Corrosion Control & MonitoringCorrosion Control & Monitoring- Cathodic Protection을 중심으로

코렐테크놀로지 이선엽syli@correltech comsyli@correltech.com

OUTLINEOUTLINE

I d i

OUTLINEOUTLINE

Introduction• Corrosion Basics

• Economics of Corrosion

• Corrosion Control Methods

Corrosion Monitoring B i f Th• Brief Theory

• Types of Corrosion Monitoring Probes

• Application

Corrosion Control by Cathodic Protection• Introduction

• Standard Specification and Recommended Practice• Standard, Specification and Recommended Practice

• Applications to Onshore Structures (Storage tanks, Pipelines, etc.)

Discussion

부식부식 C iC i부식부식 CorrosionCorrosionTh d i ll t l • Thermodynamically natural process

• 양극: M → Mn+ + ne-

• 음극: O2 + 2H2O + 4e- → 4OH-

• 부식의 4대 요인• Anode • Cathode

El t i d t• Electronic conductor• Ionic Conductor (electrolyte)

• (+) Closed circuit( )

Corrosion in an extractive metallurgy in reverse.

Chevron 2001Chevron 2001The leak caused by corrosion at this elbow started the fire that destroyed this refinery

Gas explosion caused by charged soil (15 m x 34 m) due to corrosion

Corrosion of Buried Pipe in Nuclear Power Corrosion of Buried Pipe in Nuclear Power llPlantPlant

Highway Bridges $8.3

부식비용 cost of corrosion

Gas and Liquid Transm. Pipelines

Waterways and Ports

Hazardous Materials Storage

Air Ports

$7.0

$0.3

$7.0

-

Railroads

Gas Distribution

Electrical Utilities

-

$5.0

$6 9

Drinking Water and Sewer System $36.0

Electrical Utilities

Telecommunication

Motor Vehicles

Ships

Aircraft

$6.9

-

$23.4

$2.7

$2 2Aircraft

Railroad Cars

Hazardous Materials Transport

Oil and Gas Expl. And Production

Mining

$2.2

$0.5

$0.9

$1.4

$0.1

Report No. FHWA-RD-01-156“Corrosion Cost and Preventive Strategies in the United States”, G h d H K h M P H B N G Th Y P Vi i J H

g

Petroleum Refining

Chem., Petrochem., Parm.

Pulp and Paper

Agricultural

$3.7

$1.7

$6.0

$1.1

$Gerhardus H. Koch, M.P.H. Brongers, N.G. Thompson, Y.P. Virmani, J.H. Payer, Office of Infrastructure Research and Development Federal Highway Administration, Department of Transportation, 2003

g

Food Processing

Electronics

Home Appliances

Defense

$2.1

-

$1.5

$20.0

Nuclear Waste Storage $0.1

Cost of Corrosion Per Analyzed Economic Sector, ($ x billion)

$10 $20 $30$0 $40

Causes of Failure in Refining & Causes of Failure in Refining & P t h i l Pl t i J (2004)P t h i l Pl t i J (2004)Petrochemical Plants in Japan (2004)Petrochemical Plants in Japan (2004)

# of Corrosion Failures for 4 years# of Corrosion Failures for 4 years# of Corrosion Failures for 4 years# of Corrosion Failures for 4 years

Source: http://www.engineers.org.il/_Uploads/1598AntiCorEnvironIndiaPaper06.pdf

Forms of CorrosionForms of Corrosion

Corrosion Control MethodsCorrosion Control MethodsCorrosion Control MethodsCorrosion Control Methods

Alloying to resist corrosion (SS, cupronickel, etc.)

Metallic coatings (galvanizing)

Organic coatings (paint, lining)

Electrochemical protection• Cathodic protection

• Anodic protection

Corrosion inhibitors Corrosion inhibitors• Automotive cooling systems, cooling towers, boilers, etc.

12

Corrosion Costs of Corrosion Control Methods & Corrosion Costs of Corrosion Control Methods & S i (USA 8)S i (USA 8)Services (USA, 1998)Services (USA, 1998)

MATERIAL AND SERVICESRANGE AVERAGE COST

($ x billion) ($ x billion) (%)

P i C iProtective CoatingsOrganic CoatingsMetallic Coatings

33.5-167.51.4

100.51.4

86.71.2

M t l & All 7 7 7 7 6 6Metals & Alloys 7.7 7.7 6.6Corrosion Inhibitors 1.1 1.1 1.0Polymers 1.8 1.8 1.6(Anodic) Cathodic Protection 1.97-2.46 2.22 1.9Services 1.2 1.2 1.0Research & Development 0.020 0.02 <0.1pEducation & Training 0.01 0.01 <0.1

TOTAL $48.7-$183.19 $115.95 100%

Glossary: Glossary: Inspection & MonitoringInspection & MonitoringGlossary: Glossary: Inspection & MonitoringInspection & Monitoring

(Corrosion) Inspection• The evaluation of the quality of some characteristic in relation to a standard or

a specificationa specification.

• NDT

(Corrosion) Monitoring• Corrosion measurements performed under industrial operating conditions.

