2. G.U.P PHASE II - LIQUID PIPELINES, TERMINAL & JETTIES
0
c:
1.0 INTRODUCTION
This report defines the design calculations and requirements of Cathodic Protection System
for one No. 17" existing gas pipeline and three new LPG product pipelines. An impressed
current cathodic protection system will be installed to supplement the' corrosion coating in
providing corrosion control to the pipeline. The impressed current Cathodic Protection
system for existing gas pipeline will be upgraded to suit the new requirement for existing
gas pipeline as well as new LPG product pipelines.
2.0 SUMMARY
Cathodic protection is specified for the onshore section of the subject pipeline from Dinh
Co to Thi Vai for new LPG pipeline and from Long Hi to Phu My for existing gas pipeline-length
and other parameters are as given in Secsion 4.0 of this document. Both galvanic
anode and impressed current cathodic protection systems were considered during this
design. An impressed current cathodic protection system has been selected on a technical
basis. The cathodic protection system has been designed in accordance with internationally
accepted standards and compliance the codes and standards listed in section 1.2 o
specification. A conservation design approach has been used including a 30 mA/m2 current
density and 95% coating efficiency. For future addition a 20% spare output capacity has
been provided ( NACE-1967). It has been determined that a single impressed current
system required upgrading at the Phuoc Hoa LBV and at the Dinh Co Station would
provide full cathodic protection of new LPG pipelines and existing gas pipelines.
The soil resistivities at this location justified the installation of an effective surface anode
groundbed. The groundbed will be located approximately 100 m from the pipeline and
position perpendicularly to the pipeline in accordance with the --project specification
(BS-7361 ). A rectifier will be used to energize the groundbed. They.415. VAC; three phases
power supply to the rectifier will be provided from the415;volt switchboard. Elec€rical
isolation of the pipeline will be provided by the installation of insulating flange sets
Insulating flange set shall be provided with Explosion-proof surge diverters to prevent
damage due to lightning or power surges. Test stations will be provided to monitor and
adjust the cathodic protection system . Test station also have to be provided at following
location
• Both side of the major river or road crosing.
• At all insulating joint.
• At HT overhead line crossing.
• At all vulnerable location where interferance is possible
These test stations will be located at maximum intervals of 1.5 km. All cable connections to
the pipeline will be made using the brassing thermit weld process.
3.0 SOIL RESISTIVITY SURVEY
Soil resistivity measurements have been previously carried out by others at 65 location
along the pipeline ROW. According to the information included in the contract documents.
this testing was performed using the Wenner 4-pin method at depth of 0.75, 1.5, and
metres using a .M-416 instrument made in the Soviet Union. Test equipment must have
maximum AC DC ground current rejection feature. Soil resistivities are critical to the
proper design of a cathodic protection system. They are used as a guide to determine the
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3. G.U.P PHASE II - LIQUID PIPELINES, TERMINAL JETTIES
corrosiveness of the soil and also used to select ground locations and configurations. Soil
resistivities are important regardless of whether and impressed current or a sacrificial anode
cathodic protection system is utilized. It should be understood that this cathodic protection
design has been based on the soil resistivities determined by others. Any inaccuracies in the
reported resistivity values versus the actual resistivity values could have a significant impact on
the effectiveness of the cathodic protection system. This can only be determined during
commissioning of the system when the Contractor shall check the.soil resitivity inspection
accordance with specification.
4.0
4.1
4.1.1
Y
•
DESIGN PARAMETERS
The following sub-sections include parameters which have been used for design of the
proposed cathodic protection system.
GENERAL PIPELINE DETAILS
These calculation for upgrading existing CP system for new LPG pipelines and existing gas
pipeline will be done through two (2) cathodic protection system design.
