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Water wall tubes from boiler operating for 14 years were subject to repeated failures ranging from pinholes to cracks and ruptures. A failure analysis on a received tube was carried out including destructive and non-destructive testing.
Water wall tubes from boiler operating since 14 years were subject to repeated failures ranging from pinholes to cracks and ruptures. A failure analysis on received tube was carried out including destructive and non-destructive testing. Feedwater, drum water and live steam qualities were evaluated based on the data provided by the plant authority. The results obtained through this study indicate a mechanism of caustic gouging inducing hydrogen embrittlement. The root causes determined were improper carryover control and waterline creation by low flow and/or high blow down rate. Therefore, it was recommended to conduct a total inspection of the boiler to determine the extent of the damage. As preventive maintenance, a more strict control of the carryover is necessary through the monitoring of sodium/phosphate ratio, reduction of oxygen up to the permissible level, fixation of the chemical boiler treatment dosing problems.Key words: Boiler tubes. Caustic gouging, hydrogen embrittlement, waterlines, carryover, under-deposit corrosion.
Under-deposit corrosion is a common mode of failure in boiler tubes. Mechanisms include phosphate attack, caustic gouging, hydrogen damage, and wall thinning due to metal loss. Many aspects of these mechanisms and their mitigation are well-understood, while certain specific details remain uncertain or subject to controversy.
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The purpose of this study is to investigate the effect of amount of oxygen on corrosion rate of steam loop. Consequently, to eliminate failure, more effective steam quality monitoring concept is recommended.
This paper pertains to a study of an API 5L X-60, Carbon steel, injection water pipeline, which failed prematurely in 4 years after commissioning due to under-deposit corrosion. A detailed study was carried out to investigate the failure causes.