Probing Potential and Solution pH under Disbonded Coating on … · 0 10 20 30 40 50 respectively. potential/pH microprobes installed at dis tances of 30,60,90, 120, 150, and 180

Probing Potential and Solution pH under Disbonded Coating on Pipelines

D KUANG AND YF CHENG Univers ity of Calgary Calgary Alberta Canada

This work monlrors the local paten ial and solution p H under disbanded coating on a steel pipeline The ap-plied cathodiC protection (CP) can be shielded by coating disbondmen Wh ile the open holiday is at a CP po-tential and associated with an ele-vated solu ion pH the dlsbonded re-gion especially the disbondment bottom remains at the corrosion po-tential and the original solution pH

Disbondment of pipeline coatings can

occur by a number of mechanisms In

addition to poor urface preparation and

thermal cycling during pipeline operation

cathodic disbondment is an important

mechanism that results in lost adhesion

which usually slarts at a holiday Cathodic

protectio n (CP) at coating faults could ele-

vate the electrolyte pH at the holiday

through enhanced cathodic reduction of

dissolved oxygen or water2 The alkaliza-

tion of the local solution can weaken the

bond of the coating primer to the steel

causing coating disbondment

The shielding effect of coating disbond-

ment on CP penetration into the disbond-

ing crevice has been investigated Para-

metric effects such as solution resistivity

size of the holiday temperature CP poten-

tial and disbonding geometry have been

tested CP can be shielded from reaching

the disbonded crevice bottom There are

numerous environmental conditions that

can affect the CP shielding behavior

The steel under a disbonded coating

espeCially the disbondment bottom can

experience corrosion by anodic dissolu-

tion while the open holiday remains under

effective CP The separation of anodic and

cathodic reactions could facilitate the oc-

currence of localized corrosion which has

frequently been observed on cathodically

protected pipelines where the coating has

disbonded

Fusion-bonded epoxy (FBE) is a com-

monly used pipeline coating that is com-

patible with CP However there has been

limit ed work to investigate the shielding

effect of FBE induced by geometrical fac-

tors (ie disbonding from a holiday) on CP

as well as the time dependence of this ef-

fect This work attempted to determine the

CP shielding behavior under disbonded

FBE through in situ probing of local poten-

tial and solution pH distributions under

the coating The effects of CP potential as

well as the disbonding thickness and depth

were determined

Experimental Conditions Steel coupons and coating used in this

work were X65 pipeline steel and FBE re-

spectively The chemical composition of

the steel (w1) is 004 C 02 Si 15 Mn 00l1

P 0003 S 002 Mo and balance Fe Prior to

testing the steel surface was ground with

120240400 and 800 grit emery papers

foHowed by cleaning in distilled water and

methanol

Figure 1 shows a home-designed exper-

imental setup to simulate the crevice gen-

erated by coating disbondment The di-

mension of the steel plate was 200 by 25 by

40 MAY 2015 MATERIALS PERFORMANCE NACE INTERNATIONAL VOL 54 NO5

_ mm To prepare an arti lc ial di sbo nd-

ent the FBE membrane (200lm in thick-

ss) was applied on the steel urface using

dou bleshysided selfshyadhesie tape The gap

_tween FBE and the steel as defin ed as

e disbonding thickn es Tape with a

own thickness was lave red to establish

e desired gap which was verified with a

ating thickness gauge The FBE mem-

rane was appli ed to the tape which was

hen appli ed on the steel surface The tape

as removed to form artific ial FBE di s -

ndments over the steel The boundaries

[ the steelcoating assembh were sealed

Measurement ports

Steel

shy --~----~-----~----~----~-----~ Measurement ports

i th an epox) resin

A lOshymm diameter hole was opened on FIGURE 1 Schematic diagram of the experimental setup simulating a disbonding crevice under

e coating to simulate a holida with six coating and the potentialsolution pH measurements

shyD50 shy050 shyshyOmm Cal

shy055 shyshy- 30mm shy055

shyD60 shyshyshyshy60 mm shyD60 ~ 90mm

Gl shyD 65 __120mm Gl shyD65 () ()

gt

shyD70 150 mm

~ shy+shy180mm

() ()

