Do you recommend SS bolts for marine environment? 4

[movasra]

Hi Everyone,
Is there any issue with using ss bolts for connections of a small steel rack that will be placed on an existing offshore platform. The rack is made of galvanized HILTI girders and is poweder coated. Since we cant coat the bolts, we are going to use stainless steel bolts. the temperature is very unlikely to reach 120 Fr.
Thanks a lot for your comments in advance

 

[EdStainless]

Do you need to take this off regularly?
If not then I would use double galvanized steel hardware and let it go at that.
Good corrosion resistant SS bolts are not cheep, you can't get away with 304 or 316 and expect them to not crevice corrode inside. Better alloys cost a lot. Don't bother if you don't need them.

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Plymouth Tube

 

[CoryPad]

Why can't you coat the bolts?

You should review existing standards for offshore fasteners:

DNV Report 2002-3301 Bolting & Fastener Application In The Offshore & Process Industry - State Of The Art

NACE Publication 02107 Coatings For Protection Of Threaded Fasteners Used With Structural Steel, Piping And Equipment

NORSOK M-001 Materials Selection

 

[movasra]

Once the rack is installed, it'll be their for next 20 years or more.
but do I need to coat the bolts with paint after installation? the bolts are hot-dip galvanized (1.8 mils, 45 mu.m)

 

[movasra]

CoryPad,
HILTI says they cant coat the "threads" well. And we are trying to avoide field coating if possible. Thanks a lot for the comment and the resources though.

 

[gr2vessels]

HILTI??! Bolts??! What's next??! Offshore technology at Bunnings??! Move over Hobson...new trend, new kids on the block.
Just for a quick advice, stainless steel screws with the galvanised steel rack will corrode in no time, forget the 20 month service life (oops, is it 20 years??). The galvanised bolts with the head covered in chewing gum will last longer.
I would better use the galvanised bolts (if not supplied by HILTI) and paint the bolt head and surroundings with a brush, using a good marine grade paint.
Cheers,
gr2vessels

 

[CoryPad]

Do you expect the girders to last 20 years without needing maintenance or replacement? The problem with fasteners is that you can't apply thick coatings to the threads (binding) or underhead region (relaxation). You may want to consider a multilayer zinc + PTFE coating. You may need to clean the fasteners periodically, gently, to remove deposits but not any coating.

 

[EdStainless]

When you look up the references that Cory supplied you will find that 'state of the art' is a resin coating over a double thickness galvanizing. This is the only way to go. Now just make sure that they don't tear them up installing them.

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Plymouth Tube

 

[strider6]

it depends on the SS, SS304 is a banned material by most engineering company in offshore environments. i'll use an hot dip galvanized carbon steel and make inspection and maintenance in case of damage.

S

Corrosion Prevention & Corrosion Control