BY:AFIFAH BT ABDUL RASHID

Electrochemical reaction between a material and its environments

Deterioration of material

Applied for corrosion protection Damaged during transportation, construction

or operation Therefore coatings and CP are used together

as complementary systems

Protecting one metal by connecting it to another metal that is more anodic, according to galvanic series

Impressed Current Sacrificial Anode Systems

Use an outside source of power to drive the current from anodes to the cathode

The surface of the structure is made cathodic by connecting it electrically to a sufficient mass of less noble metal buried or immersed in the common electrolyte

Material:› Aluminum› Zinc› Magnesium

Some major types of anode: Slender stand-off Elongated, flush mounted Bracelet

Top: Slender stand-offMiddle: Elongated flush-mountedBottom: Bracelet

Bracelet Anode

Anode type: Flush bracelet anode Tapered bracelet anode

Connection type: Bolted Welded

Flush Bracelet Anode

th = tapered end thickness

Lt = tapered length

θ = tapered angle (30o – 45o )

Operating temperature for Al anode < 80oC Operating temperature for Zn anode < 50oC Loss of performance at those temperatures Use of insulation to overcome the problem

Design life Current density Coating breakdown factor

Maintenance & repair of anode is generally very costly and often impractical

Normal practice is to apply the same anode design life as for object to be protected

Measure of current density demands to achieve cathodic protection of bare metal surfaces

Ref: PTS 30.10.73.32

Reduction in cathodic current density due to application of an electrically insulating coating

fc = k1 + k2tf

Massprovided ≥ Massrequired

CPR ≤ 5

Iaf ≥ Icf

Massrequired is used to calculate the mass of anode material using formula given

However anode consist of insert material made of steel

Therefore total anode mass need to consider insert materials as well

Massprovided = Masstotal – Massinsert

Massprovided ≥ Massrequired

The anode dimension is limited to a certain length to thickness ratio to prevent the potential of the anode material cracking.

The crack propensity ratio should be less than 5.

Icf is protection current demand of protection object

Iaf is current provided by anode to protect the cathode

Current provided must be greater than current needed