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

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

3. 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

4. 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

5. 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

6. 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)

7. 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

8. 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

9. 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

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

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

12. NACE SP 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)

13. 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

14. 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

15. 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 (

16. 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

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

18. 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.

19. 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

20. 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

21. 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