L51886 Performance of Magnesium Anodes

Magnesium anodes are provided to the corrosion control industry by a number of domestic and international manufacturers and distributors. Due to the difficulty and time involved in performance testing, anode composition is commonly the only criterion used for quality control by the end users. However, experience has shown that compliance of the anode chemical composition with the ASTM B843 Standard Specification for Magnesium Alloy Anodes for Cathodic Protection can be misleading and does not always differentiate between the anodes of different quality. Thousands of magnesium anodes are produced annually and provided by a number of suppliers to the corrosion control industry. Though the composition of the anodes from the various sources is comparable, the performance of the magnesium anodes is often radically different. Many of these materials have been shown to meet the compositional and potential specifications, and yet have had measured efficiencies as low as 7%. The objectives of this project were: (1) to develop quality and performance standards determined by laboratory tests and field exposures. The project included testing a variety of anodes submitted by the manufacturers/distributors and the end users, representing all spectrum of the ASTM G97 Standard Test Method-based efficiency values; the anodes were characterized with respect to the Anode source, manufacturing process, macrostructure, chemical composition, anode type (standard/H-1 family /AZ63 family versus high-potential), and microstructure. Other investigations comprised assessment of the ASTM G97 Standard Test Method parameters that were most likely to make the most significant impact on the resulting anode efficiency values, e.g., testing environment (standard testing solution and saturated backfill), and current density (the low 1/10th of the standard'), the ASTM G97 standard, and the high (10X standard) values). Testing in saturated backfill was used for a comparison between the laboratory- and the field-based efficiencies.