CRA Tubulars and Well Integrity page Introduction to CRA Tubulars: Metallurgy and Material Selection for Corrosive Environments September 25th, 2017 CRA Tubulars and Well Integrity Technical Symposium September 25, 2017
CRA Tubulars and Well Integrity page2 Agenda Corrosion Resistant Alloys Normative definition Basic metallurgy Corrosion mechanisms Material selection for CRA completions Connector selection for CRA completions
CRA Tubulars and Well Integrity page3 What is a Corrosion Resistant Alloy (CRA) CRA is an alloy intended to be resistant to general and localized corrosion and/or environmental cracking in environments that are corrosive to carbon and low-alloy steels. (ISO 13680) CRAs are used to control corrosion for the life time of the well. are chosen because other methods such as chemical inhibition are inadequate or not practical. 3
CRA Tubulars and Well Integrity page4 Normative Requirements for CRA Tubulars API 5CRA / ISO 13680 specifications Covering S13Cr up to Ni-base Alloys 4 groups defined by their composition and mechanical properties 2 Product Specification Levels (PSL) : PSL 1 is basis of API 5CRA PSL 2 : restricted chemical composition & mechanical properties Nota: Some alloys not available in PSL 2 NACE MR0175 / ISO 15156 : Guideline for selection and qualification of metallic materials used in Oil & Gas Part 3 of this specifications focuses on CRA : Environmental limits for any equipment Chemical composition per material type Comment: in OCTG, CRA usually means pipe with minimum 22% Cr content
CRA Tubulars and Well Integrity page5 Martensitic Stainless Steels 13 % Chrome alloys: L-80-13Cr covered in API5CT Reasonable resistance to CO 2 corrosion Considered by some operators for very mild sour service Most inexpensive solution to CO 2 corrosion. Super 13% Chrome alloys (13-5-2) UNS S41426 for PSL2 Covered by API5CRA 110ksi grade not covered by NACE MR0175 Improved pitting resistance (CO2 corrosion) 15% & 17% Cr alloys are being introduced with 125 ksiyield Strength for HPHT wells Improved SCC and Corrosion resistance at higher temperatures Not covered by any API Standard Strength for those alloys is achieved through heat treatment as with carbon steel (quench & temper)
CRA Tubulars and Well Integrity page6 Duplex Stainless Steel 22 % Cr & 25 % Cr alloys containing Nickel with duplex microstructure of ferrite and austenite Covered by API5CRA (PSL1 quality level for general service & PSL 2 for sour service) Improved CO 2 corrosion resistance and chloride pitting resistance in mild sour service. Offer Generally limited to 0.3 psi to 3.0 psi H2S depending upon alloy composition. Super duplex SS with 25 % Cr (PREN>40) often used in water injection wells with oxygen excursions Examples include: 22 % Cr (22-5-3) UNS S31803 25% Cr (25-7-4) UNS S32750 25 % Cr super duplex UNS S32760 & S39274 Strength for those alloys is obtained through cold-work process
CRA Tubulars and Well Integrity page7 Nickel Alloys Best available alloys for completing wells with tubing and in severe environments. Covered by API5CRA PSL1 quality level for general service & PSL 2 for sour service Increased resistance to pitting corrosion and environmental cracking Examples Alloys 28 Cr & 825 Alloy G3 higher limits for H 2 S and temp. Alloy C 276 best under all conditions Can be used in high partial pressures of H2S and sometimes elemental sulfur Strength for those alloys is achieved through cold-work process
CRA Tubulars and Well Integrity page8 General Product Offer(covered by API5CRA) Structure (as per API 5CRA) Martensitic (Group 1) Duplex steels (Group 2) Super-Duplex steels (Group 2) Austenitic steels (Fe base) (Group 3) Austenitic steels (Ni base) (Group 4) Composition (mass%) Names Category Available Grades (ksi) Cr Ni Mo Super 13Cr 13-5-2 13 5 2 80, 95, 110-13-1-0 13 0,5 80, 95, 110 22CR 22-5-3 22 5 3 65, 110, 125, 140 25CR 25-7-3 25 7 3 75, 110, 125, 140 S25CR 25-7-4 25 7 4 80, 90, 110, 125, 140 Alloy 28 27-31-4 27 31 4 110, 125, 140-25-32-3 25 32 3 110, 125, 140-22-35-4 22 35 4 110, 125, 140 Alloy 825 21-42-3 21 42 3 110, 125 G3 22-50-7 22 50 7 110, 125, 140-25-50-6 25 50 6 110, 125, 140-20-54-9 20 54 9 110, 125, 140 C276 15-60-16 15 60 16 110, 125, 140
