11 - NRG - Cathodic Protection Design

Pipeline Design Training

Pipeline Design Training

Cathodic Protection Design

Cathodic Protection Design

1 !"g"st #$$

1 !"g"st #$$

Pipeline Design Training &od"le I *

+verview

!"g"st # , !"g"st #-

/' &r. Eng 0in NG

Applicable

Codes

Wall

Thickness

Design

On-bottom

Stability

(Concrete

Coating)

Design

Pipe

Epansion

Calc!lations

"leibility

Analysis

#ethodology

Allo$able

"ree Span

Calc!lations

On-bottom

%o!ghness

Analysis

& '  

Workshop* re+ision* eercise

Pipeline

Protection

against Anchors* Wa+e ,i!e.action / Earth!ake 0 Cathodic Protection Design

1se o.

Spoilers .or

Pipe

Sel.-b!rial

Pipeline

Constr!ction

-

Con+entional / 1ncon+entional

2nstallation

Engineering

(&3')

4 5 6 7

2nstallation

Engineering

('3')

&8

Pipeline Design Training &od"le I *

2ched"le

_Weekending

_A!g

_

_A!g

_&&

_A!g

_&6

_A!g

_'0

_'6

 Applicable Codes, Wall Thickness

Design

On-bottom Stability (Concrete Coating) Design

Pipe !pansion Calc"lations, #le!ibility Analysis $ethodology  Allo%able #ree Span Calc"lations,

On-bottom &o"ghness Analysis Pipeline Protection against Anchors, Wa'e i"e*action + arth"ake Cathodic Protection Design

se o* Spoilers *or Pipe Sel*-b"rial Pipeline Constr"ction - Con'entional + ncon'entional

nstallation ngineering

1 #  3 % - 4 1$ 11 13 1( 1 1% 1- #1 ## # #3 #(

#-Workshop* re+ision* eercise

Cathodic Protection Design



In the cathodic protection anal'sis calc"lations are carried

o"t to ens"re that the anodes provided are s"5cient to

provide the total c"rrent needed to protect the pipeline

d"ring its design li6e.



 The initial and 7nal c"rrent demands are to /e chec8ed to

ens"re that the anodes can provide s"5cient c"rrent

o"tp"t to polarise the pipeline thro"gho"t its entire li6e.

Cathodic Protection Design 9cont:d;



<al6*shell al"mini"m allo' /racelet anode is t'picall' "sed

6or cathodic protection o6 pipeline.



 The CP design can t'picall' /e carried o"t "sing either one

o6 the 6ollowing codes=



DN> RP*03$1



DN> RP*?1$

 The parameters "tilised in the cathodic protection design

calc"lations and the applica/le re6erence to the appropriate

codes are presented /elow=

CAT9OD2C P%OTECT2O: DES2;: DATA

Parameters 1nit %ele+ant

Cla!ses in %P-"&8

%ele+ant Cla!ses in

%P-<8&

nternal *l"id Temperat"re o_{C Cl./.0.1}

-A:ODE S1%"ACE TE#PE%AT1%E O_{C Cl. /.1.1 Cl 2.3.4, 2.2.1}

DES2;:,2"E* T =EA%S - Cl 2.0,

C"rrent Density %hen *l"id temperat"re (T_#) 5 0/ o_C $ean mA6m0 _{Cl. /.0.3 7 /.0.1 Cl 2.3,} Table 2.3.8, Table 2.3.0. 9 Cl. /./.8, SO 8//4:-0 (Table 1) Cl 2.2./, Table 2.2.0 9 $"d6 Sea%ater &esisti'ity, ρ Ω.m Cl. /./.0 C, 4>6  Anode tilisation #actor, " - Cl. /.1.0 Cl 2.:

lectrochemical **iciency, ε_ma!  Ah6kg Cl. /.1.3, /.1.1, SO 8//4:-0

(Table 1)

Cl. 2.2.8 7 2.2.1

Coating ;reak-do%n #actor Percentage

 Anne! A8, Table  A8

Cl. 2.1, 2./ Pipeline Protecti'e Potential,  E co

!ss"mptions



 The 6ollowing ass"mptions are made in the anal'sis=



!node s"r6ace temperat"re is ass"med to /e the same as the

operating temperat"re o6 the pipeline



 The anode is ass"med to /e at the end o6 its li6etime when the

anode material is cons"med "p to the steel strap

rein6orcement

!nal'sis &ethodolog'



 The proced"res t'picall' adopted 6or CP design calc"lation

are presented /elow=

8.C"rrent Demand

n order to determine the amo"nt o* anode re"ired *or the

cathodic protection system, it is necessary to calc"late the

c"rrent demand, 

_c

, to achie'e polarisation d"ring the

design li*e o* the system as *ollo%s<

!nal'sis &ethodolog' 9cont:d;



here

Ic

A

C"rrent demand 6or a speci7c s"r6ace area

9mean 7nal; 9!;