• Acquiring data on the rate of material degradation

• Corrosion probe/sensor

14

Corrosion MonitoringCorrosion Monitoring

The practice of measuring the corrosivity of process stream condition using “probe” inserted into the process stream d hi h ti l d t th t diti

Corrosion MonitoringCorrosion Monitoring

and which are continuously exposed to the process stream condition

Mechanical, electrical or electrochemical probes

Non-Destructive Testing Ultrasonic testing Radiography

Offline Direct Radiography Thermography Eddy current/magnetic flux intelligent pigs

Analytical Chemistry pH measurement Offline IndirectAnalytical Chemistry pH measurement Dissolved gas (O2, CO2, H2S) Metal ion count (Fe2+, Fe3+) Microbiological Analysis

Offline Indirect

Operational Data pH Online Indirectp p Flow rate (velocity, turbulence) Pressure Temperature

Fluid Electrochemistry Potential measurement Online Direct Potentiostatic measurement Potentiodynamic measurement AC impedance

orOffline

or Indirect

Corrosion Monitoring Weight loss coupons Online Direct Electric resistance Linear polarization hydrogen penetration Galvanic current

M it i M th dM it i M th dMonitoring MethodsMonitoring Methods

Corrosion coupon

LPR probe

p

16

Bioprobe for monitoring bacteria

Electrical resistance probeSource: Alabama Specialty Products, www.metalsamples.com

Corrosion CouponsCorrosion Coupons

A i h d l f h l ll d id i

Corrosion CouponsCorrosion Coupons

A weighted sample of the metal or alloy under consideration.

It is introduced into the process, and removed after a reasonable time interval.

The coupon is then cleaned of all corrosion product and is reweighed The coupon is then cleaned of all corrosion product and is reweighed.

Alternatively the coupon surface and or corrosion product is analyzed by microsco-py and/or other analytical techniques.

The weight loss is converted to a total thickness loss, or average corrosion rate using proper conversion equations.

CORROSION COUPONCORROSION COUPON

Image source: Alabama Specialty Products, www.metalsamples.com

Example: Atmospheric Exposure TestExample: Atmospheric Exposure TestExample: Atmospheric Exposure TestExample: Atmospheric Exposure Test

Image source: www.corrosionsource.com

Oilfield Corrosion InhibitorsOilfield Corrosion Inhibitors

A i

Oilfield Corrosion InhibitorsOilfield Corrosion Inhibitors

DryGas

AmineSweetening

GlycolDehydrator

CompressorCooler

Producing Wells

FWKO

Oil StorageTank

HeaterTreater

Scrubber

FWKO

WaterClarifier

Source

InjectionWell Pump

WaterStorage

SourceWater

SurgeVessel

gTank

Inhibitor ComparisonInhibitor ComparisonInhibitor ComparisonInhibitor ComparisonUsing Using Coupons (Coupons (OilwellOilwell))

FLOW

35 ppm 25 ppmOil Soluble Chemical

35 ppmWater Soluble Chemical

Installing Corrosion CouponInstalling Corrosion CouponInstalling Corrosion CouponInstalling Corrosion Coupon

FLOW

22

Coupon Installation into High Pressure Coupon Installation into High Pressure iiLineLine

23

Coupon HoldersCoupon HoldersCoupon HoldersCoupon Holders

Corrosion Rate Calculation Based on Corrosion Rate Calculation Based on C i CC i C

Simplest and most reliable technique for corrosion rate determination

Corrosion CouponCorrosion Coupon

Simplest and most reliable technique for corrosion rate determination is the Weight Loss Technique.

Corrosion Rate = mass/[(exposed surface area] · [time])

oror

= Average corrosion penetration depth/time

= (mass/density/surface area/time)= (mass/density/surface area/time)

Common Corrosion Rate Units• gmd: grams of metal loss per square meter per day (mdd)• gmd: grams of metal loss per square meter per day (mdd)

• mm/y: average millimeters penetration per year

• mpy: average mils penetration per year, 1 mil = 0.001 inch)py g p p y , )

NACE RP0775NACE RP0775--2005 2005 Corrosion RatesCorrosion Rates

G l Pi i C i

NACE RP0775NACE RP0775 2005 2005 Corrosion RatesCorrosion Rates

Generalmpy

Pittingmpy

CorrosionRating

< 1.0 < 5.0 Low

1.0 – 4.9 5.0 – 7.9 Moderate

5.0 – 10.0 8.0 – 15 High

> 10.0 > 15.0 Severe

1 mpy = 0 001” per year1 mpy = 0.001 per year

Corrosion Coupon Data in Amine UnitCorrosion Coupon Data in Amine UnitCorrosion Coupon Data in Amine UnitCorrosion Coupon Data in Amine Unit

Source: http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_0031/0901b8038003151c.pdf?filepath=gastreating/pdfs/noreg/170-01408.pdf&fromPage=GetDoc

Case StudyCase StudyCase StudyCase Study

Source: http://www.gewater.com/pdf/Technical%20Papers_Cust/Americas/English/tp1120.pdf

Corrosion Monitoring ExampleCorrosion Monitoring ExampleCorrosion Monitoring ExampleCorrosion Monitoring Example

Electrical Resistance (ER) MethodElectrical Resistance (ER) MethodElectrical Resistance (ER) MethodElectrical Resistance (ER) Method

Measures the change in electrical resistance of a corroding metal elements relative to a reference non-corroding element sealed within the probe bodyprobe body.