gt

shyD70

~ shyD75 ~ shy075 co c shy080

y ~ C shyD80

~ ~ 0 c shy085 0 c shy085

shy090 shy090

shyD95 shy095

shy1 00 c~~---~~~ ~~ _~~--~~ shy100 o 10 20 30

lime (hl

shy050

shyD55

shyD60

shyD65Gl () () shyD70 gt

shyD75~ co shy080 c ~ 0 shyD85c

shy090

shyD95

shy100

shyshyOmm (bl ~ 30mm

shyshyshyshy60 mm ~ 90mm

__ 120mm

_ 150mm

shy+shy 180 mm~ ~

40 50 0 10 20 30 40 50 lime (hl

(elshyshyOmm __30mm

~ 60mm

shy90mm __ 120mm __ 150mm

shy+shy 180mm

0 10 20 30 40 50 exper- lime (hl

_e gen- FIGURE 2 Time dependence of the distributions of local potential under disbonded coating (disbonding thickness of 120 ~m) at varied disbonding shy he di- depths from the open holiday where the steel was either at corrosion potential (a) or at CP potentials of shy0875 V vs SCE (b) and shy0975 V vs SCE (c)

_ 25 by respectively

4 NO - ACE INTERNATIONAL VOL 54 MATERIALS PERFORMANCE MAY 2015 41

shyshyshyshy shy

shyshyshy

shyshyshyshyshyshyshyshyshy===

COATINGS amp LININGS

120120 Ca) (b)shyshyOmm115 115 shyshyOmm

shyshy30mm shyshy30mmshy6shy60 mm ____ 60 mm110 110 shyTshy90 mm

~ 90mm105 105shyshy120mm shyshy120 mm shy+shy 150mm10 10 shy+shy 150mm shy+shy180 mm shy+shy 180 mm95 95

I Ia a9 0 90

80 80

X75 75 [IF70 IP

70

65 65

60 60 0 10 20 30 40 50 0 10 20 30 40 50

TIme (h) TIme (h)

TIme (h)

FIGURE l Time dependence of the distributions of local solution pH under disbonded coatin9 (disbondin9 thickness of 120 tJm) at varied disbondin9 depths from the open holiday where the steel was either at corrosion potential (a) or at CP potentials of shy0875 V vs SCE (b) and shy0975 V vs SCE (c)

120 (c)

