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 13 of 24
Type:- Solid station Electrolytic tie multi pairs S.S plate grounding cell.
c) Spark Gap Arrester
- Type : Spark gap.
- Current, 8/20 : 100 Kilo Amp.
micro second wave
- Spark- over, AC Voltage
- 50 Hz : 1 KV
- Impulse (1.2/50 : 2.2 KV
micro sec)
vii) The grounding cell, spark gaparrester and polarisation cell system shall be
adequately sized and suitable for the design life of permanent CP system. The
directly buried zinc or magnesium anodes shall also be adequately sized for the
life of the permanent CP system, taking into consideration discharge from the
anodes. The grounding system shall have minimum resistance to earth to
restrict the pipeline voltage as per NACE Criteria.
viii) HT transmission overhead lines of voltage below 66KV also required mitigation
measures should be provided to take care of continuous induction of voltage
interface due to presence of transmission line in close proximity.
7.8 CP at cased crossing
7.9 Painting
i) At cased crossing where casing is coated, the casing shall be protected by
sacrificial anode installations which shall be provided at both ends of casing.
The anode installation shall be sized based on the permanent C.P. design
parameters and design life specified for the main pipeline but where casing is
uncoated additional protection for casing is not required.
The carrier pipe inside the casing shall be protected by zinc ribbon anodes weld
connected to the outer surface of bottom of carrier pipe extending upto hour
hand position of 4 and 8 o’clock. The anodes shall be placed at close intervals
as per design calculations and shall be sized based on the permanent CP
design parameters and design life.
The sheet steel used for fabrication shall be thoroughly cleaned and degreased to
remove mill scale, rust, grease and dirt. Fabricated structures shall be pickled and then
rinsed to remove any trace of acid. The under surface shall be prepared by applying a
coat of phosphate paint and a coat of yellow zinc chromate primer. The under surface
shall be free from all imperfections before undertaking the finishing coat.
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