CRA Tubulars and Well Integrity page9 Super13Cr (Martensitic Stainless Steel) Production Process 1. Hot billets are pierced into hollows 2. Hollows are further processed by hot rolling to achieve OD and Wall Thickness 3. Strength is achieved through Quench and Temper process
CRA Tubulars and Well Integrity page10 CRA ( 22Cr content) Production Process 1. Before cold working process, the billets are transformed into hollows using hot extrusion 2. Hollows are further processed by cold rolling/drawing to achieve OD and Wall Thickness 3. Strength is achieved through plastic deformation Cold Drawing Process Pilger Process
CRA Tubulars and Well Integrity page11 Corrosion There are two basic requirements for carbon steel to corrode: First, liquid water must existas a free and separate phase. Water in oil as an emulsion will not cause corrosion. Second, liquid water must wet the surface of the carbon steel equipment or tubing. The corrosivity of water will vary through a surface facility. Both CO 2 and H 2 S can corrode steel. Measure ph and chlorides. Watch out for oxygen >10-20 ppb. Track condensed vs. production water Oil wells will be corrosive when water cut increases Gas wells tend to be corrosive from the beginning
CRA Tubulars and Well Integrity page12 Environment Impacting Downhole Corrosion Components that define the severity of the environment Partial Pressure H2S Partial Pressure CO2 Chloride content Produced water rate Produced condensate/oil rate Bicarbonate content HCO3 Bottom hole temperature ph Flow velocity Free sulfur can occur as low as 4-5% H2S Acid stimulation fluids: carefully evaluate inhibitors Completion fluids: Certain fluids can be very aggressive. Scale: some scales can be beneficial
CRA Tubulars and Well Integrity page13 Main Corrosion (and Cracking) Mechanisms in OCTG CO 2 corrosion Pitting Corrosion Stress Corrosion Cracking Sulfide Stress Cracking 13
CRA Tubulars and Well Integrity page14 CO 2 Corrosion -Mechanisms Chemical reaction either localized or generalized Without water no CO2 corrosion Temperature an CO2 partial pressure have major influence Carbonic acid is formed CO2 and water (CO2 + H2O = H2CO3) Carbonic acid is reacting with Iron (2Fe + H2CO3 = Fe2CO3 + H2) A complex process with high variation of corrosion rate
CRA Tubulars and Well Integrity page15 Pitting Corrosion - Mechanism Localized attack of metal Typically due to breakdown of passive layer Most destructive and initiated by metallurgical and/or environmental factors Reinforced in presence of chlorides Difficult to predict by lab tests Difficult to stop The higher the content in chromium, nickel and molybdenum, the lower the susceptibility Self maintaining phenomenon (self-accelerating)
CRA Tubulars and Well Integrity page16 Chrome Steels to Avoid CO2 Corrosion Increasing Corrosion with ppco 2 ppco2 2 psi will induce metal loss corrosion for Carbon Steels Alloying with Cr alone, will not prevent corrosion Increasing Cr-content 13%Cr 16
CRA Tubulars and Well Integrity page17 Environmental Cracking SSC and SCC Stress Corrosion Cracking SCC Susceptible Material Environment Tensile Stress Susceptibility to cracking Sulfide Stress Cracking SSC Failure occurs below the minimum yield strength Temperature
CRA Tubulars and Well Integrity page18 Overview of Stress Corrosion Cracking - SCC Combination of corrosive environment and a mechanical stress localized corrosion and tensile stresses in the presence of water and H2S Creation of crack with multiple branches Progressive cracking with delayed failure Potential failure mechanism of all CRAs and Chrome Steels Crack growth rate from mils/day to in/day SCC will increase with decreasing water ph increasing pph2s and Temperature SCC is almost always associated with chlorides Elemental sulfur deposits are a powerful agent for SCC SCC occurs below the yield strength of the alloy Traditional safety factors for design are no longer valid to prevent failure.
