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A simple modification in the engineering design may turn out to be of significant impact in the way systems perform and increase its functional reliability. This image presents a good example in which the blowdown drain system in a power plant was affected by severe flow-accelerated corrosion and fatigue-cracking. As a consequence, multiple fractures were found in many interconnections with the flash tank.

We run a computational simulation to better understand the nature of the fluid dynamics involved in the process and the results suggested the potential root-cause of the failure. Tilting 45º degrees all drain connections with regard to the main header would prevent the system from turbulences, flow divergences, vibrations and steam-hammer. All these process dysfunctionalities will ultimately affect the stability of the magnetite layer, leaving the system unprotected and subject to operational deterioration.

Heat-affected zone infiltration may be a potential cause of erosion/corrosion failures of carbon steel piping when exposed to a continuous stream of wet steam or feed water. The problem is associated with high-velocity and turbulences created by the presence of the welding penetration as a flow obstacle.

The deterioration is developed for two reasons:
1) The mechanical wear due to the increase of velocity (red color area) would abrade the welding;
2) The turbulences generated in the region downstream the welding (blue area) would affect the formation of the protective metal-oxide layer and erode the surface.
3) Localized turbulences may also contribute to release CO2 or other acid-forming anions contained in the water chemistry and develop weak acid attack (see microscope image)

As a result, carbon steel piping becomes vulnerable to general deterioration and wall thickness dissolution. Make sure to have a good field supervisor on board… and better welders!