Failure analysis of an economizer tube sheet & its cover due to corrosionand imperfection

The boiler's economizer was found to be inefficient. Corrosion is suspected to be the source of the economizer's pressure reduction. The examinations included visual inspection, stereomicroscope, metallography, elemental microanalysis by EDS, and chemical composition analysis. The economizer failed due to a weld crater caused by improper welding, which induced residual welding stress. The slight sulfur content of the condensed or flue gas that causes rusting on the economizer's outer cover is not considered a severe failure issue. Material SUS304 stainless steel is the right selection for economizer materials.

STUDY KEGAGALAN AKIBAT KOROSI PADA PIPA ECONOMIZER

Failure analysis to the economizer tube of boiler with operation pressure ± 190 bar, in holding time 6 hour have been investigated. The economizer tube is carbon steel, ASTM A210 Grade C, outside diameter ± 51 mm and thickness ± 6 mm. The investigation cause of failure from the economizer tube included : chemical composition and metallography analysis, visual examination at outer and inner fire side, measuring thickness and densities of the scale at inner fire side and wall side, chemical composition analysis of the at surface crust the economizer tube. From the results of visual investigation to both outer and inner fire side of the economizer tube shown that at fire side occur decrease thickness of the wall tube, with minimum thickness are 1.37 mm and 2,50 mm, respectively. Those caused by erosion corrosion result from effect the fly ash. Beside that, at inner fire side of the economizer tube occur light pitting corrosion result by oxygen corrosion.Keywords : Economizer tube, boiler, fire side, fly ash, erosion corrosion, pitting corrosion, scale, oxygen

Mechanism Analysis of a Boiler Economizer Corrosion

Reasons for boiler economizer tube corrosion were discussed based on results of macroscopic inspection, metallurgical microstructure examination, SEM and EDS fracture analysis. Results showed that the tube corrosion was due to sulfur corrosion that resulted in matrix exposure and led to further oxygen corrosion.