Corrosion Overview: Internal Corrosion, External Corrosion .

Corrosion Overview: Internal Corrosion,External Corrosion and Cathodic Protection2016 AGA/SPE Underground Storage Operators WorkshopApril 5, 2016Presented by:Lindsey Rennecker & Deborah Sus1

Industry Trends55 reportedincidents foronshore gasgathering since1996Corrosionresponsible forapproximately halfof reported incidentfor gatheringsystemsSource: US DOT Pipeline and Hazardous Materials Safety Administration2

Industry TrendsIn light of recent incidents and in keeping with overall move toward anintegrated Process Safety culture, several new recommendations may affectgas storage operations PHMSA NPRM: Safety of Gas Transmission andGathering Pipelines PHMSA Advisory Bulletin ADB-2016-02 Safe Operation of UndergroundStorage Facilities for Natural Gas API 1170 “Design and Operation of Solution-minedSalt Caverns Used for Natural Gas Storage” API 1171 “Functional Integrity of Natural GasStorage in Depleted Hydrocarbon Reservoirs andAquifer Reservoirs” State regulations3

Corrosion MechanismAnode Where current leaves the metal surface into theelectrolyteCathode Where current enters the metal surfaceElectrolyte Solution capable of conducting electricity Water or soilMetallic Path4

Internal CorrosionInternal corrosion is most significant failure mode for gatheringsystems transporting corrosive fluidsSource: US DOT Pipeline and Hazardous Materials Safety Administration5

Internal CorrosionUniform Corrosion Distributed more or less uniformly over surface Can occur in isolated areas where water tends toaccumulateLocalized Corrosion Small, discrete sites of metal loss – pits or cavities May or may not be associated with corrosion productLocalized Corrosion - Under-DepositCorrosion Deep penetration with lesser general corrosion insurround areas Under or around deposits or collection of material6

Internal CorrosionGalvanic Corrosion Electrical coupling of two dissimilar metalsVelocity/Flow-Related Corrosion Erosion Corrosion, cavitation, impingement In storage, periods of heavy abrasion from particulatescoming up from wellEnvironmentally Assisted Corrosion (EAC) Cracking of a metal through electrochemical processesenhanced by particular pipeline environments Hydrogen-Induced Corrosion (HIC) Hydrogen Embrittlement (HE) Stress Corrosion Cracking (SCC) Often difficult to detect during the pre-failure phase7

Internal CorrosionMicrobiological Induced Corrosion (MIC) Biological processes of microorganisms can altermetal surface by physical & chemical means Typically two modes of existence: Planktonic (free floating) Sessile (attached to pipe wall) Prominent bacteria important in corrosion include: Sulfate-Reducing Bacteria (SRB) Acid-Producing Bacteria (APB) Other microorganisms Sulfate-reducing Archaea (SRA) or Sulfate-reducing prokaryotes (SRP) Standard bacteria culture testing may not correlateto MIC caused by other microorganims8

Internal Corrosion MonitoringAsset SurveyI/W WellsWater RemovalEquipmentRisk Assessmentand Risk RankingGathering SamplingSolidAnalysisBoreScope9

Internal Corrosion MonitoringMonitoring Locations Vessels Piping, Stub Ends andWellhead Sweeps Drips I/W Wells Receivers (pigging)10

Internal Corrosion MonitoringComplementary testing Coupons/Probes Bacteria Analysis Liquid/Solids Sampling Gas Sampling Non-destructive Testing Field SeparatorsWellhead SeparatorsDripsBottlesPipingCorrosion ssistedFlow AssistedH2 ProbeXXAcoustic Inspection and Analysis Visual Inspection (cut-out) In-Line Inspection11

Internal Corrosion MonitoringCorrosion coupons are small,weighed and measured specimen ofmetal that are inserted into a system andexposed to that environment for aspecified period of time.ER probes determine metal loss overtime by measuring the increase in theelectronic resistance of an electrode asits cross-sectional area is reduced bycorrosion.LPR probes instantaneously measure acorrosion rate by measuring the degree ofresistance to a small applied potential.12

Internal Corrosion MonitoringGalvanic probes are used in waterinjection systems to measure the galvaniccurrent in the circuit between a steel and abrass electrode, which can be sensitive to theamount of oxygen in the water.Hydrogen Probes monitor hydrogenpermeation in steels, which can lead toembrittlement, blistering, and decarburizationresulting in the failure of the material.Electrochemical Noise (ECN) are similarto LPR, can be flush or “finger-like”, anddistinguish between general vs. localized.Acoustic Solids Monitoring monitors forsolids, but does not directly monitor damageto pipe from erosion13

Internal Corrosion MonitoringMicrobiological Testing Serial Dilution Method Bio-ProbesAPBSRBANAEROBESAEROBES Used to suspend sampleelements in the area to bemonitored for bacteria. Other techniques Isotope Analysis Adenosine Triphosphate(ATP) Photometry Hydrogenase Measurements Adenosine Phosphosulfate(APS) Reductase – specific toSRB Quantitative polymerasechain reaction (qPCR)14

Internal Corrosion MonitoringWater / Fluid Analysis Liquid collection sites On-site / laboratory testing (pH, iron,manganese, chlorides)Solids / Debris: Cleaning pig runs, Cut-outs, Coupons On-site and Laboratory Analysis (Elemental,EDS, XRD, XRF)Gas/Liquid Hydrocarbon Carbon Dioxide, Hydrogen Sulfide, Oxygen,Sulfur Compounds, Water contentChemical makeup provides significantinformation relative to corrosivity15

