A round robin evaluation of the corrosiveness of wet residential insulation by electrochemical measurements

The results of a round cabin evaluation of the use of an electrochemical method of calculating the corrosion rate of low carbon steel in environments related to cellulosic building insulations are reported. Environments included the leachate from a wet cellulosic insulation and solutions based on pure and commercial grades of borax, ammonium sulfate and aluminum sulfate. The pH values of these environments were in the range of 2.5 to 9.5. Electrochemical measurements were made using a direct reading corrosion rate instrument. The calculated corrosion rates were compared with those determined directly by weight loss measurements. Electrochemical measurements were made over a period of 48 hours and weight loss exposures were for two weeks. Poor agreement was observed for the corrosion rates determined electrochemically and the values were consistently larger than those based on weight loss. Reasons proposed for these results included the complex nature of the corrosion product deposits and the control these deposits have on oxygen diffusion to the metal interface. Both factors influence the validity of the calculation of the corrosion rate by the direct reading instrument. It was concluded that development of a viable electrochemical method of general applicability to the evaluation of the corrosiveness of wet more » residential building thermal insulations were doubtful. Because of the controlling influence of dissolved oxygen on the corrosion rate in the insulation leachate, an alternate evaluation method is proposed in which a thin steel specimen is partially immersed in wet insulation for three weeks. The corrosiveness of the wet insulation is evaluated in terms of the severity of attack near the metal-air-wet insulation interface. With thin metal specimens, complete penetration along the interface is proposed as a pass/fail criterion. An environment of sterile cotton wet with distilled water is proposed as a comparative standard. 9 refs., 2 figs., 3 tabs. « less