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• High-turbulent fluid pressures led to an erosion-wear corrosion failure mechanism and anti-abrasive coating can be used to modify the tube surface. • Wet H2S environment and iron oxidation led to tube pitting, leading to stress cracking that can be mitigated using claddings. • Humid environment with high sulfateate compounds and tensile residual stresses caused crack propagation. Excess residual stresses can be reduced by heat treatment. 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 (H 2 S) 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. Additionally, 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. [ABSTRACT FROM AUTHOR]

Abstract: Pin-hole leakage was observed in a number of 90/10 cupronickel evaporator tubes of a chilling plant which was in service for about 6years. Chilled water is cooled from 12°C to 7°C which flows inside the evaporator tubes, while the OD side has LiBr environment. The failure investigation of the failed tubes revealed greenish/blackish uniform deposits together with some spots where localized thick deposits on the ID surfaces were present. Underdeposit corrosion beneath these thick deposits was the primary reason for failure of the tubes. Intergranular corrosion was also observed underneath the thick deposits. The ID surface of the failed tubes confirmed the presence of wide variety of deposits, e.g. carbonates, silicates, phosphates, and sulphur-bearing compounds. The stagnant conditions under the thick deposits alter the chemistry inside the crevices thus formed. The altered chemistry conditions caused rapid corrosion (and intergranular attack) on the cupronickel tubes. Remedial measures that may be undertaken to prevent future occurrence of the problem are addressed. [Copyright &y& Elsevier]

Abstract: The failure of 90/10 cupronickel heat exchanger tubes in hydrogen coolers were seen after few years in use. The tubes had river water flowing at a velocity of 2.5m/s. The shell side was exposed to hydrogen at a pressure of 3.5kg/cm2. The inlet and outlet temperature of the cooling water of the cooler are 37°C and 47°C, respectively. The failures were pin hole type with a thick layer of muck deposit on the inner side of the tube. The metallographic studies carried out for the tube showed a well annealed microstructure. The region near the pit showed attack along the grain boundaries with dislodging of the grains. The electron probe micro analysis (EPMA) studies revealed the denickelification near the pits. The energy dispersive spectroscopy (EDS) analysis of the pit showed the presence of copper chloride and also the variation in the copper and nickel concentration with respect to the unaffected regions of the tube. Microbial presence was detected in the water as well as the muck deposits in the tubes. The pin hole failure of the tube was a result of the combined action of the chloride as well as the deposits in the tube which gave a conducive environment for the microbial activity to flourish which has caused the propagation of the pit through intergranular corrosion. [Copyright &y& Elsevier]

Abstract: Failure analysis of cupronickel condenser tubes of a crude distillation unit of a petrochemical refinery has been conducted. Condenser tubes carrying sea water were found to undergo premature failure which was preceded by extensive overall thinning, formation of shallow channels, pits, etc., and greyish-black internal deposits in one of the units. In the other unit, the failure of tubes was noticed without any significant overall thinning and in the presence of adherent, hard and black-brown deposits. The studies indicated that the increased velocity of sea water as well as the deficiency of iron in the alloy had resulted in failure in one case whereas relatively low velocity of water associated with deposition of sludge and bio-fouling were the causes of failure in the other case. The failure of tubes could be controlled by maintaining the water velocity within a specified range, flushing the tubes with clean water, use of anti fouling paints, selecting a more appropriate composition of the cupronickel alloy, through control of sea water sulphur level, etc. [Copyright &y& Elsevier]