
C. Remote Operated Vehicle (ROY)
A remotely operated vehicle (ROY) is a tethered underwater video camera platform, sometimes equipped with manipulator systems, and an electric or electro-hydraulic propulsion systems. A ROY is controlled from the surface by means of a video system, for operator observation; and “joystick” type propulsion and manipulator controls. Originally the vehicles were designed for extremely deep diving and to provide video inspection in places that were inaccessible or too hazardous for conventional diving, such as polluted, contaminated or extremely cold water.
Although the dependability of the ROY has steadily increased, some problems still remain. The ROY can only supply a two-dimensional view of a problem; the full extent of any defects generally cannot be obtained from a picture. In murky water, the effectiveness of a ROY is extremely limited; a diver can at least conduct a tactile inspection. It is difficult to know the exact orientation or position of the vehicle to accurately identify the area being observed and the operator may also encounter problems with controlling the vehicle in a current or tangling its umbilical.
D. Inspection Tools
To work effectively underwater, the diver must have the proper tools and equipment. Much of the underwater work in inspection diving involves cleaning of structural elements. Sampling and testing may also have to be accomplished. The use of specialized tools may be necessary for testing. Both power and hand tools are used underwater.
This is part 3 of a 4-part series.
You can find part 1 here.
You can find part 2 here.
Read the 4th of this 4-part series here.