IDENTIFYING CORROSION MECHANISMS BASED ON CORROSION COUPON ANALYSIS Ballot Idea ID: 2835 Proposed by Xihua Shewa He Southwest Research Institute

Introduction: Pipeline Internal Corrosion Mechanisms CO2 corrosion H2S corrosion O2 corrosion Sulphur corrosion Organic acid corrosion Methanol corrosion Solids related corrosion

CO2 corrosion Corrosion reaction Fe + H2O + CO2  FeCO3 + H2 Iron carbonate formation susceptible to flow damage General and pitting corrosion are both forms of corrosion damage Pitting Mesa attack Flow-assisted damage

H2S corrosion Corrosion reaction: Fe + H2S FeS + H2 Forms of corrosion include pitting, underdeposit corrosion, environmentally assisted cracking (SSC, HIC, SOHIC) Iron sulfide (FexSy) formation Cubic FeS Pyrite FeS2 Fe3S4 Sulfide scales: black, electrically semi-conductive, cathodic to iron, less susceptible to velocity effects

Mixed CO2 and H2S corrosion Depends on partial pressure ratio of CO2 and H2S pp CO2:H2S 2000:1: CO2 dominated <20:1: H2S dominated

4Fe + 6H2O + 3O2  4Fe(OH)3  2Fe2O3 + 6H2O O2 corrosion Causes corrosion in even minor concentrations (10-50 ppb) Enhances corrosion reactions Renders previously protective scales non-protective Causes precipitation of oxides, hydroxides, and free sulfur Allows growth of aerobic microorganisms O2 sources Open tanks, trucked-in fluids, sources water (river, lake, sea, shallow wells), ingression of pump seals, etc. Overall reaction 4Fe + 6H2O + 3O2  4Fe(OH)3  2Fe2O3 + 6H2O Appears in forms of pitting and crevice corrosion Oxygen scales FeO(OH) (goethite) Fe2O3 (hematite) Fe3O4 (magnetite) FeO(OH) (ferrous hydroxide)

Microbiologically Influenced Corrosion Common bacteria Sulfate reducing bacteria Iron-oxidizing bacteria Acid producing bacteria Sulfur-oxidizing bacteria Manganese oxidizing bacteria Slime-forming bacteria Metabolic products Sulfides, CO2, alcohols, ammonia Organic acids Corrosive deposits Polymeric material Usually appears in form of pitting corrosion

Sulfur Corrosion Precipitation of sulfur Release from gas/liquid phase Change in pressure, temperature, gas composition Reaction product Deposition of sulfur Deposition of sulfur to components induced by surface forces, changes in gas velocity, flow path restrictions, filters, liquids in pipes and vessels Sulfur in contact with metal surface is corrosive Fe + S  FeS

Organic Acid Corrosion Acetic acid Propionic acid Butyric acid Formic acid Weakens existing iron carbonate layer by producing more soluble iron acetate layer or others FeCO3 + 2HAc  Fe(Ac)2 + H2CO3 Depolarizes cathodic reaction resulting in corrosion reaction acceleration

Methanol corrosion Affects FeS structure Increase risk of SSC and SOHIC Increase Top of Line corrosion Increase O2 solubility Reduce corrosion inhibitor effectiveness

Solids corrosion Sand, formation fines, scales, corrosion products Bound in organic materials

NACE SP0775-2013 Standard Practice: Preparation, Installation, Analysis, and Interpretation of Corrosion Coupons in Oilfield Operations Corrosion coupons are used in oilfield drilling, production, and transportation operations Evaluate corrosiveness of various systems Monitor effectiveness of corrosion-mitigation programs Evaluate suitability of different metals for specific systems and environments Outlines procedures for preparing, installing, and analyzing metallic corrosion coupons Provides average corrosion rate and maximum pitting corrosion rate No correlation with corrosion mechanisms is provided (identified research need)

2019 Research Idea ID 2835 Project Title: Identifying Corrosion Mechanisms based on Corrosion Coupon Analysis Project objectives Build a digital inventory of corrosion monitoring coupons and pipe samples where possible corrosion mechanisms have been identified by physical and chemical analysis methods Develop a tool to identify corrosion mechanisms based on monitoring coupon analysis and comparison to information in a database Identify gaps in standard practices and guidelines that operators use related to internal corrosion coupon and corrosion mechanisms

Four Tasks Task 1: Compile Corrosion Coupon and Pipeline Sample Analysis Data With Known Corrosion Mechanisms Task 2—Apply Machine Learning Techniques to Classify and Associate Information With Possible Corrosion Mechanisms Task 3—Test the Feasibility of a Selected Machine-Learning Algorithm Function to Identify Corrosion Mechanisms Task 4—Provide Recommendations on Standard Practices

Task 1: Compile Corrosion Coupon and Pipeline Sample Analysis Data With Known Corrosion Mechanisms Data sources Internal corrosion monitoring coupons or pipe samples from various PRCI member organizations Pipeline sample inventory at PRCI Technology Development Center in Houston Coupon and pipeline sample data reported in the literature [e.g., NACE International (1982) presents detailed case histories and illustrations of specific forms of corrosion, including 188 figures, other NACE publications, conference papers] National Transportation Safety Board Pipeline Accident Reports (https://www.ntsb.gov/investigations/AccidentReports/Pages/pipeline.aspx)

Task 1: Compile Corrosion Coupon and Pipeline Sample Analysis Data With Known Corrosion Mechanisms Data include: Pipeline operating conditions Coupon or pipeline sample locations Practices used to preserve coupons from field to laboratory, analyze coupons in the laboratory, and identify corrosion mechanisms Chemical composition, surface morphology, crystal structure, and biofilm characteristics Photographs or micrographs of coupons capturing corrosion morphologies Identified corrosion mechanisms

Task 2: Apply Machine Learning Techniques to Classify and Associate Information With Possible Corrosion Mechanisms

Task 3: Test the Feasibility of a Selected Machine-Learning Algorithm Function to Identify Corrosion Mechanisms Test using data collected from Task 1 but withheld from the design of the MLA function during Task 2 confirmation of the existence of information patterns that can be used to reliably identify some or all corrosion mechanisms observed in pipelines Establish a computable database structure to compile the information so that additional information may be gathered in a manner that can be accessed and used by the MLA.

Task 4: Provide Recommendations on Standard Practices A list of recommendations regarding suggested standard practices and guidelines will be developed A final project report will be produced, including documentation of the accuracy of the MLA functions

2019 Research Idea ID 2835 Sponsor/Technical Lead Mark Linville at Dominion Energy Transmission, Inc. Proposed Contractor Southwest Research Institute Continuing or Follow-on work? This is a new project; follow-on projects include: Verification of corrosion mechanism vs. coupon analysis correlation Development of NACE standard practice Prior Work Status There is no prior PRCI work on this topic

2019 Research Idea ID 2835 Roadmap Link (Specific Gap Addressed) Corrosion: IC-7 (Pipeline Operational Practices to Prevent and Minimize Internal Corrosion) RO Link: Objective 7Reduce all product leaks and equipment emissions from all parts of the hydrocarbon transport and storage infrastructure by developing, demonstrating and validating processes and technologies to detect, quantify and mitigate such releases. Benefit for the Industry Identify corrosion mechanism based on coupon analysis Find root cause of corrosion Mitigate and prevent corrosion Stop pipeline leak