It is necessary to determine the purity of sulfur hexafluoride (SF6) gas through an integrated system of international standards and advanced detection technology. According to IEC 60376 standards, the purity of industrial grade SF6 must be ≥99.9%, moisture ≤5ppm, acidic components (e.g., HF) ≤0.3ppm. Taking the international market in 2023 as a case, traders selling compliant sulfur hexafluoride gas for sale are required to provide gas chromatochromatomass spectrometry (GC-MS) test reports, with one test around 500-800 US dollars, 4-6 hours, and with an error range of ±0.02%. For example, the suppliers are requested to offer test results of 10 independent samples for each batch of SF6 gas by Schneider Electric, offer a standard deviation of concentration of impurities less than 0.01ppm, and test the conformity rate of a batch ≥99.5% using Monte Carlo simulation. After the test is carried out and finds that the moisture is beyond the standard (e.g., an Indian supplier batch’s moisture content reaches 8ppm), then the company can risk equipment insulation failure, which causes a 30% increase in GIS switchgear failure rate, and the maintenance cost is more than $100,000 / time.
Third-party certification labs are an important method of ensuring purity. 90% of the manufacturers of high-voltage equipment around the globe rely on institutions such as UL Solutions or SGS providing the IEC 62271-200 compatibility report, and one certification costs a rate that absorbs 3% to 5% of the purchasing budget, the cycle is approximately 7 days. For example, TUV Rheinland of Germany designed a rapid detection system based on Fourier infrared spectroscopy (FTIR), which is capable of performing SF6 purity synchronous analysis, SF4 (toxic by-products) and air mixture within 20 minutes with 99.99% detection accuracy and can save 15% of the detection time cost for European power grid companies in 2023. State Grid of China requires its suppliers to supply quarterly SF6 gas lifecycle traceability data including production date, charging pressure (commonly 20MPa), transport temperature (-20°C to 40°C range), and authenticate data through a blockchain platform. 12 batches of dirty gas (only 98.5% purity) were found and intercepted in 2022, amounting to more than 8 million yuan.
The rapid on-site inspection technology can increase the verification efficiency. The portable SF6 purity meter (for example, GA-45 by WIKA, Switzerland) is able to indicate gas purity, density (reference value 6.14g/L) and decomposition concentration in 5 minutes with a ±0.05% error of detection, unit cost of around $12,000, and maintenance fee of 8% of equipment cost annually. In 2022, one Brazilian substation used the instrument to find out that a sale batch of sulfur hexafluoride gas contained the content of SO2 to 1.2ppm (safe limit is 0.5ppm) and canceled at once the purchase contract to avoid potential shutdown losses of about $500,000. Apart from that, laser spectroscopy technology (such as the NDIR sensor) can also monitor real-time gas purity fluctuations by analyzing the absorption strength of SF6 at 10.6μm band, and ABB Group in the United States incorporated it into smart GIS equipment in 2023, allowing the operation personnel to obtain purity data every 15 minutes, with a 60% improvement in the speed of fault warning response.
Supply chain traceability and production auditing are the rationale for purity assurance. SF6 producers are required by EU F-gas regulation to disclose publically the source of feedstock uranium hexafluoride (UF6) and its nuclide abundance (e.g., U-235≤0.7%) to conform to IAEA requirements. In 2023 Linde Group was penalized €2.5 million for failing to disclose the Russian origin of UF6 in a shipment of SF6 gas, and its market share fell by 5%. Companies can also evaluate the production process through supplier factory audits (such as ISO 9001 certification), e.g., ensuring the accuracy of the temperature control of the fluorine (F2) and sulfur reactor (target value 500°C±2°C), the frequency of replacement of the adsorbent in the gas purification tower (every 100 tons of production), and the quality of the product. Results of helium gas spectrum leak detection in the filled container (leakage rate ≤1×10^-9 mbar·L/s) were obtained as well. A typical example is Japan Toshiba’s checking of a Vietnamese supplier found its aging of purification equipment, resulting in SF6 O2 content to 0.15% (norm ≤0.05%), eventually stopped cooperation and switched to South Korean manufacturers, procurement prices increased by 8%, but qualified rate purity increased to 99.8%.
Purity checking in circular economy mode has special considerations. The recovered SF6 gas should be dried, filtered, and broken down by catalysis, and the recovery rate of purity is usually 92-97%. For example, Norway’s mobile recovery unit NEL Hydrogen can increase the SF6 purity of the exhaust gas from 85% to 99.5% on site at a treatment cost of around $30 /kg, 40% cheaper than newly purchased gas, but with the price of additional detection of oil content (≤1mg/kg) and particulate contamination (≤1000 units/cubic feet) in the recovered gas. The SF6 closed-loop management system set up by China Pinggao Electric in 2023, by the online humidity sensor (accuracy ±0.1ppm) and regular dielectric strength test (every 6 months, breakdown voltage ≥75kV/cm), the insulation performance of recycled gas is kept at 98% of that of new gas, saving the annual procurement cost of over 20 million yuan. With SF6 being covered under the EU Carbon Border Tax (CBAM) accounting, purity testing would also have to be associated with carbon footprint information (235,000 tons of CO2 equivalent per ton of SF6), pushing detection technology towards high-precision and full-parameter integration.