Preventative Measures to Help Retain Strength and Reduce Avoidable Replacement Costs
By Randy Marquardt
Wood utility poles numbering more than 140 million support the delivery of high voltage electric transmission and distribution service throughout North America. After many decades of use, the wood pole remains a preferred material because of its durability, strength, availability in multiple lengths and classes, and low acquisition and life cycle costs. Wood poles are also a renewable resource.
Utility standards engineers and procurement personnel typically require their poles to be manufactured following American National Standards Institute (ANSI) and American Wood Protection Association (AWPA) guidelines to ensure the desired size, strength, material quality, original treatment loadings and decay resistance properties are present.
Utility pole owners would be well-served through a greater understanding of the deterioration modes for wood poles. Greater knowledge of wood as a material may lead pole owners to implement preventative measures that help retain pole strength, maintain pole condition, increase reliability, and reduce avoidable repair and replacement costs.
|The Pole Topper creates a durable, long-lasting barrier against moisture and sunlight that helps maintain structural stability and preservative retention.|
The Vulnerability of Pole Tops
Wood poles are susceptible to degradation by a variety of agents, both abiotic (non-living) and biotic (living). Abiotic deterioration can be caused by ultraviolet (UV) light, water, mechanical activities, chemicals or temperature. UV sunlight is probably the most obvious abiotic agent damaging pole tops. It degrades the wood and the preservative, causing the wood to become weaker and more likely to be eroded by weathering. In addition, the pole top suffers most from preservative depletion through the force of gravity and constant exposure to wet-dry and hot-cold weathering cycles.
As the protection provided to the pole top by the original treatment is weakened, cracks and checks develop near the pole top surface, exposing untreated heartwood or inner sapwood to wood-destroying fungi. Once these conditions are present, decay can advance rapidly in the pole top area.
The Risks and Costs of Pole Top Decay
Decayed pole tops can lead to split or weakened pole tops. These conditions eventually lead to problems with the integrity of the connection between the pole and the hardware it supports. Loose insulators and floating conductors can lead to outages and increased safety risks for the public and utility personnel. When a utility has to deal with these problems on an unplanned basis, there are valuable man-hours invested in repairs and, in many cases, revenue is lost. If the pole top cannot be repaired, there are additional monies spent on pole replacement.
|Hazardous conditions caused by pole tap deterioration.|
Extending Pole Tops' Service Life
Pole top protection-such as the Pole Topper, CoverCap and Polecap-extends wood pole service life by providing a "roof" for the vulnerable, exposed pole top. These protective roofs are designed to prevent UV degradation of the preservative and exposed wood fiber. Pole top protection also significantly reduces moisture-a necessity for decay-limiting attack from wood destroying fungi. High moisture content also encourages freezing and splitting of the pole top. Without pole top protection, pole tops are highly vulnerable to premature aging. The installation of a pole top protection device allows older, in-service pole tops to exhibit new characteristics even though the pole may be decades old. In this way, pole top protection devices help ensure it is not the pole top that limits the life expectancy of wood poles.
Evidence that this strategy works is being validated through a study sponsored by Oregon State University - Utility Pole Research Cooperative. The Rural Utilities Service (RUS) has also accepted a pole top protection device for use on new pole construction.
Justifying the Investment in Pole Top Protection
It is rare to find a simple, straight return on investment (ROI) for preventative maintenance actions. Most often, one can identify tangible financial and operational benefits to support a persuasive business case for these investments. In this case, the pole top protection helps eliminate pole top degradation as a reason for pole replacement.
Over an extended number of years of service life, how many pole replacements can be avoided by managing the aging of pole tops? How many poles that otherwise may have been candidates for pole restoration will have to be replaced because they did not have pole top protection?
As an example, one utility-in an area prone to high decay-inspected 61,958 poles in one year. Inspectors identified 18,026 poles with significant pole top decay (29 percent) and 3,712 poles (6 percent) with split tops. For this utility, pole replacement costs range from some $2,000 to $5,000 per pole, depending on the number of attachments. Conservatively assuming that 20 percent of these 21,738 decayed and split poles will become rejects far sooner than their counterparts without pole top damage, it's reasonable to assume this utility could have avoided or at least deferred 4,347 (20 percent) of these pole replacements. At an average replacement cost of $3,500, more than $15 million in replacement costs could have been avoided or deferred with a minimal investment in pole top protection.
Furthermore, how many outage risks related to pole top integrity can be eliminated? Wide-scale investments in pole top protection may be justified through consideration of combining the advantages of financial savings and risk avoidance. It is also proposed that the severity of the risk-floating conductor, outages, "hot" poles-be included as part of the analysis.
Many utilities include the cost of pole top protection in the capital budget for materials for new pole installations (which are depreciated over time), creating future savings for operation and maintenance, and capital accounts.
About the Author: Randy Marquardt is Vice President - Products at Osmose Utilities Services Inc. He has more than 20 years of experience helping utilities inspect, maintain and restore transmission and distribution infrastructure. For more information about fire protection products, please contact Marquardt at email@example.com.