Protection cathodique

1. Technical Seminar for Cathodic Protection
to GOGC Design Unit Specialists
Dr. Nick Kioupis, Cathodic & Lightning Protection
Section Head, DESFA

2. Cathodic Protection for Complex Structures
 Cathodic protection of complex structures is protection
applicable to structures which need to be cathodically
protected but cannot be electrically isolated, whether for
technical or safety reasons, from foreign metallic structures
situated in the same electrolyte as the structure to be
protected.
 Such a structure is referred to as a “complex structure”
 EN 14505:2005 „Cathodic protection of complex protection
structures‟ covers these situations

3. Cathodic Protection for Complex Structures
 EN 14505 is not applicable to structures covered by
EN 12954 (and draft CEN ISO 15589) or where
unwanted contacts with foreign structures or
defective isolation exists.
 It is always better to follow the requirements as
described in EN 12954 (and draft CEN ISO 15589)
before applying this standard.

4. Cathodic Protection for Complex Structures

5.  The design and installation of CP systems for complex buried
structures presents a unique challenge to the cathodic
protection engineer engineer.
 There are a multitude of different materials, processes,
operating temperatures, coatings, buried and immersed
structures that can suffer from both internal corrosion caused
by the products contained within the system and external
corrosion caused by the environment in which it is situated.
Cathodic Protection for Complex Structures

6. The following structures would normally be considered
to require cathodic protection.
• Pressurized carbon steel hydrocarbon pipelines
• Bottom or soil side of above ground storage tanks
• Buried storage tanks and sumps
• Carbon steel/ductile iron drain lines
• Buried portions of process, gas, water, firewater or liquids
pipelines
• Buried portions of steel valves, hydrants, monitors and fittings
Cathodic Protection for Complex Structures

7. These structures are constructed from a number of different
materials, e.g.
• carbon steel,
• ductile iron,
• high tensile steels,
• stainless steels,
• corrosion resistant alloys
• steel in concrete,
• galvanized steel,
• copper etc.
Cathodic Protection for Complex Structures

8. Plant facilities usually require a considerable
amount of cathodic protection current because
of the large surface areas of buried, often bare,
metalwork and are therefore normally
protected with an impressed current cathodic
protection system unless soil resistivities are
very low.
Cathodic Protection for Complex Structures

9. Cathodic Protection for Complex Structures
Current densities to protect the various metals vary considerably
as shown in the table below:
STRUCTURE MATERIAL SURFACE CURRENT DENSITY
(mA/m2)
Uncoated copper 50.00 or more
Uncoated steel 20.00
Poorly coated pipe 5.00
Tape or PE Wrap 1.25
Coal tar enamel 2.00
Epoxy wet applied 0.75
Fusion bonded epoxy (FBE) 0.10
Extruded Polyethylene 0.10

10.  The ICCP systems utilize a variety of anode configurations, e.g.
distributed anodes, local or remote surface groundbeds
installed horizontally or vertically, local or remote deep anodes
or a combination of the above.
 When choosing and/or combining anode bed types, the
conceptual and the final designs must be coordinated with
other plant operators to ensure all existing facilities are known,
together with any planned extensions or new facilities.
Cathodic Protection for Complex Structures

11. Remote vs. close Groundbed
Flow of current from an anode to a structure will be
accompanied by a potential difference between the earth and the
pipeline. The potential difference is used in certain criteria for
determining the degree of cathodic protection being afforded to
the pipeline. This potential difference can be accomplished in
either of two ways:
• by making the pipeline negative with respect to remote earth,
i.e. a remote groundbed, or
• by making the earth positive with respect to the pipe in local
areas, i.e. close anodes
• • •
• anodes.
Cathodic Protection for Complex Structures

12. For Complex Structures, two basic cathodic
protection principles may be employed:
1. Isolated systems
2. Non-isolated or total system
Cathodic Protection for Complex Structures

13. Isolated systems where every single piece
where of buried pipework or structure that requires to
be cathodically protected is isolated by means of
insulating joints / flanges where it comes above ground.
This can give rise to a very large number of insulated
flanges which in turn leads to maintenance and
reliability problems.
Cathodic Protection for Complex Structures

15. Cathodic Protection for Complex Structures

16. NON ISOLATED SYSTEMS
With the issue of EN 14505:2005 Cathodic protection of complex
structures, a whole new approach was introduced and backed up by an
International standard.
The main obstacles with the plant operators for a non isolated system are :
1. They do not understand it and consider it is dangerous to have cathodic
protection current flowing through all the pipework
2. That there were no authoritative standards recommending this principle.
EN 14505:2005 changed all that.
Cathodic Protection for Complex Structures

17.  A complex structure is defined as a structure to be
protected and one or more foreign electrodes, which,
for safety or technical reasons, cannot be electrically
separated from it.
 The term “complex structure” does not refer to the
complexity of the structure or to the complexity of the
cathodic protection system but more to the fact that
there are different types of structure and metals used.
Cathodic Protection for Complex Structures

18.  In a complex structure, all metallic parts of the
structure included in the cathodic protection scheme
must be electrically continuous.
 Isolating joints in incoming or outgoing pipelines are
the only isolation required and these should be
located outside the zone of influence of the
cathodically protected complex structure so that
unacceptable interference by the cathodically
protected complex structure is avoided.
Cathodic Protection for Complex Structures

19. Cathodic Protection for Complex Structures

20. Cathodic Protection for Complex Structures

21. Cathodic Protection for Complex Structures

22. Cathodic Protection for Complex Structures

23. Eon ≤ - 1,2 Vcse
if the measuring point outside the area of influence of the large
cathode (e.g. reinforced concrete or copper) and if ρsoil < 100 Ω.m.
Eon < - 0,8 Vcse
is sufficient at entries to, and in the vicinity of, reinforced concrete
structures and large copper earthing systems acting as foreign
cathodes (i.e the formation of a galvanic cell with steel in concrete is
prevented)
CRITERIA for Cathodic Protection of Complex
Structures
CRITERION 1

24. Demonstration that current is able to enter the structure either:
a) directly (i.e. when the protection current is switched on, a
negative shift of the free corrosion potential En by at least 0,3 V
will indicate that current is entering the structure);
or
b) by means of test probes or coupons at critical locations of
the structure.
CRITERIA for Cathodic Protection of Complex
Structures
CRITERION 2

25. A positive shift (depolarisation) on test probes or coupons of at
least 0,1 V measured 1h after they have been disconnected from
the structure to indicate that the structure is polarized.
The test probes/coupons are temporarily disconnected only for measurements
CRITERIA for Cathodic Protection of Complex
Structures
CRITERION 3

26. Thank you for your attendance
Cathodic Protection for Complex Structures