steel protective coatings 1

[dison]

(I originally posted this in the steel coatings forum, but with no response - so, I am trying this forum since it is active. Thanks in advance.)

I am seeking opinions and/or recommended sources of information on the following:

What would be the best method to protect steel from corrosion when it is buried in soil in a location where both moisture and oxygen would be available to promote the corrosion? For the sake of making a comparison, use a long term design life (say 100 years) and a non-reactive soil (no chlorides, etc). Use of additional steel thickness to offset loss due to corrosion? Galvanizing? Painting? Epoxy coating? Specialized paint application? Asphalt or other roof coating material? Concrete cover? Cathodic protection? A combination of protection methods?

Will a bolted connection in this region affect the appropriateness of the recommended system? ~dison

 

[Ron]

Asphaltic coatings and passive cathodic protection will be your least expensive alternative. Galvanizing will work as will other coatings, just that asphaltic coatings are a bit more forgiving of application technique.

 

[dlew]

dison,

I am not a corrosion or paint expert but the common practice for steel poles embeddd directly into the soil is to galvanize the complete pole, and to coat the embedded portion with a heavy coat of bitumastic paint or epoxy coating.

Steel sheet piles used for bulkheads in a marine environment, are made of corrosion resistant steel and are also coated with bitumastic paint. In some cases, cathodic protection is used.

Steel piles for foundations on high ground most of the time are not protected against corrosion, except thickness of metal is increased by 1/16" or 1/8" as a corrosion tolerance.

Hope this could give you a general perspective.

AEF

 

[amokhta]

Are you going to drive this piece of steel into soil? If yes, any type of coating may get damaged during the driving process.

What is this piece of steel? Depending on its shape and function different solutions exist. Provide more info.

 

[dison]

Thanks for the good replies!

The steel in question will be part of the connection for precast concrete backwall and wingwall pieces on a bridge abutment, which will be constructed and then have the embankment fill placed over the top. So - no driving.

My preferred method would be a little extra steel than needed for strength and a coating of some bituminous substance after installation. An application of epoxy might work just as well. Galvanizing is not used anywhere else on the bridge, so I would like to stay away from that. ~dison

 

[rkchalla]

This is from ASTM web site. I have recommended using this steel before for piling applications.


Specification A588/A588M-01 Standard Specification for High-Strength Low-Alloy Structural Steel with 50 ksi [345 MPa] Minimum Yield Point to 4-in. [100-mm] Thick

Copyright 2001 AMERICAN SOCIETY FOR TESTING AND MATERIALS, West Conshohocken, PA. All rights reserved.


1. Scope
1.1 This specification covers high-strength low-alloy structural steel shapes, plates, and bars for welded, riveted, or bolted construction but intended primarily for use in welded bridges and buildings where savings in weight or added durability are important. The atmospheric corrosion resistance of this steel in most environments is substantially better than that of carbon structural steels with or without copper addition (see Note 1). When properly exposed to the atmosphere, this steel is suitable for many applications in the bare (unpainted) condition. This specification is limited to material up to 8 in. [200 mm] inclusive in thickness.

 

[dison]

rkchalla:

It is my understanding that A588 steel must be 1) exposed and 2) free to drain (no standing water). Without meeting these two requirements, A588 steel actually performs worse than carbon structural steels when it comes to corrosion.

In this particular situation, since the steel is covered with fill soil and is not necessarily free to drain (moist or saturated soil could be around for a significant amount of time), use of A588 would not be of benefit. However, we are using A588 in its unpainted form for many components of the bridge structure exposed to the atmosphere. ~dison

 

[BarryMartin]

A combination of coating plus cathodic protection is usually optimum for the life of structure. You can reference underground gas pipelines.

A well coated structure would have 1~3% holidays that the cathodic protection would protect. Otherwise you have the expense of trying to ensure a perfect coating through manufacture, construction and installation.

Galvanic or impressed current cathodic protection systems could be used although if power is not locally available, then galvanic would probably be cheaper. However, I think that the upfront cost of a galvanic is often higher than for impressed current. You'd need to check with the detailed designer and/or supplier to make a decision.

 

[kieran1]

Can you encase the steel in concrete ? 100-150mm should be adequate for 100year protection Kieran