Corrosion – A Persistent Battle
Corrosion – the deterioration of a material or its properties due to a reaction of that material with its chemical environment – has been with us forever. People have recognized, accepted, coped with and, occasionally, battled corrosion for millennia. In the 19th century, we began taking steps to understand, prevent, and treat corrosion, and we have gradually expanded these efforts ever since. But recently, corrosion has become a major concern, partly because our demands for more complex and sophisticated systems and products have been satisfied by materials that are more susceptible to corrosion. The insidious and pervasive effects of corrosion have now reached the point where it is a major cost for our economy and quality of life – in fact recent studies estimate the direct cost of corrosion in the United States to be nearly $300 billion dollars per year.
Life Cycle Costing Comparison: Miscellaneous Metals
There are many options available to the architect or engineer when selecting a protective coating system for steel. Several factors must be considered during the selection process. Remember, the “cheapest” system based on initial cost may wind up being the most expensive over the life of the project. That is why many professional associations and Public Sector Agencies mandate the use of Life Cycle Costing in specifying coating systems.
We are pleased to provide you with data which will assist you in selecting a long lasting corrosion protection system that is aesthetically pleasing and will provide the owner with many years of maintenance-free operation.
List Of Assumptions
In reviewing the most common coating systems, there were certain assumptions made:
- The steel in question is considered miscellaneous or ornamental iron. This would include tubular, ornamental, flat bar or pipe.
- Costs listed are for one (1) ton of steel.
- The service atmosphere in the subject location is considered seacoast/heavy industrial (within one mile of the seacoast and/or salt water). This includes virtually every major metropolitan area on the Eastern seaboard.
- A product is installed and all painting is done at ground level and not “in the air”.
- Maintenance is considered at “practical life” not “optimum life”. Practical life is the time until 5-10% breakdown occurs, active rusting of the substrate occurs, and maintenance should be initiated.
- The goal is to achieve a 50-year life for the product.
- Costs are in base year dollars. Future values were not calculated but should be expected to increase through normal inflation.
In preparing the study, several sources were used. Included were:
- H. Brevoort, A.H. Roebuck, “Simplified Cost Calculations and Comparisons of Paint and Protective Coating Systems, Expected Life and Economic Justification” CORROSION/79, Paper No. 37, National Association of Corrosion Engineers
- H. Brevoort, A.H. Roebuck, “Costing Considerations for Maintenance and New Construction Coating Work” CORROSION/92, Paper No. 335, National Association of Corrosion Engineers
- “Abrasive Blasting Guide for Aged or Coated Steel Surfaces” T&R Bulletin 4-21. The Society of Naval and Marine Engineers
- “Standard Method of Evaluating Degrees of Rusting on Painted Steel” Steel Structures Painting Council (SSPC) and American Society for Testing and Materials (ASTM)
- “Good Painting Practices” Steel Structures Painting Council
- “Cost-Effectiveness of Hot Dip Galvanizing for Exposed Steel” Transportation Research Board, National Research Council
Life Cycle Cost Analysis of Various Coating Systems For Miscellaneous Metal
|Coating System||Initial Cost
|Cost Over a 50 Year Cycle Per Ton|
(Hot Dip Duragalv? Galvanizing
Duragalv? with field coats
(Hot Dip Duragalv? Galvanizing with field applied metal primer and two coats of field applied high gloss Alkyd Enamel topcoat)
Duragalv?– No Coating
(Hot Dip Duragalv? Galvanizing)
Shop applied Universal Metal Primer with two coats of High Gloss Enamel
Shop applied Inorganic zinc rich primer, tie coat of high build polyamide epoxy and topcoat of aliphatic urethane
|Duragalv? is Duncan’s name for an enhanced hot dip galvanizing process which combines long-term corrosion protection with an aesthetically pleasing finish.|
Notes to Life Cycle Cost Analysis of Various Coating Systems: Miscellaneous Metals
The following definitions will apply to the analysis of the various coating systems reviewed:
|Coating System:||The metal coating systems reviewed are those most commonly used on construction projects of this type. They represent the broad spectrum of steel corrosion protection systems available which encompass cost, maintenance, corrosion protection and durability.|
|Initial Cost:||This is the price per ton of miscellaneous metals which would be used on this project. The price is based on the per pound cost of the material, surface preparation process and application and is multiplied by 2,000.|
