The steel specimens are first exposed for 48 h to the vapor of an 0.001 mol dm −3 sodium bisulfite solution maintained at 54 ☌ (humid SO 2-containing atmosphere) to stimulate corrosion under atmospheric conditions. 180,181 have used open-circuit potential versus time measurements and cathodic reduction of rust patinas for the rapid laboratory evaluation of the performance of low-alloy weathering steels. Relationship between potential (determined during initial immersion using the equipment in Figure 13) and time for steels that form protective (1, 2, 3, 7) or nonprotective (4, 5, 6) patinas. In a variation of the apparatus, a Luggin capillary is attached to the sample so that the potentials can be measured during the period when the specimen has emerged from the solution but is still wet.įigure 14. The solution can be made to circulate slowly by allowing it to drip from a feed and overflow via a siphon. taken from the terminals can be fed to a multipoint recorder so that a recording of the E–time relationship may be obtained for each specimen. Measurement of the potentials of the specimens at the beginning and end of the immersion period is effected by means of the commutators, which are attached to the spindle but electrically insulated from it, and a reference electrode. An electric lamp is placed above the tank so that the specimens remain wet for a time after withdrawal from the solution, but are completely dried during the cycle. Two specimens of the metal or alloy under study are attached to a spindle that rotates slowly (about 1 rev h −1) so that the specimen is immersed in the solution for approximately half the time and exposed to the atmosphere for the remaining time.
The apparatus ( Figure 13) consists of a glass tank containing an appropriate electrolyte, such as a natural or artificial water. The use of electrochemical tests for rapid assessment of the performance of these steels has attracted interest, and Pourbaix 179 has devised an apparatus in which potential measurements are used to evaluate the protective nature of corrosion products formed on low-alloy steels, such as the weathering steels, during periodic wetting and drying. Lai, “Galvanic Corrosion Risk of Using Galvanized A325 Bolts in Corrosion-Resistant Steel Bridges”, J. Lai, “Galvanic Corrosion Risk Assessment of Bolt Materials in Contact with ASTM A1010 Steel Bridges,” in Corros. Using paint systems to cover the steel and prevent atmospheric corrosion or weathering the steel prior to installationĪdditional References Pertaining to Case Studyġ. Saline environment with a high 90% relative humidity at 35☌Įxposure to salt and high humidity in presence of oxygen and connection of dissimilar metals The salt spray testing follows the ASTM B117-16 procedure Rust formation on weathering steel plate and zinc dissolution on galvanized boltsĢ weeks experimental exposure to salt fog chamber. Salt fog chamber testing of steel plates and connection bolts used in steel bridge constructionĪtmospheric corrosion and galvanic corrosion Weathering steel plate and ASTM A325 galvanized steel bolt The main applications for WS include civil structures such as bridges and other load-bearing structures, road installations, electricity posts, utility towers, guide rails, ornamental sculptures and façades and roofing. Besides possessing greater mechanical strength and corrosion resistance than CS, the patina is also valued for its attractive appearance and self-healing abilities. The enhanced corrosion resistance of WS in relation to CS is due to the formation in low aggressive atmospheres of a compact and well-adhering corrosion product layer known as patina. Weathering steels (WS), also known as low-alloy steels, are steels with a carbon content of less than 0.2 wt% to which mainly Cu, Cr, Ni, P, Si and Mn are added as alloying elements to a total content of at least 1.00 wt% and no more than 5.00 wt%, a higher proportion than is normally encountered in mild or plain carbon steels (CS) ( Murata, 2000). Daniel de la Fuente, in Encyclopedia of Materials: Metals and Alloys, 2022 Introduction
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