CRA Tubulars and Well Integrity page19 Overview of Sulfide Stress Cracking - SSC Even with small amounts of H 2 S, steel become sensitive to H 2 S corrosion/cracking Cracking is caused by hydrogen in the material H collects at stressed locations Material becomes brittle and fails below yield strength limit Very quick propagation leading to sudden failure SSC is generally associated with cracking of Carbon Steels, Martensitic Stainless Steels (13Cr, S13Cr) and Duplex Stainless Steels (22Cr & 25Cr) SSC will increase with: decreasing water ph and Temperature increasing pph2s Higher water cut to promote water wetting of equipment can increase SSC
CRA Tubulars and Well Integrity page20 Options to Prevent Corrosion Design Use a corrosion allowance Regular replacement Material selection Selection of a Metallurgy immune to corrosion/cracking in a given environment Use Corrosion Resistant Alloy (CRA) Use Non-Metallic Material Change the environment Inhibitor: Chemical additives when added in small quantities stop or slowdown the corrosion. Maintenance: e.g. pigging Coating Short term Long term
CRA Tubulars and Well Integrity page21 Material Selection
CRA Tubulars and Well Integrity page22 Evaluation of Service Condition to Enable Material Selection Define all environments that material will be exposed to over lifetime of completion Production environment: short term & long term Water cut, bubble point, ph, chlorides Partial pressure H2S & CO2 (reservoir souring, SRBs) BHT & surface or mudline temp BHP Contaminants Desired project life Annular Environment: short term & long term Chlorides type of brines, NaCl, ZnBr2, ph, oxygen scavanger, corrosion inhibitor, biocides Effect of gas leaks up the anulus Workover conditions
CRA Tubulars and Well Integrity page23 Tools For Material Selection NACE MR0175/ISO15156 (Guideline only, no warranty and no advice on metal loss corrosion) Part I: General Principals Part II: Carbon & Low Alloy Steels Part III: Corrosion Resistant Alloys Company guidelines & philosophy Literature & Publications Software Socrates ECE Actual Test Data Material testing and qualification
CRA Tubulars and Well Integrity page24 Simplified Material Selection Decision Tree Consider all potential scenarios during well life Basis of Design (BoD) Exposure to produced fluid possible? Yes Short or long term Long Asses metal loss corrosion (CO2) No Short No Yes Assess Sour Service (H2S) Assess Sour Service (H2S) No Yes T and Cl - limitations No Yes Verify Sour Service limitations Standard low Alloy Carbon Steel Sour Service Grades 13% Chrome CRA 24
CRA Tubulars and Well Integrity page25 Long Term Exposure Risk of Metal Loss Corrosion No industry standards available 0.1mm/yr considered as no metal loss Models and guidelines available to evaluate metal loss / corrosion rate DeWard Milliams NORSOK Cassandra (BP) PREDICT (Intercor) etc.
CRA Tubulars and Well Integrity page26 H 2 S Limits for CRA Tubular Components NACE MR0175/ISO15156 - Part 3 Alloy Material Group Table H2S Limit (psi) Temp Limit ( F) 13Cr Grade L80 Martensitic SS A.19 1.5 (ph 3.5) None (*) S-13Cr Grade 95 Martensitic SS A.19 1.5 (ph 3.5) None (*) 22CR / 25Cr Duplex (PREN 30-40) A.25 1,5 None(*) S25CR Super Duplex(PREN>40) A.25 3 None (*) 825, 28CR Nickel Base (4C) A.14 200 350 Alloy G3 Nickel Base (4D) A.14 300 425 C-276 Nickel Base (4E) A.14 1000 450 (*) Temp limit was not necessarily determined but mechanical properties will suffer too much at very high temperatures Other downhole environmental factors may have an influence on selecting the most appropriate alloy.
