Papers by Keyword: Crevice Corrosion

Abstract: It is commonly believed that stainless steel cannot rust. However, this erroneous assumption is very often disproved in practice. Either the stainless steel is chosen for the manufacture of a piece of equipment working in the conditions where its corrosion resistance is no longer satisfactory, or, more often, the prescribed procedures for its protection are not followed during operation. The article gives examples where an incorrectly chosen disinfecting procedure for a food processing plant with a chlorine-based product caused pitting corrosion of ceiling panels and low-quality weld joints caused crevice corrosion of cold drinking water pipes in food processing plants.

Abstract: Duplex stainless steels (DSSs) are being increasingly employed in the oil and gas and chemical industries, which, despite their high alloying degree and high resistance to general corrosion, are subject to pitting and crevice corrosion. According to their resistance to pitting and crevice corrosion, steels are ranked according to the PREN. However, nowadays there are many grades of DSSs, in which the content of Cr, Mo and N varies in different quantities, therefore the selection of the grade must be carried out with great care, considering not only PREN, but also the production technology, operating conditions, and the geometry of products. The crevice corrosion behaviors of three grades of duplex stainless steels quenched from 1050, 1100 and 1200 °C were studied in FeCl₃ solution at 50°C. It is shown that PREN allows to rank only different grades in terms of corrosion resistance. With a constant PREN value, but with different contents of ferrite and austenite in steel, completely different values of the corrosion rate can be obtained, therefore, PREN must be used with great care. It was found that in the studied steels, the optimal ferrite content, at which the lowest crevice corrosion rate is achieved, is at 65 vol.%.

Abstract: Pitting and crevice corrosion resistance of 321 stainless steel and non-vacuum electron-beam cladded stainless steel have been investigated by using potentio-dynamic polarization curve plotting. Lock-Ringer Salt Solution (LRSS) was used as biological media for corrosion test measurements. Microstructural research of samples after corrosion was carried out by using scanning electron microscopy. The experimental results show that the cladded stainless steel possesses higher pitting and crevice corrosion resistance.

Abstract: The surface line type defects on the can twist-off lids from lacquered tinplate material have been analyzed. The analyzed defects manifested themselves like the lines bulged above the surrounding surface. They were aligned roughly perpendicular to the lid circumference; they were mostly arranged on the lower part of lid circumference edge. The defects surface was fully covered by lacquer layer. After lacquer layer removal it was visible in the defective area that tin layer was damaged on some defect areas. The defect presented itself like filiform corrosion which occurred in conditions slightly above room temperature and high humidity under the originally continuous covering layer. According to the findings, corrosion occurred on the hidden sheet cut edges and then propagated first perpendicular to the circumference into the sheet. Then sometimes its direction changed into the sheet rolling direction along the lines with less but still suitable tin layer thickness. This defect can be controlled by special protecting of lid cut edge against corrosion or decreasing of the temperature and the humidity conditions in the stores.

Abstract: Crevice corrosion of 3.5NiCrMoV and 13Cr steels, which are used as low-pressure (LP) steam turbine materials, was investigated by electrochemical corrosion tests in the simulated boiler water contained chloride and sulfate ions. For 3.5NiCrMoV steel, by comparison with the surfaces outside crevice, the surfaces inside crevice of the specimens coupled with both of the same steel and 13Cr steel showed no remarkably corroded pattern even though pitting corrosion was observed. The specimen of 13Cr steel coupled with the same steel plate exhibited pitting corrosion inside the crevice, and a lower open cycle potential (Ocp) than the single plate of 13Cr steel. On the other hand, the specimen of 13Cr steel coupled with 3.5NiCrMoV steel plate showed the lowest Ocp, as the anodic dissolutions of 3.5NiCrMoV steel became the dominate corrosion mechanism.

Abstract: Crevice corrosions of duplex stainless steels were investigated under the aggressive condition of sea water pumps in offshore petroleum platforms. The study aims to compare crevice corrosion behavior of three grades of duplex stainless steels, UNS S32101 (2101), UNS S31803 (2205) and UNS S32750, in seawater with 200 ppm of hypochlorite. Duplex steels were compared with a widely used austenitic steel UNS S31603 (316). Specimens were tested under synthetic sea water prepared at pH4, pH6 and pH8 by the cyclic potentiodynamics polarization technique and the potentiostatic technique. The results show that the duplex stainless steels had higher corrosion resistance compared with the 316. The released charges and the corrosion rates of the 2101 and the 2205 were similar, but much lower than those of the 2507especially after 3 months period.

Abstract: The crevice corrosion behaviors of X52 carbon steel in two typical Cl--containing solutions were investigated by electrochemical noise and electrochemical impedance spectroscopy. Results show that oxygen concentration difference leads to the coupled current in NaCl + NaHCO3 solution while HAc concentration difference causes the coupled current in NaCl solution saturated with CO2 in the presence of HAc. There exists an apparent incubation stage during the crevice corrosion process of X52 carbon steel in the former. However, no obvious incubation period of crevice corrosion can be observed in the latter. Micrography shows that the crevice corrosion occurs indeed and the corrosion inside the crevice is not uniform.

Abstract: Crevice corrosion (CC) was investigated for a number of selected corrosion resistant alloys in natural seawater containing microorganisms for up to 18 months under stagnant conditions. Experimental controls consisted of tests in natural seawater filtered in accordance with hydrostatic testing procedures. The corrosion potential of alloys was monitored throughout exposure and corrosion was evaluated by weight loss and 3D optical microscopy. CC was initiated on several alloys and corrosion rates in time indicated a positive effect of seawater filtration on the long-term performance of the alloys. Microbial adhesion, as indicated by fluorescence microscopy, occurred mainly outside the crevice and differed according to the nature of the substratum surface.

Abstract: A triplex plunger pump used for activating the journal bearing in cold rolling machine, could work only for one week comparing with the design life for two years in normal condition. The valve seat of the pump, which is made from 42CrMo4, was corroded on its exterior surface and plowed on its seal face. Since this failure, the pump could not work in its operating pressure. By evaluation and numerical simulation of the pump, results indicate that the failure occurred because of crevice corrosion and cavitation corrosion on seat surface and seal face, respectively. The reason to cause the corrosion was clarified and corresponding measures were put forward. Hence, the pump works in a normal condition.

Abstract: The effect of sulfate reducing bacteria (SRB) on the corrosion of Q235 steel has been investigated in the crevice under the simulated disbonded coating with aperture width of 1.0 and 0.5mm in the soil-extract solutions (SES) by using electrochemical methods. The results show that the existence of SRB in SES can cause corrosion potential of the working electrode to shift to a more negative value, and the formation of pitting on the surface of the electrode. Compared with the crevice width of 1.0mm, the corrosion potential of the electrode shows a little more positive at the crevice width of 0.5mm. The corrosion rate of the electrode increases with the increase of aperture width in the SES without SRB, however, decreases with the increase of aperture width in the SES with SRB. The results obtained indicate that either bio-film on the surface of the electrode formed by SRB in SES or aperture width has obvious influences on the crevice corrosion process of the carbon steel.