115

110

105

10 shyshyOmm shy- 30mm

95 shyshyshyAshyshy 60 mmI a

90

80

75 ~ 90mm

shy+shy 120 mm 70 shyshy+shy 150 mm

65 shyshy+shy180 mm

60 0 10 20 30 40 50

respectively

potentialpH microshyprobes installed at dis-

tances of 306090 120 150 and 180 mm

from the holiday The distance of the prob-

ing position to the open holiday was de-

fined as the disbonding depth

A nearshyneutral pH (75) bicarbonate so-

lution was used to simulate the electrolyte

trapped under the disbonded coating The

solution was 001 M sodium bicarbonate

(NaHCO) and was purged with 5 carbon

dioxide (COz)nitrogen (Nz) for 48 h prior to

the test

The corrosion potential of the steel in

the solution was measured as shy0755 V vs

saturated calomel electrode (SCE) Various

CP potentials were applied to the coated

steel through a Solartron 1280Ct electro-

Trade name

42 MAY 2015 MATERIALS PERFORMA NCE

chemical system using SCE as the refer-

ence electrode and the steel as the working

electrode All tests were conducted at 23 C

Results Figure 2 shows the time dependence of

the distributions of local potential under

disbonded coating (disbonding thickness

of 120 11m) at varied disbonding depths

from the open holiday where the steel was

either at corrosion potential or at CP po-

tentials of shy0875 V vs SCE and shy0975 V vs

SCE respectively It is seen that prior to CP

application the local potentials at all prob-

ing positions are N shy0755 V vs SCE which

is the corrosion potential ofX65 steel in the

test solution When the potential of shy0875

V vs SCE is applied the potential at the

holiday (ie 0 mm in the figure) is the ap-

plied CP value However the potential at

the position of 30 mm from the holiday is

less negative (ie shy0800 V vs SCE after 48

h of testing) With the increase in the dis-

bonding depth (ie the probing pOSition is

farther away from the holiday) the local

potential is less negative than that at the 30

mm position but the potential difference is

not distinguishable At the CP potential of

shy0975 V vs SCE the potential at the holi-

day is still the applied value but the local

potentials at the probing positions are

shifted less negatively With the increase in

disbonding depth the potential becomes

less negative The disbonding depth at the

local potential is not distinguishable as this

CP level is increased to 150 mm

Thus the applied CP can be shielded

from reaching the coating disbondment

NACE INTERNATIONAL VOL 54 NO 5

shyshyOmm (a)

shyshy30 mm shyshy6shyshy 60 mm ~ 90mm

shyshy+shy 120mm ___ l50 mm ___ 180 mm

~ ~

~ -

~

shyamp shy

shy060shy060 shyshyOmm (b) shyshy30 mm shyshy6shyshy 60 mmshy065 shy065 ~ 90mm

shyshy+shy 120mm ___ 150mmWW

() shy070() shy070 C)C) shy+shy 180 mm gtgt ~ shy075~ shy075 iiiiii

shy ~ c 0 shy080 shy080~

ClCl

shy085shy085

shy090shy090 0 10 20 30 40 50 0 10 20 30 40 50

Time lth) Time (h)

shy060 shyshyOmm (d --- 30 mm

-065 --6--60 mm --90 mm --+- 120mm

IJ -070 -+- 150 mm(J C) -+- 180mm

gt -075 ~ e g

-080laquogt (5 Cl

-085

-090 0 10 20 30 40 50

Time (hl

FIGURE 4 Distributions of local potential under disbonded coating at varied disbonding depths from the open holiday where the CP potential of -0875 V vs 5CE is applied under various disbonding thicknesses (a) 120 ~m (b) 240 IJm and (c) 360 ~m

With the increase in dis bonding depth to-

ward the disbondment bottom the CP

shielding is more apparent The shielding

effect can be mitigated by application of

more negative CP potentials

Figure 3 shows the time dependence of the distributions of local solution pH under


of 120 flm) at various disbonding depths where the steel was either at corrosion po-

tential or at CP potentials of -0875 and

-0975 V vs SCE respectively Prior to CP

application the solution pH is N7S the

value of the prepared solution at all prob-

ing positions Upon CP application the so-lution pH is elevated Moreover when the

CP potential is more negative the solution

pHis further elevated at individual probing

positions For exampleat the open holiday

NACE INTERNATI O NAL VO L 54 0 5

the steady-state solution pH is 85 at -0875

V vs SCE and 110 at -0975 V vs SCE

However the CP driven pH elevation be-

comes less obvious with the increasing

disbonding depth especially at the dis-

bondment bottom Figure 4 shows the distributions of local

potential under disbonded coating at var-

ied disbonding depths from the open holi-day where the CP potential of -0875 V vs

SCE is applied under various disbonding

thicknesses Identical to previous results

the CP is shielded from reaching the dis-

bondment Only at the open holiday the

measured value is the same as the applied CP potential Under the coating disbond-

ment the potential tends to be less nega-

tive Moreover with the increase in dis-

bonding thickness the CP shielding effect

becomes less significant For example at

the disbonding thickness of 120 flm thE

local potential at the probing position of3C

mm is -0810 V vs SCE When the dismiddotN

bonding thickness is increased to 240 an

360 flm the potentials at the same positior

are -0855 and -0865 V vs SCE respecmiddot

tively Therefore as the coating disbondmiddot ment becomes wider (ie with an increasec

disbonding thickness) the CP shielding ef

fect is less significant Figure 5 shows the distributions of solumiddot

tion pH under disbonded coating at variec

disbonding depths from the open holida)

where the CP potential of -0875 V vs SCI

is applied under various disbonding thick nesses The applied CP is able to elevatl

solution pH especially at the open hoJida) With the increasing disbonding depth thl

MATERIALS PE RFO RMANCE MAY 2015 4

shyshy

12 12 (al (bl-Omm -Omm

- 30mm -- 30mm ____ 60 mm11 11 ____ 60 mm ---- 90 mm ---- 90 mm __ 120mm __ 120mm