AL

R

Image source: Alabama Specialty Products, www.metalsamples.com

ER Probe TypesER Probe TypesER Probe TypesER Probe Types

Image source: (1) Alabama Specialty Products, www.metalsamples.com(2) S.Y. Li et al., Mat. Chem. Phys., 103 (2007) 9

V = I*R

Electrical resistance probe

R = ρprobe

*l/A

ER ProbeER Probe

C

ER ProbeER Probe

Corrosometer

33

Typical Response of ER ProbeTypical Response of ER ProbeTypical Response of ER ProbeTypical Response of ER Probe

34

Typical Response of ER ProbeTypical Response of ER ProbeTypical Response of ER ProbeTypical Response of ER Probe

Installation ExampleInstallation ExampleInstallation ExampleInstallation Example

Application Example Application Example –– Steel BridgeSteel BridgeApplication Example Application Example Steel BridgeSteel Bridge

37

Thin Film ER Probe Thin Film ER Probe –– Steel BridgeSteel BridgeThin Film ER Probe Thin Film ER Probe Steel BridgeSteel Bridge

0.8

1.0

0 2

0.4

0.6

R0/R

0 10 20 300.0

0.2

Time (day)

SW

1.0Stage I: incubation time

0.6

0.8

Stage II: Active corrosionCorrosion Rate: 0.074 mm/y

R 0/R

0.2

0.4

AverageCorrosion Rate: 0.026 mm/y

38

0 10 20 30 40 50 60 70 800.0

Time (day)

Linear Polarization Resistance Method (LPRM)Linear Polarization Resistance Method (LPRM)Linear Polarization Resistance Method (LPRM)Linear Polarization Resistance Method (LPRM)

Within ~10mV more noble or active than the Ecorr, i is a line f n tion of the ele t ode potenti l

E

linear function of the electrode potential.iapp = |ia-ic| = f(E)

E = Eapp - Ecorr

= alog ia/io M - alog icorr/io M

Ecorr

Eappic ia

alog ia/io,M alog icorr/io,M

= a log ia/icorr

= a/2.303 ln ia/icorr

/ i log iia = icorr e2.303E/a

Similarly, i = i e-2.303E/c

io,a log i

ic = icorr e /c

iapp = ia - ic = icorr (e2.303E/a – e-2.303E/c )= icorr (2.303E/a + 2.303E/c)= 2.303icorrE(a + c)/ac = icorrE/B Stern Geary equation

assuming that 0 12assuming that a = c = 0.12Rp = E/iapp = B/icorr = 0.026/icorr

Rp: polarization resistance.

LPR Method (LPR Method (선형분극법선형분극법))LPR Method (LPR Method (선형분극법선형분극법))

Cooling water systems

Secondary recovery system

P t bl t t t t d di t ib ti t Potable water treatment and distribution systems

Amine sweetening

Waste water treatment systems Waste water treatment systems

Pickling and mineral extraction processes

Pulp and paper manufacturing Pulp and paper manufacturing

Hydrocarbon production with free water

40

Linear Polarization Resistance ProbeLinear Polarization Resistance Probe

• Gives instantaneous corrosion rates

Only used in conductive• Only used in conductive solutions

• Based on the current flowBased on the current flow between two or more electrodes

R i th f t• Requires the surface to become passivated (or polarized) and current resistance is measured.

• Sometimes probe has a reference electrode as well.

H ll’ S tCET® f b k d Honeywell’s SmartCET® uses a sensor for background electrochemical noise to detect pitting along with LPR probe.

Faraday’s LawFaraday’s LawFaraday s LawFaraday s Law

MnFQ

m

WhereQ = charge (C) = I × tF = Faraday’s constant (96500 C/eq)F Faraday s constant (96500 C/eq)n = number of equivalents (moles of electrons) transferred per mol of meta

lm = mass of metal corroded (g)m mass of metal corroded (g)M = molecular (atomic) weight of metal (g/mole)

So if Q is known mass loss by corrosion can be determinedSo, if Q is known, mass loss by corrosion can be determined.

The details of corrosion rate determination by electrochemical techniques will be covered laterovered later.

Corrosion Rate CalculationCorrosion Rate CalculationCorrosion Rate CalculationCorrosion Rate Calculation

• If the imeasured = 10-5 A/cm2measured

• Using Faraday’s Law the corrosion rate is calculated as:

scmg1092

cmA10molg56CRm 29

25

scmg109.2molC964852

CRm

I bl it (di id b th d it 7 86 • In a more useable unit … (divide by the density – 7.86 g/cm3 for iron; convert cm to mm and seconds to years)

yr/mm12.0yr/m116CR

44

Corrosion Monitoring of MEG Corrosion Monitoring of MEG ReboilerReboiler with with b bLPR ProbeLPR Probe

