Test plan for the selection of the ENRAF gauge wire material

The measurement of liquid levels is the primary method of early leak detection in some underground waste storage tanks at Hanford, as well as for the detection of intrusion of liquids into the tanks. The gauges used for many years for this purpose are no longer available and are rapidly failing. After extensive evaluation and testing, the ENRAF Series 854 level gauge was selected as the primary instrument for monitoring waste surface levels. The material for the wire from which the displacer of the gauge is suspended was selected to be type 316 stainless steel based upon its excellent corrosion resistance in Hanford tank wastes. After approximately 10 weeks of service, the displacer attached to the gauge installed in tank 241-S-106 separated from the wire. It was determined that the wire failure was due to chloride ion stress corrosion cracking of the 316 wire. Radiation induced breakdown of the polyvinyl chloride (PVC) riser liners is suspected to be the source of the chloride ions. The task team proposed short-term and long-term actions. The short-term actions included evaluating the source of the chloride ions, while continuing to monitor liquid levels. One of the long-term actions is the selection of a wire material that is compatible with the PVC liner and the tank waste environment. This document describes the test plan for the selection of one material, from the list of candidate materials, that is the most suitable material for use in the combined environment of the PVC liner and the tank waste. The candidate materials to be tested are Hastelloy C-22, Pt-10% Rh, Pt-20% Rh, and Pt-20% Ir