Where is the appropriate place to take samples from a tank truck?
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We produce methyl acetate, and the moisture content of our product is generally kept at around 200 ppm. When sending samples for testing, we take samples by opening the lid at the top of the tank truck; the moisture levels in these samples meet the specified standards. However, one of our customers always takes samples from the discharge valve of the tank truck, and the moisture levels detected in those samples are always above the limit, sometimes reaching several thousand ppm. I would like to know what the appropriate location is for taking samples from a tank truck, and why does the moisture level be higher when samples are taken from the bottom? Thank you
We take two samples each, one from the top and the other from the discharge valve of the tank truck.
Methyl acetate has a density of 0.93, which is less than that of water.
For materials with a density lower than that of water, the moisture content in samples taken from the bottom will definitely be high. Generally, sampling is done in three stages: a sample is taken from the upper part, one from the middle part, and another from the bottom part, which are then mixed together to serve as the standard for analysis of that sample
Is there any standard for this, that is, a standard for sampling? Normally, the moisture content in our products is around 200 ppm; they are lighter than water. But the moisture level at the discharge port shouldn’t rise to several thousand ppm – that’s way too much. The tank trucks are also dry inside. We can only unload a little amount of material from the discharge port each time to reduce the moisture content, and then load in a little more to make up for it, so that the moisture level can be lowered.
It’s all water below, so of course the level is high; shake it together and then take a sample, haha
Has the possibility of contamination at the sampling port been ruled out? The lack of dust protection at the sampling port can easily lead to testing errors~~
Generally, the upper, middle, and lower parts are taken； If it has to be at the discharge port, then some material is taken at that discharge point and poured into the tank truck; this is called a transfer port, and it’s quite normal
The petroleum industry has a standard, GBT4756-2015, for manual sampling of petroleum liquids; this standard also specifies sampling from the top, middle, and bottom layers followed by comprehensive analysis. It is likely not applicable to the chemical industry, but it can still serve as a reference
Sampling can be done at multiple points; given the significant fluctuations in moisture levels, it is important to ensure thorough replacement of the fluid during sampling. Additionally, the sampling bottles must be stored properly to prevent contamination by moisture in the air.