Category: Industry examples

Corrosion of concrete electric poles

Concrete electric poles have been used extensively for supporting heavy transmission lines for several years. In this article, we will cover the types of concrete poles, their requirements, their corrosion, and their inspection techniques.

Source

Types of concrete poles

There are two types of concrete poles:

  • PCC: PCC stands for Plain Cement Concrete. This type of PCC pole has an entire concrete structure without any metallic reinforcement. The preparation comprises of inserting a high-tensile steel wire in a mould and stretching it to a predetermined extent. Another wire, which is galvanised steel wire, is introduced as the earth wire in the mold. The mould is then filled with concrete mix, which is then compressed. Such poles are also called pre-stressed cement concrete poles (PSC) as the compression leads to a stress generation in the concrete mix.
  • RCC: RCC is short for Reinforced cement concrete. As the name suggests, this type of concrete pole is reinforced with TMT steel bars for greater strength and endurance. In the production of RCC poles, a structure of TMT bars is first assembled and then embedded in pol-shaped concrete slabs.

Specifications

Specifications for PSC electric poles

  • Overall length of pole
  • Working load
  • Bottom depth
  • Top depth
  • Breadth
  • Depth of planting
  • Factor of safety
  • Diameter of HT pre-stressing wire
  • Minimum tensile strength of HT pre-stressing wire
  • Number of HT wire
  • Concrete grade
  • Ultimate load
  • Cube crushing strength of concrete at 28 Days
  • Allowable max compressive strength in concrete at working load

Specifications for RCC electric poles

  • Overall length of poles
  • Cement grade and composition
  • Composition and grade of aggregates
  • Mechanical properties of reinforcing bars and wires
  • Surface condition and preparation of reinforcing bars
  • Composition of admixture
  • Quality and composition of water used for concrete preparation
  • Maximum wind pressure
  • Depth of planting
  • Transverse strength at failure
  • Welding and lapping of reinforcement
  • Earthing wire installation

Corrosion of PSC and RCC poles

  • Spalling of concrete cover
  • Uniform or localized corrosion of metallic wires and bars due to ingress of moisture and oxygen through the concrete pores
  • Soil corrosion and concrete degradation in the areas buried under the earth due to ingress of chlorides, sulphates, nitrates, and moisture from the soil.
  • Saturation of concrete at the soil/atmosphere interface due to capillary absorption of groundwater due to wicking effect
  • Wind erosion of the concrete at greater heights.
  • Crevice corrosion of wires and poles at the inlet and outlet points of wires inserted in the poles.
  • Uniform corrosion of bare wires
  • Pitting corrosion at areas left bare due to insufficient or damaged coating
  • Stress corrosion cracking of the reinforcing bars or embedded wires due to local stress concentrations in the concrete

Inspection and testing

Here are a few typical inspection measures and tests conducted to assess the integrity of the concrete electric poles:

Wrap up

Concrete poles have been used extensively for transmission lines and utilities. While the basic specifications are common, there may be variations in certain parameters with respect to the location and climate.

Hence, a comprehensive view of the requirements and testing conducted globally will help assess the corrosion causes and select the most suitable inspection measures to nip the corrosion in the bud.

References

  • https://www.cracindia.in/admin/uploads/IS-785.pdf
  • https://www.wbsedcl.in/irj/go/km/docs/internet/webpage/techspec/Technical_Spec_of_Pole.pdf
  • https://www.materialsperformance.com/articles/material-selection-design/2019/01/control-of-environmental-degradation-of-concrete-power-poles
  • https://www.materialsperformance.com/articles/corrosion-basics/2020/11/bend-test-of-concrete-power-poles
  • https://www.irjet.net/archives/V8/i5/IRJET-V8I5749.pdf

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

Corrosion in fertilizer industry – 1.2 Elemental sulphur attack

WATCH THE VIDEO HERE

OR READ ON BELOW!

  •  Elemental sulphur attack is NOT sulphidation or hydrogen sulphide corrosion.
  • It is an aqueous corrosion phenomenon.
  • It considers two modes – 
    1. acidification of sulphur – formation of sulphuric acid
2.    direct cathodic reduction of sulphur with anodic dissolution of iron

  • The lowering of pH is the main source of corrosion in both the methods.
  • The phenomenon is temperature dependent. It increases with increase in temperature and becomes particularly severe above the melting point of sulphur (~112.8 degree Celsius).
  • Hydrogen sulphide present in the petroleum may aggravate the sulphur attack by enhancing uniform pitting corrosion.
  • Monoethylene glycol is used to prevent condensate formation ans may be present in traces in the feedstock petroleum. This enhances the sulphur attack in the form of uniform corrosion, and crevice corrosion.

