The information on Metalizing.com answers many frequently asked questions about the metalizing process from the very basic, such as how is the metallic coating applied to steel and what materials are used to protect steel, to more complex matters like what is sealing and what are its benefits.
Metalizing.com relies primarily on two national standards that deal with metalizing to make a case in favor of metalizing steel bridges: the British Standard 5493,
Code of practice for Protective coating of iron and steel structures against corrosion,2 and Canadian Standards Association G189,
Sprayed Metal Coatings for Atmospheric Corrosion.3 We quote from these and other documents and let them speak for themselves. Opinions are clearly marked.
The FHWA report,
Corrosion Costs and Preventive Strategies in the United States 4 estimated that bridge steel corrosion cost the United States $276 billion per year. This sum is sure to grow in the future because of the age of our bridges, a maintenance backlog, rework, and inflation. Consider the following three quotes taken from that report.
There are 583,000 bridges in the United States (1998). Of this total, 200,000 bridges are steel, 235,000 are conventional reinforced concrete, 108,000 bridges are constructed using prestressed concrete, and the balance is made using other materials of construction. Approximately 15 percent of the bridges are structurally deficient, primarily due to corrosion of steel and steel reinforcement.[FHWA-RD-01-156]
As if the number of
structurally deficient bridges isn’t enough to distress drivers and, more importantly taxpayers, this FHWA report continued by summarizing just how much money is needed to maintain U.S. bridges
The annual direct cost of corrosion for highway bridges is estimated at $8.3 billion, consisting of $3.8 billion to replace structurally deficient bridges over the next 10 years, $2.0 billion for maintenance and cost of capital for concrete bridge decks, $2.0 billion for maintenance and cost of capital for concrete substructures (minus decks), and $0.5 billion for maintenance painting of steel bridges. Life-cycle analysis estimates indirect costs to the user due to traffic delays and lost productivity at more than 10 times the direct cost of corrosion maintenance, repair, and rehabilitation.[Emphasis added.] [FHWA-RD-01-156]
And later on in Corrosion Costs and Preventive Strategies in the United States we read
. . . the total annual cost of [paint] coating application ranges from $33.5 billion to $167.5 billion (an average of $100.5 billion)
The total market for metalizing and galvanizing in the United States is estimated at $1.4 billion. This figure is the total material costs of the metal coating and the cost of processing, and does not include the cost of the carbon steel member being galvanized/metallized.5 [FHWA-RD-01-156]
This report describes a grim situation. From the first two quotes, we learn 1) bridge steel corrosion is extensive and may even jeopardize the safe use of some bridges; and 2) bridge maintenance painting is expensive, costing the United States taxpayer many billions of dollars per year. Quote number three begs the question: why aren’t galvanizing and metalizing used more than is reported here?
There are people in the bridge coatings world who present paint as the universal coating, always the practical, economical, and best choice for protecting structural steel. This view is incorrect and it must be challenged for it ignores what is known to be true: a metallic zinc coating can protect steel better than paint and it provides the longer coating service life that is not available by painting. Metalizing with zinc is a proven cost-effective coating for steel structures and it is the means by which structure owners can get beyond paint’s short maintenance interval and endless repainting.
The claim that metalizing is too expensive for use on large steel structures is myth, a vestige of the days of flame-spray before the development of high production arc-spray equipment. This myth persists in part, 1) because of the fallacy of first-cost, and 2) because of the misuse of paint topcoats in combination with sprayed-metal coatings.
It is generally accepted that life-cycle cost analysis is the objective way to compare the costs of metalizing versus painting, taking into account service lives and dollars to be spent for each coating type. Comparing metalizing and painting on a first-cost basis is subjective, and creates the illusion of saving by ignoring the second part of life-cycle cost - metalizing’s very long service life. This is Paint’s Fallacy of First-Cost.
In most cases, multiple layers of paint over sealed-sprayed-metal are not necessary for corrosion control and do little to improve the service life of the sprayed-metal. Further, the addition of paint has consequences for future coating maintenance, or as British Standard 5493 puts it,
. . . the future maintenance intervals will be those of the metal-plus-paint system, which is often less than that for the bare metal coating but longer than for a similar paint system applied directly to steel. In other words, the paint will perform better over the sealed-sprayed-metal than if applied directly to steel, but it will deteriorate and will require repainting to maintain the aesthetic quality of the structure. [BS 5493]6
That unnecessary painting also increases the price of metalizing as an alternative to the common three coat paint systems.
Most bridge owners know well the principle of life-cycle cost (LCC) and the advantages to be gained by metalizing with zinc, but sometimes these engineers and managers face a dilemma. With too many bridges in need of repair and too few dollars in their budgets to do the required work, bridge owners may have to choose between service life and first-cost. We assume that these circumstances force owners to compromise on LCC, accept paint’s short service life, and paint bridges. It is a completely different matter, however, if the choice to paint is an effort to play catch-up on bridge painting. Playing catch-up, painting many bridges at a lowest possible price,7 does not work; it compounds the problem of bridges with failed or failing paint.
Granted, department of transportation decision makers are in a difficult position, but such a policy cannot solve the problem.
We ask our friends in the departments of transportation, are you open to the idea of substituting sprayed metallic zinc for your department’s standard paint coating to achieve a longer coating service life, less traffic disruption and lower life-cycle cost?
lowest qualified bid price.