It can be problematical to take all level samples reliably as it is difficult to remove the stopper at the bottom of the tank. This may cause the sampler to insert the cork too loosely, so that it falls out of the bottle before reaching the bottom, an event that may remain undetected and ruin the sample. Another problem can occur if the sampler fails to begin raising the bottle as soon as the stopper is out. The sample will then contain too much product from the lower part of the tank. For these reasons, an all-level sample is not recommended. 2.3.2 Running Sample A running sample is obtained by lowering an open (unstoppered) device to the bottom of the bottom of the outlet suction level, but always above any free water, and returning it to the top of the product at a uniform rate such that the sampling device is between 70% and 85% full when withdrawn from the product or discarded. Flow restrictors are used if the bottle cannot be moved through the liquid rapidly enough to achieve this result. 2.3.3 Spot Samples Spot samples are those samples taken from a specific location in a tank, (refer to the diagram on the following page), or from a pipeline.
Spot samples are taken by lowering a stoppered bottle to a designated point in the tank, removing the stopper with a sharp jerk, and allowing the bottle to fill completely before withdrawing it. After removing the bottle from the tank, product is poured from the bottle, so it is around full before closing. Spot samples can be taken from any point in the tank; however, API MPMS Chapter 8.1 defines certain specific points where spot samples are routinely taken. These include: TOP: Six inches below the upper surface of the liquid. UPPER: Middle of the upper third of the liquid. MIDDLE: Middle of the liquid. LOWER: Middle of the lower third of the liquid. BOTTOM: Bottom surface of the tank, sometimes called the Dead Bottom. 3", 6", etc: Sample taken a specified distance from the bottom of the tank, usually using a Bacon bomb with an extension rod.
2.3 Types of Samples s What samples should be taken? This is a key critical item. This information is usually provided to us in the inspection nomination and this information is passed onto you, the inspector, on your job instruction form. It is normal to take multiple samples on a product transfer. For example, typical sampling instructions would be to take upper, middle and lower samples from each shore tank; a spot sample from the shore pipeline at start up and a running sample out of each barge tank. 2.3.1 All Levels Sample An all-levels sample is taken by lowering the stoppered device to the bottom of the outlet suction level, but always above any free water, then opening the sampler and raising it at a uniform rate such as it is between 70% and 85% full when withdrawn form the product . For light products or deep tanks, a restricted opening may be necessary to avoid filling the bottle. No product should be poured from the bottle before closing. If the bottle is more than 85% full the sample should be discarded, and the sampling repeated.
26
Made with FlippingBook Digital Publishing Software