Sensitivity to trace elements
Duplex stainless steels for nuclear applications20th June 2019
Langley Alloys has recently completed a contract for the supply of duplex stainless steel, for application in a nuclear power station.
Duplex stainless steels are commonly specified for applications involved with water treatment, desalination and distribution. This is due to their improved corrosion performance compared with more standard 3-series stainless steels. Langley Alloys supplies a number of leading manufacturers who produce pumps, valves and fittings from forged bars.
Here, the final application is shafts that will be deployed within a nuclear application, most likely pump components for the water cooling circuits. Due to the very specific requirements of the final end use, we had to firstly confirm the absence of both silver and antimony from the alloy. Neither element are deliberate editions to duplex stainless steel (UNS S32205 / S31803 / F51 / F60 / Sanmac 2205 / 1.4462), but they are widely used in a variety of electronic equipment that could potentially contaminate steel scrap. For instance, silver is widely used as a conductor in printed electronics, whilst antimony is increasingly used in batteries, low-friction metals and also ball-bearings.
However, both elements can potentially be activated and become radioactive – for instance, small particles worn from a shaft, impeller or bearing would be circulated through the reactor close to the neutron flux. These potentially radioactive particles would then be circulated throughout the complete water circuit, resulting in far greater amounts of equipment being contaminated than might otherwise be expected.
Although we operate our own ‘PMI’ guns (handheld x-ray fluorescence analysers), the customer specification demanded that test pieces be analysed in an accredited laboratory. This is to ensure freedom of these trace lements to the very low levels specified. Neither element has any particular impact upon the mechanical properties or corrosion resistance of duplex stainless steel when present in low levels. Following successful testing of the bars, they were released to the customer for machining.
Langley Alloys maintains a series of comprehensive procurement standards, and demands complete test reports from our mill partners. However, there will be occasions where supplementary testing is required due to the sensitive nature of the final application. We routinely undertake additional ultrasonic inspection in-house, but also send out samples for more sensitive analysis of composition, additional mechanical tests (for instance high-temperature tensile tests, low temperature impact tests) and extra corrosion tests. All of these processes are robustly managed within our quality system, and customer specifications retained for future review. If you require more than just the supply of alloy bars from stock, our experienced team and in-house metallurgists are here to provide support. Please contact us today with your enquiries.
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