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2.4.3.10 Underwater Surveys.: Dry Dock Condition Assessment 49

An underwater survey will inspect the submerged portions of the dry dock for cracks, spalling, corrosion, or other degradation. Thickness measurements using ultrasound or calipers will physically measure steel thickness in highly corroded areas. The survey will also include measuring the elevation of the graving dock floor, checking for movement of the graving dock walls, witnessing the complete operation of the dry dock, and verifying the calibration of instruments.

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47 views1 page

2.4.3.10 Underwater Surveys.: Dry Dock Condition Assessment 49

An underwater survey will inspect the submerged portions of the dry dock for cracks, spalling, corrosion, or other degradation. Thickness measurements using ultrasound or calipers will physically measure steel thickness in highly corroded areas. The survey will also include measuring the elevation of the graving dock floor, checking for movement of the graving dock walls, witnessing the complete operation of the dry dock, and verifying the calibration of instruments.

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DRY DOCK CONDITION ASSESSMENT 49

2.4.3.10 Underwater Surveys. An underwater survey of the sub-


merged portion of the gate, gate seating area, waterfront bulkhead, and
other areas of the dock that cannot be inspected when the dock is dewa-
tered shall be conducted. The surveyor shall inspect for cracks, spalling,
corrosion, or other types of degradation.
Where corrosion of steel structural members has caused a loss of metal
thickness or where as-built member thicknesses are in question, UT mea-
surements may be necessary to confirm actual member thicknesses. See
2.4.3.15 for more information on UT measurements.

2.4.3.11 Grade Survey of Graving Dock Floor. The elevation of the


floor slab shall be measured and recorded for future reference. This infor-
mation will be used in future surveys to determine whether the slab is
rising or settling.

2.4.3.12 Displacement Survey of Graving Dock Walls. If there are


visual indications that the side walls may have moved from their original
location, the actual position of the walls should be determined and
recorded for future reference. This information will be used in future
surveys to determine whether the walls are continuing to move.

2.4.3.13 Witness of Dock in Operation. The surveyor should witness


one complete cycling of the dock, including flooding of dock, opening of
gate, closing of gate, and dewatering of dock.

2.4.3.14 Verification of Calibration of Instruments. If, during the


operational test, the water level indicator gages, ammeter gages, valve
position indicators, or other instrumentation do not reflect the actual
condition, the errant gages should be recalibrated and checked by com-
paring the physical measurement to the reading on the gages.

2.4.3.15 Thickness Measurements. Use UT measurements and/or


calipers to physically measure steel thickness in areas of high corrosion.
The number and frequency of readings will vary as to the condition of
the dock. Steel that still retains all of its protective coating, or steel with
many holes through it, may require no readings because the condition is
obvious. Steel that is questionable will require readings to establish
remaining thickness. Steel that is due for repair may require many read-
ings to establish the extent of replacement.
If UT measurements are required, a grid pattern shall be established
and readings taken at those intervals. Examples are a reading every 10
feet longitudinally and 5 feet vertically on plate, or three readings on the
web and flange of each vertical stiffener in the gate (one each in the upper,
middle, and lower zones). The engineer or naval architect in charge of the

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