Temp. : 140oCsolution : EG + inhibitor

0 300

0.325

0.350

0.375

0.400solution : EG inhibitor

Ar blowing (+ NaCl 16%) Air blowing (+ NaCl 16%) Ar blowingAir blowing

0.200

0.225

0.250

0.275

0.300

EG:water

60:40/yr

Air blowing

0 075

0.100

0.125

0.150

0.175

EG:water78:22

mm

22 24 26 28 30 32 34 36 38 40 420.000

0.025

0.050

0.075

water %

Effect of Inhibitor Concentration on CorrosionEffect of Inhibitor Concentration on CorrosionEffect of Inhibitor Concentration on CorrosionEffect of Inhibitor Concentration on Corrosion

350.0k

400.0k 1/2 dilution 1/20 dilution 1/200 dilutionT t

250.0k

300.0k

2 )

Tap.water

150.0k

200.0k

Rp (

cm

50.0k

100.0k

0 600 1200 1800 2400 3000 3600 4200 4800 5400 6000 6600 72000.0

Time(s)

46

산업용산업용 부식속도부식속도 측정법측정법

원리 장점 단점

선형분극법(Linear Polarization Resistance Method; LPR)

전기화학적 특성측정이 쉬움검증된 방법

측정장비 설치 문제전기화학적 지식 요구

금속시편을 이용한 무게 감량법(Weight Loss Measurement)

부식으로 인한 시험편의무게감량 측정

정확한 정보 제공부식환경에 따라서 오랜시간 소요

초음파 두께 측정 (UT)초음파 반사파를 이용한잔여 두께 측정

측정 용이On-line 감시 어려움부식기구에 대한 정보 제공하지 않음공하지 않음

전기저항법(ER method)

부식으로 인한 금속의 전기저항 변화 측정

측정 용이부식원리에 대한 특별한지식 불필요

센서 형태/두께에 따라 민감도/수명 변화

지식 불필요

47

Selection Selection Selection Selection Guideline Guideline between between between between ER & LPR ER & LPR ProbeProbeProbeProbe

Source: P.R. Roberge, Handbook of gCorrosion Engineering (1999)

Corrosion Monitoring Points Corrosion Monitoring Points i i ill i li i ill i lin Distillation Columnin Distillation Column

PracticePracticePracticePractice

In practice, the choice of monitoring points is also dictated by the existence of suitable access points, especially in pressurized systemssystems.

It is usually preferable to use existing access points, such as flanges, for sensor installations for sensor installations.

If it is difficult to install a suitable sensor in a given location, additional bypass lines with customized sensors and access fittings may be a bypass es t custo ed se so s a d access tt gs ay be apractical alternative. One advantage of a bypass is that it provides the opportunity to manipulate local conditions to highly corrosive regimes in a controlled manner, without affecting the actual operating plant.

Typical Internal Monitoring Points in CDU & Other Typical Internal Monitoring Points in CDU & Other O h dO h dOverheadsOverheads

Source: www.cosasco.com

51

Corrosion as a Process VariableCorrosion as a Process VariableCorrosion as a Process VariableCorrosion as a Process Variable

CATHODIC PROTECTIONCATHODIC PROTECTION

C th di P t tiC th di P t tiCathodic Protection:Cathodic Protection:

An electrical method ofmitigating corrosion on

t lli t t th tmetallic structures that areexposed to electrolytes suchexposed to electrolytes suchas soils and waters.

Sacrificial Anode Cathodic Protection Sacrificial Anode Cathodic Protection ( )( )(SACP)(SACP)

CURRENTCURRENT

SACRIFICIALSACRIFICIALANODEANODE

Impressed Current Impressed Current CP (ICCP) SystemCP (ICCP) SystemImpressed Current Impressed Current CP (ICCP) SystemCP (ICCP) SystemImpressed Current Impressed Current CP (ICCP) SystemCP (ICCP) SystemImpressed Current Impressed Current CP (ICCP) SystemCP (ICCP) System

PowerSource

+-

CU

RREN

CU

RREN

+-CU

RREN

TCU

RREN

T

NT

NT

ANODEANODE

전기방식의전기방식의 원리원리 ––열역학적열역학적 관점관점FeFe의의 Pourbaix DiagramPourbaix Diagram

방식전위와방식전위와 부식속도부식속도

40

4

10-3

10-2

10-1

30

mm

/y

10-8

10-7

10-6

10-5

10-4

-2 0 -1 5 -1 0 -0 5 0 0 0 5 1 0 1 5

i, A

/cm

2

20

on

Rat

e, m

2.0 1.5 1.0 0.5 0.0 0.5 1.0 1.5

E, V/CSE

10

m C

orr

osi

o

0Ma

xim

um

-800 -600 -400 -200 0 200

Potential mV/CSEPotential, mV/CSE

방식전위와방식전위와 상대부식속도상대부식속도

5835.234.23125 4

100

3125.4

10

1 미방식1

부식

속도

1, 미방식1

상대

부

0 04

0.1

0.04

0.018, 방식기준0.01

-1000 -800 -600 -400 -200 0 200

전위 (mV/CSE)

외면부식외면부식 사례사례

피복강관의 전식

외면부식외면부식 사례사례

피복강관의 미생물부식 피복강관의 전식(stray current corrosion)

AC-induced corrosion Crevice corrosion Corrosionunder disbonded coating

CPCP와와 부식부식CPCP와와 부식부식산성염기성

방식전위가 낮아질 수록 pH는 증가

전기방식 실시 이후 누적 누수 빈도가 감소

전위에 따른 부식속도

방식전위가 낮아질 수록 부식속도는 감소

61

A. W. Peabody, Peabody’s Control of Pipeline Corrosion, 2nd .ed.

CP 적용에 따른 누설율 감소 사례

전기방식전기방식 효과효과 ((고압가스배관고압가스배관))

피복이 손상된부분이라도

전기방식이 잘 되고 있다면

모재의 손상이 없음

토양부식성이토양부식성이 작은작은 경우경우토양부식성이토양부식성이 작은작은 경우경우

피복손상부 존재피복손상부 존재전기방식 불량 구간토양부식성 작음(~8,000 Ωcm)

No corrosion !!

