Adaptation of the Method of Polarization Resistance to the Evaluation of Corrosion Rate in the Formation of Deposit of D
- PDF / 381,123 Bytes
- 6 Pages / 594 x 792 pts Page_size
- 36 Downloads / 174 Views
ADAPTATION OF THE METHOD OF POLARIZATION RESISTANCE TO THE EVALUATION OF CORROSION RATE IN THE FORMATION OF DEPOSIT OF DIFFICULTLY DISSOLVED IRON OXIDES G. S. Vasyliev
UDC 620.193
We study the possibilities of application of the method of polarization resistance to the evaluation of corrosion rate in tap water. Under the analyzed conditions, iron oxyhydroxides β - and γ -FeOOH are
formed on the surface of the gauge. If the external polarization is applied, then oxyhydroxides participate in electrochemical transformations, which leads to the overestimation of the measured values of corrosion rate. The effects of the water hardness, temperature, and flow rate on the composition, structure, and electrochemical activity of corrosion products are analyzed. It is shown that, in cold tap water, the presence of corrosion products leads to a 3.5-times overestimation of the results. In hot water, the surface is mainly covered with iron-oxide compounds, which do not participate in the electrochemical transformations. Hence, the results are overestimated by a factor of at most 1.6 times. As the flow rate of hot water increases to 0.45 m/sec, the influence of corrosion products becomes weaker. To guarantee the agreement between the weight-loss and electrochemical techniques, it is proposed to decrease the recalculation coefficient B in Stern’s equation down to 8 mV for cold tap water and to 14 mV for hot tap water if the flow rates do not exceed 0.3 m/sec.
Keywords: low-carbon steel, polarization resistance, corrosion monitoring, akageneite, lepidocrocite, goethite, calcite.
Introduction The transportation of tap water and heat carriers in heating systems is often realized through pipelines made of low-carbon steels without internal zinc coatings. In neutral aqueous media, the process of corrosion of steel is accompanied by oxygen depolarization whose high rates lead to the deterioration of the quality of drinking water, significantly decrease the lifetime of the pipes [1], and results in the appearance of emergency situations [2]. To guarantee the possibility of safe operation of pipeline networks, it is necessary to perform continuous monitoring of the corrosion rate in the metal, which enables one to apply anticorrosion measures at the proper time. As a simple efficient method for the determination of the instantaneous corrosion rate K corr of the metal, we can mention the method of polarization resistance (MPR) based on the inverse proportionality of the corrosion current and the polarization resistance of the metal [3–6]:
icorr =
B . RP
For waters with pH 6–9, the overestimated values of the corrosion rate are frequently measured by MPR as compared with those determined by the weight-loss method (WLM) [7]. The cause for the difference of results “Igor Sikorsky Kiev Polytechnical Institute” Ukrainian National Technical University, Kiev, Ukraine; e-mail: [email protected]. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 55, No. 1, pp. 119–124, January–February, 2019. Original article submitted November 20,
Data Loading...
