Materials Performance

AUG 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

Issue link:

Contents of this Issue


Page 41 of 92

39 MATERIALS PERFORMANCE: VOL. 57, NO. 8 AUGUST 2018 Steel H-piles that support the down- town parking garage and bus parkover were installed in the mid-1980s. The original coating on these piles had failed long ago in the tidal and splash zones, which led to corrosion-induced section loss of the steel. The sheet pile seawall at Marine Park was recoated in the late 1990s. Similarly, this coating failed in the tidal and splash zones. The marine side of the sheet piling is pro- tected with cathodic protection (CP) that utilizes aluminum anode sleds installed in 2000. These sleds are still providing protec- tion to the structure but are near the end of their design life. To protect the soil side of th e sh eet piles and th eir tieback s, an impressed current CP (ICCP) system was designed that includes two shallow anode wells. Figure 2 shows a map of the repairs. To address the ongoing corrosion of the parkover and garage H-piles, a corrosion plan was developed that included direct- welded aluminum anodes and petrolatum- filled pile jackets (Figure 3). Galvanic CP was selected for this work over an ICCP system to avoid the risk of stray current interference from cruise ships. CP requires an electrolyte to provide protective current so corrosion on submerged and buried structures is ef fectively mitigated . For structures in seawater, the CP system pro- tects submerged areas (with seawater act- ing as the electrolyte), but provides dimin- ishing protective current in the tidal zone. B e c a u s e s e a w a t e r s u b m e r s i o n t i m e decreases with increasing elevation, the upper parts of the tidal zone may be left with essentially no CP protection. In atmospheric environments where CP is ineffective or minimally effective, barrier systems are often employed. These systems can include coatings, galvanizing, wraps, tapes, and jackets. In this case, a petrola- tum-filled jacket system was selected due to its longevity ; minimal surface prepara- tion requirements; and durability in resist- ing physical damage from flotsam, a com- mon cause of damage to structures in onshore marine environments. When designing for any coastal work in southeast Alaska, undoubtedly one of the major factors to consider is the tides. In FIGURE 1 Map of site locations. FIGURE 2 Juneau site map and repair locations. Juneau, daily tide swings are frequently over 23 ft (7 m). This can create problems for designers—principally it creates prob- lems when designing repairs that are con- structible. Extreme tide swings in Juneau means that some high tides submerge por- tions of the pile caps, making permanent fixed scaffolding and staging impossible. Floating scaffolding needs to be removed before high tides to prevent damage to the pile caps and scaffolding, which creates additional work. A second obstacle to performing repairs is the seasonal schedule. Work in the win- t er i s imp o ssi bl e for many t a sk s and extremely difficult for many others. The cruise ship schedule at Steamship Wharf requires any work performed to occur

Articles in this issue

Archives of this issue

view archives of Materials Performance - AUG 2018