The Performance of Copper Naphthenate Treated Wooden Pole Stubs After 12 Years of Field Exposure¹

By

 H. M. Barnes²
M. H. Freeman³

 ABSTRACT

Naphthenates have been used for the preservation of timber and cellulose since their original identification in Russia in the early 1880's as part of a series of petroleum characterizations.  Later work in the development of copper naphthenate as a heavy-duty preservative for poles led to the development of various treating cycles similar to other oil-borne systems.  Recent work concerning' the post treatment steam conditioning of copper naphthenate treated southern pine has determined that some amorphous copper naphthenate is converted to a crystalline cuprous oxide.  In small laboratory tests, this was later determined to be less efficacious than copper naphthenate.  This paper reviews the performance of actual pole diameter stubs placed in a high hazard location containing both termites and potential for early decay attack.  Various treating cycles were used to treat the pole stubs in this test including various post-treatment conditioning methods.

  INTRODUCTION

Copper naphthenate (CuNap) has been documented as being a very effective wood preservative (2, 3, 6, 8, 9, 13).  When the U.S. Environmental Protection Agency reviewed all the major wood preservatives, including pentachlorophenol (penta), creosote, and the inorganic arsenicals, manufacturers of CuNap began to actively promote the chemical as a viable alternative to pesticides.  Although efforts to use CuNap as an extender for creosote began during the war effort of the 1 940's due to a shortage of creosote, widespread use of CuNap has occurred only within the last decade, Efforts were made within the American Wood-Preservers' Association (AWPA) to have standards for specific commodities for wood treated with CuNap as early as the mid-1980's (1).

The treatment of poles with CuNap began commercially in the late 1980's.  For a variety of reasons, early failures of CuNap-treated poles were experienced by utilities.  Recent publications in the literature have indicated that, in small scale laboratory tests, samples of southern pine wood that have been treated with CuNap in P-9 Type A oil, undergo a change from amorphous CuNap to crystalline cuprous oxide (11, 12).  At low retention's, this conversion to cuprous oxide in small laboratory samples has been as much as 50% of the available copper.  The extent to which this is anything but a surface phenomenon has yet to be shown.  Additional tests have shown that CuNap has a more biologically active form of copper than many other copper complexes or copper salts, with the exception of oxine copper (5).  As a result of the changes noted in small laboratory tests and the incidence of early failures of poles in service, the executive committee of the AWPA issued the following instruction to Subcommittee P-3 Organo and Organometallic Preservatives: "Review, with particular emphasis on the effects of pre- and/or post-steaming on the efficacy of CuNap preservative systems, including degradation of CuNap into possible less-efficacious forms of copper" (7).  The purpose of this study is to detail our experience with pole-sized material in exterior exposure.  Hopefully, this research will answer some of the practical concerns posed by producers and users of treated poles.

EXPERIMENTAL PROCEDURE

In 1987, pole sections treated with CuNap (4) were placed in storage in an above ground environment as well as placed in ground contact in a high decay, high termite attack area (AWPA Hazard Zone 4) near Starkville, MS (Figure 1).  Data and conditions of these pole stubs have not previously been reported since their installation over 12 years ago.  

Many of the pole stubs in this test were exposed to steaming conditions, either pre-steaming for conditioning purposes, post-steamed for aesthetic reasons, or a combination of these two steaming conditions.  Other variables included in these pole stub tests were initial conditioning method (air-dried or steam-conditioned), varying solution temperature conditions, and use of a final fixation/expansion bath (10).  Details of the treating and conditioning processes and procedures can be found in the literature (4).  A summary of the treatment details is given in Table 1.