10 __ 150mm 10 __ 150mm ~ 180mm ~ 180mm

JJ c 9c 9

~

8 J 8 x

IIF r

7 7

6 6 0 10 20 30 40 50 0 10 20 30 40 50

Time (hl Time (hl

12 (el

-Omm 30 mm11

---- 60 mm ---- 90 mm - ltII 120 mm10

150mm ~ 180mm

J c 9

---8

7

6 0 10 20 30 40 50

Time (hl

FIGURE 5 Distributions of solution pH under disbonded coating at varied disbonding depths from the open holiday where the CP potential of

-0875 V vs 5CE is applied under various disbonding thicknesses (al 120 ~m (bl 240 ~m and (cl 360 ~m

solution pH tends to be the value of the ment becomes wider the CP-enhanced pH tive shift of CP potential the enhancement originally prepared solution As the dis- elevation is more appreciable is more apparent Thus the solution pH is bonding thickness increases the CP- further elevated induced pH elevation becomes more obvi- Discussion When CP is applied on a coated steel ous even at the disbondment bottom For In deoxygenated near-neutral pH bicar- electrode containing a holiday the CP is

example at the disbonding thickness of 120 bonate solutions the anodic and cathodic primarily applied on the open holiday The

flm the solution pH at the disbondment reactions during corrosion of pipeline steel solution pH at the holiday is elevated with

bottom (ie 180 mm from the holiday) is are primarily the iron oxidation and reduc- the negative shift of CP potential as shown ~75 This indicates that the CP does not tion of water respectively In the absence of in Figure 3 The nonuniform distribution of penetrate into the disbondment bottom CP the steel corrodes at both the holiday solution pH from the open holiday to the

When the dis bonding thickness is in- and under the disbonded coating Upon CP disbondment indicates that the CP-creased to 240 and 360 flm the solution pH application the cathodic reaction is en- induced pH elevation is not fully realized

at the disbondment bottom is 79 and 81 hanced resulting in the generation of OH- under the disbonded coating

respectively Thus as the coating disbond- to elevate the solution pH With the nega- The measurements of the potential dis-

44 MAY 2015 M ATERIAL S PERFORMANCE NACE INTERNATIONAL VOL 54 NO 5

50


shy he CP shieldirg =

iepends not 0

Jisbonding geo t

also o n the cond

e t rapped solutio er

oating

shyr ibution from the holid a~ to

oondment bottom indicate tha th

P is shielded at least p r tJaJl~ un e di bonded coating (Figure 2) The en-

als are consistent with the pH u ~ _ 1

be disbonding thickne of J_0 un only

he open holiday is under full Ppo en~ ith the increasing distance from the holl-

d y (ie the increasing disbondin_ dep

shyhe local potential tends to e I nega e until the steadyshystate corrosion potential -

reached Due to the shie ldi n g e([ed the eel under the disbonded C031io_ L not

under CP The potential re ord al 0 indi -

cate that in order to cathodically protec

the steel under coating di bondment lhe CP potential must be suffi cienL negatiye