Portion 1: (CP Station at Dinh Co location )
Gas pipeline (Long Hai to Ba Ria)
Length of pipeline 16.5 km a
Pipeline diameter 406.4 mm 1 /17
Pipeline number 1
Coating Coal tar enamel
LPG pipelines (Dinh Co to Ba Ria)
Length of pipeline 7.5 km
Pipeline diameter 168 mm C L
Pipeline number 3
Coating Polyethylene
4.1.2 Portion 2: (CP Station at Phuoc Hoa location )
Gas pipeline (Ba Ria to Phu My)
Length of pipeline 21.5 km
Pipeline diameter 426 mm
Pipeline number
Coating Coal tar enamel
LPG pipelines (Ba Ria to Thi Vai)
Length of pipeline 17 km
Pipeline diameter 168 mm
Pipeline number 3
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5. G.U.P PHASE II - LIQUID PIPELINES, TERMINAL JETTIES
Coating Polyethylene
4.2 CATHODIC PROTECTION DESIGN LIFE
In accordance with the contract documents, the impressed current cathodic protection
system will have a design life of 30 years. The cathodic protection Contractor shall
demonstrate the design life of his proposed CP system.
4.3 ANODE TYPE
1 T' 'um tubular anodes with a mixed metal oxide coating will be installed. These anodes
have proven to have superior operating characteristics over silicon iron and graphite anodes.
Titanium / mixed metal oxide anode are also of lighter weight and capable of significantly
higher current outputs and longer life.
4.4 COATING EFFICIENCY
A common method to assess the pipe coating condition is to use a factor referred to
percent bare. For a normal factory applied coaltar enamel coating system which would be
inspected and repaired prior to back filling. of the pipe, a value of a approximately I to 2
percent bare would be experienced immediately subsequent to construction. However,
during the service life of the pipeline with expansion and contraction of the pipeline due to
thermal effects, soil movement, water ingress through the coating etc, the condition of the
coating will deteriorate.
A conservative coating efficiency of 95% has been used for this cathodic protection design.
This means that over the 30 year life, the cathodic protection system will have the capacity
protect an average of 5% of the total surface area of the pipeline.
4.5 CP CURRENT DENSITY
The National Association of Corrosion Engineers (NACE) Recommended practice
RP-0169-92 and DNV RP B401 specifies a current density of 10-30 mA/m2 for bare steel
structures in soil. The soils along the proposed ROW for this pipeline are very aggressive
with high moisture content, high salinity and low soil resistivity. Therefore, this design uses
a
conservative 30 mAIm2 current density.
4.6 SOIL RESISTIVITY
4.6.1 Dinh Co Location
As mentioned in previous Section 3.0, soil resistivity testing along the pipeline ROW has
been previously carried out by others. A review of this data indicates that points R-18 and
R-19 are located relatively near Dinh Co:
Depth (m) Soil Resistivity (ohm cm)
R-18
0.75 8000
1.50 4200
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6. G.U.P PHASE II - LIQUID PIPELINES, TERMINAL JETTIES
3.00 1050
R-19
0.75 3600
1.50 1300
3.00 500
The deep-well anode system will be installed for cathodic protection, The average resistivity
value for the above two points at a 1.5m depth is 2750 ohm-cm and will be used t For
groundbed design at Dinh Co.
4.6.2 Phuoc Hoa Location
Also mentioned in previous Section 3.0, soil resistivity testing along the pipeline ROW has
been previously carried out by others. A review of this data indicates that points BH23 aid
BH24 are located relatively near Ba Ria ( at Phuoc Hoa ) where the impressed current CP
system will be located. The soil resistivity values reported at these locations are :
Depth (m) Soil Resistivity (ohm ern)
BH23
0.75 1300
1.50 1500
3.00 1000
BH24
0.75 1500
1.50 1500
3.00 800
The average resistivity value for the above two points at a 1.5m depth is 1500 ohm-cnl _:d
will be used for groundbed design at Phuoc Hoa.
4.7 CATHODIC PROTECTION CRITERIA
NACE Recommended Practice RP-0169-92 addresses cathodic protection criteria --Dr
underground and submerged metallic piping systems. Applicable excerpts of this st.and=d
relative to CP criteria for this project are as follows-
A negative (cathodic) potential of at least 85OmV with the cathodic protecti'Dn
applied. This potential is measured with respect to a saturated copper / copper ulfat.e
reference electrode contacting the electrolyte. Voltage drops other than those across
the structure to electrolyte boundary must be considered for valid interpretation of
this voltage measurement.
A negative polarized potential of at least 850 mV relative to a saturated copper /
copper sulfate reference electrode.
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7. G.U.P PHASE II - LIQUID PIPELINES, TERMINAL JETTIES
A minimum of 100 mA of cathodic polarization between the structure surface and a
stable reference electrode contacting the electrolyte. The formation or decay of
polarization can be'measured to satisfy this criterion.