희생양극법희생양극법희생양극법희생양극법

희생양극법이란 ? 희생양극법이란 ?• 방식대상 구조물 대신 희생양극이 부식되어 구조물을 방식하는 방법

희생양극법의 회로도• 양극• 금속 사이의 연결선, Re

• 구조물(음극)• 용액 Ri용액, Ri

• 양극과 음극 사이의 전위차, E

양극의 종류 양극의 효율

• 양극에서 발생하는 전류 중 구조물의 방식에 이용되는 전류량의 비율

희생양극의희생양극의 종류종류희생양극의희생양극의 종류종류

Mg 양극 Mg 양극 전위 : -1.55V, -1.75V 효율 : 50% 용량 1102 A h /k 용량 : 1102 A-hr/kg 주 사용처 : 토양중의 철구조물

Zn 양극 전위 1 1 V 전위 : -1.1 V 효율 : 90%, 95% 용량 : 738A-hr/kg 주 사용처 : 바다에 설치된 구조물 주 사용처 : 바다에 설치된 구조물

Al 양극 전위 : -1.1V 효율 : 85% 95% 효율 : 85%, 95% 용량 : 2534 - 2833 A-hr/kg 주 사용처 : 바다에 설치된 구조물

희생양극법의희생양극법의 적용적용희생양극법의희생양극법의 적용적용

량의 방식전 가만 필 할 때 소량의 방식전류 증가만 필요할 때 외부전원법의 사용이 어려울 때 국부적인 방식 (spot protection)이 필요할 때 외부전원법 전기방식을 실시하기 전 시공단계에서 임시방

식이 필요할 때식이 필요할 때

시공시공시공시공

희생양극의 시공 희생양극의 시공• 직접연결• 지상에서 연결지상에서 연결

충전제의 사용• Mg 양극에 사용되는 backfill의 성분

• Ground hygrated Gypsum (CaSO4): 75% • Powdered bentonite (clay): 20% Powdered bentonite (clay): 20% • Anhydrous sodium sulfate (Na2SO4): 5%

• Zn 양극에 사용되는 backfill의 성분• Ground hygrated Gypsum: 50% • Powdered bentonite: 50%

Anode BackfillAnode BackfillAnode BackfillAnode Backfill

전 효율 향상 전류효율 향상 국부적인 부식 가능성 해소 양극 주변에 항상 습기가 있도록 유지 유효양극면적의 증가

외부전원법외부전원법외부전원법외부전원법

외부전원법이란 외부전원법이란• 정류기의 +를 양극에, -를 배관에 연결하여 배관을 음극화시켜 방

식하는 방법

외부전원법 회로도• 정류기기전력(V)

양극접지 저항• 양극접지 저항• 토양저항• 배관접지저항배관접지저항• 배관금속저항• 전선저항

외부전원법의 장단점 외부전원법의 장단점 외부전원용 양극

외부전원용외부전원용 양극양극외부전원용외부전원용 양극양극

Graphite• 건조한 토양에 적용이 좋음• 염소 반응이 주인 바다에서 사용가능• 염소 반응이 주인 바다에서 사용가능• 산소발생반응에서는 소모율이 큼• 깨어지기 쉬움깨어지기 쉬움

고규소철 (high silicon cast iron; HSCI)• 조성 : 규소 (Si) : 14.2 - 14.75%, 크롬 (Cr) : 3.25 - 5%, 망간 (Mn) : 1.5%,

탄소 (C) : 0.75 - 1.15, 철 (Fe) : 잔량

Platinized Niobium (Chloride환경)

MMO (mixed-metal oxide) coated Ti anode

MMO Anodes

양극표면에서의양극표면에서의 전형적인전형적인 반응반응양극표면에서의양극표면에서의 전형적인전형적인 반응반응

Electrolysis of water: 2H2O 4H+ + O2 + 4e

Oxidation of chloride ion: 2Cl Cl2 + 2e

Oxidation of carbon: C + 2H2O 4H+ + CO2 + 4e

C + H2O 2H+ + CO + 2eoror

결과(1) 물의 소비

72 of 159

( )(2) 기체 발생(3) pH 감소

희생양극배치희생양극배치희생양극배치희생양극배치

출처: Cathodic Protection Design Coursebook, NACE International

외부전원법외부전원법 전기방식의전기방식의 종류종류외부전원법외부전원법 전기방식의전기방식의 종류종류

외부전원 집중배치 (천매)

