Wall Washing Tanks
Small, clean plastic bags (or clean paper envelopes) for rust samples. Laboratory filter papers. Note: Clean plastic gloves, forceps, or tweezers should be used to handle filter papers. Sufficient wash liquid (usually reagent grade Methanol). Caution: Any liquid used for wall washing must first be determined to be safe for use in a confined space. Clean wiping rags. 7.5 General Procedures Prior to tank entry, wall wash personnel will be equipped with safety equipment (such as gloves, masks, and respiratory protection equipment) whenever the liquid used for wall washing may adversely affect the gas free condition of the tank interior. Use the following chart determine the minimum number of areas to be selected for wall washing in any tank.
Note: If you are in doubt about the size of nontypical areas, keep wall washings separate and report the approximate size of the tank and of the nontypical areas represented by the sample. Tank bottoms (floors) often do not require wash testing. However, if wash testing is required, use the Blotter Method. 7.5.1 Funnel Method Put on plastic gloves prior to starting the test. Rinse wash bottle, funnel, and sample bottle with a small amount of washing liquid. Place the spout of the funnel into the sample bottle and hold the flat side of the funnel firmly against the surface to be tested. Caution: To avoid possible contamination of samples with suspended matter, care must be taken not to scrape zinc tank coatings with the edge of the funnel. Using the wash bottle, spray a steady stream of the washing liquid to the surface of the tank wall (as high as possible), and about 3 ft. (1m) above the funnel, with the wash bottle held about 15 cm (6 inch) away from the wall. Allow the wash liquid to run down the wall into the
Minimum no. of areas to wash
Tank capacity
<3000 bbl (<500m 3 )
5 7 9
3000-6300 bbl (500-1000m 3 )
>6300 bbl (>1000m 3 )
The following procedures are recommended for all tank wall-washing operations: Do not perform wall washes on wet tanks. Request vessel personnel to dry the tanks. Discoloured patches, tank coating breaks, or exposed sections and all other nontypical areas on the tank walls of tanks and tank floors must be noted on the report and tested as follows: In any tank where the nontypical area is less than about 20% of the total surface area of the tank, include the wall washings with those from the rest of that tank. When the nontypical area exceeds 20% of the tank surface area, keep wall washings from these areas in a separate bottle and perform separate analysis.
funnel and into the sample bottle. Approximately 100ml should be applied at each wash site.
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