Advances in Corrosion Testing of Metals in Contact With Treated Wood

Wood preservatives are metallic or organometallic compounds used to inhibit fungal decay and insect attack.  Recently, a regulation change in North America, Europe, and Australasia has increased the use of newer wood preservatives, such as alkaline copper quaternary (ACQ) and copper azole (CuAz).  These preservatives contain high amounts of cupric ions, which may be reduced to copper metal at the expense of less noble steel and galvanized fasteners in the wood.  Preliminary testing using extreme accelerating conditions suggested newer preservatives are more corrosive than the historical benchmark preservative chromated copper arsenate (CCA), although it is unclear how corrosion rates measured in these extreme conditions relate to milder in-service conditions. 

In this paper, we present a comprehensive view of advances in corrosion testing for metals in wood.  In addition to controlled exposure studies, electrochemical methods have been modified so that they can be run in solid wood, corrosion of metals in extracts of the solid wood have been examined, and tests to examine the effects of organic components of wood are also being studied.  Specifically, this paper will summarize the challenges of applying conventional corrosion test methods to wood and the current understanding of the corrosion mechanism based upon new test methods.  The paper will also discuss questions that still need to be answered before the results of this research can be applied to develop better test methods, less corrosive treatments, and more corrosion resistant fasteners.