However hydrogen evolution must aJ 0 be

considered

The shielding effect of c a i n_ di bond-

nent on CP permeation is af ~ cted by the

disbanding thickness as shown in irures 4

and 5 The measurements of bo th local po-

tential and solution pH und middot r d i b onded

coating show that the CP shieldin a tends to

be mitigated when the disbonding lhick-

1ess is increased and the potentials under

disbonded coating approach tho e at t he

open holiday Moreover the pH elenltion

under disbondment is more apparent

Thus the geometrical factor 0 the coating

disbondment plays an essential role in CP

shielding

The CP shielding by disbanded coating

is primarily attributed to the blocking ef-

fect of coating disbondment on CP current

Under narrow disbonding gaps the di stri-

bution ofCP current is highIv nonuniform

at the open holiday and under the dis-

banded coating This effect is further en-

hanced by limited diffusion of conductive

NACE INTERN ATIONAL VOL 5 C

ionic species through the thin solution

layer trapped under the coating Thus al-

though the open holiday is under full CP

the disbonded region is shielded from CP

either partially or completely Vith the in-

crease in disbonding thickness the distri-

bution of CP current can be improved

around the holiday The increased solution

volume under the wider coating disbond-

ment enhances the diffusion of species fa-

cilitating the CP permeation into the dis-

bondment Thus the CP shielding effect

depends not only on the disbonding geom-

etry but also on the conductivity of the

trapped solution under coating

The CP shielding by coating disbond-

ment can result in cathodic polarization of

shy eel at the holiday while the steel at the

di bondment bottom can be at its corro-

ion potential depending on the disbond-

In thickness and applied CP The potential

dif erence produces separate anode and

cathode sites The cathodic reaction occurs

at the holiday and the anodic reaction at

th e disbondment bottom The disbond-

ment can become full of corrosion product

hi h is difficult to diffuse through further

increasing the blocking effect on CP per-

meation This is the key mechanism result-

ing in localized corrosion on pipelines that

are under CP This phenomenon has been

demonstrated by frequent field experiences

that extensive corrosion pits are found

under disbonded coating on a cathodically

protected pipeline

Conclusions CP can be shielded by coating disbond-

ment With the increase in disbonding

depth toward the disbondment bottom the

shielding effect is more apparent The CP

shielding can be mitigated by more nega-

tive CP potentials

The geometrical factor of the coating


shielding When the disbondment becomes

wider the shielding effect is mitigated

The CP shielding can result in separate

anodic and cathodic reactions which

occur at the disbondment bottom and the

open holiday respectively This is the key

mechanism that causes localized corrosion


protected pipeline

References eG iIlunger Corrosion Prevention by Protec-

tive Coatings 2nd ed (Houston TX NACE

International 1999)

2 JJ Perdomo I Song Chemical and Electromiddot

chemical Conditions on Steel Under Dis-

bonded Coatings The Effect of Applied

Potential Solution Resistivity Crevice

Thickness and Holiday Size Corros Sci 42

(2000) pp 1389shy1415

3 DT Chin Current Distribution and Electromiddot

chemical Environment in a Cathodically Pro-

tected Crevice Corrosion 55 (1999) pp 229-

237

4 Ae Toncre N Ahmad Cathodic Protection

in Crevices Under Disbonded Coatings IP

19 (1980) pp 39shy43

5 X Chen XG Li CW Du YF Cheng Effect

of Cathodic Protection on Corrosion of Pipe-

line Steel Under Di sbonded Coating Corras

Sci 51 (2009) pp 2242shy2245

6 TR Jack G Van Boven M Wilmott RL

Sutherby RG Worthingham Cathodic Pro-

tection Potential Penetration Under Dis-

bonded Pipeline Coating kIP 33 (1994) pp

17shy21

7 A Fu Y Cheng Characterization of Corro-

sion of X65 Pipeline Steel Under Disbonded

Coating by Scanning Kelvin Probe Corros

Sci 51 (2009) pp 914shy920

8 A Fu YF Cheng Characterization of the

Permeability of a High Performance Com-

posite Coating to Cathodic Protection and

its Implications on Pipeline Integrity Prog

Organ Coal 72 (2011) pp 423shy428

9 IVI Baker Jr Integrity Management Pro-

gramshyStress Corrosion Cracking Studies

Final Report Office of Pipeline Safety TTO-

8 Department ofTransportation 2004

D KUANG is a PhD student at the Univer-sity of Calgary MEB 2500 University Dr NW Calgary AB T2N 1N4 Canada eshymail dkuangucalgaryca His research interest is pipeline corrosion and coating disbondment under alternating current in-terference

YF CHENG is a professor and Canada Research Chair in Pipeline Engineering at the University of Calgary eshymail fcheng ucalgaryca He is an internationally re-puted researcher in pipeline corrosion NP