References: 
    • Fang, Haitao, Brown, Bruce, Young, David, and Srdjan Nešic. “Investigation Of Elemental Sulfur Corrosion Mechanisms.” Paper presented at the CORROSION 2011, Houston, Texas, March 2011.
    • Yoon, Yuhchae, Srinivasan, Sridhar, Yap, Kwei-Meng, and Russell D. Kane. “Elemental Sulfur and Speciation in High Pressure High Temperatures Oil and Gas Well Environments: Their Role in Stress Corrosion Cracking of Corrosion Resistant Alloys.” Paper presented at the CORROSION 2017, New Orleans, Louisiana, USA, March 2017.
    • Yaakob, Nurul & Singer, M. & Young, David. (2015). Elemental sulfur corrosion of carbon steel in the presence of sulfur solvent and monoethylene glycol. NACE – International Corrosion Conference Series. 2015. 

        😀Happy learning!😀

        Corrosion in fertilizer industry – Part 1.1

        The fertilizer industry is as complex as any other industry in terms of corrosion.

        Its corrosion issues begin from the storage area itself.

        There are four major areas that need to be looked at from the corrosion point of view –

        1. Production
        2. Storage
        3. Transportation
        4. Field application

        In the production stage, there are a few sub-steps.

        The first step begins with desulphurization.
        The motive is to remove the sulphur.
        This sulphur is present in the feedstock, which is the raw material to make the hydrogen for ammonium.
        The feedstock is petroleum and sulphur is an impurity. Along with this, there may be some produced water as well.
        This petroleum is stored in tanks made of carbon steel.
        It is transported to the process through carbon steel pipelines.
        Carbon steel is said to have less severe corrosion due to elemental sulphur.

        This corrosion due to elemental sulphur has mechanisms different from sulphidation and hydrogen sulphide corrosion.

        Watch the video for a detailed explanation

        Click here for PART 1.2!


        😀Happy learning!😀

        Corrosion risk planning – 2 – Above ground storage tanks – oil and gas- PART 2

         Above ground storage tanks – PART 2

        9.    Splash plate

            • corrosion at welds
            • atmospheric corrosion
            • coating damage, if applicable
            • pitting due to chloride salt deposition in marine environment

        10.    Spiral staircase

            • corrosion at welds of individual bars and critical joints to the tank
            • coating damage and delamination
            • cracks near welds
            • uniform corrosion at exposed surface near delamination
            • galvanic corrosion near weld/staircase/tank interface due to dissimilar alloys

        11.    Manometer

            • corrosion of screws, nuts, and bolts used for attachment
            • possible moisture penetration in case of cracks due to improper handling

        12.    Manhole

            • Internal corrosion due to water either as a moisture or as storage product
            • External coating damage due to moisture penetration, dust, rainfall, UV radiation
            • Coating damage at fixtures and edges
            • galvanic corrosion at nuts and bolts due to dissimilar alloys
            • atmospheric corrosion at area where coating is delaminated
            • galvanic/atmospheric corrosion of and at hinges, corrosion product buildup

        13.    Drain valve

            • galvanic corrosion in case of dissimilar metals. If valve is of brass, surrounding steel will corrode
            • pitting in case of stagnated water with chloride salts

        14.    Concrete drain

            • moisture ingress in concrete
            • possible corrosion of reinforcements especially if any remain exposed

        15.    Main inlet

            • Corrosion at welds
            • Crevice corrosion

        16.    Automatic tank gauge

            • corrosion at fixtures

        17.    Secondary inlet

            • Corrosion at welds
            • Crevice corrosion

        18.     Bund wall

            • Concrete degradation due to moisture ingress.
            • reinforcement corrosion at exposed areas
            • Possible biological contamination in case of stagnant undrained water

        19.    Pipe bends

            • internal erosion corrosion at the bends
            • external coating damage
            • atmospheric corrosion at point of coating delamination

        20.    Floor plates

            • soil side corrosion
            • Insufficient CP
            • coating damage and locoalized corrosion, if coating is used for underside
            • underdeposit corrosion

        21.    Foundation settlement

            • soil side corrosion
            • rain water absorption and migration to tank bottom
            • loosening of soil
            • uneven foundation, tilting of tank, preferential corrosion on one side

        22.    Roof

            • External atmospheric corrosion
            • coating damage
            • corrosion at welds
            • localized corrosion at points of stagnation
        Would love to hear your experience and comments!

        Click here for part 1!

