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APIPowerchem
  

Last updated: 26.04.2018
  

Contents Issue 02 (2018)

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Investigation of the Efficiency of Film Forming Amines for System Component Corrosion Protection by the Inhibition of the Electrocatalytic Reaction of N,N-diethyl-p-phenylene-diamine with Chloropentaaminecobalt(III) Complex
Ute Ramminger, Ulrich Nickel, and Jörg Fandrich


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PPChem_2018_20_02_72-79.pdf

The application of film forming amines (FFAs) as an effective protection against general and selective corrosion phenomena has been proven as a successful water chemistry improvement method for water-steam cycles of pressurized water reactors (PWRs). Since 2011 Framatome GmbH (formerly AREVA GmbH) has performed ten FFA applications worldwide as a regular complement to the applied secondary side water chemistry treatment with the main goal of establishing a hydrophobic and protective film on all inner surfaces of the water-steam cycle which are exposed to corrosion attack.

So far well-known practices have been applied to evaluate the effectiveness of the film formation on metal and metal oxide layers, for example hydrophobicity testing and contact angle measurements. Electrochemical methods have been investigated with respect to their applicability to provide additional information on the homogeneity of FFA films on metal and metal oxide surfaces and thus their ability as corrosion inhibitors.

This paper describes a method to determine qualitatively the completeness and homogeneity of the film formation on FFA pretreated corrosion specimens by the inhibition of the electrocatalytic reaction of a N,N-dialkylated p-phenylenediamine with chloropentaaminecobalt(III).

PowerPlant Chemistry 2018, 20(2), 72–79
Case Studies and Findings on High-Temperature Oxidation in Supercritical/Ultra-Supercritical Boilers
Zhi-gang Li, Yu-bo Zhang, and Bing-yin Yao


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PPChem_2018_20_02_82-89.pdf

After investigating and analyzing several cases where large areas of the oxide layer exfoliated from the steam-touched surfaces of tubes in the high-temperature areas in supercritical and ultra-supercritical boilers in 2013, this paper sorts out factors affecting the growth of oxide layers in high-temperature areas of the boiler and exfoliation of these oxide layers from the steam-touched tube surfaces.

The results indicate that, firstly, stainless steel (TP347H) tubes with coarse grain size show a faster rate of oxide growth at high temperatures; secondly, early oxide layer exfoliation tends to appear in boilers with steam temperatures lower than the design value; thirdly, alarm values for the tube wall temperature from boiler manufacturers cannot effectively prevent oxide growth; and finally, there is no direct relationship between oxygenated treatment of the boiler feedwater and the exfoliation of large areas of the oxide layer.

PowerPlant Chemistry 2018, 20(2), 82–89
Chloride Contamination of the Water/Steam Cycle in Power Plants: Part VI. Confirmation of Chlorinated Vapor Ingress Hypothesis by Regression Model Prediction of Boiler Chloride to Sodium Ratios
Emmanuel K. Quagraine


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PPChem_2018_20_02_94-112.pdf

This paper builds on earlier hypotheses that chlorinated compounds with significant vapor pressures can ingress in gaseous/vapor forms into the condenser shell through weak seals and/or porous de-alloyed brass tubesheet at tube-to-tubesheet joints. The issue was addressed by tubesheet hole repairs with titanium epoxy and plastic epoxy application on all tubesheet faces.

The paper consists of two parts: 1) a cursory review of the literature on oxidative degradation of polymers and how it can initiate leak paths for gas, vapor, and liquid permeation; and 2) derivations and validations of predictive models to account for variations in boiler chloride to sodium ratios (BCSRs) at various stages of operation after the epoxy resin repairs and condenser re-tubing. The models (developed using multiple regression analysis) explained the variations well and confirmed the hypotheses of chlorinated compound vapor ingress alongside water seepage into the condenser shell from the cooling water (CW).

Earlier (the first 1½ years) in operation, vapor diffusion flux of chloramines, being favored by temperature increase, was implicated as the dominant process of chlorine contaminant transfer from the CW into the water/steam cycle, resulting in higher BCSRs. However, this mode of transport was sporadic in these early stages. At later stages of operation, after an episode that seemed to have caused damage to the titanium epoxy and tube-to-tubesheet joints, the chloride cycling became more persistent. The derived model at this stage however showed (by p-statistics) a weak influence of temperature. It also suggested: a) a blend of both diffusive and convective flows of chloramines as transfer processes promoting higher BCSRs, and b) convective flux of liquid (aqueous CW) contributing relatively higher sodium (than chloride), thereby lowering BCSRs. Through all stages, CW free chlorine was found as the main influencing factor on the convective flux of aqueous CW into the water/steam cycle.

PowerPlant Chemistry 2018, 20(2), 94–112
  
  
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