Sulfur containing sediments influenced wear of superheater tubes
- Israel Electric Corp. Ltd., Haifa (Israel)
The failed superheater tube was investigated at the point of failure and at a distance of 25 cm. At both of the cross sections two layers of sediment were detected. The external one contains Na2SO4 and Na3VO3 in concentration relation 6.4:1 approximately. The internal layer that situated on the tube surface consisted of V2O3 mainly (about 70%) and sodium pyrosulfates Na2SO3{center_dot}xSO3. The tube surface was covered with usual passive oxides such as Cr2O3, Fe2CrO4, and magnetite. In the failed section the last layer contained iron and chromium sulfides. Thinning of the wall was detected in both sections, but it was more evident in the failed section. Thermodynamic and kinetic estimations of the results were carried out. The following failure mechanism was proposed: (1) at 460 C the pyrosulfate dissociates with SO3 emanation, during SO3 interaction with steel both passive oxides and iron sulfide are produced simultaneously, sulfides damage the passive (protective) film; (2) in vicinity of partition the temperature increases and the structure of steel is changed, SO3 penetration along grain boundaries is possible, and it leads to embrittlement of the steel through sulfidization; (3) the embrittled layer is stripped off by falling ash deposit and collapsed passive film, thinning of the tube is accelerated at such a region. So, sulfur containing sediment accelerates the wear of the tube. This acceleration is strong especially in the vicinity of the boiler walls.
- OSTI ID:
- 376089
- Report Number(s):
- CONF-960389-; TRN: IM9642%%177
- Resource Relation:
- Conference: National Association of Corrosion Engineers (NACE) annual corrosion conference and exposition: water and waste water industries, Denver, CO (United States), 24-29 Mar 1996; Other Information: PBD: 1996; Related Information: Is Part Of Corrosion/96 conference papers; PB: 6615 p.
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
FOSSIL-FUEL POWER PLANTS
BOILERS
SUPERHEATERS
IRON BASE ALLOYS
CORROSION
CHROMIUM ALLOYS
FAILURES
SODIUM SULFATES
VANADATES
SODIUM COMPOUNDS
IRON SULFIDES
GRAIN BOUNDARIES
OPTICAL MICROSCOPY
SCANNING ELECTRON MICROSCOPY
X-RAY SPECTROSCOPY
X-RAY DIFFRACTION
IRON OXIDES
CHROMIUM OXIDES
THERMODYNAMICS
KINETICS