Corrosion Protection

Presenter: Dr. Zalilah Sharer

© 2016 Gas Technology Centre

Universiti Teknologi Malaysia

27 February 2016

Cathodic Protection Design and Factors to be Considered

Part 6

General Design Objectives

To provide sufficient current achieve selected criteria

General Design Objectives

To minimize the interference currents on neighbouring underground structures

General Design Objectives

To provide adequate design life or to meet periodic rehabilition of the anode system

General Design Objectives

To provide adequate allowance for anticipated changes in current requirements with time To install anodes where the possibility of disturbance of damage is minimal To provide adequate monitoring facilities to test and evaluate the system performance

Additional Consideration

Recognition of hazardous conditions, ensure safe installation & operation Specification of materials & installation practices ---> international standard, economical Minimal detrimental effects by stray

current to foreign metallic structures

Additional Consideration

Cooperative investigations Presence of sulfides, bacteria, disbonded coatings, thermal insulating coatings, elevated temperatures, shielding, acid environments, dissimilar metals Cathodic disbonment due to over protection Amphoteric metals (Al), too high pH ---> cathodic corrosion

How to Measure the Soil Electrolyte Resistivity

Most popular method ----> Wenner 4-pin method Driving 4 steel pins into earth in a straight line, equal spaced. Pin spacing = depth

Soil resistivity = average resistivitiy at that particular depth

How to Measure the Soil Electrolyte Resistivity

Soil Box ---> soil samples Collect soil sample to fill up the soil box, then measure resistivity by resistance meter. Use same arrangement, i.e. C1,C2,P1,P2

How Coatings Effectively Affect Cathodic Protection

Coatings resist corrosion by creating resistance within the circuit of corrosion cell “Perfect Coatings” is practically infeasible ---> always with “holidays” “pin holes” However, if 99% perfect, only 1% need CP

What system to recommend? Sacrificial Anode or Impressed Current

SACRIFICIAL ANODE: 1. Small structures 2. Well coated 3. Short pipeline 4. Local protection for large structures 5. Temporary purpose 6. Hot spots

IMPRESSED CURRENT: 1. Large structures 2. Permanent

A Comparison of Sacrificial Anode and Impressed Current System

SACRIFICIAL ANODE: 1. Independent of electric power source 2. Localised, limited current output 3. Restrict by high electrolyte resistivity 4. Easy to install, additional can be made

IMPRESSED CURRENT: 1. Requires electric power source 2. Wide range of application 3. Less restricted by the electrolyte resistivity 4. Needs careful design and allow proper output tolerance

A Comparison of Sacrificial Anode and Impressed Current System

SACRIFICIAL ANODE: 5. Inspection at anode locations & between anode 6. Large quantity for longer life can be added when required 7. Less interaction & stray current possibility

IMPRESSED CURRENT: 5. Relatively few locations e.g. Test posts 6. Less anode for same design life 7. Higher Possibility

A Comparison of Sacrificial Anode and Impressed Current System

SACRIFICIAL ANODE: 8. Output cannot be controlled 9. Less possibility of cathodic disbonment 10. Any wire or connector will be protected 11. Cannot be misconnected

IMPRESSED CURRENT: 8. Can be adjusted 9. Higher possibility 10. Wire & connectors can be part of anode ---> corrode ---> cut 11. Misconnect ---> pipe corrode

What other factors that are more important than normal practices

1. Commonly ---> good design, good construction practice + good maintenance programmes. 2. Post installation maintenance. 3. Technical capability of maintenance personnel

What other factors that are more important than normal practices

4. If no expertise to carry out proper maintenance ……. No choice, provide systems required least expertise ----> could be expensive 5. Always try to have most promising CP systems.

What other factors that are more important than normal practices

1. Are other u/g metallic structures within the area of influence surrounding the g.b. 2. Is proposed site on or off the pipeline r.o.w. ? If off (normally on ICCP), can r.o.w. be procured ? 3. If ICCP, is there power line present ? If not, extension from nearest source practicable ?

What other factors that are more important than normal practices

4. Is the site reasonably accessible for construction and maintenance purposes ? 5. Are there plans for building construction (new pipeline, highway etc) that will make the site untenable in the near future ? 6. Remoteness (normally min. 100m from nearest point to be protect and 300 m from others)

Types of Basic ICCP Groundbed Design

1. Standard Horizontal 2. Vertical Anode 3. Borehole (Deepwell) 4. Cannistered

Anode Types for ICCP

Silicon iron, graphite & magnetite, platinised titanium(Pt/Ti) Mixed metal oxide tubular titanium ---> light weight, easier to install

Carbonaceous Backfill

Coke materials, high carbon content, low resistivity (5-50 ohm-cm) When used together with anode ---> increases the effective size of the anode ---> lower electrode resistance Will be consumed as current discharge

How to Confine CP current to Structure of Concerned?

CP effectiveness depends on current provided by the system to the concerned structures Important to stop (confine) the current !!! Also, earthing system (copper) By, electrical isolations, for pipelines…. Insulating Flange by IF kits or insulating joint using monobloc

What factors affecting cathodic protection design for buried structure

Nature of the environment Nature of the coating Polarization level Linear electrical resistance Extent of neighbouring structures Availability of power Stray current

Special Considerations for Onshore CP Systems

a. Sparking hazards b. Earth electrode c. Sleeved crossing d. Valve pits e. AC induced effects

Do not forget .....

Monitoring

&

Maintenance

Question?

The End

Thank You for the Attention!