The Weakest Link of Hot Dipped Galvanized Lattice Structures.

The weakest links on lattice structures are found at the fasteners, where joints are clamped together. The weakest links on carbon steel lattice structures are the high strength fasteners (bolts, nuts and washers) that are small relative to the structure to which they are clamped. Fasteners have different corrosion potentials to the lattice steel members (multimetals) and when moisture is present the corrosion effect is exacerbated. A further contributory factor is the too thin layer of galvanising on the fasteners.

The best corrosion protection for jointed areas will always be to hot dip galvanise the members, then to over coat the jointed area with an active seal duplex coating (traditionally passive barriers are used), to extend the life cycle of fasteners for periods exceeding 30 years in corrosive environments.

However, passive barrier coatings only form an inert shell over metal and they usually crack where lattice structures move (joints), thus allowing the ingress of moisture and oxygen. Extended periods of moisture ingress into these micro-environments leads to crevice corrosion at the joint, threatening the integrity of the fastener’s tensile strength.

Active seal coatings react with the surface of the metal, changing the environment on the surface to protect the steel. This type of coating technology, generically known as High Ratio Calcium Sulfonate Alkyd (HRCSA), has passed a rigorous test conducted by South Africa’s state-owned utility, Eskom, for two years in the most corrosive environment in South Africa with great success. HRCSA provides significant joint protection because of its chemical reaction to metallic surfaces, because the polar end of the sulfonate/carbonate complex attaches to the metallic substrate and demonstrates exceptional adhesion through van der Waals forces (dipole–dipole), causing HRCSA to have a greater attraction to metal than water, even when the coating film is damaged.

The HRCSA, trademarked as AFRISUN-HRCSA™, active seal reacts with the zinc carbonate layer on the surface of the galvanising, thereby lifting the surface pH > 10.1, thus inhibiting corrosion. HRCSA’s alkyd constituent will not cause sulfonation because of the small amount of alkyd in the coating. Furthermore, the AFRISUN-HRCSA™ active joint seal is hydrophobic, preventing moisture and oxygen ingress into the joint, eliminating the electrolyte and oxygen needed for a corrosion cell to form. The AFRISUN-HRCSA™ exhibits a very low conductance of electricity, preventing the electron flow/stray currents to enter the jointed area. The ability to flex with moving joints makes AFRISUN-HRCSA™   a proven and tested solution to protect fasteners against corrosion.

All African Power Elites are invited to read Afrisun’s editorial on “The weakest link of hot dipped galvanised lattice structures” published in ESI Africa Issue 4 2017.

 

 Van der Waals forces are the relatively weak attractive forces that act on neutral atoms and molecules and that arise because of the electric polarisation induced in each of the particles by the presence of other particles.
 Dipole-dipole forces – with a strength range from 5kJ to 20kJ per mole – are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule.

The erosion rate of coatings must be taken into serious consideration by Utilities, given the corrosive environment in which structures are erected.

The AFRISUN-HRCSA™   technology has been formulated to offer the following benefits:

1.            The coating is thixotropic, allowing a film build of up to 1,500 micron with one coat

2.            The coating stays firm and will not get hard and crack

3.            The erosion rate of AFRISUN-HRCSA™   is slower than conventional passive barrier coatings

4.            The AFRISUN-HRCSA™   offers an extended service life that benefits Utilities because maintenance programmes are costly and disruptive when planned outages cut power to consumers.

 

 

 

Electrical towers

The Weakest Link of Hot Dipped Galvanized Lattice Structures.

The weakest links on lattice structures are found at the fasteners, where joints are clamped together. The weakest links on carbon steel lattice structures are the high strength fasteners (bolts, nuts and washers) that are small relative to the structure to which they are clamped. Fasteners have different corrosion potentials to the lattice steel members (multimetals) and when moisture is present the corrosion effect is exacerbated. A further contributory factor is the too thin layer of galvanising on the fasteners.

The best corrosion protection for jointed areas will always be to hot dip galvanise the members, then to over coat the jointed area with an active seal duplex coating (traditionally passive barriers are used), to extend the life cycle of fasteners for periods exceeding 30 years in corrosive environments.

However, passive barrier coatings only form an inert shell over metal and they usually crack where lattice structures move (joints), thus allowing the ingress of moisture and oxygen. Extended periods of moisture ingress into these micro-environments leads to crevice corrosion at the joint, threatening the integrity of the fastener’s tensile strength.

Active seal coatings react with the surface of the metal, changing the environment on the surface to protect the steel. This type of coating technology, generically known as High Ratio Calcium Sulfonate Alkyd (HRCSA), has passed a rigorous test conducted by South Africa’s state-owned utility, Eskom, for two years in the most corrosive environment in South Africa with great success. HRCSA provides significant joint protection because of its chemical reaction to metallic surfaces, because the polar end of the sulfonate/carbonate complex attaches to the metallic substrate and demonstrates exceptional adhesion through van der Waals forces (dipole–dipole), causing HRCSA to have a greater attraction to metal than water, even when the coating film is damaged.

The HRCSA, trademarked as AFRISUN-HRCSA™, active seal reacts with the zinc carbonate layer on the surface of the galvanising, thereby lifting the surface pH > 10.1, thus inhibiting corrosion. HRCSA’s alkyd constituent will not cause sulfonation because of the small amount of alkyd in the coating. Furthermore, the AFRISUN-HRCSA™ active joint seal is hydrophobic, preventing moisture and oxygen ingress into the joint, eliminating the electrolyte and oxygen needed for a corrosion cell to form. The AFRISUN-HRCSA™ exhibits a very low conductance of electricity, preventing the electron flow/stray currents to enter the jointed area. The ability to flex with moving joints makes AFRISUN-HRCSA™   a proven and tested solution to protect fasteners against corrosion.

All African Power Elites are invited to read Afrisun’s editorial on “The weakest link of hot dipped galvanised lattice structures” published in ESI Africa Issue 4 2017.

 

 Van der Waals forces are the relatively weak attractive forces that act on neutral atoms and molecules and that arise because of the electric polarisation induced in each of the particles by the presence of other particles.
 Dipole-dipole forces – with a strength range from 5kJ to 20kJ per mole – are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule.

The erosion rate of coatings must be taken into serious consideration by Utilities, given the corrosive environment in which structures are erected.

The AFRISUN-HRCSA™   technology has been formulated to offer the following benefits:

1.            The coating is thixotropic, allowing a film build of up to 1,500 micron with one coat

2.            The coating stays firm and will not get hard and crack

3.            The erosion rate of AFRISUN-HRCSA™   is slower than conventional passive barrier coatings

4.            The AFRISUN-HRCSA™   offers an extended service life that benefits Utilities because maintenance programmes are costly and disruptive when planned outages cut power to consumers.