The National Academies Press

Currently Skimming:

Pages 42-64

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.

From page 42... ... 42 Steel is used for several elements of bridges, including towers, piers, girders, and trusses. Steel components in bridges often are protected from corrosion with protective coatings. Read the entire page →
From page 43... ... Corrosion Control of Coated Steel Bridges 43 Coating Material Alternatives Figure 31 shows the popularity of various coating systems as indicated by a 2014 survey of state bridge coating maintenance practices (KTA-Tator 2014) and the survey portion of this synthesis. Read the entire page →
From page 44... ... 44 Corrosion Prevention for Extending the Service Life of Steel Bridges A significantly wider range of coating chemistries is used for spot touch-up and overcoating. Figure 33 shows the various types of coatings used for spot touch-up and overcoating as reported by agencies in a 2014 survey (KTA-Tator 2014) Read the entire page →
From page 45... ... Corrosion Control of Coated Steel Bridges 45 intermediate, and topcoats all provide different functions. The zinc-rich primer serves as a barrier but more importantly provides corrosion prevention at defects where the steel is exposed (Ault and Farschon 2008) Read the entire page →
From page 46... ... 46 Corrosion Prevention for Extending the Service Life of Steel Bridges In addition to cathodically protecting the steel, inorganic zinc primers form a hard barrier layer upon reaction with the environment. This barrier mechanism works in conjunction with the cathodic protection afforded by the zinc particles. Read the entire page →
From page 47... ... Corrosion Control of Coated Steel Bridges 47 the environment and sacrificial cathodic protection. If the surface becomes scratched, exposing the base metal, the zinc coating is slowly consumed while the substrate remains protected. Read the entire page →
From page 48... ... 48 Corrosion Prevention for Extending the Service Life of Steel Bridges conducted at the galvanizer's plant before shipment. Because the service life of a galvanized coating is directly related to the zinc coating thickness, thickness and coverage are critical checks of galvanized coating quality. Read the entire page →
From page 49... ... Corrosion Control of Coated Steel Bridges 49 Metallizing Metallizing is a process in which molten metal or ceramics are sprayed onto a substrate. There are several metallizing technologies, including arc wire, flame, plasma, and high-velocity oxygen fuel (HVOF) Read the entire page →
From page 50... ... 50 Corrosion Prevention for Extending the Service Life of Steel Bridges coatings originally were relatively thin and intended to seal any porosity that might exist in the metallizing. However, full-thickness organic coatings have taken the place of sealers, and the terminology "duplex coatings" now is commonly applied to systems with either galvanizing or metallizing. Read the entire page →
From page 51... ... Corrosion Control of Coated Steel Bridges 51 Specifications Based on the survey conducted for this synthesis, all the respondents said their state has a qualified products list for protective coatings. Five agencies (states of Michigan, Minnesota, Wisconsin, and Florida, and New York City) Read the entire page →
From page 52... ... 52 Corrosion Prevention for Extending the Service Life of Steel Bridges the NTPEP data. Therefore, two-thirds of the states use the NTPEP program to inform their structural steel coating selection. Read the entire page →
From page 53... ... Corrosion Control of Coated Steel Bridges 53 Table 13 shows how the survey respondents specify corrosion prevention during maintenance (note that respondents could select more than one option, so the categories do not add up to 100%) Read the entire page →
From page 54... ... 54 Corrosion Prevention for Extending the Service Life of Steel Bridges metallizing, the design details include ensuring all surfaces are accessible for proper surface preparation and thermal-spray metallizing. Organic Zinc versus Inorganic Zinc Primers Zinc-rich, three-coat systems entail either an organic or inorganic zinc-rich primer, a barrier midcoat, and durable topcoat. Read the entire page →
From page 55... ... Corrosion Control of Coated Steel Bridges 55 whether to use metallizing or galvanizing, the main deciding factors are usually the size of the pieces to be coated and the complexity of their detailing. Duplex Coatings versus Metallic Coatings As described, duplex coatings consist of metallizing or galvanizing coatings top-coated with a urethane or other polymer. Read the entire page →
From page 56... ... 56 Corrosion Prevention for Extending the Service Life of Steel Bridges • Extended service lifetimes can be achieved in marine environments (Chang and Georgy 1999a; Kogler 2015) Read the entire page →
From page 57... ... Corrosion Control of Coated Steel Bridges 57 application can be achieved. As such, care should be taken to ensure the weather conditions are as specified for the coating application and during the coating cure or field containment may be necessary to control the environment conditions, which can increase the application cost (Chang and Chung 1999; Kogler 2015) Read the entire page →
From page 58... ... 58 Corrosion Prevention for Extending the Service Life of Steel Bridges Drainage areas. Drainage areas see increased time of wetness, larger amounts of dirt and debris, and may be exposed to deicing salts. Read the entire page →
From page 59... ... Corrosion Control of Coated Steel Bridges 59 Service Environment Considerations Bridge location and exposure environment can affect bridge service life. Proximity to chloride or industrial chemical sources can also be important. Read the entire page →
From page 60... ... 60 Corrosion Prevention for Extending the Service Life of Steel Bridges at what point the contractor becomes accountable for the defect (Chang and Georgy 1999b) Read the entire page →
From page 61... ... Corrosion Control of Coated Steel Bridges 61 Figure 37. Initial and life-cycle costs for six steel bridge coating scenarios for a 60-year service life in a corrosive environment (re-created from Farschon et al. Read the entire page →
From page 62... ... 62 Corrosion Prevention for Extending the Service Life of Steel Bridges Do Nothing The decision to do nothing is made when no maintenance action is required. The existent coating may be in good condition. Read the entire page →
From page 63... ... Corrosion Control of Coated Steel Bridges 63 Spot Painting Spot painting is a maintenance practice in which discrete areas are prepared and coated. These discrete areas may be where the coating deteriorated or localized corrosion occurred. Read the entire page →
From page 64... ... 64 Corrosion Prevention for Extending the Service Life of Steel Bridges design details by revealing the extent of corrosion damage and resulting in a more-efficient overall project by taking advantage of access, lane closures, and other resources. New steel being installed as part of a project is most effectively coated in the shop before erection. Read the entire page →

From page 42...

... 42 Steel is used for several elements of bridges, including towers, piers, girders, and trusses. Steel components in bridges often are protected from corrosion with protective coatings.