This is necessary because the purity of many chemicals is so critical that impurities that are not even visible to the naked-eye can taint a cargo. Even the tank atmosphere can be sufficient to contaminate a cargo if it contains: Chlorides from a salt in the atmosphere,
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6.3 Field Tests It is common for a chemical inspector to perform basic or preliminary analytical testing in the field when loading or discharging a cargo. This is usually performed on wall-wash samples, first- foot or manifold samples and is typically limited to critical specifications such as color. It is important to understand the many tests that are performed in a laboratory and their significance to the handling of each particular grade. There are hundreds of different commercial grades of chemicals and petrochemicals. This necessitates a chemical inspector to refer to numerous technical reference publications regarding topics such as, compatibility, safety, and physical properties. 6.4 Tank Inspection Tank inspection for a petroleum cargo is frequently performed at deck level by measuring residues. Even for cargoes that require physical tank entry, such as gasoline and jet fuel, a visual inspection is usually sufficient. Physical tank entry is almost always required when inspecting a tank prior to loading a chemical cargo. Additionally, a chemical analysis of residues on the internal tank surfaces (wall-washing) is frequently requested.
While a chemical inspection is essentially the same as a petroleum products inspection, there are never- the-less many differences, and these differences can be significant because the emphasis and focus are driven by different factors. When comparing the two types of inspection, such elements as taking a level gauge and tank temperatures are basic to both. However, this cannot be said for other elements such as: Tank inspection. Sampling. Shore line condition. Calculations 6.2 Quality A petroleum inspection tends to focus its attention on quantity discrepancies. A chemical inspection, while still focused on quantity must be equally focused on quality. Therefore, a considerable amount of total survey time is spent on tank inspections, checking lines and pumps, taking and monitoring check-samples, reviewing records of previous cargoes, etc.
Moisture from humidity in the air, Oxygen, if the cargo is hygroscopic, Odor from a previous cargo, Or a combination of all the above.
6.5 Sampling The manual methods by which chemical samples are taken are similar to those used for petroleum cargoes; however, more quality control samples are taken with chemicals and extreme care must be taken to ensure that the equipment used is clean and does not contaminate the sample. For example, the sample cord should always be changed as residue from a previous cargo could find its way into the sample. It is generally preferable to use new glass bottles, that have been rinsed with product, for taking samples. In addition to ship and shore samples, shore line, manifold and first-foot samples are usually taken to ensure no quality degradation occurs during transfer.
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