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Zinc-coated roofing steel loses its zinc coat after about ten years because of being exposed to elements and it has to be painted. Zinc-coated powerline posts lose zinc too and experience corrosion, however they are built of thick parts which are "eaten up" slowly and once enough cross-section is lost they are replaced.

However I've recently seen a culvert assembled from pieces of corrugated steel with coating looking like zinc. Parts were something like 5 millimeters thick and connected with numerous bolts and the culvert diameter was about 1,5 meters.

The water passing through a culvert bring sand and other particles which surely grind the surface. I assume this should remove the coating from the submerged part of the culvert within several years and then corrosion will start and eat the not so thick steel rather quickly.

How is abrasion by solid particles addressed in culverts made of galvanized steel?

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The design and establishment of a culvert, or any structure, is influenced by the materials available, the environmental conditions that the culvert will withstand, water pH, soil type and the amount of money available for the project.

Nothing lasts for ever and all engineering structures have an anticipated/designed service life, after which, if possible the service life of the structure may be extended by some form of refurbishment or the structure is replaced.

By way of example, this manufacturer of steel pipes, makes pipes that can be used for culverts and the service life of each the product depends on the different type of coatings applied to the pipes:

  • Zinc – 25 years
  • Aluminium – 75 years
  • Asphalt & polymer laminate – 100 years

As the website state:

choice of coatings depends on the soil conditions and other site or application factors

If galvanised steel is being used in a culvert there is already an expectation that it's service life will be less than if it were constructed from something else such as aluminium or concrete.

This site has a design guideline for culvert design. Point 4 states:

Determine which abrasion level most accurately describes the typical storm event (2 year storm). The expected stream velocity and associated abrasion conditions should be based on a typical flow and not a 10 or 50-year design flood

and Point 5 states:

determine whether the structural gage for the selected material is sufficient for the design service life

If galvanised steel has been used to construct a culvert it's design life has been determined and accepted and deemed suitable for the application based on factors such as these.

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Are you sure it wasn't aluminium? The differences when searching for images is not that big. Another option is that it has been coated with some polymer.

Aluminum pipes are also corrugated and can be constructed as either structural plates or from a single piece of aluminum. Due to their high resistance to corrosion aluminum pipes do not develop rustlines and are often used in high corrosion environments such as saltwater applications.

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  • $\begingroup$ Almost sure - aluminum parts would very likely be stolen in no time. $\endgroup$ – sharptooth Apr 13 '15 at 10:45
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    $\begingroup$ @shar: Digging out a pipe from a culvert that is big enough to be assembled from multiple sections bolted together is not a simple midnight dig and run job. Realistically it would take mechanized equipment and at least a few hours. Unless the culvert is in a very remote location, nobody is going to steal it. $\endgroup$ – Olin Lathrop Apr 13 '15 at 13:52
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    $\begingroup$ @OlinLathrop No need to dig out the entire pipe. Simply chop or unscrew part of it, sell that as scrap, buy booze, be happy for a while, then optionally get jailed. $\endgroup$ – sharptooth Apr 14 '15 at 6:36

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