5.0 CATHODIC PROTECTION DESIGN CALCULATIONS
5.1 DINH CO LOCATION
5.1.1 Pipeline Total Surface Area
The onshore portion of Long Hai to Ba Ria gas pipeline and Dinh Co to Ba Ria LPG
pipelines has a total surface area as follows:
Sa = (Pi) (d) (1)
Sa (3.1416)-[(0.406,x 16500) + (3 x 0.168 x 7500)]
Sa = 32921 (m2)
Where: Sa = Surface area (m2 )
Pi = 3.1416
1 Length of pipeline (m)
Diameter of pipeline (m)
5.1.2 CATHODIC PROTECTION CURRENT REQUIREMENT
The cathodic protection system will have a DC output capacity as follows:
(Sa) (Id) (Cb)
It
It
It =
ZSF
1000
(32921) (30) (0.05)
X1.1
1000
54.32 (A)
Say 55 amperes
Where: Sa Total surface area (m2 )
Id = CP current density (mA/m2 )
Cb = Coating breakdown factor (%)
SF = Safety factor (1.1)
5.1.3 CATHODIC PROTECTION ANODE REQUIREMENT
Chosen output rating of 2 Ampere for each anode, the number of anodes:
N = It/2 = 54.32/2 = 27.16
No. of anodes based on current requirement
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m.1
8. G.U.P PHASE II - LIQUID PIPELINES, TERMINAL JETTIES
N = 30
Another, maximum anode current output for each anodeto be determined as follows :
LogL= 3.3 - LogId
Where : L = design life in years
Id = Maximum anode current density (A/m2 )
For L = 3 0 years
The anode has a dimension of 31.75mm dia x I000mm legth with a.total area of 0.1m2
Therefore, Id =.66.5 A/m2
Maximum current output of anode = 0.1m2 x 66.5 A/m2 =6.65A
Hence 3 0 anodes will give 6.65 x3 0 = 199.5 A Required 54.3 2 A
noe wegt requ id re , W =
W
W =
(0) (It)(y)
Uf
0.1 (54.32) (30)
0.6
271.6 kg
Anodes No. required based on weight requirement :
N W/Wa
271.6 / 20
13.6
No. of anodes based on weight requirement, N = 14
Where Q Anode consumption rate (kg/amp-year)
It = Cathodic Protection current ( A )
Y = Design life of the system ( years )
Uf = Anode Utilization factor ( 0.6 for a conservative design )
Wa = Weight of individual anode ( kg )
Hence anode No. chosen is 30
There are 20 canister anodes in existing groundbed at Dinh Co, so that 10 canister anodes
which are the same existing anode specification will be required to add in this location.
5.1.4 GROUNDBED RESISTANCE
Installation of 30 canister anodes on 5 metre spacing in 2750 ohm-cm soil results in an
estimated groundbed resistance of 0.5844 ohm as follows:
Rn = RI + R2 ( NACE - 1967, page 95 )
Where Rl Anode to backfill resistance
R2 Backfill to soil resistance
Pb BLcr - 1+ 2La
R1
N.yLcrx6.28
[In
do S
In(0.656N)]) { NACE - 1967 )
.- I + (2)(100)
R1' = 50 Fn (8)(100)
ln(0.656)(30)]
(30)(100)(6.28) 3175 500
Ri 0.0152 (ohm)
Rev. D
-
9. G.U.P PHASE II - LIQUID PIPELINES, TERMINAL JETTIES
Where: Pb
La =
da =
S =
N
Backfill resistivity (ohm-cm)
Length of anode- excluding backfill (cm)
Diameter of anode- excluding backfill (cm)
Spacing of anodes (cm)
Number of anodes..
Ps 8Lc -1 + 2Lc
R2
R2
NxLcx6.28
2750
[In In(0.656N)J) (NACE - 196J )
do S
(8) (150) (2) (150)
-1 + in(0.656)(30)J
(30)(150)(6.28) [in 76 500
R2 = 0.5692 (ohm)
Where: Ps Soil resistivity (ohm-cm)
Lc Length of anode- including backfill (cm)
dc Diameter of anode- including backfill (cm)
S. Spacing of anodes (cm)
Number of anodes.
