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Figure 1 – SilcoNert 420 regulator.


This ensures minimal potential off-gassing, less potential to absorb com- ponents and compatibility with PTFE or PCTFE.


The choice of materials was once limited to 316L stainless steel. However, with increasingly lower concentrations of reactive materials requiring accurate analysis and the greater reactivity of these compounds—such as NOx and SO2 below 10 ppm, H2S and TRS (COS and CS2), as well as ppb-level volatile organic compounds (VOCs)—stainless steel is no longer sufficiently inert or nonreactive. SilcoNert 420 pressure-control devices from CONCOA (Virginia Beach, Va.) (Figure 1) have specially treated 316L stainless steel base materials with a layer of amorphous silicon providing a surface finish that is essentially an Ra


(roughness average ) of


0.1 with the inertness of pure silicon. Developed by SilcoTek (Bellefonte, Penn.), the chemical vapor deposition (CVD) process used in the pressure- control devices deeply embeds the silicone into the stainless base material and becomes the wetted surface bound to the actual base material, not a mere coating. The blue coloration on the wetted surface materials is the specific wavelength of light reflecting back through the silicon surface, much like a prism.


When analyzing multiple-component sulfur components, exposure to even bare 316L stainless steel can cause sulfur reduction reactions that transform one component into another. It can also lead to desorption of previous calibration constituents, give false readings and eliminate the absorption of NOx and SO2 concentrations below 10 ppm and ppb-level VOC standards; though the concentrations are small, they may result in calibration inaccuracy.


The extreme inertness of SilcoNert 1020 or similar treatments eliminates reactions, and calibration is 10 times faster than when materials are untreated. This reduces calibration gas usage and ensures accuracy. A 0.5-ppm variation in a 5-ppm mixture results in an inaccuracy of 10%. Figure 2 shows the improvement in calibration time using SilcoNert 1020 versus bare stainless steel. Mixtures that can benefit from SilcoNert 1020 are shown in Table 1.


AMERICAN LABORATORY 29


Table 2 – Differences in corrosion resistance among SilcoNert 1020, Hastelloy C22 and bare 316L stainless steel


Figure 2 – The extreme inertness of the SilcoNert 1020 eliminates reac- tions and hastens calibration times over untreated materials, as shown in comparison with bare stainless steel.


Table 1 – Concentrations of gas mixtures benefiting from the SilcoNert 1020 process


The high concentration of H2S in mixtures used for refinery flare mea- surement can be thousands of parts per million, which means they are extremely toxic. At such a high concentration, the presence of moisture can cause extreme corrosion effects. Measures must be taken both to protect operators from exposure and the pressure control devices from corrosion. Table 2 compares the corrosion resistance of SilcoNert 1020, Hastelloy C22 and bare 316L stainless steel.


The device shown in Figure 3 purges dry nitrogen through the system prior to introducing the high-concentration H2S mixture to reduce corrosion


APRIL 2016


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