Buried Pipe Corrosion in the Power Plant Environment

Transcription

1 Buried Pipe Corrosion in the Power Plant Environment Assessment and Mitigation in Nuclear Power Plants IAEA Technical Meeting on Buried Pipe October 15, 2014 Kurt M. Lawson Mears Group, Inc.

2 Topics Background Buried Pipe Corrosion Problems in the Plant Environment Combined Approach to Asset Integrity 2

3 Formed in 1970 and acquired By Quanta Services in Mears Group is comprised of: Mears Horizontal Directional Drilling (HDD) Mears Integrity Solutions > Inline Devices 11 Offices Worldwide: U.S, Canada, Abu Dhabi, Malaysia, Australia and India.

4 MEARS Quanta Services NYSE: PWR Member: S&P 500 Index Market Cap: $4.5 Billion 35 Operating Entities 17,000 Employees Electric Power Pipeline Infrastructure Telecommunications

5 Quanta Operating Entities

6 Global Reach Quanta has successfully completed projects that are local, regional, national and international in scope Countries where Quanta has a permanent office or has worked. Australia Belize Brazil British Virgin Islands Canada Costa Rica Guam Guatemala Honduras India Indonesia Iraq Liberia Luxembourg Mexico Netherlands Nicaragua Panama Peru Republic of Chad South Africa Trinidad United Arab Emirates Venezuela

7 Buried Pipe Corrosion An electrochemical process governed by electrical laws NACE International The deterioration of a metal as a result of a reaction with its environment

8 Energy The Life Cycle of Steel IRON OXIDE BLAST FURNACE BESSEMER PIPE MILL REFINING PROCESS CORROSION PROCESS STEEL PIPE PIPE CORRODING IRON OXIDE

9 Energy Required to Convert Ore to Metal Most Energy Required Least Energy Required Potassium Magnesium Beryllium Aluminum Zinc Chromium Iron Nickel Tin Copper Silver Platinum Gold

10 ELECTROMOTIVE SERIES Neutral Soil Material V, (Cu/CuSO4) Mg (Galvomag Alloy) Mg (H-1 Alloy) Zn -1.1 Al (Alclad 3S) -1.0 Cast Iron -0.5 Lead -0.5 Mild Steel (Clean) -0.2 to 0.8 Mild Steel (Rusted) -0.2 to 0.5 Mild Steel (in Concrete) -0.2 Copper -0.2 High Silicon Cast Iron -0.2 Stainless Steel (Type 304) to 0.6 Carbon (Graphite, Coke) +0.3

11 CORROSION CELLS Requirements Anode Cathode Electrolyte Shared by Anode and Cathode (Soil) Metallic or Electron Path between Anode and Cathode

12 CORROSION CELLS Dry Cell Battery Carbon + - Zinc Zn +2 H 2 NH 4 Cl Solution

13 Graphite-Zinc Battery I Carbon Rod (cathode) + Zn +2 - Zinc Case (Anode) NH 4 Cl Solution

14 CAUSES OF CORROSION Differential Soil Aeration Differential Soil Chemistry Dissimilar Metals Contact Stray Current Microbiological

15 Challenges in the Plant Environment In a plant (world) there is really no such thing as a non-corrosive soil Galvanic effects Complex piping CONFIGURATIONS Electrically discontinuous piping

16 Corrosivity of Soils Corrosivity of a particular soil is based on the interaction of several parameters: Resistivity Dissolved salts, Moisture content, ph Presence of Bacteria, Amount of oxygen, and Others

17 Cathodic Protection Challenges in the Plant Environment Complex Piping Current Distribution Monitoring Deep Piping Monitoring Galvanic Issues Current Distribution Monitoring Geometry Current Distribution

18 Complex Piping

19 Galvanic issues with Reinforcing Steel

20 Geometry and Grounding

21 ELECTROMOTIVE SERIES Neutral Soil Material V, (Cu/CuSO4) Mg (Galvomag Alloy) Mg (H-1 Alloy) Zn -1.1 Al (Alclad 3S) -1.0 Cast Iron -0.5 Lead -0.5 Mild Steel (Clean) -0.2 to 0.8 Mild Steel (Rusted) -0.2 to 0.5 Mild Steel (in Concrete) -0.2 Copper -0.2 High Silicon Cast Iron -0.2 Stainless Steel (Type 304) to 0.6 Carbon (Graphite, Coke) +0.3

22 Role of Electrical Grounding Three Important Functions Personnel Safety from Electrical Faults Lightning Protection Termination Point for Instrumentation Shields Accomplished Through Direct Buried Copper Cables and Vertical Ground Rods > In Grids > In Longitudinal Runs > Around perimeter of Buildings/Pedestals 3

23 Impact on Corrosion Grounding Comprised of Copper Material Plant Piping/Buried Structures Carbon Steel Cast/Ductile Iron Stainless Steel Copper/Aluminum Bronze Reinforced Concrete Pre/Post tensioned Concrete 7

24 Impact of Grounding on Corrosion Driving Force For Corrosion = Voltage Difference Voltage or Potential An electromotive force, or a difference in potential expressed in volts. Voltage is the energy that puts charges in motion. 8

25 Piping Corrosion Rates in Soils (Uhlig/Romanoff) Environmental Factors General Corrosion Rates, mpy Pitting Corrosion Rates, mpy Maximum Minimum Average Maximum Minimum Average Soil Resistivity Less Than 1, ,000 to 5, ,000 to 12, Greater Than 12,000 Drainage Very Poor Poor Fair

