We recently completed a contract to supply duplex stainless steel for use in a nuclear power station, meeting a specification that required the alloy to be free of both silver and antimony.
Duplex stainless steels are commonly specified for water treatment, desalination and distribution, thanks to their improved corrosion performance over more standard 3-series stainless steels. We supply a number of leading manufacturers who produce pumps, valves and fittings from forged bar.
The final application here was shafts to be deployed in a nuclear setting, most likely pump components for water cooling circuits. Because of the very specific end use, we first had to confirm the absence of silver and antimony from the alloy. Neither is a deliberate addition to duplex stainless steel (UNS S32205 / S31803 / F51 / F60 / Sanmac 2205 / 1.4462), but both are widely used in electronic equipment that could contaminate steel scrap. Silver is used as a conductor in printed electronics, while antimony is increasingly used in batteries, low-friction metals and ball-bearings.
Both elements can be activated and become radioactive. Small particles worn from a shaft, impeller or bearing would circulate through the reactor close to the neutron flux, then move throughout the water circuit, contaminating far more equipment than might otherwise be expected.
Additional testing
Although we operate our own PMI guns (handheld X-ray fluorescence analysers), the customer specification required test pieces to be analysed in an accredited laboratory, to confirm these trace elements were below the very low levels specified. Neither element has any particular effect on the mechanical properties or corrosion resistance of duplex stainless steel at low levels. Following successful testing, the bars were released to the customer for machining.
We maintain comprehensive procurement standards and demand complete test reports from our mill partners. On occasion, the sensitive nature of an application calls for supplementary testing. We routinely carry out additional ultrasonic inspection in-house, and also send samples out for more sensitive analysis of composition, additional mechanical tests (such as high-temperature tensile and low-temperature impact tests) and extra corrosion tests. All of these are managed within our quality system, with customer specifications retained for future review. Where you need more than the supply of alloy bar from stock, our experienced team and in-house metallurgists are here to help.