Bolted Protection Cover 3

[dik]

We have an existing high strength steel anchorage system that we are proposing to protect the exposed end for several decades.

There is a welded stainless steel(316L) protection cap assembly that bolts to the anchorage end. The entire assembly will be submerged in slow flowing river water and submerged approx 15'. The stainless steel cap is not watertight.

There is discussion in the office about the type of fastener to secure the stainless steel end cap to the high strength steel anchorage, the choices being: stainless steel, mild steel or HDG steel.

The mild steel and HDG can be dielectrically isolated from the stainless steel cover using an epoxy coating. The fasteners which attach to the high strength steel anchor will be submerged in the river water; they will be somewhat protected by the stainless steel cap.

Any comments, problems, or suggestions would be appreciated.

Dik

 

[desertfox]

Hi dik

Look at this site:- you might suffer pitting corrosion of the stainless steel cover:-

http://geminimarinesurvey.com/yahoo_site_admin/assets/docs/Marine_Metal_Corrosion.325111027.pdf

 

[SJones]

You will not get reliable isolation from simply using an 'epoxy coating.' In the absence of cathodic protection, it would be advisable to use a suitable corrosion resistant alloy fastener.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[dik]

Thanks, gentlemen...

The protection cap assembly and the fasteners are somewhat consumable and can be replaced if necessary. The cover is 1/2" 316L stainless and should have some durability. The cap's function is to protect the anchorage from damage and the fastener's purpose is to secure the cap to the anchorage.

The concern is corrosion damage to the high strength steel anchorage. Would the stainless steel, mild steel or HDG steel provide the least likely corrosion?

I was a bit surprised that the epoxy coating would not act as a dielectric 'barrier'.

Dik

 

[EdStainless]

Most epoxy coatings are not robust enough to provide good isolation. If you use a three coat system that builds a total thickness of 0.100" or more then you would be fine.
In place of 316 use 2205. It is stronger, more corrosion resistant (especially the welds), and about the same price.

Any chance of adding galvanic protection for the steel?
If not you may be better off using plain steel for the cap.
The last thing that you want is the SS cap causing corrosion of the anchorage.

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Plymouth Tube

 

[dik]

Thanks Ed... by galvanic protection, do you mean HDG? or will a zinc rich epoxy coating provide similar (albeit lesser) protection? The main body of the cap assembly consists of 6" sched 80 pipe. Can this be supplied in 2205 SS? Your last statement is on the mark... the anchorage is prime importance.

We had already looked at using HDG for the assemblies, but timing is critical.

Dik

 

[EdStainless]

I was thinking of sacrificial anodes, usually Zn-Al.

You can get about any product form in 2205, distributors in Houston stock a lot of it for refinery usage.

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Plymouth Tube

 

[dik]

Thanks EdStainless... Zn-Al 'hockey pucks' are likely out of the question. I will run with HDG fasteners and replace them if required. These should prevent corrosion of the anchorage.

Dik