Pickling Brass

[jake_leg]

Here excerpts from an experimental paper relevant to the subject of corrosion in lead containing brass. Boldface emphasis added. The pickling procedure is slightly different from the well-known procedure recommended by John Palmer in How To Brew (slow pickle in dilute acetic acid rather than fast pickle in acetic/peroxide) but the idea is the same, to take the surface lead into solution as lead acetate. The tests were done over long periods in distilled water but brass corrosion could be expected to be many times quicker in acid and the presence of organic substances, conditions that might pertain in a fermenter or boiling vessel with brass fittings.

CORROSION / Volume 48 / Issue 12 / CORROSION ENGINEERING

Leachability of Lead from Selected Copper-Base Alloys
Corrosion 48, 1040 (1992); doi:10.5006/1.3315907 (7 pages)
J. I. Paige and B. S. Covino, Jr.

Abstract

The Bureau of Mines has conducted research on the selective leaching of lead from copper-base alloys in high-purity water. The alloys in this study were selected as representatives of those used in various plumbing system fixtures such as faucets and valves. Leaching tests were conducted for a total period of 14 days and at temperatures of 25, 50, and 75°C. An acetic acid pretreatment was used in an effort to reduce the amount of lead that was leached from the alloys. The results show that, with the exception of the more complex yellow brasses, more lead is leached into water from alloys containing greater concentrations of lead and that the rate of lead leaching decreases with exposure time. Higher temperatures had relatively little effect on the leaching of lead. Lead was preferentially dissolved from all of the alloy groups. Of the small total amount of alloy dissolved, more Pb, 10 to 59 times, was dissolved than would be predicted from the proportional quantity of Pb present in the alloy (0.1 to 7.0 wt% Pb). Typically, the amount of Pb dissolved in any given test period exceeded the Environmental Protection Agency proposed action limit of 0.015 mg∕L.

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Effect of Pretreatment

A preliminary study was conducted on alloy C83600 to determine if the smeared Pb film could be successfully removed by a pretreatment procedure. Samples of alloy C83600 were leached in 1.2 N acetic acid for 4 h-, 8 h-, and 24-h periods. Then, the sample surfaces were examined using EDS on the SEM. The examination revealed that approximately 50% of the Pb was removed after 4 h, approximately 75% was removed after 8 h, and it was difficult to find any traces of Pb remaining after 24 h of treatment.
Based on these findings, the second series of tests was conducted in a manner identical to the first series with the exception that all alloys were preleached in 1.2 N acetic acid for 4 h and the only temperature tested was 25C. A comparison of the results for series no. 1 and no. 2 can be seen in Figure 3 and Table 3. This shows that the total amount of lead leached from most of the alloys did not decrease. In fact, the treated model alloys actually showed a substantial increase in the amount of Pb leached from the samples. However, an analysis of the percentage of lead leached during the first 24-h period shows that the pretreatment does have a positive effect. On average, one fourth of the total lead leached in 2 weeks, a reduction over non-pretreated samples, was leached out during the initial 24 h of the exposure period.



[Here are the results graphically] for the semi-red brasses, alloys C83600 and C84400, which are reported to be the most heavily used alloys for production of plumbing fittings in the United States.



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Conclusion

Pretreatment to remove lead from the surface did not significantly reduce the total amount of lead leached from any alloy during testing.