Corrosion Failure of a Distiller Pipe

A horizontal carbon steel distiller tube used to precipitate copper out of a solution containing ammonia, CO₂, and water failed while in service. Division rings were welded into the tube. The tube was installed in 1990; however, in 2022, abrasion resistant plates were installed after material loss was observed on the inside of the tube. Accelerated corrosion was observed approximately 4 years ago which has reduced the operating life of similar tubes from approximately 30 years to 7 years. The distiller tube section exhibited circumferential cracking and grooving.

Significant material loss was observed on the ID surface of the tube as well as heavy deposits. A wavy texture on the tube wall suggested turbulent flow leading to preferential abrasion of the deposits along one side of the division rings. The circumferential crack was located on the opposite side of the division ring from the erosion features. Fractographic evaluation of the circumferential crack revealed a flat fracture surface; however, heavy corrosion/surface deposits obscured and/or obliterated any meaningful fractographic features.

Metallurgical sections through and remote from the fracture revealed spheroidization of the pearlite and carbides at the ferrite grain boundaries, indicative of long term overheating. The tube ID at the fracture location showed heavy surface deposits. EDS of the deposits revealed high concentrations of copper as well as chlorine and sulfur.

Hardness testing of the tube showed a reduction in expected mechanical properties, consistent with the indications of long-term overheating.

The fracture mechanism of the tube was fatigue/corrosion fatigue; however, the underlying cause of failure was material loss from galvanic corrosion of the steel tube due to contact with copper deposits as well as potential chloride contamination of the solution.