Inspection and Remediation to Increase Service Life of Wood Poles

L. Gastonguay and J.-F. Labrecque Institut de Recherche d’Hydro-Québec

1800 Lionel-Boulet Varennes, Québec, Canada, J3X 2J8

e-mail; gastonguay.louis@ireq.ca

Abstract—During the latest years, public utilities looked at different approaches to enhance the service life of their assets. One of the main assets is wood poles used for distribution network. At Hydro-Québec, more than 2 million wood poles are used to distribute the electricity to our customers. The increase in service life will save money for the company as well as preserve the environment by using fewer trees. Within the last few years, Hydro-Québec has implemented an inspection and remediation program to enhance the service life of wood poles. Preliminary results showed than we can increase the service life of our wood poles by about 10 to 15 years.

Keywords-wood, poles, inspection, remediation, service life

I. INTRODUCTION Hydro-Québec is a public utility that produces,

transports and distributes the electricity throughout the province of Québec in Canada. Roughly 96% of our electricity is produce with water (hydroelectricity). Our distribution network is composed of about 2 million wood poles. From this perspective, it is obvious that we want to optimise the service life of our wood poles. The expected service life of a wood pole initially treated with PCP (pentachlorophenol) should be between 35 and 40 years. Early fungal degradation was observed for some of our wood poles. In order to asses this phenomena, measurements were done in 2002 in order to determine the residual concentration of PCP in wood poles as a function of the number of years in service. Results showed that after 20 years in service roughly 20% of our poles have PCP concentration below the toxicity threshold (3,0kg/m3). This number increase to 40% after 25 years in service. A concentration below the toxicity threshold value means that fungal degradation could take place. These results are shown in figure 1 for three different regions and explained the early failure that we observed for some of our poles. These failures are costly for the utility as well as for the environment because of the early replacement that we observed.

Figure 1: Percentage of poles below the toxicity threshold as a function of

time

II. MATERIALS AND METHODS Degradation of wood poles usually appears at the ground

line level where conditions for fungal attack are observed. In order to reduce fungal degradation and enhance the local toxicity, different approaches are possible from bandage to liquid to fumigant to solid rods. In this paper, only one approach will be look at and it is possibility of using solid rods containing either boric acid or sodium fluoride. Three companies are selling solid rods for remediation: Genics with the CobraRods, Sasco Products with ImpelRods and Osmose with Flurods. An example of theses rods is shown in figure 2.

Figure 2: Solids rods (Genics)

In order to asses the efficacy of theses rods to enhance the service life of wood poles, tests were done at our research facility and on our distribution network. Results presented here have been observed at our research field. At our research facility, pole sections (6 feet) were used without initial chemical treatment to accelerate the degradation

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Fraction of wood poles with PCP conc. below toxicty threshold (3,0 kg/m3) versus service life

Chicoutimi Rive Sud Trois Rivières

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2011 2nd International Conference on Environmental Science and Technology IPCBEE vol.6 (2011) © (2011) IACSIT Press, Singapore

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Figure 6: Diffusion of chemicals after 7 years

The same result was observed for two of the rods. The other one seems to diffuse faster at the beginning of the test but also leach faster out of the wood and become less effective for the long term protection. In comparison, we can see degradation for some of the reference as shown in figure 7.

Figure 7: Degradation at the groudline for a reference section

Figure 5 and 6 have shown visually the diffusion of the chemicals contained inside the rods. Measurements were also done to determine the concentration of each of the chemicals as a function of time. All the results obtained for the different pole sections will not be presented in their entirety in this paper. Only the final results will be discussed. These results are presented in table 1.

For the different chemicals contained inside the rods, the toxicity threshold is around 1 kg/m³. In order to determine the efficacy of these rods, the number of wood pole sections with chemical concentration above the toxicity threshold was tabulated.

TABLE 1: NUMBER OF SECTIONS WITH CHEMICAL CONCENTRATION ABOVE 1KG/M³.

Rods # of sections conc. > 1

kg/m³

# of sections conc. > 1

kg/m

After 2 years After 7 years

#1 15 4

#2 10 19

#3 9 19

These measurements are in accordance with the visual

observation that we made above. For two of the rods, we observed an increase in the number of section, as a function of time, with concentration above the toxicity threshold. For the other rod, we observed that the diffusion takes place very quickly after the beginning of the test but also that the chemicals are leaching faster outside the pole sections as it can be seen by the decrease of the number of pole sections

with concentration above 1 kg/m³ after 7 years. Complete results of this study will be published elsewhere.

IV. CONCLUSION The results observed for two of the rods indicated that it

is be possible to increase the service life of our utility poles by the implementation of the test and treat program. For the following years, approximately 100k/year poles will be inspected. At the present time, already the program has given us a very good payback as the service life of our wood poles is now expected to be around 45 years comparing to 35 years before our test and treat program.

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