Galvanic Anodes Period 3 Intermediate Corrosion Course 2017

Transcription

1 Galvanic Anodes Period 3 Intermediate Corrosion Course 2017 February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 1

2 Overview Definitions and Terminology Galvanic Anodes An Overview Magnesium Zinc Testing Sample Calculations Anode Current and Life February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 2

3 Definition of Corrosion Practical Definition The Tendency of a metal to revert to its native state Current discharge Golden Rule of Corrosion, if current discharges off the metallic surface, then there will be metal loss, resulting into corrosion Scientific Definition Electrochemical degradation of metal as a result of a reaction with its environment February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 3

4 Corrosion Process IRON OXIDE BLAST FURNACE BESSEMER PIPE MILL REFINING PROCESS CORROSION PROCESS STEEL PIPE IRON OXIDE PIPE CORRODING Iron Ore is electrically charged through the molding process. Once formed into a pipeline, and placed into the ground, the pipe will lose it s electrical charge and try to resort back to it s natural state. February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 4

5 Electro-Chemical Process of Corrosion The Basic Four Elements to create a galvanic corrosion cell Anode on the galvanic series charts, the metal that is the most negative charged and less noble (The area were corrosion will occur) Cathode on the galvanic series charts, the metal that is the most positive charged and more noble (The area that will be cathodically protected) Electrolyte any substance that can conduct electricity, the surrounding environment of the anode and the cathode Metallic Connection any metallic connection between the anode and the cathode that exist February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 5

6 Electro-Chemical Process of Corrosion Conventional Current Flow Known as the flow of electrical current for design and theory purpose Where current will flow from the + to - direction Electron Flow Contribute to ion movement The movement of the electrons from the - to the + direction Opposite of Conventional Current Flow February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 6

7 Corrosion Cell on a Pipeline Cathode Anode Microscopic Corrosion Cell on the Surface of a Pipeline Remember the golden rule of the point of current discharge, metal loss will occur (Corrosion) February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 7

8 Galvanic Series Chart February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 8

9 The Electrical-Chemical Process of Corrosion Corrosion Golden Rule Any time Current discharge from a metallic surface, then metal loss will occur (Corrosion) Metallic connection Electrolyte Conventional Current Flow (positive) + to (negative) - Cathode Anode Positive Negative V V February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 9

10 The Electrical-Chemical Process of Corrosion The conventional current flow path The current will flow from the Cathode electrode to the Anode electrode through the metallic connection The current will flow from the Anode to the Cathode through the electrolyte Returning back to the Cathode surface Impressing current onto the surface, applying cathodic protection February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 10

11 The Electrical-Chemical Process of Corrosion In a nut shell, Galvanic anodes are typically high in a negative potential, so that there is a significant driving potential, when connected to the cathode (for example pipeline) The driving potential (Open circuit potential) will decide the amount of CP currents to be applied Driving force February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 11

12 The Electrical-Chemical Process of Corrosion In a nut shell, continue The currents will travel from the Cathode to the Anode through the lead wire (metallic Connection) The currents will leave the anode surface, causing corrosion, travelling to the Cathode surface (holiday areas) through the electrolyte A protective film is created onto the surface of the Cathode Also known as Cathodic Protection The anode sacrifices, it s self, to protect the pipelines (Cathode) Better known as Sacrificial Anodes February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 12

13 The Electrical-Chemical Process of Corrosion H2O (water molecule) e- Metallic connection Electron Flow e- e- e- e- e- H+ H+ H+ Electrolyte H2O H+ HO- HO- HO- e- Mg+ Mg+ Mg+ Mg+ Mg+ Electron Flow (negative) - to (positive) + Cathode H2O H2O HO- Anode Positive Negative V V February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 13

14 The Electrical-Chemical Process of Corrosion As the Cathode gains the e- (electrons), it approaches to a more negative state e- Metallic connection Electron Flow e- Electrolyte + e- e- e- e- H+ H+ H+ H+ H2O HO- HO- HO- e- Mg+ Mg+ Mg+ Mg+ Mg+ Cathode H2O H2O HO- Anode - Positive V Negative February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 14