MATERIALS PERFORMANCE MAY 2015 45

_ mm To prepare an arti lc ial di sbo nd-

ent the FBE membrane (200lm in thick-

ss) was applied on the steel urface using

dou bleshysided selfshyadhesie tape The gap

_tween FBE and the steel as defin ed as

e disbonding thickn es Tape with a

own thickness was lave red to establish

e desired gap which was verified with a

ating thickness gauge The FBE mem-

rane was appli ed to the tape which was

hen appli ed on the steel surface The tape

as removed to form artific ial FBE di s -

ndments over the steel The boundaries

[ the steelcoating assembh were sealed

Measurement ports

Steel

shy --~----~-----~----~----~-----~ Measurement ports

i th an epox) resin

A lOshymm diameter hole was opened on FIGURE 1 Schematic diagram of the experimental setup simulating a disbonding crevice under

e coating to simulate a holida with six coating and the potentialsolution pH measurements

shyD50 shy050 shyshyOmm Cal

shy055 shyshy- 30mm shy055

shyD60 shyshyshyshy60 mm shyD60 ~ 90mm

Gl shyD 65 __120mm Gl shyD65 () ()

gt

shyD70 150 mm

~ shy+shy180mm

() ()

gt

shyD70

~ shyD75 ~ shy075 co c shy080

y ~ C shyD80

~ ~ 0 c shy085 0 c shy085

shy090 shy090

shyD95 shy095

shy1 00 c~~---~~~ ~~ _~~--~~ shy100 o 10 20 30

lime (hl

shy050

shyD55

shyD60

shyD65Gl () () shyD70 gt

shyD75~ co shy080 c ~ 0 shyD85c

shy090

shyD95

shy100

shyshyOmm (bl ~ 30mm

shyshyshyshy60 mm ~ 90mm

__ 120mm

_ 150mm

shy+shy 180 mm~ ~

40 50 0 10 20 30 40 50 lime (hl

(elshyshyOmm __30mm

~ 60mm

shy90mm __ 120mm __ 150mm

shy+shy 180mm

0 10 20 30 40 50 exper- lime (hl

_e gen- FIGURE 2 Time dependence of the distributions of local potential under disbonded coating (disbonding thickness of 120 ~m) at varied disbonding shy he di- depths from the open holiday where the steel was either at corrosion potential (a) or at CP potentials of shy0875 V vs SCE (b) and shy0975 V vs SCE (c)

_ 25 by respectively

4 NO - ACE INTERNATIONAL VOL 54 MATERIALS PERFORMANCE MAY 2015 41

shyshyshyshy shy

shyshyshy






I Ia a9 0 90

80 80

X75 75 [IF70 IP

70

65 65

60 60 0 10 20 30 40 50 0 10 20 30 40 50

TIme (h) TIme (h)

TIme (h)


120 (c)

115

110

105



90

80

75 ~ 90mm


65 shyshy+shy180 mm

60 0 10 20 30 40 50

respectively


tances of 306090 120 150 and 180 mm










the test






Trade name







































shyshyOmm (a)



~ ~

~ -

~

shyamp shy





ClCl

shy085shy085

shy090shy090 0 10 20 30 40 50 0 10 20 30 40 50

Time lth) Time (h)


-065 --6--60 mm --90 mm --+- 120mm

IJ -070 -+- 150 mm(J C) -+- 180mm

gt -075 ~ e g

-080laquogt (5 Cl

-085

-090 0 10 20 30 40 50

Time (hl



















































shyshy



10 __ 150mm 10 __ 150mm ~ 180mm ~ 180mm

JJ c 9c 9

~

8 J 8 x

IIF r

7 7

6 6 0 10 20 30 40 50 0 10 20 30 40 50

Time (hl Time (hl

12 (el

-Omm 30 mm11

---- 60 mm ---- 90 mm - ltII 120 mm10

150mm ~ 180mm

J c 9

---8

7

6 0 10 20 30 40 50

Time (hl











50



iepends not 0

Jisbonding geo t

also o n the cond


oating














considered














shielding












































protected pipeline






tive CP potentials











protected pipeline



International 1999)






(2000) pp 1389shy1415




237



19 (1980) pp 39shy43




Sci 51 (2009) pp 2242shy2245





17shy21




Sci 51 (2009) pp 914shy920













shyshyshyshy shy

shyshyshy






I Ia a9 0 90

80 80

X75 75 [IF70 IP

70

65 65

60 60 0 10 20 30 40 50 0 10 20 30 40 50

TIme (h) TIme (h)