CRA Tubulars and Well Integrity page27 Simplified Material Selection Chart CO 2 > 2 psi Usage Domaine of Chrome and Nickel Alloys 27
CRA Tubulars and Well Integrity page28 Testing and Material Qualification Tests performed to evaluate Sulfide Stress Cracking SSC Stress Corrosion Cracking SCC Mass Loss Corrosion NACE testing (SSC resistance) Autoclave (crevice, pitting, SSC, HPHT) Typical protocols/standards used NACE MR0175 (Material Recommendation & Part 3 Annex B) NACE TM0177 NACE TM0198 Metallurgical analysis Numerical analysis and simulation NACE RP0775
CRA Tubulars and Well Integrity page29 NACE TM0177 Testing Methods Test method NACE A NACE B NACE C NACE D Stress application Tensile % of SMYS 3 points bent C ring Wedge Duration 720 hours 360 hours Results Rupture / No rupture S c Rupture / No rupture Stress Intensity Factor
CRA Tubulars and Well Integrity page30 Considerations for Testing Oxygen exclusion H2S and oxygen can react to alter the test environment Simulated downhole environments exclude oxygen to be representative of actual conditions Corrosion of test specimen and effect on solution Especially corrosion of carbon & low alloy steels can effect the test environment and reduce severity Guidelines for solution volume-to-specimen surface area Saturation of H2S test gas Rapid purge of gas for one hour or less Additional purge duration may be necessary for large vessels Elevated temperature stress relaxation All specimen rely on fixture to apply stress to specimen At significantly elevated temperatures (>300 F) the fixturing may thermally expand and relax the applied load Specimen surface finish Surface finish can effect test results
CRA Tubulars and Well Integrity page31 Connection Selection
CRA Tubulars and Well Integrity page32 Connection Selection Connection shall meet the well loads and be qualified accordingly Load points and protocol to be agreed on Consider Temperature effect on yield and tensile properties CRA specifics to be considered compared to Carbon Steel CRA tend to increase galling risk Anisotropic material behaviour of CRA (does not apply to martensitic steels)
CRA Tubulars and Well Integrity page33 Connection Qualification Protocol In January 2017, API agreed and published the 4 th edition of API RP 5C5 API RP 5C5 4 th edition (Jan.2017)is now the latest standard for Premium Connection testing VAM TOP tubing VAM TOP HC VAM TOP HT NAM TEO/3 ISO13679:2002 ISO113679:FDIS2011 API RP 5C5 2017 CAL I CAL II CAL III CAL IV CAL I CAL I-E CAL II CAL III-A CAL III / IV CAL I (gas) CAL II CAL III CAL IV VAM 21 VAM HTTC
CRA Tubulars and Well Integrity page34 Anisotropic Material Behaviour Performance Impact Q2 Internal Pressure Q1 Reduction in compression rating Smaller Envelope in Q2 Compression Tension Connection VME (95% AYS) Q3 Pipe VME External Pressure Q4
CRA Tubulars and Well Integrity page35 Reduce Galling Risk Dope Free Solution by VAM Operational savings in the yard Operational savings on the rig - Running time reduction Improved safety and reduced environmental impact Eliminates equipment plugging issues and formation damage
CRA Tubulars and Well Integrity page36 Conclusions Operator often reluctant to buy CRA due to higher initial purchasing cost Consider life of the well and TCO as well as risk of failure and associated safety hazard Differentiate between Metal Loss Corrosion and Cracking No official standard to guide metallurgy selection to avoid meal loss corrosion Only one official standard to support SSC and SCC decision making process Complex process with a lot of uncertainties Consider complete well life and potential scenarios Chrome and CRA resist metal loss corrosion but show varying performance of SSC and SCC Verify suitability of product through material qualification / ask your supplier for corrosion test data Cold worked CRA mechanical performances are different than martensitic stainless and carbon steels Latest API5C5 shows limitation in Q2 due to anisotropic behavior
CRA Tubulars and Well Integrity page THANK YOU CRA Tubulars and Well Integrity Technical Symposium September 25, 2017 page37