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Discussions on NACE TM0177 and API 5CT DCB Tests

Discussions on NACE TM0177 and API 5CT DCB Tests . Xin Long Pete Moore U. S. Steel Tubular Products Westminster, CO 06/12/2012. Acknowledgments. Dr. Karol Szklarz Dr. David Sponseller. Outline. Introduction Effects of Slot/Crack Tip Location on K ISSC & K Iapplied

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Discussions on NACE TM0177 and API 5CT DCB Tests

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  1. Discussions on NACE TM0177 and API 5CT DCB Tests Xin Long Pete Moore U. S. Steel Tubular Products Westminster, CO 06/12/2012

  2. Acknowledgments • Dr. Karol Szklarz • Dr. David Sponseller

  3. Outline • Introduction • Effects of Slot/Crack Tip Location on KISSC &KIapplied • Effects of Fatigue Precrack on KISSC • Summary

  4. Introduction • DCB Test (Dynamic Process) Includes: • Mechanical Driving Force: Cracking • Electro-Chemical Driving Force: Cracking Resistance • Interaction between Mechanical and Electro-Chemical Driving Forces

  5. Effects of Crack / Slot Tip Locations on KIapplied In Proposed Revision of NACE TM0177-2005 h Both can affect KIapplied B ai=1.50" Bn Chevron crack starter slot (highest KIapplied) Example: C110 in 100% H2S d = 0.02 inch KIapplied(Chevron starter) = 31.3 ksi in0.5 KIapplied(precrack) = 29.3 ksi in0.5 KIapplied(EDM slot 1) = 28.1 ksi in0.5 KIapplied(EDM slot 2) = 25.5 ksi in0.5 ai=1.58" Precrack (0.04-0.12") with Chevron slot (medium KIapplied) ai=1.63" EDM slot (0.125“) slot (medium KIapplied) ai=1.75" EDM slot (0.25“) slot (lowest KIapplied)

  6. Effects of Crack / Slot Tip Locations on KISSC &KLIMIT [1] KISSC variation caused by different arm displacement, it should also apply to KISSC variation caused by crack length In NACE TM0177-2005 It may also affect KLIMIT KIapplied (Chevron crack starter) KIapplied(Chevron with Precrack) KIapplied (EMD slot 2) [1] KLIMIT figure from David Sponseller ‘s presentation at API summer meeting in 2011, San Francisco, CA

  7. Rationale ap ap Standard KIapplied Standard KIapplied ap expected apexpected ap actual apactual Smaller Kiapplied (lower initial load) Larger Kiapplied (larger arm displacement) Arm Displacement Effect Crack Length Effect Higher electro-chemical driving force results in to a lower KISCC for smaller KIapplied Decreased electro-chemical driving force with the time increasing results in to a higher KISCC for lager KIapplied

  8. Crack / Slot Locations: Recommendation B ai Bn Chevron crack starter (highest KIapplied) slot ai Precrack (0.04-0.12") with Chevron (medium KIapplied) slot ai EDM slot (0.25" / 0.125") (lowest KIapplied) slot ai EDM slot to line up with Chevron base slot 0.25” • For mild sour environment: • Need to study if the EDM affect the crack initiation.

  9. Crack / Slot Tip Locations: Compliance Slightly compliance change for EDM slot due to more material removed, and results in KIapplied4-5% lower than Chevron slot. [commented by Dr. Karol Szklarz] B ai Bn Chevron slot ai • Initial calculation: • 0.25” EDM slot and 0.125” EDM slot has 0.013 in3 and 0.008 in3 less material than Chevron specimen, respectively. • EDM slot line up has 0.001 in3 less material than Chevron sample • expecting similar compliance to Chevron specimen. EDM slot (0.125” /0.25”) slot ai slot EDM line up • Austrian student has lined EDM slot up middle of the Chevron and got same results as Chevron slot. [commented by Dr. David Sponseller]. It was found it has 0.005 in3 more material. • Need more detail compliance study [commented by Dr. Karol Szklarz] EDM line up 2 slot

  10. Crack / Slot Locations: Compliance FEA CEB a/h

  11. Effects of Fatigue Precracking on KISSC • Fatigue Loading for Precrack • NACE TM0177 • Max. KI for precrackloading is the lesser of 70% of expected KIappliedand 27 ksi in0.5 • Crack should be sharpened at 2/3 of the max loading at final stage. • API 5CT • Max. KI for fatigue loading < 18.6ksi in0.5 Feasible ???

  12. Effects of Fatigue Precracking on KISSC • What Happens if Fatigue Precrack Loading Is too High? Scatter Szklarz, K.E. and Perez, T.E., “Observation on the Use of the Double Cantilever Beam Specimen for Sulfide Stress Corrosion Tests”, NACE CORROSION 1995, paper No.95048. (Houston, TX, 1995)

  13. Fatigue Precracking: Recommendation • Fatigue Loading for Precrack • Max. KI for precrack loading is less than 90%expected KIapplied Suggested by Dr. Karol Szklarz

  14. Summary • Initial crack length should cause attention. • EDM slot line up with Chevron base. • Possible work group for compliance development. • Max. KI for fatigue precrack to be less than 90% of expected Kiapplied.

  15. Questions? • Thank you!

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