Corrosion Allowance in Splash Zone

[Mboundi]

Hi,
I have to design a clamp system in the splash zone of a platfrom. The clamps are coated with 1.5 - 3 mm of epoxy coating.
Do I have to consider the corrosion allowance in the design?
Wath is the amount of corrosion per year and wath are the reference standards?

Thanks.

 

[SJones]

The first reference standard will be the design code of the structure to which the clamp will be attached. The corrosion allowance requirement will be governed by that which is already instituted at the attachment location but could be reduced based on a comparison with the original allowance, the projected design life of the clamp, the reliability of the coating protection, maintenance plans etc etc.

Steve Jones
Materials & Corrosion Engineer

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

 

[PAN]

Mboundi,

This depends on the design life of your clamps. Your epoxy coating may not last longer than 5 years without maintenance...

 

[Mboundi]

The design life of clamps is 25 years.
In the preliminary design i selected 5mm of corrosion allowance. Is this value acceptable?

 

[EricFrance]

See DNV RP B401 Cathodic Protection Design, Or DNV RP F103 Cathodic protecton of pipeline, section 8.
normally you find that value.
Eric

 

[SJones]

NORSOK M-001, subclause 4.3.4 may be of some assistance for a Northern location.

Steve Jones
Materials & Corrosion Engineer

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

 

[Deepray]

You should worried so much about the corrosion allowance of the clamp as the clamp should be protected with CP system from the jacket.

Its the type and thickness of coating on the clamp for the splash zone that you need to consider.

 

[BigInch]

CP doesn't work without continuity of current, something that is only present in the splash zone when wave crests are passing and are high. What you are suggesting would require that a cathodic CP system work in air. Additionally, in many cases a brace is isolated from the platform by neoprene coated clamps, just as is the clamp isolated from the pipeline on the other end, so no CP system may be protecting the brace. In the case of the splash zone, the only corrosion protection system is the coating system itself.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Deepray]

This is not the case, only the riser end clamp will be isolated by means of neoprene. Nobody will isolate the brace end at the jacket end. Clamps is always protected by CP from the jacket in most cases; otherwise you will have your clamps, bolts and nuts corroded in no time.

 

[BigInch]

The jacket end is often isolated with neoprene, to protect the coating on the jacket.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Mboundi]

In this case i had two type of clamps in splash zone:
1 with brace welded on the platform leg and
1 clamped on platform leg with neoprene as internal protection coating.

The client considered this section of riser not cathodically protected and suggested a corrosion allowance of 5 mm to be considered in the design.

Is this a reliable approach?

 

[BigInch]

Yes.

Deepray, as you can see, its a pretty common criteria.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/