7.4 Safety Requirements Never enter any tank without having received Confined Space Entry Training - Entrant Level; and, complying with the Operational Integrity requirements for confined space entry. Always refer to the SDS for the product you are to load and the wash liquid. Minimum personal protective equipment required is a hard hat, safety glasses, gloves, explosion- proof flashlight, respirator, safety shoes, gloves, respirator, and any additional P.P.E. that may be required by the client or directed by your supervisor. 7.4.1 Equipment Plastic gloves (for skin protection and to prevent chloride contamination of sample). Explosion proof flashlight. Laboratory wash bottle. Wall wash funnel. Wall wash sample collection bottles with poly seal caps (for Funnel Method). Wide mouth sample collection bottles with plastic lined caps (for Blotter or Filter Paper Method).
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7.3 Methods There are two methods for conducting a wall wash test; the funnel method and the filter-paper or blotter method. Both methods require the wash liquid (usually methanol) to be poured over an area of the tank's internal surface. The difference is in how the wash liquid is collected. In the funnel method, a funnel that has been cut to fit flat against the tank bulkhead is used to collect the sample. In the filter-paper or blotter method, filter paper is used to collect the sample. 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. Note: API MPMS Chapter 17 cautions, "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." However, we have had a number of clients who request us to use this method. When this situation occurs we should advise them of this caution when confirming the job nomination.
Wall washing is a technique that is used almost exclusively for, and prior to, loading a chemical cargo. The purity of some chemicals is such that even very small residues left on the internal structures of a tank can cause that product to become off-specification. These residues are not visible to the naked-eye and can be from previous cargoes, such as hydrocarbon, or, from tank cleaning, such as chlorides or cleaning chemicals. The wall wash test is a procedure for washing selected areas such as the interior bulkheads, tank bottoms and sumps of cargo tanks with an appropriate wash liquid; and, subsequently, testing the wash liquid for the presence of material which might contaminate the cargo to be loaded. 7.2 Standard Wall wash test procedures can be found in API MPMS Chapter 17, Section 8, "Guidelines for Pre- Loading Inspection of Marine Vessel Cargo Tanks and Their Cargo-handling Systems”.
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