Crude Oil or Product Tanker Calculations

CAUTION:  Since all filter papers in the same container may not be free of contaminants, or may not have the same level of contaminants, the result of laboratory tests of wall wash samples could be adversely affected by the filter papers.

9. 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.

10. Clean wiping rags,

Note: Clean plastic gloves, forceps, or tweezers should be used to handle filter papers.

GENERAL PROCEDURES

Prior to tank entry, wall wash personnel shall 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 to determine the minimum number of areas to be selected for wall washing in any tank.

Table Wall Washing Tanks

The following procedures are recommended for all tank wall washing operations:

1. Do not perform wall washes on wet tanks. Request vessel personnel to dry the tanks.

2. Each washed area should be about 3 ft. (1m) wide and 6 ft. (2m) high from the bottom of each tank. Higher areas that can be safely accessed may also be washed.

3. Discoloured patches, tank coating breaks, or exposed sections, and all other non-typical areas on the tank walls of tanks and tank floors must be noted on the report and tested as follows:

   1. In any tank where the non-typical 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.

   2. When the non-typical area exceeds 20% of the tank surface area, keep wall washings from these areas in a separate bottle and perform separate analysis.

   It may be noted that if you are in doubt about the size of non-typical areas, keep wall washings separate and report the approximate size of the tank and of the non-typical areas represented by the sample.

    

4. Tank bottoms (floors) often do not require wash testing.  However, if wash testing is required, use the Blotter Method.

5. The laboratory must be informed in advance if analysis is required on wall wash samples. The laboratory is responsible to communicate test results promptly to inspection personnel.

FUNNEL WALL WASH PROCEDURE

1. Put on plastic gloves prior to starting the test.

2. Rinse wash bottle, funnel, and sample bottle with a small amount of washing liquid.

3. 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.

4. Using the wash bottle, spray a steady stream of the washing liquid on the surface of the tank wall, about 3 ft. (1m) above the funnel, with the wash bottle held about 18 in. (0.5m) away from the wall.  Allow the wash liquid to run down the wall into the funnel and into the sample bottle.

5. Continue spraying until about 50 ml of wash liquid has been used.

6. Repeat steps c through e until a sufficient quantity of wall washing liquid has been received into the sample bottle for the entire tank.  Samples must also be taken from horizontal pipelines, large baffles, dividers and superstructures.

7. Rinse the inside of the bottle cap with a small amount of wash liquid and place securely onto the bottle.

8. Prepare a blank sample (an unused portion of the wash liquid before it was used for wall washing).

9. Tag each wall wash sample and the blank sample immediately to avoid losing the identity of the samples.

10. Submit to the laboratory for required analysis

11. Wall wash reports should specify where each wash sample was taken in the tank.

BLOTTER WALL WASH PROCEDURE

It may be noted that since filter papers are not consistent in chemical composition, the blotter wall wash procedure should be used only when it is not practical to use the funnel wall wash procedure.

1. Put on plastic gloves prior to starting the testing.

2. Rinse wide-mouth sample bottle with a small amount of wash liquid.

3. Hold a piece of laboratory filter paper against the surface of the wall a few inches above the floor.  Use the laboratory wash bottle to spray about 50 ml of wash liquid onto the test section, about 3 ft. (1 m) above the floor, in a stream about 4 in. (0.1 m) wide.  Allow the wash liquid to run down the wall and be absorbed by the filter paper being held near the floor.  Do not rub or wipe the filter paper on the tank wall.

It may be noted that clean plastic gloves, forceps, or tweezers should be used to handle filter papers.

4. As the test papers are saturated, carefully fold and place them in the wide-mouth bottle.

CAUTION: Perspiration will contaminate the samples.  Do not permit perspiration to drop into the sample bottle or onto the filter papers.

5. If required, wash the tank bottom by placing a filter paper on a spot wetted with the wash liquid.  Then lift the filter paper carefully, fold it, and place into the wide-mouth bottle.  Do not take tank bottom samples where there has been foot traffic.

6. Rinse the inside of the plastic cap with a small amount of wash liquid and cap the bottle containing the wall wash filter papers.

It may be noted that the following steps may be performed after leaving the tank.

7. Prepare a blank sample as follows: 

• Rinse a wide-mouth bottle with a small amount of the wash liquid.

• Take an unused filter paper from the box and place it into the rinsed wide- mouth bottle.

• Add wash liquid from the wash liquid spray bottle.

• Rinse the plastic cap with wash liquid and securely cap the bottle containing the blank sample and filter paper.

8. Immediately identify both samples with appropriate sample tags and deliver promptly to the laboratory.

Sections of text taken from API - MPMS Chapter 17 Marine Measurement