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Severe Under-Deposit Corrosion Inducing Hydrogen Embrittlment in Water Wall Tubes

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.

Product Number: 51317--8889-SG
ISBN: 8889 2017 CP
Author: Abdelkader Meroufel
Publication Date: 2017
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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.

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.

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