Analysis of the tube-sheet cracking in slurry oil steam generators

• Tube-sheet cracking always occurred in the shortest tube–tube ligaments.
• All the cracks initiated near the expansion joints where stresses concentrated.
• Iron oxides distributed on the original fracture surfaces.
• This brittle fracture was SCC induced by cooling water rather than slurry oil.

Tube-sheet cracking is a severe problem in the oil refinery industry with the consequences of shortened service life and increased costs. In this study, the mechanisms of the tube-sheet cracking in slurry oil steam generators have been investigated using optical and scanning electron microscopy with energy dispersive spectrometry. It has been found that the cracks always occurred in the shortest tube–tube ligaments. All the cracks initiated near the expansion joints about 15 mm away from the oil-side surface where stress concentration existed. It was concluded that stress corrosion cracking occurred in the tube sheets due to the high-temperature (200–242 °C) and high-pressure (3.5 MPa) water, rather than the slurry oil containing elemental sulfur and chlorine.

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