Volume-II of IV - GAIL

MECON LIMITED
Delhi
PROCESS & PIPING
DESIGN SECTION
TECHNICAL SPECIFICATION FOR
TEMPORARY CATHODIC
PROTECTION SYSTEM
TECHNICAL SPECIFICATION NO. : MEC/TS/05/62/016A REV-1 Page 4 of 19
4.1 Protection current density
(i) Pipe lines having polyethylene coatings
Pipeline
Protection current density*
surrounding Temporary CP Permanent CP
(µA/m²)
(MA/m²)
Normal soil 50 0.120
Marshy area/
100 0.120
buried in sea
water/
crossing
HDD
High resistivity
25 100
area (more than
100Ω m)
(ii) Pipe lines having FBE Coatings
Pipeline
Protection current density*
surrounding Temporary CP Permanent CP
(µA/m²)
(MA/m²)
Normal soil 200 0.300
Marshy area 300 0.500
High resistivity
150 0.250
area (more than
100Ω m)
Pipe to soil "ON" potential shall not be more negative than (-) 1.5V.
* Actual current density to be adopted shall be decided based upon soil and other
environmental conditions, proximity of foreign pipelines and structures affecting
interference. Where considered necessary for satisfactory protection of pipeline the
current density shall be suitably increased by contractor.
4.2 Safety factor for current density : 1.3
4.3 Anode utilisation factor : 0.65 for Mg. Anode
0.80 for Zn Anode
4.4 Pipeline natural potential : (-) 0.45 V
4.5 Unless otherwise specified in project specification the design life of temporary CP shall
be one year and that of permanent CP shall be 30 years.
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