Measurement of Seawater Flow-Induced Erosion Rates for Iron Surfaces using Thin Layer Activation Technique

Abstract

Abstract. The laboratory-scale erosion-corrosion testing facility at BATAN's Center for Radioisotope and Radiopharmaceutical Technology (PTRR) in Serpong was employed to simulate flow-induced corrosion of iron surfaces. Surface loss rates were measured by a nuclear technique called thin layer activation (TLA) analysis. A 10-MeV proton beam generated from a typical CS-30 cyclotron was used to produce 56 Co radionuclide layers on iron surfaces via a 56Fe(p,n) 56 Co nuclear reaction. The labeled iron specimens were then exposed to circulating seawater simulated in BATAN's flow-induced corrosion test facility. The experimental results indicated that the TLA technique was able to measure a very low flow-induced erosion rate of 0.91±0.3 µm/hr. There was no significant difference in the measured surface loss rates between the remaining activity method and the concentration method. The iron surface loss in seawater was lower than that of the same material in HCl solution observed in earlier studies. Keywords:56 Co radionuclide; cyclotron; flow-induced corrosion; nuclear technique; thin layer activation (TLA). IntroductionThin layer activation (TLA) is a nuclear technique previously developed to help measure very low wear and erosion-corrosion rates of industrial components [1][2][3][4][5][6]. It involves target irradiation using a beam of charged particles such as protons, deuterons, He-3 and He-4 or neutrons to directly label the surface of interest (widely called a coupon) with a very thin layer containing radioactive isotopes (a few hundred µm thick). Following the target irradiation, the activated surface layer is exposed to a flowing corrosive fluid. This is eventually followed by measurement of its radioactivity ratio before and after erosion-corrosion takes place. The radioactivity loss is directly proportional to the surface loss and therefore its erosion-corrosion rate can be determined precisely [7]. In order to get information on the surface loss of the coupon specimen, a calibration curve, which represents the relationship between radioactivity ratio and surface loss, must first be prepared by means of either a stacked-foil or an abrasion method [8]. Also, theoretical calibration curves canSeawater Flow-Induced Erosion Rates for Iron using TLA 483 be calculated for a given projectile, beam current, energy, target geometry and irradiation time [8].Two methods have been developed to measure the radioactivity loss of a specimen/coupon, i.e. the remaining activity method and the concentration method. The remaining activity method measures the radioactivity left over in the coupon at a certain time during the erosion-corrosion process and then compares the radioactivity with a calibration curve prepared earlier to obtain the corresponding surface loss. On the other hand, the concentration method detects the specific radioactivity removed from the coupon's surface, after which the same procedures as in the first method are applied.Flow-induced corrosion (sometimes also called erosion-corrosion) of iron-based m...

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