Low-temperature corrosion damage and repair of boiler bottom panel tubes

Abstract

The method used for repairing of the bottom panel of hot water boiler of 30 MW power, manufactured by Remming (a part of the 'Valjevo' Heating Plant) is presented in this paper along with the reasons why damage has occurred. The damage appeared on bottom panel as a consequence of service conditions to which the boiler was subjected. It has resulted in the thinning of tube walls in the bottom panel. Low-temperature has been determined as the cause of the tube damage, i.e. due to the presence of sulphuric acid. For the purpose of damage analysis and proper selection of the repair welding technology, the first tube wall measurements were performed in the boiler bottom panel. Upon determining the necessary repairs, and due to damages not originally included, the wall thickness tests are repeated and microstructural analysis by metallographic replica testing (for one tube) is performed. No major microstructural defects typically caused by exploitation conditions have been detected on the examined screen tube surface. The repair welding procedure which involved replacing of the bottom panel is also shown, along with suggestions for further damage prevention. Repair welding is performed using MAG welding procedure, combined with gas welding.