15 The Electrical-Chemical Process of Corrosion e- Metallic connection Electron Flow e- + e- e- e- e- Cathode Positive H+ H+ H+ H+ H2O Electrolyte H2O HO- HO- HO- HO- H2O e- Mg+ Mg+ Mg+ Mg+ Mg+ Anode Negative V - As the Anode loses the e- (electrons), it approaches to a more positive state February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 15

16 The Electrical-Chemical Process of Corrosion e- e- e- e- e- Cathode Metallic connection Electron Flow H+ H+ H+ H+ H2O Electrolyte H2O HO- HO- HO- HO- H2O e- e- Mg+ Mg+ Mg+ Mg+ Mg+ Anode Polarization Process The Cathode becomes more Negative The Anode becomes more positive Positive V = Negative V February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 16

17 Polarization Process e- Electron Flow e- e- e- e- e- Cathode Positive H+ H+ H+ H+ H2O Electrolyte H2O HO- HO- HO- HO- H2O V = e- Mg+ Mg+ Mg+ Mg+ Mg+ Anode Negative V Now, what is the potential difference? February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 17

18 The Electrical-Chemical Process of Corrosion The water molecule will separate in the electrolyte allowing a surplus of Positive charge Hydrogen ions and Negative charge Hydroxyl ions The positive charged Hydrogen ions will meet the negative charged electrons on the surface of the Cathode electrode creating a Hydrogen film, also known as polarization The Negative charge Hydroxyl ions will meet the positive charge metal ions at the surface of the Anode electrode creating oxidation (rust); also known as Corrosion February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 18

19 Preventing Corrosion Remove the metallic connection Insulators Remove the electrolyte Coatings Remove the Anode and Cathode Cathodic and Anodic polarization Galvanic Anodes Impressed Systems February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 19

20 Corrosion Effects on Carbon Steel Pipelines February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 20

21 Defense against Corrosion Coatings are the number One defense against corrosion But do not provide a 100% protection Due to coating flaws known as Holidays, we need a secondary supplemental application of Cathodic Protection; such as Galvanic or Impressed anode systems February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 21

22 Galvanic Anodes - Types Magnesium Fresh Water Soil Zinc Low Resistance Soil < 1500 Ω CM Brackish water Aluminum Salt Water Saline Muds February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 22

23 Candidates for Galvanic Anodes Low Cathodic Protection Currents requirements Typically < 1 amp Isolated fittings Small cross areas No Access to any AC power sources Limited UV Exposures Low Soil Resistivity Typically < 10,000 Ω CM Distribution in high resistance soils Distributed application to lower driving potentials Anodes can be placed relatively close to the pipeline structure, along a considerable length of the pipeline circuit In areas where interference with other structures may occur High traffic areas with other foreign or self structures in the vicinity February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 23

24 Galvanic Anodes - Types The two most common for buried pipelines are Magnesium and Zinc galvanic anodes February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 24

25 Magnesium Anodes February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 25

26 Magnesium Anodes - Shapes Cast Ingots Copper lead wires Used mainly in soil applications Steel straps (Marine) Extruded Ribbon Caps February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 26

27 Varity Type of Magnesium Anodes February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 27

28 Magnesium Anodes - Composite HP Magnesium Anodes most popular use in the field application for carbon steel pipelines in the North America due to it s high driving potentials HP Magnesium Anodes 97% magnesium purity 3% - Aluminum and Zinc February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 28

29 Magnesium Anodes - Composite Normally packed in a low resistivity back fill Provides low resistance around the anode so corrosion will occur uniformly to extend the anode life Attracts moisture from the soil Provides a homogeneous environment Prevents passivation of the anode Major two types of back fill 75% Gypsum a hydrous form of Calcium sulfate 20% Bentonite (attracts moisture) 5% Sodium Sulfate February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 29

30 Magnesium Anodes - Composite Normally 10 of #12 AWG coated copper solid wire connected to the magnesium bar February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 30

31 Magnesium Anodes Applications Drive-in anodes or known as spike anodes Excellent for isolated risers February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 31

32 Magnesium Anodes Applications Anodes installed in water heaters Magnesium slab Anodes on bulk head of boat February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 32

33 Zinc Anodes Normally used in Low soil resistance Excellent ground source Lower driving potential than Magnesium Higher efficiency 90% February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 33

34 Zinc Anode - Composite 99.9% purity of Zinc Open Circuit potential -1.1 Volts CSE Passive state with soils of high concentrates of Oxygen Ions Carbonates Phosphates February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 34