외부전원 집중배치 (심매)외부전원 집중배치 (심매)• 지하의 토양비저항이 낮을 때• 복잡한 지역의 피방식구조물• 양극설치 부지가 없을 때

외부전원법외부전원법 전기방식의전기방식의 종류종류외부전원법외부전원법 전기방식의전기방식의 종류종류

외 전원 분산배치형 외부전원 분산배치형• 소요전류량이 많음, 타시설물과 절연되지 않음• 공단내 구조물• 공단내 구조물• 해수 강관 파일• 피복되지 않고 절연되지 않은 배관피복되지 않 절연되지 않은 배관• 매설된 저장탱크

Test station Test station Test station Test station

Test Box

양극 영구기준전극 절연시설물 타시설물과 교차할 때 전류량을 측정하는 장치

Cost Comparison: Corrosion Damage vs. Cost Comparison: Corrosion Damage vs. CPCP

CP Criteria CP Criteria

-850mVCSE or more negative with current appliedCSE

-850mVCSE “instant-off”

-100mV Shift between “instant-off” and “native”

Potential Criteria from British Standard (BS 7361)Potential Criteria from British Standard (BS 7361)( )( )

Material Potential, CSE

Soils and Fresh Water

Potential, Silver-silver Chloride

SeawaterFresh Water Seawater

Iron and Steel Aerobic environment

–850 mV –800 mV

Iron and Steel Anaerobic environment

–950 mV –900 mV

L d 600 V 550 VLead –600 mV –550 mV

Aluminum Not to exceed

–950mV –1200 mV

–900 mV –1150 mVNot to exceed 1200 mV 1150 mV

Copper Alloys –500 to –650 mV –450 to –600 mV

79 of 159

Other CP CriteriaOther CP CriteriaOther CP CriteriaOther CP Criteria

Shell DEP 30.10.73.31: • Design of Cathodic Protection Systems for Onshore Buried Pipelines

전기방식전기방식 기준기준 CP CriteriaCP Criteria전기방식전기방식 기준기준 CP CriteriaCP Criteria

NACE RP0169• 전위기준

• -850 mV/CSE (ON 전위)

850 V/CSE (OFF 전위 분극전위 IR f 전위)• -850 mV/CSE (OFF 전위, 분극전위, IR-free 전위)

• 분극량 기준• 100 mV 분극변위100 mV 분극변위

ISO 15589-1• 부식속도가 < 0.01 mm/y 가 될 수 있는 전위부식속 가 y 가 될 수 있는 전위• -850 mV/CSE (분극전위)

• 100 mV 분극

Cathodic Protection of Cathodic Protection of Underground MetallicUnderground MetallicUnderground Metallic Underground Metallic Structures Structures in Plantin Plant

Types of underground metallic structures in PlantTypes of underground metallic structures in PlantTypes of underground metallic structures in PlantTypes of underground metallic structures in Plant

Highly congested underground structures• Pressurized steel hydrocarbon pipelines• Pressurized steel hydrocarbon pipelines

• Bottom or soil side of aboveground storage tanks (ASTs)

• Buried storage tanks

• Sea walls and associated anchors• Sea walls and associated anchors

• Buried portion of process, gas, water, firewater or liquids pipelines

• Buried or buried portion of steel valves, hydrants, monitors and fittings.

• C di id• Copper grounding grid

• Steel of reinforced concrete piles

• Reinforced concrete foundations

St d i d it f d • Storm drains and gravity-fed sewers

• Electrical duct banks

Isolation problems

Maintenance issues

For CP

사례사례사례사례

시공전 굴착 케이블 포설

Splice kit 조립 양극 설치 1차 되메움

전선관 설치 경고띠 포설 되메움

전신주 설치 양극매설지 복구완료 정류기 설치 안내문 설치

CP MaterialsCP MaterialsCP MaterialsCP Materials

정류기 양극 벤트 파이프

HMWPE케이블 22mm2ELP 주름관 28Φ매설용 기준전극 접지봉, GV 케이블

절연 파이프 케이싱 관

시공전 시험 굴착 Boring

양극 시공양극 시공

케이블 포설 Splice kit 연결 1차 되메움

경고 테이프 설치 심도 측정 되메우기 및 복구 완료

외부전원법외부전원법 -- 심매양극심매양극 설치설치 작업작업외부전원법외부전원법 심매양극심매양극 설치설치 작업작업

시험 굴착 보링 (1차 10m 절연용) 보링 (2차 35m 케이싱용) 보링후 심도 측정

양극 투입 Coke breeze 투입

배관 본딩 케이블 전선관 매설 Junction box 설치/결선 정류기

Ideal SolutionIdeal SolutionIdeal SolutionIdeal Solution Isolated system where every buried structure is isolated where it

b dcomes above ground.• A large number of insulated flanges/joints

• Maintenance and reliability problems• Maintenance and reliability problems.

