Davies Preaches Corrosion Assessment
One of the five leading causes of tower
failure is anchor failure, says David Davies. He
is a veteran of the tower
industry and author of several industry-related papers and the Electrical Grounding
and Corrosion chapter of the TIA/EIA code. Davies is working with Ernie Jones,
founder of Consolidated Engineering Inc., a structural consulting firm
specializing in broadcast towers.
It is easy to forget about what is
buried underground. But anchor failure is responsible for 10 percent of broadcast
tower failures. The percentage is even higher in the cellular industry. Recent
years have seen an increase in failures due to anchor steel corrosion.
Davies has developed a method for
evaluating corrosion risk that the industry has not employed previously. He’ll
discuss it during the upcoming NAB Show.
Broadcasters are relatively unfamiliar
with steel anchor corrosion and subsequent failure. Hoping to increase awareness,
Davies says broadcasters should become more educated about the corrosion
“Half of tower owners have maybe only
seen their tower but a couple of times, and don’t consider the parts the tower
they can’t see, the ones that are underground,” he told Radio World. “So for
them to be aware of the problem (corrosion of anchors) is the first step to
For Davies, the process of making anchor
inspections more accessible and cost-effective started four years ago, working with
Scott Kisting of Midwest Underground Technology Inc., or MUTI.
Davies integrated non-invasive ultrasound
testing, when applicable, to evaluate buried anchor shafts. This method avoids
or limits the number of anchor shafts that required excavation to determine
steel loss. About two years into
the collaboration, he said, CEI and MUTI sensed a need for an accurate,
cost-effective approach of evaluating and categorizing individual tower sites more
efficiently, enabling a customer to prioritize and allot their maintenance
budget in a more focused manner.
After implementing such a method, some 50
sites were excavated and contrasted against the findings of the Corrosion Risk
Assessments, confirming the accuracy of this process.
The CRA provides a Risk Index based
on several factors, ranking each site on a scale from 1–10. For each increment
and circumstance, one or more actions are recommended.
“The key to accuracy is proper weighing
and grading,” Davies said. “I call it vertical and horizontal integration. It
tells you if you have a problem and how urgently you need to act.”
The process involves a mathematical
algorithm based on a number of risk factors available for each site: soil type
and characteristics, including moisture content and chemical properties, pH and
Electrical Conductivity (EC). The age and geometric shape of the anchor are
also variables, as is the presence of concrete encasement. The presence of
stray electrical current is also included in the equation.
“We determine the presence of stray
current emanating from pipelines and certain types of industry, all of which
may be in close proximity to the site.” Agricultural influences may alter site
soil characteristics. The information contained in the Corrosion Risk
Assessment provides insight as to the health of a tower’s anchors, resulting in
peace of mind, or the ability to take a proactive approach to protect their
“There is no reason to lose sleep over
something that is not a problem, though sleeping through a problem is foolish. The
CRA lets them know how well they should sleep.”
failure caused by anchor rod corrosion.
“We recently concluded a study in the
Midwest in which 89 sites were investigated,” Davies said. “Approximately 60
percent of these sites were either highly or moderately corrosive. I would
guess approximate 20 percent were highly corrosive, with a recommendation for immediate
He noted that these percentages may be
a function of geography and should not be applied on a national basis.
Corrosion is typically found in areas
where the soil tends to be clay-like. Dry, sandy soils usually present a lower
risk. But again, these are very generalized statements.
Davies also will present various
prevention/abatement and inspection methods that can be used in conjunction
with a CRA. Even a low ranking on the CRA Risk Index scale will generate steps recommended
to abate corrosion.
Installing a passive sacrificial anode
seems to be the universal fix. “Anodes don’t repair what’s already corroded,
but help prevent future damage. For around $500 an anchor, anodes are more
cost-effective than the other choices, which are coatings and concrete
For tower owners and stakeholders, Davies
encourages site education and taking time to research site conditions.In using the CRA model, he feels, catastrophic
failure of tower anchors will be largely avoided. He believes it is a simple
and cost-effective tool that gives a clearer view of what may be occurring
underground and out of sight.
The presentation “Preventing the Next
Tower Disaster” is part of the Broadcast Engineering Conference session on “Disaster
Preparedness and Recovery,” scheduled for Wednesday of the NAB Show.