!c

A

2"r6ace area to /e protected 9m#;

icm

A Design mean c"rrent densit' 9!Bm#;

Dic

A C"rrent densit' temperat"re ad"stment 9!Bm#BC;

ic

A

Design mean c"rrent densit' at #( oC 9!Bm#;

6c

A

Coating /rea8down 6actor 9mean 7nal;

The c!rrent demand .or mean and .inal li.e o. the anode is determined

by the abo+e e!ation>

!node Nett &ass



 The total mass o6 anode &

_re"ired

 re"ired to maintain

cathodic protection 6or the design li6e can /e calc"lated as

6ollows=

ε 

× × ×

u

t 

 I 

mean c_{( )}

 

8760

$

_re"ired

=

$

_re"ired

=

Total nett anode mass re"ired (kg)



_c(mean)

=

$ean (maintenance) design c"rrent

density (A6m

0

₎

4>2?

=

@o"rs per year (hr6year)

t

=

Design li*e (years)

u

=

 _{Anode "tilisation *actor}

e

=

lectrochemical e**iciency (A.h6kg)

The total nett anode mass pro'ided, $

_pro'ided

, m"st be more than or e"al to that

re"ired, $

_re"ired

 *or cathodic protection to be s"stained thro"gho"t the design li*e.

!node C"rrent +"tp"t



 The anode c"rrent o"tp"t Ia is o/tained 6rom +hm:s Faw=



_a

=

af   o a o c

 R

 E 

 E  −



_a

=

initial6*inal c"rrent

o"tp"t (A)

o c

 E 

=

Design protecti'e potential (9)

o a

 E 

=

Design closed circ"it potential o* the anode (9)

R 

af 

=

Anode resistance (

Ω

)

 A

 ρ 

315 . 0

*or *l"sh-mo"nted bracelet anode

=

ρ

=

Sea %ater resisti'ity (

Ω

.m)

A =

AnodeBs e!posed s"r*ace area (m

0

₎

!node C"rrent +"tp"t 9cont:d;



 The 7nal anode resistance is determined 6rom the 7nal

anode dimensions.



 The 7nal anode resistance is calc"lated /' ass"ming that

the anode is cons"med to its "tilisation 6actor " which

wo"ld give a 7nal eposed s"r6ace area and corresponding

anode resistance.



?or cathodic protection to /e eHective thro"gho"t the

design li6e the 7nal c"rrent o"tp"t Ia m"st e"al or

eceed the 7nal c"rrent demand Ic.

Eamples ?or Comparison +6 RP*03$1

and RP*?$1

P2PE,2:E A:D A:ODE DATA

Parameters 1nit ?al!e

nternal *l"id Temperat"re o_{C 3?}

 AOD S&#AC T$P&AT& o_{C 3?}

DS#,T Eear /?

PP OTSD DA$T& mm :81.1 (32-inch) FT&A COAT $AT&A - 3-layer P FT&A COAT T@CGSS mm 0./?

PPT@ m /???

 AOD $AT&A - Al-based

 AOD T@CGSS mm 4?

 AOD DSTE g6cm3 _0.>??

CATHODIC PROTECTION DATA AND RESULTS

Parameters 1nit %P-<8& %P-"&8

<!ried 1nb!ried <!ried 1nb!ried

Cathodic Protection Data

C"rrent Density %hen *l"id temperat"re nitial mA6m0 _{0? 8/? -} -$ean 0? >? 0? /? #inal 0? :? - -9 ?.:/ 8.?/ 8.?? 8.?/ 9 ?.4 ?.4 ?.4 ?.4 $"d6 Sea%ater &esisti'ity, ρ Ω.m 8?? 3? 8?? 3?

 Anode tilisation #actor, " - ?.4 ?.4

$a!. lectrochemical **iciency, ε_ma!  Ah6kg 0??? 0??? 0/??

lectrochemical **iciency, ε  Ah6kg 8>3? 82?? 0???

Coating ;reak-do%n #actor Percentage

nitial - ?.?0 ine Pipe Coating (a = ?.8 b = ?.??3)

#ield Hoint Coating (a = 3 b = ?.3)

$ean ?.?:

#inal ?.8:

Cathodic Protection Resuts

 AOD $ASS kg 8/? 8/? 8/? 8/?

engtho*Anode mm 01? 01? 01? 01?

 AOD T@CGSS mm 4? 4? 4? 4?

 Anode Spacing Ioint 0 0 01J 01J

$ass o* Anode &e"ired kg 3?>/? 3?>/? 0>?? 0>?? Pipeline Protecti'e Potential, o

c

 E 

Close Circ"it Anode Potential *or Al"mini"m,  E ao

Pipeline Design Training