Overprotection on short pipe line(below 50m) by sacrificial anode

[andykurnia]

hello

i just want to ask is there any chance overprotection on gasline pipe below 50m by sacrifial anode(magnesium anode)? and does length of magnesium anode affect current output that makes overprotection (protection potential above -1200mV)?

 

[brimmer]

Yes it is possible to get potentials less than -1200mV using magnesium anodes, and sizing. You can get potential of around -1.6V. If you want less, use a different anode material such as zinc. Current density will also be higher with magnesium compared to zinc.

 

[andykurnia]

@brimmer

thanks for the answer, so if i choose 14.5 kg magnesium anode on short pipeline(below 50m) can cause overprotection, can i choose 7kg to make potensial under -1200mV?

 

[Chumpes]

@andykurnia :

I think you ment "make potential ABOVE -1200mV"

I don't think reducing the mass of anode will have any effect. Raising of protection potential within acceptable range should be achieved by change of anode material, or maybe by increasing distance between anode and structure to be protected.

 

[SJones]

Why not perform a basic calculation as shown in ISO 15589-1, assuming an onshore buried line, and confirm an acceptable material, anode shape, and weight?

Steve Jones
Corrosion Management Consultant

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

All answers are personal opinions only and are in no way connected with any employer.

 

[brimmer]

You need to do current requirement calculations and size accordingly. It depends on soil resistivity, condition of coating, etc.