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Rapid Improves Analysis of Pipeline Deposits - Wednesday, February 18, 2009
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In gas transmission industry it is common to draw samples of liquid and solids from separators or traps. Properly identifying the nature of solids is important in assessing the overall condition and integrity of the pipeline system upstream of the sample point.
In the past operators and chemical company technicians would perform spot-tests using acid and magnets as an indication of the type of solid compound present. It is now believed these methods are misleading and completely incorrect. For example, the technician performing such spot-test might record an effervescence of the solid and record the presence of carbonates, iron carbonate or calcium carbonate.
However it is known that the iron sulfide solid Mackinawite is highly acid-soluble and reacts with hydrochloric acid to evolve hydrogen sulfide gas. Equally, the iron sulfide species pyrrhotite, troilite, marcasite, and pyrite are less reactive. So the bottomline here is that a spot-test failing to produce hydrogen sulfide does not guarantee that a solid corrosion product removed from a gas transmission line is free of sulfides.
Using a magnet to identify the solid leads to erroneous results. If a sample is found to be magnetic it is considered to be magnetite, but that doesn't consider that greigite is also magnetic and these two forms of iron sulfide are formed under completely different conditions.
Air contamination of samples can greatly alter the substance and create erroneous findings. Technicians with Rapid collect samples in pressure cylinders where the samples are kept in the same gas environment as the gas transmission line until it arrives at the testing laboratory. Once in the lab, analytical chemists draw samples out of the pressure cylinder and perform a range of analytical procedures immediately, thereby lessening the effect of oxygen on the sample.
Analyzing samples of corrosion products removed from natural gas transmission can provide useful information in determining the overall status of corrosion within the pipeline, proper analytical procedures insure that results are meaningful.
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