Internal Corrosion MonitoringNon-Destructive Evaluation Manual Ultrasonic Testing Different scanning techniques (Ascan/ B-scan) Grids Automated Ultrasonic Testing Multi-Channel imaging X-RayEstablish monitoring interval specific to site location. A Rating (High corrosion rate 5.0 MPY or nearing wall thickness tolerance) B Rating (Moderate corrosion rate 1 - 5.0 MPY) C Rating (Low corrosion rate 1.0 MPY)16

AssessmentIn-Line Inspection (ILI) Design requirements / limitations ILI Applications (Tethered, Launcher /Receiver) Requires using cleaning tool prior to useof smart tool. Scraper discs/cups, brush-type, bladecleaning elements. ILI Smart Tools Magnetic Flux (MFL), transverse,crack detection, combo Tool Results Accuracy Predicted Failure Pressures ValidationPhoto obtained from http://www.tremcopipeline.com.au/GIRARD Pipeline Pigs.html17

AssessmentOpportunity inspectionsILI validations Expected results based on othermonitoring data Validation digsVisual Inspection Scale/Liquids Corrosion/Pitting18

AssessmentSurface Evaluation Surface cleaning / prep Initial observations may not beaccurate in terms of wall loss Gas-liquid/scale interface Under-deposit corrosion MIC Pitting appear small but be very largebelow the surface19

Monitor / Repair / ReplaceMonitor Reassessment intervals / Continual Monitoring Corrosive environments, non-linear growth rates MitigationFitness-for-Service (FFS)Repair / Replace Short-term solution vs. Long-term planning Replacement tends to be “when” not “if” Holistic approaches, prioritize lines/wells May repair more severe indications while scheduling future fieldmodifications Consequence of failure Ability to shut in affected lines, reroute gas flow Cyclic operations Projected growth rates and time to failure20

External CorrosionExternal corrosion is another root cause that affects gatheringsystemsSource: US DOT Pipeline and Hazardous Materials Safety Administration21

External CorrosionPipeline Coatings The first and foremost defense in corrosion control Fusion-bonded epoxy, extruded polyolefinsystems, multi-layer epoxy, mill applied tape, coaltarCathodic Protection (CP) CP supplements coating for 100% protection Reduce the corrosion rate by making it thecathode of an electrochemical cellNACE SP0169 The addition of current to a more electronegativestate Per 49 CRF 192 Subpart I, cathodic protectionsystem must be placed in operation within 1 yearof pipeline operation Negative (Cathodic)potential of at least 850 mVNegative polarizedpotential of 850 mVA polarization of aminimum of 100 mV22

CP Design TypesGalvanic Anode Current provided by dissimilar sacrificial metal The anode is active (negative) with the respect to the other and corrodes Current is discharged from active metal and flows to the protected asset Anode backfill provides low resistivity environment and prevents passivation23

CP Design TypesImpressed Current Current provided from external power source Rectifier used in conjunction with anodic ground-bed to disperse current Current dispersed through ground-bed follows return path through pipeback to rectifier24

CP Design TypesImpressed Current Rectifier Negative cable connection to pipe Converts AC power to DC power Ground-bed Positive cable connection torectifier Consists of a bed of anodes to aidin current dispersal Backfill surrounds anodes toprovide uniform current distribution25

CP Design TypesGalvanic AnodeImpressed CurrentSmall current requirementHigher current requirementLower soil resistivity'sHigher soil resistivityLocalized protectionLarge protection fieldPower source not requiredExternal power sourceLower costHigher costMinimized stray currentinterferenceIncreased stray currentinterferenceEvenly distributed along asset withhigh frequencyMinimized pipeline connections26

CP Design TypesGround-bed Configurations Deep Well Distributed Linear Conventional Shallow Horizontal anode placement Vertical anode placement27

CP Design TypesPreferred CP Design in StorageFields Impressed current design Soil resistivity measurements atdepth important Remote deep well ground-bed Critical for protection current toreach pipe at excessive depth Designed to protect piping, well,casings and all associatedappurtenances Isolated wells may require separate CPsystem28

CP Design ProcessDesign Factors Environment corrosivity Soil structure and resistivity Bare or coated asset Coating quality and electric strength Metal or alloy of asset Asset size (diameter, length, wall thickness, etc.) Presence of other metallic structures and stray current Historic CP measurements or existing systems29

CP Design ProcessSoil ResistivityMetallic Surface Area Coating efficiency Calculate bare metallic surface areaCurrent RequirementAnode Data Anode PotentialCircuit Resistance Anode Efficiency Linear Pipeline Resistance Design Life Wire Resistance Anode Utilization Factor Current Attenuation Anode/Ground-bed Resistance Remote Earth30

CP Design ProcessAdjust variables to improve designCalculations Determine Ground-bed Type Current Attenuation Conventional Horizontal or Vertical Deep Well Determine Anode Characteristics Ground-bed Resistance Anode type and size Number of Anodes Length and size of anode bed Rectifier sizing Other Resistances Remote DistanceCircuit Characteristics V, I & R31

CP MonitoringElectrical Isolation Isolated flanges, di-electric unions,weld-end-insulatorsTest Stations Two-wire Foreign crossings and bonding AC/DC Coupons IR drop CasingsReference CellsRemote Monitoring32

CP Monitoring & MaintenancePeriodic Surveys Potential Measurements Monthly, Bi-monthly, Annual Readings Close-Interval Surveys (CIS) Line Current Survey Pipeline Current Mapper (PCM) Coating Surveys Alternating Current Voltage Gradient (ACVG) Direct Current Voltage Gradient (DCVG) Rectifier and Ground-bed voltage and current outputEquipment Maintenance CP System Components Coatings Test PointsDirect Examinations33

Questions34

1 Corrosion Overview: Internal Corrosion, External Corrosion and Cathodic Protection 2016 AGA/SPE Underground Storage Operators Workshop April 5, 2016