Box sections in Marine environment

[Amar Yarli]

Hi,

Is it recommendable to use steel box sections in marine environment ?
Please give your thoughts and suggestions.

 

[hokie66]

Can be done. It requires a lot of attention to corrosion protection systems.

 

[SAIL3]

internal corrosion would be a major concern...

 

[SlideRuleEra]

If the structure will be close (say within 200 meters) of a shoreline with breaking salt-water waves, I would not use box sections for any reason. The salt spray from the breaking waves causes significant corrosion.

If more than 200 meters from the shoreline, you probably can get reasonable life from box sections using modern corrosion protection, as hokie66 suggested. The problem is internal corrosion, per SAIL3.

Marine shorelines are subject to storm surge flooding (with salt water) in some areas. If this flood water gets inside the box section... its days are numbered.

I would not use box sections until well beyond the storm surge flood area. This could be several miles in some locations.

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[Settingsun]

As usual, it depends. Here's a few points in favour of them.

A common argument against hollow sections is that the inside can't be inspected. On the other hand and despite best intentions, it's quite common for the maintenance budget to become zero dollars over time, in which case the advantage of an open section is that you can clearly see that *both* sides are rusting away, instead of just the outside of the hollow section.

Hollow sections can and have performed well when properly sealed. Properly sealed means remembering that the seal plate will also corrode so a 3mm plate as might be used in a dry environment is inadequate. Use a big weld too.

Hollow sections can be wrapped if required but this is difficult for open sections.

Circular hollow sections are commonly used as piles in marine structures so they have a considerable track record.

Sealed hollow sections are subject to buoyancy force if submerged which should be borne in mind.

 

[hokie66]

As steveh49 noted, circular steel piling is often employed in marine structures. Coal loading piers often extend long distances to sea. The ones I have seen typically use bents consisting of battered circular piles, with rectangular hollow section headstocks. Not sure of the corrosion protection systems used, but some of these have been in service for 50 years or more.

 

[SlideRuleEra]

Hollow steel pipe piling are used in some marine structures because there are no reasonable alternatives. If the water is "deep" and/or the soil is "poor", any piling will have a very long unbraced free-standing length. Until recently the largest steel H-piles were HP 14. Now, HP 16 and HP 18 are available - still not very "big". With a long unbraced length, the piling has to have a large moment of inertia and section modulus for good load capacity. Hollow steel pipe can cost effectively give the needed structural properties without being unimaginably heavy for driving.

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