Abstract:
This study examined the premature failure of cupronickel (CuNi10Fe) tubes in a shell-and-tube
heat exchanger after five months of service. An investigation to identify the root cause of the
tube burst was carried out using macroscopic and microscopic inspection, chemical analysis, and
mechanical analysis. The optical microscopy (OM) and scanning electron microscopy (SEM)
evaluation revealed crack propagation characterized by pits and inclusions at the tube surface.
This was due to the diffusion of hydrogen ions into the material from the hydrogen sulfide (H2S)
rich geothermal environment. Furthermore, high tensile residual stresses of 172 MPa were
recorded in the failed tube, leading to stress cracking in hydrogen-containing material. Addi tionally, the high sulfide content in corroded water and condensate samples suggests that the
leading cause of tube rupture was through hydrogen embrittlement and sulfide stress cracking
mechanism in the presence of hydrogen sulfide. Therefore, the use of laser cladding to protect
tubes using functionally graded materials is recommended to mitigate degradation in aggressive
environments, through careful material selection and additional water treatment to eliminate the
contaminants.