TIme (h)


120 (c)

115

110

105



90

80

75 ~ 90mm


65 shyshy+shy180 mm

60 0 10 20 30 40 50

respectively


tances of 306090 120 150 and 180 mm










the test






Trade name







































shyshyOmm (a)



~ ~

~ -

~

shyamp shy





ClCl

shy085shy085

shy090shy090 0 10 20 30 40 50 0 10 20 30 40 50

Time lth) Time (h)


-065 --6--60 mm --90 mm --+- 120mm

IJ -070 -+- 150 mm(J C) -+- 180mm

gt -075 ~ e g

-080laquogt (5 Cl

-085

-090 0 10 20 30 40 50

Time (hl



















































shyshy



10 __ 150mm 10 __ 150mm ~ 180mm ~ 180mm

JJ c 9c 9

~

8 J 8 x

IIF r

7 7

6 6 0 10 20 30 40 50 0 10 20 30 40 50

Time (hl Time (hl

12 (el

-Omm 30 mm11

---- 60 mm ---- 90 mm - ltII 120 mm10

150mm ~ 180mm

J c 9

---8

7

6 0 10 20 30 40 50

Time (hl











50



iepends not 0

Jisbonding geo t

also o n the cond


oating














considered














shielding












































protected pipeline






tive CP potentials











protected pipeline



International 1999)






(2000) pp 1389shy1415




237



19 (1980) pp 39shy43




Sci 51 (2009) pp 2242shy2245





17shy21




Sci 51 (2009) pp 914shy920













shyshyOmm (a)



~ ~

~ -

~

shyamp shy





ClCl

shy085shy085

shy090shy090 0 10 20 30 40 50 0 10 20 30 40 50

Time lth) Time (h)


-065 --6--60 mm --90 mm --+- 120mm

IJ -070 -+- 150 mm(J C) -+- 180mm

gt -075 ~ e g

-080laquogt (5 Cl

-085

-090 0 10 20 30 40 50

Time (hl



















































shyshy



10 __ 150mm 10 __ 150mm ~ 180mm ~ 180mm

JJ c 9c 9

~

8 J 8 x

IIF r

7 7

6 6 0 10 20 30 40 50 0 10 20 30 40 50

Time (hl Time (hl

12 (el

-Omm 30 mm11

---- 60 mm ---- 90 mm - ltII 120 mm10

150mm ~ 180mm

J c 9

---8

7

6 0 10 20 30 40 50

Time (hl











50



iepends not 0

Jisbonding geo t

also o n the cond


oating














considered














shielding












































protected pipeline






tive CP potentials











protected pipeline



International 1999)






(2000) pp 1389shy1415




237



19 (1980) pp 39shy43




Sci 51 (2009) pp 2242shy2245





17shy21




Sci 51 (2009) pp 914shy920













shyshy



10 __ 150mm 10 __ 150mm ~ 180mm ~ 180mm

JJ c 9c 9

~

8 J 8 x

IIF r

7 7

6 6 0 10 20 30 40 50 0 10 20 30 40 50

Time (hl Time (hl

12 (el

-Omm 30 mm11

---- 60 mm ---- 90 mm - ltII 120 mm10

150mm ~ 180mm

J c 9

---8

7

6 0 10 20 30 40 50

Time (hl











50



iepends not 0

Jisbonding geo t

also o n the cond


oating














considered














shielding












































protected pipeline






tive CP potentials











protected pipeline



International 1999)






(2000) pp 1389shy1415




237



19 (1980) pp 39shy43




Sci 51 (2009) pp 2242shy2245





17shy21




Sci 51 (2009) pp 914shy920













50



iepends not 0

Jisbonding geo t

also o n the cond


oating














considered














shielding












































protected pipeline






tive CP potentials











protected pipeline



International 1999)






(2000) pp 1389shy1415




237



19 (1980) pp 39shy43




Sci 51 (2009) pp 2242shy2245





17shy21




Sci 51 (2009) pp 914shy920













Documents

Probing Potential and Solution pH under Disbonded Coating on … · 0 10 20 30 40 50 respectively. potential/pH microprobes installed at dis tances of 30,60,90, 120, 150, and 180