Search for a command to run...
This work focuses on the development of an in situ sensitization remediation heat treatment in Al-Mg alloy structural components retrieved from operating vessels, with emphasis on the influence of microstructure, residual stresses and operational history on the desensitization kinetics. Optimal conditions vary based on the above mentioned parameters for different vessels. Optimum conditions were identified as 280oC for 2 hours for Vessel I and 320oC for 2 hours for Vessel II in laboratory scale. The Degree of Sensitization was able to be reduced from 54-61 mg/cm2 and 97.60 mg/cm2 to below 10 mg/cm2. The minimum time required to achieve a measurable DoS reduction was 40 minutes for Vessel I (partial mitigation), while achieving DoS lower than 20mg/cm2 required at least 70 minutes for laboratory scale samples however in case of Vessel II 2 hours was the minimum time required. The experimental results demonstrated that indeed the initial microstructure, the residual stress state and the operational history critically influence the response of the remediation treatment. Metallography revealed disruption and coarsening of the intergranular β phase network with minimal grain growth consistent with diffusion controlled transformation. Discontinuous Precipitation reaction was detected in an intermediately sensitized specimen remediated to 21 mg/cm2, representing the first such observation in the Al-Mg system. It is stressed that large specimens from real vessels and not tiny lab scale specimens that are usually tested required considerably longer treatments, confirming that effective remediation demands tailored treatment conditions based on the individual structural and service characteristics.