Hence Rn = 0.0152 + 0.5692
0.5844 (ohm)
5.1.5 TRANSFORMER RECTIFIER DC OUTPUT VOLTAGE
It is estimated that the transformer rectifier will require a 45 volt output to achieve :Lie
desired 54.32 ampere DC current output as follows:
It.(Rn+Rc) + Bemf
E 54.32x(0.5844 + 0.2) + 2
E 44.6 volts
Say 45 volts
Where : E Rectifier DC output voltage (volts)
It = Rectifier output current (amp)
Rn = Total groundbed resistance (ohm)
Rc Total cable resistance (0.2 ohm)
Bemf = Dropped voltage between pipeline and ground (-2.0 volts)
Note : Pipe to earth resistance (Rpe) has not been considered since the coating resistari :e is so
high.( 1010 ohm-mz ) that all current will pass through 5% bare areas through r±e pipeline
coating.
Rev. D
10. G.U.P PHASE II - LIQUID PIPELINES, TERMINAL JETTIES
5.1.6 TRANSFORMER RECTIFIER AC INPUT
Actual DC power output required : Pd = 44.6 x 55.32
2422.672 (W)
DC power requirement including 20% overvoltage provision (20% spare Capacity )
= 1.2x44.6x54.32=2907.2 (W)
Now, considering overall system P.F (power factor) = 0.8
and Transformer Rectifier Unit efficiency (E.F) = 0.85 (85% )
For 3 phases, 415V, 50Hz supply input to Transformer Rectifier Unit :
Input current
2907.2
Ip
Ip =
Jx415x0.8x0.85
5.95 A
Hence, AC power input ( including 20% spare capacity) is :
43 x 415 x 5.95 x 0.8
3420.23 Watt
5.1.7 CHANGE IN EARTH POTENTIAL DUE TO FORCED DRAINAGE
When CP current is injected into ground through anode bed, the current flow results in a
potential gradient in the earth. _...
The change in earth potential near the pipelines
(Ps)(It)
V =
27r(r)
(2750)(54.32)
V
Where : Ps
It
r
5.2 PHUOC HOA LOCATION
5.2.1 Pipeline Total Surface Area
27zx10000
2.38 Volts
Soil resistivity ( ohm-cm )
Cathodic Protection current ( Ampere )
Distance between pipeline and anode bed (cm )
The onshore portion of Ba Ria to Phu My gas pipeline and Ba Ria to Thi Vai LPG pipelines
has a total surface area as follows:
Sa _ (Pi) (d) (1)
Sa (3.1416) [(0.426 x 21.500)+ (3 x 0.168 x 17000)]
Sa = 55691 (m2 )
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11. G.U.P PHASE I1- LIQUID PIPELINES, TERMINAL JETTIES
Where: Sa Surface area (m2 )
Pi 3.1416
I Length of pipeline (m)
Diameter of pipeline (m)
5.2.2 CATHODIC PROTECTION CURRENT REQUIREMENT
The cathodic protection system will have a DC output capacity as follows:
It = 91.89 A
( ) * *
(55691 ) * 30 * 0.05
It = x
Say 92 amperes
Where: Sa Total surface area (m2 )
Id = CP current density (mA/m2 )
Cb = Coating breakdown factor (%)
SF = Safety factor (1.1)
5.2.3 CATHODIC PROTECTION ANODE REQUIREMENT
Chosen output rating of 2 Ampere for each anode, the number of anodes:
N = It/2 92/2 = 45.95
No. of anodes based on current requirement
N = 50
Another, maximum anode current output for each anodeto be determined as follows :
LogL=3.3 -Log Id
Where : L = design life in years
Id = Maximum anode current density ( A/m2 )
For L = 30 years
The anode has a dimension of 31.75mm dia x 1000mm legth with a total area of 0.1m2
Therefore, Id = 66.5 A/m2
Maximum current output of anode = 0.1 m2 x 66.5 A/m2 = 6.65A
Hence 50 anodes will give 6.65 x 50 = 332.5 A Required 92 A
(Q)(It)(Y)
Anode weight required, W =
W
=
Uf
(0.1) (92) (30)
0.6
460 kg
Page I 1-of 14-
Rev. D
xSF
Sa Id Cb
It
1000
=
1.1
1000
12. G.U.P PHASE II - LIQUID PIPELINES, TERMINAL JETTIES
Anodes No. required based on weight requirement :
N = W / Wa
460 / 20
23
No. of anodes based on weight requirement, N = 23
Where Q = Anode consumption rate (kg/amp-year )
It = Cathodic Protection current (A )
Y = Design life of the system ( years )
Uf = Anode Utilization factor ( 0.6 for a conservative design
Wa = Weight of individual anode ( kg )
Hence anode No. chosen is 30
There are 20 canister anodes in existing groundbed at Phuoc Hoa, so that 30 canister
anodes which are the same existing anode specification will be required to add in this
location.
