O'Brien Selection Guide for Electropolished Tubing (click on the title to view the complete selection guide)
Electropolished Tube Selection for Analyzer Sample Systems - Selecting the optimum process tube for use in analyzer sample transport systems requires critical consideration of process conditions.
Selecting Tube Material
Consider the level of protection needed against corrosion, porosity, and adsorption as well as the size, wall thickness and metallurgy (or coating) of the tubing.
When using stainless steel as the transport tubing, adsorption and desorption will exhibit itself as a delay in detecting changes of trace amounts of component (especially moisture and sulfur compounds, H2S and SO2.) The structure of commercial stainless steel tubing is such that compounds may
be caught up in the "crevices" and not reach the analyzer.
Once the tube is saturated the levels will equalize relative to the process as long as the process composition, temperature and pressure remain constant. Any change in composition, temperature or pressure will cause compounds to be adsorbed at a different rate by the tube or released at different rates from the tube surface and create a false “spike” in the analyzer readings. As a result adsorption and desorption create inconsistent and unpredictable results. This is sometimes referred to as the "memory effect".
This problem can often be solved by the use of electropolished and/or SilcoNert coated tubing.
(click on the title to view the complete selection guide)