EL ENFOQUE LECTO-ESCRITURAL

Site 2 was located in Cory, Saskatchewan, approximately five miles southwest of Saskatoon, Saskatchewan (Figure 3.6), adjacent to a potash mine and the Cory Co-Gen Substation. Inspection of Site 2 took place on 9 September 2015.

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(b) Figure 3.6 Site 2: (a) map indicating site and pole locations; and (b) photographic

The transmission line poles were located less than 100 ft from the mine processing facilities, which emitted smoke likely to contain corrosive pollutants. Due to the close proximity to these facilities, the poles were deemed to be exposed to an industrial atmosphere.

At the time of inspection, the transmission line at Site 2, Line Q3C, operated at a voltage of 138 kV. This line was installed in 2002. Out of five WS poles on site, one pole (Q3C-2R) was assessed based on visual inspection, and three poles (Q3C-1L, Q3C-1R, and Q3C-2L) were inspected using the full spectrum of field test methods detailed in Chapters 4.0 and 5.0. Poles Q3C-1L and Q3C-1R together formed an H-frame structure, while the other poles were split into single pole structures (Figure 3.6b). All four poles at Site 2 were made of Type AT steel (CSA 2013) and had a circular cross section at the base, with a nominal diameter of 18 in. Poles Q3C-1L and Q3C-1R had a nominal wall thicknesses of 5/16 in., and Poles Q3C-1L and Q3C-1R had a nominal wall thicknesses of 3/8 in. These four structures are shown in Figure 3.7.

All four poles were grounded using a similar type of grounding rod electrode system and GEC configuration (Figure 3.8). Poles Q3C-1L, Q3C-2L, and Q3C-2R utilized 32-lb magnesium anodes, which were installed at time of construction, as supplementary cathodic protection. Pole Q3C-1R did not feature a magnesium anode connection because the anode attached to Pole Q3C-1L was designed to protect both poles, which were connected to form an H-frame.

(a) (b) (c) (d) Figure 3.7 Site 2 poles: (a) Q3C-1L; (b) Q3C-1R; (c) Q3C-2L; and (d) Q3C-2R.

Figure 3.8 Corrosion prevention measures seen on Site 2 poles, including GEC link to grounding rod and magnesium anode connection.

The four poles were coated with a 3M Skotchkote 352 polyurethane coating (Johnson 2013), directly embedded into the ground, and backfilled with gravel. The use of this particular coating has since been discontinued. At their highest positions, the coatings extended above the ground line approximately 18 in. for Poles Q3C-1R and Q3C-2R, 24

in. for Pole Q3C-1L, and 30 in. for Pole Q3C-2L. Severe degradation was evident as significant coating lip delamination was observed around the entire circumference of each pole. The worst case of coating lip delamination (on Pole Q3C-1L) had resulted in an 8-in. drop from the original coating height (Figure 3.9). Such defects facilitate moisture penetration and stagnation. As a result, pack rust was observed at these coating crevices and discontinuities.

Figure 3.9 Severely delaminated coating line accompanied by widespread pack rust and pack out on ladder clip.

On some poles, bands of discolored orange-brown rust (indicative of non-protective patina) were seen to stretch from the lips to the level where the coatings originally terminated. Pitting was also common around this region, generally at a severity of Level A3-B4 per ASTM G46 (ASTM 2013c). One way that coating delamination was seen to propagate was through the formation of pack-out rust at the pole wall-coating interface, which is clearly evident on Poles Q3C-2L and Q3C-2R (Figure 3.10). This pack-out damage results in steel section losses while at the same time prying the coating from the pole. These phenomena are reasonably attributed to repetitive moisture entrapment

underneath the protective coatings. Wherever pack-out rust forms, it opens up a new gap for water to stagnate, leading to more oxidation and coating delamination. Debonding from the WS substrate was also observed within the bodies of some coatings. Multiple near- circular holes, spanning up to 6 in. across, were present in the coating of Pole Q3C-2L. One such defect was located at only 3 in. from the ground line (Figure 3.7). These issues may generate due to material quality, adhesion, and installation procedures.

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Figure 3.10 Pack-out corrosion damage: (a) rust removed from coating line; and (b) easily removed rust layer, with pack rust still visible along coating line.

Problems were not isolated to the coating and ground-line regions. While the patina for each pole was dark-brown for the most part, grain size and roughness of the patina visibly increased on surfaces closer to the potash plant. This increase in coarseness was an indicator of the non-adherence of the patina. In fact, the plant-side outer oxide layers on Poles Q3C-1L and Q3C-1R would slough off 2-5 mm rust pieces by simply running a hand across the WS surface (Figure 3.11).

Figure 3.11 Non-adherent patina sloughing off with light rubbing of pole wall surface.

These instances of corrosion damage pointed to the formation of a non-protective oxide layer due to the continuous exposure to an industrial atmosphere. The adjacent potash mine provided a ready source of corrosive sulfur dioxide (SO2) with the dust and exhaust

fumes from its processing facilities. It is noted that the potash produced here has primarily been of the potassium chloride variety (PotashCorp 2015). A relevant implication is that, as a result of potash processing, atmospheric chlorides have also contributed to the environmental corrosivity of Site 2, lowering the effectiveness of the protective patina of nearby WS structures. This is highlighted since, to the best of the authors’ knowledge, no study has been published on this type of corrosive environment, different from atmospheric chlorides at marine locations and from the use of deicing salts.