35 Zinc Anodes - Composite Normally packed in a low resistivity back fill Provides low resistance around the anode so corrosion will occur uniformly to extend the anode life Attracts moisture from the soil Provides a homogeneous environment Prevents passivation of the anode Sulfate ion s in the Gypsum back fill Major two types of back fill 50% Gypsum a hydrous form of Calcium sulfate 50% Bentonite (attracts moisture) February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 35

36 Zinc Anodes - Composite Typically Type I is used for sea water applications February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 36

37 Zinc Anodes - Shapes Cast Bars Normally used with back fill material for soil applications Bracelets Normally used in underwater applications Slabs Buttons Normally used for exposed carbon steel bolts Extruded Ribbon Normally used in AC mitigation Pencils and Rods Normally used in isolated fittings February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 37

38 Zinc Anodes Applications Type 1 Cast Zinc Anodes used on sea water ships Maritime ship hulls February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 38

39 Zinc Anodes Applications Type II - Extruded Zinc Ribbon anode Mainly used for AC interference mitigation February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 39

40 Anode Testing Due to high amount of bad anodes received over seas, testing has become more important than ever Testing recommendation practice Third Party ASTM G97 (Laboratory Evaluation of Magnesium Test Specimen for Underground Applications) Test pencils taken from a random selected batch Tested for a period of 14 days During the test and at the conclusion of the test Open circuit potentials measured Weight loss measured Material Composite of the anode and the back fill material Two Key Factors Open Circuit Potentials Anode Efficiency February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 40

41 Anode Testing Magnesium Open Circuit Potentials Norm -1.7 in reference of a Calomel electrode or in reference of a copper-copper sulfate electrode Anode Efficiency Norm 50% 500 amps per Hour (amp/hr) February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 41

42 Anode Testing Meaning of Results Open Circuit Potentials Decides the output of the anode Less Open Circuit Potentials ( CSE), Less protective currents Anode Efficiency Decides the life expectancy Less Eff. % (50%) February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 42

43 Cost of Testing Normally Expensive In the range of $ to $1, Depending on the amount data requested In Comparison to possible failures of Anodes in the field, very in-expensive Some anodes found with a life expectancy of 5 years or less (based field trials and laboratory testing) Rework frequency cost can exceed in the millions. February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 43

44 Anode Life Expectancy Formula Zinc and Magnesium Magnesium Anode Formula - Anode Life = x anode weight (lbs) x eff. x Utilization Factor Design Current (amperes) Zinc Anode Formula - Anode Life = x anode weight (lbs) x eff. x Utilization Factor Design Current (amperes) February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 44

45 Anode Life Expectancy Anode Life = x anode weight (lbs) x eff. x Utilization Factor Design Current (amperes) Theoretical ampere-hour per pound of the anode material Given by manufacture. February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 45

46 Anode Life Expectancy Anode Life = x anode weight (lbs) x eff. x Utilization Factor Design Current (amperes) Anode weight Expressed in pounds of the magnesium bar not the entire package, for example, 17lb anode is the weight of the mag. bar, therefore, 17 would be the correct number to enter. February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 46

47 Anode Life Expectancy Anode Life = x anode weight (lbs) x eff. x Utilization Factor Design Current (amperes) Efficiency percentage - Expressed in a decimal number, for an example, 50% would be expressed as.50 February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 47

48 Anode Life Expectancy Anode Life = x anode weight (lbs) x eff. x Utilization Factor Design Current (amperes) Utilization Factor It represents the percentage of the anode being used before failure, for an example, magnesium anodes is 85% utilization, so it will be represented in the formula as.85 February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 48

49 Anode Life Expectancy Anode Life = x anode weight (lbs) x eff. x Utilization Factor Design Current (amperes) Design Current (amperes) Express as the anode output with the surrounding environment, placed in the formula as a decimal format, for an example, 100 milliamps would be written as.100 amps February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 49

50 Anode Life Expectancy Sample calculation Magnesium anode with an output of 100 milliamps 8.3 yrs Anode Life = x 17(lbs) x.50 x amps What if, efficiencies drop below 50%? 5.0 yrs Anode Life = x 17(lbs) x.30 x amps Life expectancy of anode has dropped The efficiency is now at 30% February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 50

