How can oil and solids affect the measurement of hardness using an APA6000 analyzer?

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Document ID TE8092


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Published Date 07/28/2017
How can oil and solids affect the measurement of hardness using an APA6000 analyzer?
Considerations concerning oil and solids in a sample to be measured for hardness using the APA6000.

1.  Oil content < 3 ppm - probably will not be a problem in the analyzer.  The analyzer automatically cleans itself with an acid-surfactant solution once per day, and the frequency can be increased to as often as every four hours if necessary.   

2.  It is more likely that oil in the sample will be problematic outside the analyzer, coating and clogging filters.  The APA6000 uses a 0.5 um ceramic filter at its sample inlet, and I suspect this filter would clog quite quickly - perhaps lasting only a few days.  I suspect that the application might require removal of the ceramic filter element and substitution of a more robust external filter.  If this is necessary, then our Microfilter System may prove useful. 

3.  Depending on the size and abrasiveness of suspended solids, it is possible that a sample filter might not even be necessary.  I recommended this recently for a customer at a petroleum drilling site after numerous problems with clogging filters.  Though the solids in the sample would clog filters within a day, and their presence contributed visible turbidity to the sample, testing proved these were harmless to the analyzer and did not interfere significantly with sample measurement accuracy.  (The solids in this case were mostly tiny droplets of hydrocarbons and byproducts from bio-growth in the system; filters clogged so quickly due to formation of a coating of "slime".) 

4.  The analyzer is rated for sample temperature up to 50°C.  60°C is a little higher than spec, but I doubt any harm would result.  If sample temperature is likely to peak higher than 60°C, then a sample cooler will be required to prevent physical damage to the analyzer. 

5.  Measuring range 0.05-5.00 ppm.  Depending on the typical hardness level in the sample, a sample that is turbid or colored might affect measurement accuracy.  If sample will be typically above 1 ppm, then a random interference of +/- 0.1 ppm may be acceptable.  If hardness must be controlled at a much lower level (e.g. to protect RO membranes), then random interference of +/- 0.1 ppm could make a control limit of 0.200 ppm very difficult to maintain. 

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