Estimating the Time to First Maintenance of a Duplex HDG Steel System



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03 October 18
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A duplex HDG steel system combines the protection of galvanized coating with the benefits of a secondary corrosion protection system, such as paint or powder coating.

Duplex HDG steel systems can either be produced at the time of HDG steel manufacturing (such a system is referred to as pre-painted steel) or post manufacturing as per convenience. Usually, the former option is preferred for it offers superior performance characteristics to post manufacturing painted or powder coated HDG steel.

Like any HDG steel system, knowing the Time to First Maintenance of a duplex HDG steel system is of critical importance to manufacturers, designers and contractors.

What is the Time to First Maintenance?

The Time to First Maintenance is the time it takes for the base HDG steel to lose 5% of its galvanized coating. In simpler words, it’s the time to first touchup or repair for a HDG steel system.

How do you estimate the Time to First Maintenance of a duplex HDG steel system?

Anyone familiar with estimating the Time to First Maintenance of a normal HDG steel system, knows that the calculation requires the use of TFM Chart. However, since the TFM Chart does not account for the additional protection available in duplex HDG steel systems, it cannot be used for the estimation of the Time to First Maintenance of a duplex system.

Instead, the Zinc Coating Life Predictor tool is used for estimating the Time to First Maintenance of a duplex HDG steel system.

You’ll first estimate the Time to First Maintenance of the HDG steel system independent of the paint/powder system using the Zinc Coating Life Predictor tool. To perform the calculation, you’ll need to input the thickness of the zinc coating and the values of the average annual environmental factors for the area where the structure is to be deployed, or the product is to be used.

Once you’ve calculated the Time to First Maintenance of the HDG steel system, next you need to estimate the paint/powder system life. This information is typically provided by the paint/powder system manufacturer.

After calculating the Time to First Maintenance of the HDG steel system and the life of the paint/powder system, add the two values and multiply the result with the duplex multiplication factor.

What is duplex multiplication factor?

Duplex multiplication factor is a compensating factor that accounts for the additional protection available in duplex HDG steel systems when estimating the Time to First Maintenance for these systems.

The duplex multiplier ranges from 1.5 to 2.3.

Which multiplication factor should you choose for you calculation?

The selection of a duplex multiplication factor is dictated by the environmental conditions in which the system is to be deployed:

  • 5 is used for extreme pollution and extreme marine environments
  • 6 is used for sea water applications
  • 7-2.0 is used for marine and industrial environments
  • 0-2.3 is used for non-robust environments

Multiplying the sum of the Time to First Maintenance of the duplex HDG steel system and the life of the secondary protection system with the duplex multiplication factor will give you an estimated Time to Maintenance of your duplex HDG steel system.

Do you have any other questions about using duplex HDG steel systems for construction or product fabrication? Feel free to reach out; our duplex HDG steel system experts will be happy to help you.

We also manufacture and supply high quality prepainted galvanized steel coils in bulk. If you’re looking to source high quality duplex HDG steel for your project, we can deliver it to you right at your doorstep.

A BONUS read: Cut Edges on Pre-Painted Steel are Tougher Than You Think!

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