Corrosion of buried steel anchor shafts is common, unavoidable and occurring continuously. Unfortunately, most partial (also referred to as 'surface' or 'shallow') excavations will not detect this phenomenon, as it tends to occur further below grade, at the point where the shaft enters the concrete block.
Except where dig-to-block is concerned, anchor shaft inspection is a gray area. Industry documents and guidelines, including the JHA, refer to "checking"
anchors and shafts. What, exactly, does this mean? Industry publications and resources state very few installers look at a tower's anchors, prior to climbing.
The TIA-222-H Standard clarifies the tower owner is responsible for
inspection and maintenance of the anchor system and must
initiate and implement a Corrosion Management Program for each tower.
One thing is certain: The responsibility to maintain a tower's anchor shafts lies with the owner. Speak with your insurance carrier to find out if you're covered, should your tower fail due to corrosion-related causes.
Coverage for this type of disaster isn't guaranteed - especially if owners cannot prove due diligence,
with respect to their anchor shafts.
Safe2Climb works with some of the industry's best-known corrosion specialists and engineers,
creating Corrosion Management programs in keeping with today's
Standards best practices. Properly maintaining and protecting out-of-site anchor shafts
will add years to the life of your tower and put a smile on your underwriter's face.
View the latest revision of the Anchor Inspection/Safe to Climb guide, provided by NATE, below -
one of many Climber Safety resources available from NATEHOME.ORG.
SOIL IS NOT THE ONLY CORROSION CONCERN
SOIL - CHEMICAL PROPERTIES AND CHARACTERISTICS
Soil chemistry plays a major role in the corrosion of buried steel - the starting point for investigation.oil chemistry and characteristics, including pH, salinity, electrical conductivity, excessive organic matter and the presence of surface and underground water features play an important role in the risk and formation of corrosion,
material loss and potential anchor shaft failure.
Soil permeability and the propensity to retain water has a direct influence on the corrosion process.
ELECTRICAL CONDUCTIVITY, STRAY & TRANSIENT CURRENT
Specific types of industry can exacerbate corrosion, as a function of their activities. Pipelines and welding/plating facilities inject stray/transient current injected into the earth, potentially picked-up through nearby anchors. Electrical power stations, sub-stations, overhead electrical transmission lines and AM-towers emanate radiated current. Agriculture, both crop and animal farming, pose a risk by altering soil through the application of pesticides, herbicides, and fertilizer. Irrigation practices not only facilitate the movement of chemicals,
they create unduly wet conditions, not taken into consideration during the design process.
Lincoln, NE - October 2017 A 500' guyed tower failed at 7:55 am, due to anchor shaft corrosion 10-feet below the surface. A crew was scheduled to arrive and climb this structure at 8:30 am. A PDF of this catastrophe has been inserted, below. Had the anchor maintained another couple hours, the consequences would have been fatal.
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