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 20 of 24
Interference situations shall also be identified and mitigated by comparing
different sets of readings taken at same test stations at different intervals of
time under identical conditions where positive potential swing exceed 50 mV.
xv) Final records of testing and commissioning including graphical representation
of final structure to electrolyte potential readings shall be compiled with
interpretation in consolation with owner/ owner's representative and
submitted.
xvi) As a result of these tests, if any deficiencies are found in the system, the same
shall be rectified by the contractor at no extra cost or time effect, to the
complete satisfaction of Owner/ Owner's representative. Such deficiencies shall
include mitigation of interference problems that may be found existing in the
course of testing and commissioning. A set of PSP observations shall also be
taken during the peak of the first dry season after commissioning the system
into regular operation. Any deficiency found in the protection of the pipeline
shall have to be rectified by the contractor at his own cost.
xvii) If it is found during commissioning that the sites of occurrence of least
negative protective potentials are less negative than (-) 1.00 V even after 72
hrs. of operation, then the drainage point potentials shall be increased
depending upon anode ground bed currents in consolation with Owner/
Owner's representative In any case, the drainage point protective 'ON'
potential values shall not exceed the PSP values specified at cl. 5.1 of this
document and the pipe to soil 'OFF' potential shall not exceed a value more
negative than (-) 1.20 V at any location on the pipeline.
xviii) The current dissipated by individual anodes shall be measured from the anode
lead junction box and corrected for equal dissipation to the extent possible
keeping the total ground bed current same.
12.0 INTERFERENCE MITIGATION
12.1 Investigation shall be made for stray current electrolysis of the pipeline, mutual
interference between the pipeline and foreign pipelines / structures, interference on
foreign pipelines / structures due to the CP of the pipeline and ground bed,
interference on metallic structures which lie in between pipeline and ground bed or
near to ground bed, AC induction on pipeline due to overhead high voltage power
lines, interference due to high voltage DC lines, electric traction etc.
12.2 Measurements including pipe to soil potentials and pipe currents etc. on the pipeline /
structure being CP protected and on foreign pipelines / structures, and ground
potential gradient etc. shall be made to investigate the current discharge and pickup
locations. In case of fluctuating stray currents, investigations shall be made
continuously over a period of time and if required simultaneously at different locations
to find out the stray current source (s). Recorders shall be preferably be used for long
time measurements.
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