Evaluation & Condition Monitoring of CP System

Cathodic Protection is used to control the corrosion of a wide variety of buried and submerged metallic structures. It is a cost-effective way to extend the life of a structure and to ensure integrity throughout its operating life.

Cathodic Protection can be defined as…“the control of electrolytic corrosion…by the application of direct current in such a way the structure to be protected is made to act as the cathode of an electrolytic cell”.

WHY Cathodic Protection

Cathodic protection provides effective corrosion control on steel structures and pipelines by creating a potential (voltage) gradient opposing the flow of ions away from the surface, thus preventing the anodic corrosion reaction. Cathodic protection may be used alone or in combination with an insulating coating. In such systems, the coating forms the first line of defense and where it is adherent and undamaged, the corrosive environment is kept away from the structure: where the coating is damaged, however, corrosion can occur and cathodic protection provides protection. It is worth nothing that cathodic protection can only be applied in the presence of an electrolyte – it is not an antidote for atmospheric corrosion.

Methods of applying Cathodic Protection

 Sacrificial Anode System
 Impressed Current System Evaluation & Condition Monitoring of CP System For Onshore & Offshore Steel Structures

Choosing a Cathodic Protection System

To achieve no corrosion at the cathode surface, it is important to ensure that protective current is passing onto all parts of the cathode surface. The current for full protection can vary considerably with environmental conditions - from 200mA/sqm in turbulent aerated seawater, to 1mA/sq-m for some onshore pipelines. Deciding which type of protective system to adopt therefore, depends on many factors - size and complexity of structure, nature of the electrolyte, availability of power supply, proximity of ‘foreign’ structures which may affect, or be affected by, the flow of current, etc. A detailed economic appraisal based on technical surveys is required.

VELOSI Methodology

The Job protocol is broadly classified into two parts:
 Data review & engineering works
 Field works – surveys, inspections and investigations VELOSI has identified seven (7) key steps to carry out evaluation  & condition monitoring of CP system:
 Pre-Assessment Study
 Preparation of Methodology and Procedures
 Technical Audit of Existing CP System Installation of Main Pipelines & Performance Assessment of Tank Form Area, Pump Stations Facilities and associated piping network
 On/Off Potential Survey, CIP Survey and Line Current Survey
 Visual Inspection of Heat Shrinkable Sleeves
 Review & Evaluation of Remote Monitoring and Control System
 Post Assessment of the Project – Final Reports & Deliverables

Applications of Cathodic Protection
  

Structures that arStructures that are commonly protected by cathodic protection are:
 Underground Pipelines
 Well Head Casings
 Ships’ hulls
 Storage tank bases
 Jetties and harbor structures
 Steel sheet, tubular and foundation pilings
 Offshore platform, floating and sub sea structures
 Storage Tanks (oil and water)
 Water-circulating systems
 Steel embedded in reinforced concrete structures (bridges, buildings etc.) VELOSI Experience VELOSI’s involvement with more than 30 studies worldwide of different Cathodic Protection Systems in onshore/offshore Pipelines, tank bottom and allied on-plot metallic facilities/topsides, subsea pipelines reveals that Evaluation & Condition Monitoring of CP system, impressed current or Sacrificial helps to:
 Ensure reliability and longevity
 Assess efficacy & effectiveness of the CP system
 Evaluate the remnant life of the CP System
 Recommend upgradation and improvements

The industry recommended practice for corrosion protection package is the application of 'Protective coating in conjunction with effective cathodic protection system’; where the CP system provides a 2nd line of defense to retard external corrosion threats.