Volume-II of IV - GAIL

MECON LIMITED
Delhi
PROCESS & PIPING
DESIGN SECTION
TECHNICAL SPECIFICATION FOR
PERMANENT CATHODIC
PROTECTION SYSTEM
TECHNICAL SPECIFICATION NO. : MEC/TS/05/62/016B REV-1 Page 6 of 24
5.15 Coating Resistance : 10,000 ohm/m 2 for normal soil
4,500 ohm/m 2 for marshy area
15,000 ohm/m 2 for high resistvity area
5.16 Steel resistivity : 2.2 x 10 -5 ohm-m
5.17 Cathode Polarisation at Drainage Point
(Off Potential)
5.18 Cathode Polarisation at farthest Point
(Off Potential)
D:\old data\FATEH\MP Region\Kailaras\Tender RFQ\TCP&PCP\Permanent Cathodic Proection - 016B-R1.doc
: (-) 1.25 V (max.)
: (-) 0.95V (min)
5.19 Pipeline Natural Potential : (-) 0.45 V
6.0 CATHODIC PROTECTION DESIGN CRITERIA
Cathodic protection system shall be designed to meet the following criteria:
i) The pipe to soil potential measurements shall be between (-) 0.95 V (Off)
(-) 1.25 V (Off) with respect to a copper/ copper sulphate reference electrode
using current interrupter installed in power supply line.
ii) In rare circumstances, a minimum polarisation shift of (-) 100 millivolts may be
accepted as an adequate level of cathodic protection for the pipeline with the
written approval of owner.
Discretion to use any of the criteria listed above shall solely rest with the
owner/ owner’s representative.
iii) A positive potential swing of 50 to 100 millivolts shall be considered as
sufficient to indicate the presence of an interaction situation requiring
investigation and incorporation of mitigation measures by the CONTRACTOR.
7.0 SYSTEM DETAILS
The system shall include the following major equipment / sub-system unless otherwise
specified in project specifications :
- CP stations
- TR units/ cathodic protection power supply modules (CPPSM).
- Anode ground beds and anodes.
- Anode lead junction box.
- Test stations.
- Permanent reference cells.
- Electrical resistance probes.
- Polarisation cell/ surge divertor/ grounding cell/ spark gap arrester
- CP system at cased crossing.
- Cables.