절연시설물의절연시설물의 종류종류절연시설물의절연시설물의 종류종류 Insulation Flange

• 절연볼트, 절연와셔, 절연가스켓• 시간 경과에 따른 절연 불량 가능성

Ins lation Joint Insulation Joint• 공장 일체형• 현장에서 용접하여 연결현장에서 용접하여 연결• 절연불량 가능성 거의 없음• 고비용 소요

llCP Maintenance: potential measurementCP Maintenance: potential measurement• P/S potential measurementP/S potential measurement

• Pipe to Soil potential• Reference electrode: Sat. Cu/CuSO4 ref. electrode

• Potential measurement at test post (point)voltmeter

Potential measurement at test post (point)V

Ref.electrode

pipe

Test post (box)

CIPSCIPS 필요성필요성 ((예예))CIPSCIPS 필요성필요성 ((예예))

-600

-500

-800

-700

CP criteriaE)

-1000

-900

CP criteria

TB 4TB 5

TB 315.4mA

TB 80 Aia

l (m

VC

SE

-1200

-1100 TB 126.8mA

TB 2

TB 414.7mA

511.4mA

TB 619.2mA

TB 734.3mA

0 mA

TB 925.2mA

P/S

po

ten

t

-1400

-1300

TB 255mA

P

0 1 2 3 4 5 6 7 8 9 10-1500

Distance (km)Distance (km)

Test points 전위는 양호해도 TP와 TP사이의 전위는 불량한 경우 존재

CP Potential Survey Results (CIPS) on Underground CP Potential Survey Results (CIPS) on Underground Pi I h LNG R i i T i lPi I h LNG R i i T i l

NG pipes

Pipes at Incheon LNG Receiving TerminalsPipes at Incheon LNG Receiving Terminals

Vent stackTK-207TK-208

TK-209 TK-212

TK-213

TK-216

TK-217

TK-220

TK-205 TK-206 TK-210TK-211

TK-214

TK-219

TK-218

TK-215

Fuel gas pipes

TK-203TK-204

TK-201 TK-202

Seawater pipes

NG pipes

Firewater pipes

방식방식 누설누설 전류전류방식방식 누설누설 전류전류 누설전류

• 배관방식용 전류 중 배관이 아닌 타 시정류기

배관방식용 전류 중 배관이 아닌 타 시설로 유입되는 전류

누설전류의 원인• 배관과 타시설의 금속 접촉• 접지 기초콘크리트의 철근 등

기

• 접지, 기초콘크리트의 철근 등 대책안

• 타시설과의 절연• 타시설 방식 소요전류량을 고려한 방

i1

i2양극

타시설 방식 소요전류량을 고려한 방식 설계

• 탄소강 : 10mA/m2

• Rebar : 5mA/m2

• 구리접지봉 : 300mA/m2

정류기

• 구리접지봉 : 300mA/m2

• 심매양극보다는 천매양극 분산배치가 유리

방식대상체와 타시설물과의 간격• 법적 간격 : 30cm• 가까운 경우 : 방식전위 차이에 의한

간섭 발생• 금속접촉이 없으면 누설전류와는 무 i1

i2천매

금속접촉이 없으면 누설전류와는 무관 심매

Alternative methodsAlternative methodsAlternative methodsAlternative methods Blanket system where no isolation is provided.

• All buried metal work on the site is cathodically protected including earthingsystems.

• Require a considerable amount of CP currents Require a considerable amount of CP currents

• Generally, ICCP unless soil resistivities are very low.

저장탱크저장탱크 바닥바닥 방식방식저장탱크저장탱크 바닥바닥 방식방식• 토양부식

• 탱크바닥에 자갈,clay 등이 있는 경바닥에 자 , y 이우 local cell 형성

• 수분 차이에 의한 local cell 형성•

• Galvanic corrosion• Galvanic corrosion• 탱크 바닥이 다른 금속과 연결되어

있는 경우 (접지/배관/철근)

S i• Stray current corrosion• 타 방식 설비에 의한 부식

Deep well anodebeds vs. Shallow anodesDeep well anodebeds vs. Shallow anodes

CP of AST BottomCP of AST Bottom (PETRONAS)(PETRONAS)CP of AST Bottom CP of AST Bottom (PETRONAS) (PETRONAS) (From engineering spec. PRR2(From engineering spec. PRR2--COMCOM--ELEL--H119)H119)

d d f ld d f lUnderground Corrosion of AST: ExamplesUnderground Corrosion of AST: Examples

CP appliedNo CP

Storage Tank Storage Tank 하부하부 방식방식 ((기존기존))

Oiled sand

• 기존의 탱크하부 방식 문제점

수분 유입Deep well 방법의 전기방식

• 기존의 탱크하부 방식 문제점– Oiled sand의 문제점 –불균일한 수분 유입에 의하여 부식 발생– (수분침투지점의 부식억제가 어려움)– Oiled sand에 의한 CP 전류 shielding효과 정류기

부식발생Oiled sand에 의한 CP 전류 shielding효과

– 외부 타시설에 방식 전류 분산(절연문제)Oiled sand

수분

정류기

수분 방식전류

Result of thickness testResult of thickness test

Thickness test result on the tank having no CP systemno CP system• hundreds of points were corroded

(criteria : 30%) • Dozens of points : less than 50% Dozens of points : less than 50%

thickness• Corrosion mechanism

• Oil was leached out• W t i i• Water ingression

• Corrosion points were distributed irregularly

• oiled-sand cushion did almost no role in preventing corrosion

100mmOiled-sand

soil ring wall

oilwaterwater

부식생성물부식생성물 분석분석 (AST bottom)(AST bottom)

