No abstract

The corrosion behavior of three stainless steels (316L, Alkrothal 720 and Kanthal-APM) in static LBE with oxygen concentration of 10-5 wt% at temperatures of 700°C for 230 hours and 800°C for 360 hours was studied. The steel surface morphology of the oxide scales formed was investigated by SEM, XRD and Raman spectroscopy and the cross-section and by SEM and EDX. A transitional inner-layer of Fe-Cr-Al oxides was found at the substrate interface and an Al-oxide outer layer on the Fe-Cr-Al alloys. Fast growing non-protective oxide scale with underlying dissolution was observed on the 316L alloy.

Diffusion bonding is a solid-state welding technique to join metallic and non-metallic materials. Due to geometrical considerations, fabrication and possible materials choices diffusion bonding was chosen here to support tube-to-tube sheet joints of large coil-wound heat exchangers (CWHE) made from 316L stainless steel. In contrast to traditional diffusion bonding where pressure is applied constantly during heat treatment, pressure is applied here initially prior to heat treatment using a commercial three roller tube expander. Processing parameters of this novel approach are presented in this study. Mechanical pull-out tests were conducted to evaluate if the manufactured joints are sufficiently bond to guarantee safe operation of the device. It was found that diffusion bonding followed tube expansion increases the pull-out force nearly threefold from a mean of 3.4 kN to 9.2 kN at which level the tube ruptures so that higher loads could not be measured. Tube-to-tube sheet joints fabricated using tube expansion and diffusion bonding met the engineering requirement, tube rupture against mechanical pull-out, set for this study.

No abstract

No abstract