5.2.4 OROUNDDED RESISTANCE
Installation of 50 canister anodes on 5 metre spacing in 1500 ohm-cm soil results in an
estimated groundbed resistance of 0.19 ohm as follows:
Rn = R1 + R2
Where R1 = Anode to backfill resistance
R2 Backfill to soil resistance
R1=
R1=
La
2 *100
R1 = 0.0094 Ohm
Pb
50
Where: Pb
La
8 *100
La =
da =
S =
N =
Backfill resistivity (ohm-cm)
Length of anode- excluding backfill (cm)
Diameter of anode- excluding backfill (cm)
Spacing of anodes (cm)
Number of anodes.
− +
× ×
(ln 0.656 )
2
1
8
6.28
N
S
da
Ln
N La
− +
× ×
(ln 0.656 * 50 )
500
1
3.175
50 100 6.28
Ln
13. R2=
R2 =
Lc
2 *150
8 *150
R2= 0.196 (ohm)
Lc
Pb
50
Where:. Ps = Soil resistivity (ohm-cm)
Lc = Length of anode- including backfill (cm)
dc Diameter of anode- including backfill (cm)
S Spacing of anodes (cm)
Number of anodes.
Hence Rn 0.0094 + 0.196
0.2054 (ohm)
5.2.5 TRANSFORMER RECTIFIER DC OUTPUT VOLTAGE
It is estimated that the transformer rectifier will require a 42 volt output to achieve
the desired 92mpere DC current output as follows:
It.(Rn+Rc) + Bemf
E 92 x (0.2054 + 0.2) + 2
E 39.29 volts
Say 42 volts
Where.: E Rectifier DC output voltage (volts)
it = Rectifier output current_ (amp)
Rn _ Total groundbed resistance (ohm)
Rc = Total cable resistance (0.2 ohm)
Bemf = Dropped voltage between pipeline and ground (-2.0
volts)
Note : Pipe to earth resistance (Rpe ) has not been considered since the coating
resistance
is so high ( 1010 ohm-nag ) that all current will pass through 5% bare areas
through the
pipeline coating.
5.2.6 TRANSFORMER RECTIFIER AC INPUT
Actual DC power output required : Pdc = 39.29 x 92
3614.68 ( W)
− +
× ×
(ln 0.656 )
2
1
8
6.28
N
S
dc
Ln
N Lc
− +
× ×
(ln 0.656 * 50 )
500
1
3.175
50 150 6.28
Ln
14. DC power requirement including 20% overvoltage provision (20% spare Capacity)
= 1.2x39.29x92=4337.6 (W)
Now, considering overall system P.F ( power factor) = 0.8
and Transformer Rectifier Unit efficiency (E.F) = 0.85 ( 85% )
For 3 phases, 415V, 50Hz supply input to Transformer
Rectifier Unit : Input current
IP=
4337 .6
3 x 415 x 0.8 x
0.85
Ip =8.875 A
Hence, AC power input ( including 20% spare capacity) is :
- _
3x415 x8.875 x0.8 = 5013W
15. :
G.U.P PHASE II - LIQUID PIPELINES, TERMINAL JETTIES
5.2.7 CHANGE IN EARTH POTENTIAL DUE TO FORCED DRAINAGE
When CP current is injected into ground through anode bed, the current flow results in a
potential gradient in the earth.
The change in earth potential near the pipelines
(Ps)(It)
2 r(r)
(1500)(92)
V =
Where : Ps =
It =
r =
2xl0000
= 2.2 Volts
Soil resistivity ( ohm-cm )
Cathodic Protection current ( Ampere )
Distance between pipeline and anode bed ( cm )
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