Phosphate attack as caustic corrosion in high-pressure boiler tubes

Journal Article · Mon Mar 01 04:00:00 EST 1999 · Materials Performance

OSTI ID:6441086

Romero, M.F. de; Perez, O; Navarro, A ^[1]

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1. Univ. of Zulia (Venezuela)

Some boiler-tube failures attributed to caustic gouging actually have been caused by reaction of sodium phosphate species with boiler tube steel, boiler tube oxides, or both. This is referred to as phosphate corrosion. This produces unique wastage morphologies and characteristic corrosion products of NaFePO[sub 4]. Caustic corrosion produces well-defined depressions or gouges, as does phosphate attack at lower sodium-to-phosphate ratios. An example is a 1,300 psi (9 MPa) and 930 F (500 C) boiler. The boiler tubes, made of ASTM A 178 GrC, failed by precipitation of the phosphates used for the chemical treatment of the boiler water, coupled with contamination of the condensate with alkaline salts. Precipitation was caused by inadequate heat flow inducing a departure from nucleate boiling (DNB), steam blanketing, and deposits.

• OSTI ID: 6441086
• Journal Information: Materials Performance, Journal Name: Materials Performance Vol. 38:3; ISSN 0094-1492; ISSN MTPFBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
42 ENGINEERING
421000 -- Engineering-- Combustion Systems
ALLOYS
BOILERS
CHEMICAL REACTIONS
CORROSION
DATA
FEEDWATER
HYDROGEN COMPOUNDS
INFORMATION
IRON ALLOYS
IRON BASE ALLOYS
OXYGEN COMPOUNDS
PHOSPHATES
PHOSPHORUS COMPOUNDS
PRECIPITATION
SEPARATION PROCESSES
STEELS
TUBES
WATER