Corrosion - Case Study No. 23: Carbonic Acid Attack of Steam Condensate Pipe

Given the right conditions, steam tubes can quickly turn into condensate tubes that are ripe for carbonic acid attack. To the left is a recovered section of a carbon steel steam tube from a large heating coil. Basically, the coil was not adequately designed for uniform flow across the vast array of tubes. There were stagnant regions within the coil where the low flow steam would condense, and collect as well. The pictures below and to the right show the interior of the tube. The redish color in the middle of the tube indicates the liquid-vapor phase interface region. The CO2 rich steam entered along the top and began to condense into beads. As more CO2 was introduced, the continually forming condensate droplets turned into carbonic acid. As the acid droplets rolled down the sidewall of the tube they etched the wall before entering the sitting pool of liquid at the bottom of the tube. This tube had a liquid level of almost a third. There wasn't any kind of steam velocity in this tube. The carbon steel tubes were upgraded to type 304 stainless steel.

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