Mechanical Failure Risk Management for In-Service CSP Nitrate Hot Tanks

The hot thermal energy storage tanks in many operating (Gen2) concentrating solar power plants are designed to contain molten nitrate solar salt at 565 Degrees Celsius and are constructed from 347H stainless steel (SS). From previous work, it is known that 347H SS weldments are potentially susceptible to stress-relaxation cracking (SRC), particularly in the heat-affected zone above 540 Degrees Celsius when no post-weld heat-treatment (PWHT) is performed. However, residual stresses can be reduced when weldments receive PWHT, while at the same time a crack-resistant microstructure is being generated. The overarching goal of this project was to optimize cost-effective, thickness-dependent, localized PWHT procedures and to investigate for feasible non-destructive evaluation (NDE) at commercial scale for hot tanks in Gen2 CSP using 347H SS.