부식생성물부식생성물

Fe

#1#2 #3Fe

O

부식생성물단면

FeFe Si

: 탱크 하부의 부식생성물 분석: 탱크 하부의 부식생성물 분석- 주로 철(수)산화물- 전형적인 녹혹에 의한 통기차부식(또는 농담전지형성에 의한 부식)으로 판단됨형성에 의한 부식) 판단됨

Ineffective CP: exampleIneffective CP: example

Potential Monitoring TubePotential Monitoring TubePotential Monitoring TubePotential Monitoring Tube

New Concept for CP of AST BottomNew Concept for CP of AST Bottom

• Use of clean sand• Use of clean sand• No Current shielding due to

oiled sandsand

Rectifier_+

• Use of MMO coated Ti ribbon (grid) Anode

Anodegrid

f fNew Concept for CP of AST Bottom

Ref. Electrode

Corrosion

AST

on sensor Ti MMO Anode

Performance Test of MMO AnodePerformance Test of MMO Anode

NACE TM0108 T i f C l d Ti i A d f U i S il N l

Performance Test of MMO AnodePerformance Test of MMO Anode

NACE TM0108 Testing of Catalyzed Titanium Anodes for Use in Soils or Natural Waters

50 yr @ 17 mA/m (or 42mA/m) - test at 6.35A/m (within 3 days)y @ ( ) ( y )

Detail Design Example (2011)Detail Design Example (2011)Detail Design Example (2011)Detail Design Example (2011)

Recommended PracticeRecommended Practice

API 650 “Welded Steel Tanks for Oil Storage”

API 651 “Cathodic Protection of Aboveground Petroleum Storage Tanks”

NACE RP0193 “External Cathodic Protection of On-grade Carbon Steel Storage Tank Bottoms”

Numerical Analysis at CP Design & Maintenance Stage Numerical Analysis at CP Design & Maintenance Stage Numerical Analysis at CP Design & Maintenance Stage Numerical Analysis at CP Design & Maintenance Stage

2222ΦΦ = 0= 0

주배관주배관 임시방식임시방식 시공시공 사진사진주배관주배관 임시방식임시방식 시공시공 사진사진

해양해양 강파일강파일 -- 희생양극법희생양극법해양해양 강파일강파일 희생양극법희생양극법

출처: www.ntac.co.jp

CP on JettiesCP on JettiesCP on JettiesCP on Jetties

CP on JettiesCP on JettiesCP on JettiesCP on Jetties

Corrosion of Jetty PilesCorrosion of Jetty PilesCorrosion of Jetty PilesCorrosion of Jetty Piles

사례사례 –– 콘크리트콘크리트 구조물구조물출처: 일본 엘가드협회사례사례 콘크리트콘크리트 구조물구조물출처: 일본 엘가드협회

Total current Requirement: 2000ATotal current Requirement: 2000AAnode 835 lbs 5AAnode 835 lbs 5ATotal Number of Anodes 416ea.Total Number of Anodes 416ea.

사례사례 –– 댐구조물댐구조물 (hydraulic steel structures)(hydraulic steel structures)사례사례 댐구조물댐구조물 (hydraulic steel structures)(hydraulic steel structures)

귀수문(miter gate)의 부식피로(below a water line)

ICCP f HICCP f H il Piil PiICCP of HICCP of H--pile Pierpile Pier

Protective coating + ICCP

Ribbon anodes on wall of seaRibbon anodes on wall of sea--water intake structurewater intake structure

CP f Pili F d ti f St T kCP f Pili F d ti f St T kCP of Piling Foundation of Storage TankCP of Piling Foundation of Storage Tank

CP f C d W t BCP f C d W t BCP of Condenser Water BoxCP of Condenser Water Box

Multi-channelMulti channelRemote controllable Rectifiers

CP monitoring of offshore pipelineCP monitoring of offshore pipelineCP monitoring of offshore pipelineCP monitoring of offshore pipeline

Platform

Trailing Wire

Spooling Dispenser

Survey VesselTrailing Wire

Attached to platform riser

Tow fish with Ag/AgCl HalfCell attached

Pipeline

Standards and Standards and SpecificationsSpecificationsStandards and Standards and SpecificationsSpecifications

NACE NACE • RP0100 – Cathodic Protection of Prestressed Concrete Cylinder Pipes• SP0169 - Control of External Corrosion on Underground or Submerged Metallic Piping Systems• RP0186 - Application of Cathodic Protection for External Surfaces of Steel Well Casings• RP01 96 - Galvanic Anode Cathodic Protection of Internal Submerged Surfaces of Steel Water Storage Tanks• RP0193 - External Cathodic Protection of On-Grade Carbon Steel Storage Tank Bottoms• SP0286 – Electrical Isolation of Cathodically Protected Pipelines• RP0388 - Impressed Current Cathodic Protection of Internal Submerged Surfaces of Steel Water Storage Tanks

S O f C• SP0572 - Design, Installation, Operation and Maintenance of Impressed Current Deep Anode Bed • RP0575 - Internal Cathodic Protection in Oil-Treating Vessels

ISO BS BS

Job Spec.Client’s spec Client’s spec.

THE ENDTHE END

syli@correltech.com