Oxidation Characteristics of Porous Nickel Low-Chromium Binary Alloys in Air at 1273K for 100 h

The oxidation behavior of porous nickel low-chromium alloys containing up to 1 wt%Cr oxidized in air at 1273K for 100 h was investigated. Porous-duplex scale was formed on the 1 wt%Cr pellets while single oxide layers were obtained on the 0.25 and 0.5 wt%Cr pellets. Cavities were formed underneath the NiO scales and also between both layers formed on the oxidized 1 wt%Cr pellets. Accumulation of NiCr2O4was noticed at the oxide/ metal interface. The growth mechanism of the scales was explained on the basis of molecular oxygen inward migration.

Void Formation at the Interface of the Duplex Scale Formed on Fe-5Cr Alloy at 773 K

Void formation in a duplex scale formed on Fe-5Cr alloy at 773 K has been elucidated by oxygen chemical potential distribution, the flux of oxide ion and its divergence. The calculation predicts that voids preferentially form at the interface between inner and outer scales in the low oxygen partial pressure in which the predominant defect of iron is interstitial ion. The flux of oxide ion changes discontinuously at this interface and the divergence of the flux gives voids. Calculated volume fraction of voids at this interface is in good agreement with that has been measured.

Effects of Oxygenated Treatment on Exfoliation of Duplex Scale in Steam Path

Oxygenated treatment (OT) is an excellent choice for supercritical (SC) and ultrasupercritical (USC) fossil units to alleviate flow accelerated corrosion (FAC). Unfortunately, many large utility boilers had suffered series bursts caused by exfoliation of duplex scale in steam path after adopting OT measures. It has been hopeful always about that OT should be independent of scale exfoliation, but many tube failures in fossil power plants go by contraries. Ecocide hypothesis which has been verified reveals the secret of the causal relationship between OT and exfoliation. Ecocide is the abbreviation of “Evaporating Consumption of Chromium Induced Disastrous Exfoliation” and that’s the essence of our hypothesis. We can explain the mechanism of exfoliation of duplex scale in oxygenated steam path with the help of ecocide hypothesis, and furthermore we can predict the risk of OT. Concerned with operating utility boilers which intend to apply OT, the longer the operating history, the greater the risk; the higher the concentration of oxygen in steam, the greater the risk; the higher the parameters of steam, the greater the risk. To avoid the risk of exfoliation, OT should be synchronously scheduled in commissioning.

A study of the mechanism of corrosion of some ferritic steels in high-pressure carbon dioxide with the aid of oxygen-18 as a tracer - III. Fe-9% Cr-1 % Mo-0.26 % Si

The oxidation mechanism of a commercial Fe-9% Cr steel in high-pressure (4.1 MPa) carbon dioxide at 913 K have been investigated with the aid of charged-particle nuclear techniques and 18 O as a tracer. Duplex and multilayered oxide‒scales were examined. Both types of scale grew at the oxide‒gas interface. Substantial growth occurred in the inner half of the inner layer on the specimen with the duplex scale; very little growth occurred within the inner layer of the multilayered scale. A possible oxidation sequence which could account for the 18 O distributions is proposed.