|Time Until First Maintenance:||This is the length of time that the product will last before the owner will be required to provide any maintenance. The number of years were determined through the use of standard reference charts which are noted on the first page of this analysis. It is a major criteria in selecting a quality system.|
|Initial Cost Per Year:||This is the comparative cost of each system on an initial cost basis determined by dividing the initial cost by the time until first maintenance is required. It is the most effective method to determine the value of a system based upon initial cost analysis.|
|Maintenance Cost:||This is the cost to maintain the product during its economic life. The figures were taken from the reference charts noted on the first page of this analysis. It is an extremely useful tool to assist the owner in determining the budget and anticipated costs to be assigned to the ongoing maintenance effort.|
|Maintenance Life||This is the anticipated length of time that the product will last before any additional maintenance is required, or the intervals which will be needed to maintain the product. Again, the figures were derived from the published reference charts.|
|Maintenance Cost Per Year:||This is the figure that the owner should use when determining an annual operating cost for each system. It was calculated by dividing the maintenance cost by the maintenance life.Essentially, it is that amount which will need to be allocated to the product to maintain it in the appropriate manner.|
|Cost Over A 50 Year Life:||This is the truest test of all. It determines which system, with everything taken into consideration,will perform the best and be the most cost effective system for the construction project. It is determined by adding the initial cost, maintenance cost and the total of the number of years until 50 year life multiplied by the maintenance cost/year. For example:|
|Example||System #1||System #6|
Total of costs:
Years until 50 year life:
Additional maintenance cost:
Cost Over 50 Year Cycle:
13 years (50 – [21 + 16] )
$886.08 (13 x $68.16)
Hypothetical Comparison of the Various Coating Systems
To create a practical example, assume that there are 50 tons of miscellaneous steel used per category
|Category||System 1||System 2||System 3||System 4||System 5||System 6|
|Years Until Maintenance Is Needed||50||35||25||50||10.5||21|
|Initial Cost Per Year||$880||$1,040.50||$1,880||$500||$2,393||$2,091.50|
|Cost To Maintain The Product During Its Economic Lifetime||$0||$16,100||$37,625||$0||$37,625||$54,525|
|Maintenance Intervals||50 Years||25 Years||20 Years||50 Years||8 Years||16 Years|
|Maintenance Cost Per Year||$0||$644||$1,881.50||$0||$4,703||$3,408|
|Total Cost Of The System||$44,000||$52,500||$131,650||$25,000||$210,895||$142,754|
|There are some basic conclusions to be drawn from this analysis. When evaluating coating systems, the initial outlay should not necessarily be the single component on making a decision. While systems might appear to be less costly at first glance, a careful analysis will point out all the pitfalls and costs associated.|
Significance and Use
LCC analysis is an economic method for evaluating alternatives that are characterized by differing cash flows over the designated project design life. The method entails calculating the LCC of each alternate capable of satisfying the functional requirement of the project and comparing them to determine which has (have) the lowest estimated LCC over the project design life.
The LCC method is particularly suitable for determining whether the higher initial cost of an alternative is economically justified by reductions in future costs (for example, rehabilitation, or replacement) when compared to an alternative with lower initial costs but higher future costs. If a design alternative has both a lower initial cost and lower future costs than other alternatives, an LCC analysis is not necessary to show that the former is the economically preferable choice.
1.1 This practice covers a procedure for using life-cycle cost (LCC) analysis techniques to evaluate alternative corrosion protection system designs that satisfy the same functional requirements.
1.2 The LCC technique measures the present value of all relevant costs of producing and rehabilitating alternative corrosion protection systems, such as surface preparation, application, construction, rehabilitation, or replacement, over a specified period of time.
1.3 Using the results of the LCC analysis, the decision maker can then identify the alternative(s) with the lowest estimated total cost based on the present value of all costs.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
E917 Practice for Measuring Life-Cycle Costs of Buildings and Building Systems