26 Impact of Grounding on Corrosion of Buried Steel Piping No Copper Couple to Steel Steel Corrodes at 2-10 mils/yr (1000ths of inch/year) Copper/Steel Area Ratio = 1 Steel Corrosion Accelerates by 3x Factor Copper/Steel Area Ratio = 10 Steel Corrosion Accelerates by 10x Factor Copper/Steel Area Ratio = 20 Steel Corrosion Accelerates by 30x Factor 11

27 CP Current Distribution in a Power Plant Because the interconnection of Low Resistance Grounding Systems with High Resistance Piping Systems Majority of CP current goes to bare copper grounding 27

28 Combined Approach to Asset Integrity Assess Analyze Mitigate

29 Assessments Inspection Results With attention to locations Cathodic Protection Annual Surveys Galvanic Corrosion Soil Corrosivity

30 Gap Analysis Where are their deficiencies? Missing Data or un-assessed locations > Develop best practice for collecting needed data Corrosion > Determine root cause and mitigation approach Ineffective CP > Justification of CP level > CP Adjustments or additions Excessive CP

31 Site CP Survey Ineffective CP Adequate CP? End Insufficient current to adequately overcome corrosion cells. Balance CP Adequate CP? Yes End No Additional Monitoring Adequate CP? Yes End No CP Design

32 Determining the Effectiveness of CP Practical application makes use of structure-to-electrolyte potentials. Effective cathodic protection is achieved if NACE Criteria are satisfied.

33 Applicable NACE Standards SP0169 Control of External Corrosion on Underground or Submerged Metallic Piping Systems SP0285 Corrosion Control of Underground Storage Tank Systems by Cathodic Protection SP0193 External Cathodic Protection of On-Grade Metallic Storage Tank Bottoms SP0290 Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Structures TM0497 Measurement Techniques Related to Criteria for Cathodic Protection on Underground or Submerged Metallic Piping Systems

34 Criteria for Underground or Submerged Iron or Steel Structures V CSE potential--negative (cathodic) potential of at least 850 mv CSE with the cathodic protection applied after IR drop is considered V CSE polarized potential--negative polarized potential of at least 850 mv CSE 100 mv polarization--minimum of 100 mv of cathodic polarization Note: These are specific to carbon steel and lower temperatures.

35 Potential (-mv) Structure-to-Electrolyte Potential ( ) ON Potential IR 100 mv Polarization OFF Potential ON-IR -850 mv CSE OFF -850 mv CSE 100 mv Depolarization (+) Time Native (Free Corroding, Static) Potential

36 Notes to Criteria In the presence of bacteria or elevated temperatures, the criteria may not be sufficient. In well aerated, well drained soils, corrosion protection may be achieved at less negative potentials.

37 Criteria and Grounding SP Dissimilar Metal Piping: A negative voltage between all pipe surfaces and a stable reference electrode contacting the electrolyte equal to that required for the protection of the most anodic metal should be maintained. Measuring 100mV of polarization based upon mixed potential of a steel/copper couple may not result in adequate protection of the more anodic (steel) material. No true native carbon steel potentials exist?

38 Coupon Test Stations Coupon Test Stations Evaluate -850 mv Polarized Potential Problem Areas > IR voltage drop error > Multiple rectifier interruption > Non-interruptible stray current sources > Directly connected sacrificial anodes > Multiple pipeline potential averaging

39 Typical Installation

40 1. Freely Corroding Coupon 2. Coupon Bonded to Structure/Grounding 3. Energize CP 4-7. Adjustments to CP System 40

41 ER Coupons Corrosion Rate Coupons/Stations Provides both CP related information and Corrosion Rate Data Electrical Resistance (ER) change in resistance of a metal element as it corrodes Where: > R = Resistance > ρ = Resistivity > L = Length > A = Cross sectional area R A L

42 ER Coupons - Continued ER Continued Requires many measurements to provide statistical significance Does not distinguish between general or localized corrosion

43 ER Coupons - Response time vs. probe life

44 LPR (Electrochemical) Coupons Utilizes electrochemical measurements for direct instantaneous measurement of corrosion rate Linear Polarization Resistance

45 LPR theory Stern-Geary Relationship cor c a cor c a app app p i B i i di d R Formula uses absolute values of anodic and cathodic D F n M i mpy CR cor ) ( i cor ma/m 2 D density, g/cm 3 M molecular weight, g/mole F=96,490 coulomb/eq n- number of electrons transferred (valence)

46 Test Methods: Polarization LPR Sources of Error Tafel constants unknown Reasonable estimate V for both a and c Relative comparison (based on R p ) is accurate Oxidation reactions other than corrosion If other oxidizing species are present (sulfides, calculated corrosion current will be overestimated Typically not a concern for soils Non-steady-state conditions (time issues)

47 Test Methods: Polarization LPR measurements LPR measures instantaneous corrosion rate Can be used for continuous corrosion monitoring Can be used for periodic assessment of corrosion state Used extensively in high resistivity conditions, such as soils, concrete, non-aqueous environments Cannot determine corrosion rate of cathodically protected surface

48 Corrosion Rates Utilize Linear Polarization Resistance (LPR) for Soil Corrosivity studies Native (un-polarized coupon) Defensible and Conservative rate

49 Excessive CP Unnecessary Consumption of CP Materials Coating Damage Cathodic Disbondment Overprotection of Amphoteric Materials Lead, Zinc, Aluminum Titanium Hydriding Hydrogen Damage to High Strength Materials Bolts PCCP

50 Site CP Survey Summary Adequate CP? End We have many tools to assist in properly maintaining buried structures Balance CP Utilize all tools in a layered process to leverage cost savings and ensure integrity of buried assets Adequate CP? No Yes End Assess Analyze Additional Monitoring Mitigate Adequate CP? Yes End No CP Design 27