Impressed Current Cathodic Protection- An up to date review. Paul Chess, CPI FORCE Technology, Denmark FEREB

Transcription

1 Impressed Current Cathodic Protection- An up to date review Paul Chess, CPI FORCE Technology, Denmark

2 What is the problem? Corrosion of the reinforcement

3 General-corrosion

4 Pitting corrosion

5 UK car park 2017

6 Corrosion of steel in concrete what we know Steel is an unstable metal so it will corrode. It is all about the rate of corrosion i.e. kinetics The rate of corrosion is very low in uncontaminated concrete Different steels behave differently in the corrosion process Hugely different chloride levels are required to initiate corrosion There are many types of corrosion products found The corrosion morphology varies widely

7 Corrosion of steel in concrete what we don t know What corrosion process is occurring? The spacing of the anode and cathode? How likely is the specific reinforcement to corrode?

8 Solutions Do nothing Replace the structure Replace the chloride contaminated concrete Electro chemical chloride extraction Dry the concrete Cathodic protection

9 ICCP Power supplies Electrochemical sensors Anodes

10 Power supply with 4 outputs

11 Front screen of modern system

12 Sensors reference electrodes Silver /silver chloride Manganese oxide

13 Anode types Conductive coatings Sprayed metal anodes MMO mesh and ribbon Discrete anodes

14 Coating with carbon

15 Titanium metal anode

16 Mesh and overlay

17 Ribbon anode

18 Discrete anode

19 Discrete anodes

20 How does CP work Turns an anode into a cathode Moves aggressive ions away from the steel Increases the alkalinity at the cathode

21 Cathodic protection -what we know It seems to work Current spread is limited to 500mm from a point anode As long as the anode is operating effectively it mitigates corrosion, preventing damage

22 Cathodic protection -what we don t know Does it work equally on all forms of corrosion? How much current is required? Guess 1 current required = steel surface area Guess 2 more current required = higher corrosion rate Guess 3 when criteria achieved = corrosion stopped

23 Criteria Absolute criteria -720 mv Potential decay 100mV over 24 hours Potential decay 150mV over extended period Special criteria for galvanic anodes Anode current density and steel potential shift input into Butler Volmer formula. Passive steel is indicated by general corrosion rate of less than 1 or 2 ma /m2

24 Reasons for CP systems failing Poor design Inadequate materials Poor installation Lack of maintenance

25 Acid damage with discrete anodes

26 Transients

27 lightning

28 Flooding

29 Conductive paint breakdown

30 Slotted ribbon failure

31 How to improve the situation Improve the design Look carefully at previous similar installations Think about simple maintenance Validate the success of the CP materials to be used Avoid the cheapest is best contractor dogfight Think realistically about maintenance If the client is unlikely to maintain the system do not use CP

32 State of play for CP in different countries N. America early pioneer. Many failed systems. Coming back on private structures, but not public Scandinavia. A few failed systems. In widespread government use UK in widespread use. Poor designs common Germany. Biggest area being installed. Best organised. Failures rare France. Been successful. Relentless urge to cut costs Australia is in a similar situation to UK and France

33 Conclusions CP can prevent further corrosion damage of the steel For it to be effective it must be durable This durability is only assured by decent design Decent materials Decent installation Decent maintenance If you cannot ensure these four points do not use CP

34 Thank you for your attention