Corrosion of electric poles

What are electric poles?

Electric poles are long hollow tubular poles that host
overhead electricity distribution wires. They may also have equipment to
monitor and regulate the electric supply.

What are the types of electric poles?

There are two types of electric poles:

  1. Swaged  
  2. Stepped

What are the materials used for making electric poles?

  • Mild steel is the material of choice for electric poles.  
  • They are longitudinally welded tube sections of hot-rolled structural carbon steel.
  • There also has to be an MS base plate welded to the bottom of the pole.

The standards typically used to select the grade of mild steel are:

  • JIS G 3444 ( ST-51 )
  • DIN 17100 (ST-52)
  • BS-4360
  • IS: 2713 (Part – I, II): 1980 

Chief mechanical properties required 

  • Tensile strength
  • Yield strength

The specifications for the poles include the following
parameters:

  • Maximum Ambient temperature
  • Minimum ambient temperature
  • Maximum relative humidity 
  • Average number of thunderstorm day per annum
  • Maximum no. of rainy days/annum
  • Average Rainfall
  • Maximum Wind pressure/wind speed
  • Height above sea level (m) not exceeding
  • Earthquake acceleration horizontal seismic co-efficient

Corrosion-prone areas of electric poles

  1. The weld area of the bottom plate may undergo galvanic or uniform corrosion. It may also experience weld decay due to chlorides in the soil.
  2. The surface of poles is susceptible to uniform corrosion.
  3. Microbial corrosion of area submerged in soil.
  4. Crevice corrosion is possible at overlaps and fixtures.
  5. Pitting corrosion at areas where water can accumulate, such as nooks and corners in the design.
  6. Erosion corrosion of upper areas of the poles may occur due to dust carried through the wind.
  7. Coating delamination and uniform corrosion underneath is possible due to moisture absorption.

Coatings for electric poles

The coatings recommended for electric poles consist of the layers of the following components:

  • Galvanization layer
  • Red oxide paint
  • Black bituminous paint from the bottom of the pole up to the region buried in the soil
  • Long-oil alkyd with aluminium, zinc, or stainless steel dust
  • Epoxy coating as sealer

References