51 Anode Life Expectancy Sample calculation 8.3 yrs Anode Life = x 17(lbs) x.50 x amps What if, we could apply a small resistor into the circuit of the anode, and reduce the anode output? 16.8 yrs Anode Life = x 17(lbs) x.50 x amps Life expectancy of anode has increased (doubled) The current output is reduced to half as much by adding resistance February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 51

52 Installation of Anodes Never Pick up the anode by the wire connections Place the anode above the pipeline Place the anode flat horizontally, Position with the wire end higher then the rest of the anode body Pour water directly on pre-packaged anodes before back filling, could cause voids around anode, loss of anode output Drop anode into excavation site Place anode over voids, could cause fracture onto the magnesium bar, loss of efficiency February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 52

53 Installation of Anodes Do s Place the anode perpendicular from the pipeline Minimum distance of 2 to 3 feet If possible, stretch to the complete length of the wire with out applying tension to the point of connection Place as deep as the bottom of the pipeline Recommend to place the anode at least one foot below the pipeline, if possible February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 53

54 Installation of Anodes Do s Tamp the dirt firmly around the anode If desire to kick start anode Apply water, only after several feet of back fill has been achieved and tamped If water applied to anode directly could result in voids and drop in anode effiecicy February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 54

55 Installation of Anodes Can s Attach anode to a gathering wire to save pavement cost Also known as Banking anodes Banking Anodes Use Sundae theory to calculate anode output due to spacing's Anode currents may fight against each other and this will cause a loss of the anode current output, resulting in the CP design falling short Recommend of using a minimum of # 8 AWG copper for the gathering wire Reduce circuit resistance Follow the normal installation February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 55

56 Anode Installation - Types Single Installation or Direct connection Banking Anodes (use of a gathering wire) February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 56

57 Anode Installation Sunde Theory # of Anodes in Concentrated Bed Single Anode Current Reduction Factors (C) Anode spacing 5 Feet 10 Feet 15 Feet 20 Feet Sunde Theory Chart Design calculation used to compensate the current reduction based on spacing of the anodes February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 57

58 Anode Installation Sunde Theory # of Anodes in Concentrated Bed Single Anode Current Reduction Factors (C) Anode spacing 5 Feet 10 Feet 15 Feet 20 Feet Based on soil resistivity 5000 Ω CM Sunde Theory Chart Sample Calculation - CP Design circuit needs 125 milliamps What is the amount of anodes needed for the circuit at a spacing of 10 feet? February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 58

59 Anode Installation Anode Output Calculation Soil Resistivity Magnesium Calculation 120,000 f y ρ = I m Sample Calculation 120, ,000 ohms cm = ma 120,000 is based on DA Tefankjian of magnesium anodes for good coating. February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 59

60 Anode Installation Sunde Theory # of Anodes in Concentrated Bed Single Anode Current Reduction Factors (C) Anode spacing 5 Feet 10 Feet 15 Feet 20 Feet Based on soil resistivity 5000 Ω CM **Anode output 29 milliamps** Sunde Theory Chart Sample Calculation - CP Design circuit needs 125 milliamps What is the amount of anodes needed for the circuit at a spacing of 10 feet? February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 60

61 Anode Installation Design Sunde Theory Number of anodes = It Ia Total number of anodes needed = 125 milliamps divided by 29 milliamps 4.3 anodes, round off to the number, 4 anodes Sunde theory reduction factor x 29 milliamps = 100 milliamps Based on Sunde theory, design will fall short of 25 milliamps Another anode needs to be added to achieve the 125 milliamp design February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 61

62 Anodes - Effective in Interference Remediation (AC and DC) Interference problems, galvanic anodes can be used for mitigating the current safely from the pipelines to prevent corrosion Zinc anodes are excellent ground source for helping mitigating AC currents Zinc Ribbon Zinc Grounding Cells Zinc Voltage Gradient mats Magnesium anodes are some times used for mitigating DC interference currents, in place of a interference bond February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 62

63 In Conclusion If soil resistivity is < 1500 Ω CM, maybe best to use Zinc Anodes Test Anodes Open Circuit Potentials Efficiency Designing Life Expectancy Calculation February 21-23, 2017 Eric Langelund Piping & Corrosion Specialties, Inc. 63

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