ABSTRACT

Copper based waterborne wood preservatives are frequently used to extend the service life of wood products when subjected to frequent moisture exposure. While these copper based treatments protect the wood from fungal decay and insect attack, they increase the corrosion of metals embedded or in contact with the treated wood. Previous research has shown the most plausible corrosion mechanism involves the migration of copper ions from the wood treatment through the wood to the metal surface, where they are then reduced. Despite this, under almost all conditions, copper has not been detected in the corrosion products as the proposed mechanism would imply.

Recently, synchrotron based X-ray fluorescence microscopy (XFM) was used to examine the wood that had been in direct contact with metal fasteners in a corrosion test. These measurements showed a copper depleted region in the wood directly adjacent to the metal fastener. Based on the size of the region and the copper concentration, the amount of copper in the corrosion products was calculated to be on the order of 500 parts per million. This low concentration explains why previous attempts to find copper in the corrosion products using scanning electron microscopy, energy dispersive X-ray spectroscopy, and powder X-ray diffraction were unsuccessful.

Here, we present XFM maps of corrosion products removed from corroded fasteners that had been in contact with preservative treated wood. The XFM maps of the corrosion products clearly show the presence of copper. These measurements definitively confirm the mechanism of corrosion in treated wood and give further insights into where and how the cathodic reaction takes place.

INTRODUCTION

In typical wood construction, metal fasteners are used to join wood to wood or other construction materials. These metal connectors are subject to corrosion from moisture and organic acids within the wood.1-5 In certain cases, wood preservatives or fire retardants are added to the wood and these chemicals affect the corrosiveness of the wood.6

Keywords:
metals & mining, Subsurface Corrosion, flowline corrosion, US government, materials and corrosion, wood preservative, Upstream Oil & Gas, corrosion rate, synchrotron, Publication Division
Subjects:
Pipelines, Flowlines and Risers, Materials and corrosion, Well Integrity, Subsurface corrosion (tubing, casing, completion equipment, conductor)
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2017. NACE International
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