        😀Happy learning!😀

        Corrosion risk planning – 2 – Above ground storage tanks – oil and gas- PART 1

         Above ground storage tanks

        1. Inner walls

            • Coating degradation
            • Corrosion due to water/dissolved oxygen
            • insufficient/damaged cathodic protection system
            • dissolved sacrificial anodes

        2. Outer walls/roof

            • Atmospheric corrosion
            • coating degradation due to moisture + UV radiation + temperature
            • Erosion and wear due to wind and dust particles
            • biological growth at the bottom areas near soil
            • soil corrosion near the bottom

        3. Pipes

            • Atmospheric corrosion
            • Coating degradation
            • mechanical failure
            • internal corrosion due to water/dissolved oxygen
            • crevice corrosion in areas facing away from atmosphere
            • corrosion at welds and joints
            • microbial corrosion at 6 o’ clock positions
            • erosion corrosion at bends

        4. Railing

            • Coating degradation
            • Wrong coating selection based on pure aesthetics
            • coating damage at joints and bends
            • corrosion at welds in the railing
            • crevice corrosion at fixtures
            • pitting corrosion

        5. Breather valve

            • uniform corrosion/pitting depending on whether it is made up of carbon steel/stainless steel
            • Galvanic couple at the joining/welding point of valve to roof
            • corrosion after damage of galvanized layer

        6. Spray nozzle

            • Crevice corrosion at orifices
            • clogging
            • erosion and mechanical damage at orifices and bends
            • crevice corrosion at fixtures

        7. Manhole

            • corrosion at edges of cover
            • galvanic corrosion at contact points with neighbouring parts
            • pitting due to chloride ion contact
            • crevice corrosion at fixtures
            • pitting corrosion at welds

        8. Lagging

            • pitting due to chloride ion contact
            • crevice corrosion at overlapping joints
            • water seepage at insufficiently bonded overlaps

        Click here for part 2!

        Corrosion risk planning – 1 – Lead acid battery

        Corrosion is a quality, environment, and safety issue. Hence, it has to come under the cope of integrated management system audits

        However at the moment, it is more or less considered a quality issue.

        As such, the general tendency is to solve corrosion issues as they come.

        Especially in new inventions, the foresight to look for potential corrosion risk gets lost in the attempt to focus and highlight the amazing qualities of the said inventions.

        Hence, I have initiated this series, where I will take a component and point out the potential corrosion and damage risk areas. 

        Here goes the first one – lead acid battery cell. (Source:https://opentextbc.ca/chemistry/chapter/17-5-batteries-and-fuel-cells/)

        1.  Protective casing – 
            • effect of temperature + electrolyte + contamination in electrolyte on the polymer
            • crevice corrosion at fixtures
            • mechanical damage during handling leading to voids for moisture ingress and oxygen/electrolyte leakage
        2. Positive terminal –
            • corrosion of the material of terminal due to remnant moisture
            • galvanic corrosion due to terminal and adjoining wires/components
            • crevice corrosion at fixtures
            • effect of anodic potential generated during battery operation – polarization
            • preferential corrosion due to connection with a polymer casing
        3. Negative terminal – 
            • corrosion of the material of terminal due to remnant moisture
            • galvanic corrosion due to terminal and adjoining wires/components
            • crevice corrosion at fixtures
            • effect of cathodic potential generated during battery operation – polarization and cathodic reactions
            • preferential corrosion due to connection with a polymer casing
        4. Cell divider –
            • corrosion of material in the electrolyte
            • degradation of coating on cell divider
            • effect of the generated ions during battery operation on coating
            • mechanical damage during installation
            • friction between divider plate and electrodes
            • for thin polymer coating, possibility of filiform corrosion
        5. Positive electrode –
            • corrosion of material in electrolyte at high temperature
            • cathodic reactions during battery operation
            • excessive localized dissolution due to electrolyte contamination
            • remnant reaction products during charging/discharging leading to localized pH changes and possible galvanic coupling
            • mechanical damage due to friction with adjoining parts (casing/divider)
        6. Negative electrode –
            • corrosion of material in electrolyte at high temperature
            • partially irreversible anodic dissolution
            • excessive localized dissolution due to electrolyte contamination
            • remnant reaction products during charging/discharging leading to localized pH changes and possible galvanic coupling
            • mechanical damage due to friction with adjoining parts (casing/divider)
        7. Dilute H2SO4 –
            • dilution not sufficient for safe handling and disposal
            • contamination due to reaction products
            • concentration modification due to temperature and cathodic reactions
        8. Fixtures for cell construction –
            • Mechanical damage due to friction/installation/handling
            • galvanic coupling with surrounding components
            • localized corrosion due to moisture deposition
            • crevice corrosion