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 K ISSC & K Iapplied  Effects of Fatigue Precrack on K ISSC  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 K Iapplied Precrack ( ") with Chevron slot a i =1.58" EDM slot (0.125“) slot a i =1.63" In Proposed Revision of NACE TM h B Chevron crack starter slot a i =1.50" BnBn Example: C110 in 100% H 2 S  = 0.02 inch K Iapplied (Chevron starter) = 31.3 ksi in 0.5 K Iapplied (precrack) = 29.3 ksi in 0.5 K Iapplied (EDM slot 1) = 28.1 ksi in 0.5 K Iapplied (EDM slot 2) = 25.5 ksi in 0.5 Both can affect K Iapplied EDM slot (0.25“) slot a i =1.75" (highest K Iapplied ) (medium K Iapplied ) (lowest K Iapplied )

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

7 Rationale apap a p expected a p actual Decreased electro-chemical driving force with the time increasing results in to a higher K ISCC for lager K Iapplied Higher electro-chemical driving force results in to a lower K ISCC for smaller K Iapplied Larger K iapplied (larger arm displacement) Standard K Iapplied Arm Displacement Effect apap a p expected a p actual Smaller K iapplied (lower initial load) Standard K Iapplied Crack Length Effect

8 Crack / Slot Locations: Recommendation Chevron crack starter (highest K Iapplied ) Precrack ( ") with Chevron (medium K Iapplied ) EDM slot (0.25" / 0.125") (lowest K Iapplied ) slot aiai aiai aiai BnBn B EDM slot to line up with Chevron base slot aiai For mild sour environment:  Need to study if the EDM affect the crack initiation. 0.25”

9 Crack / Slot Tip Locations: Compliance Chevron EDM slot (0.125” /0.25”) slot aiai aiai BnBn B Slightly compliance change for EDM slot due to more material removed, and results in K Iapplied 4-5% lower than Chevron slot. [commented by Dr. Karol Szklarz] EDM line up slot aiai Initial calculation:  0.25” EDM slot and 0.125” EDM slot has in 3 and in 3 less material than Chevron specimen, respectively.  EDM slot line up has in 3 less material than Chevron sample expecting similar compliance to Chevron specimen.  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 in 3 more material.  Need more detail compliance study [commented by Dr. Karol Szklarz] slot EDM line up 2

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

11 Effects of Fatigue Precracking on K ISSC  Fatigue Loading for Precrack  NACE TM0177  Max. K I for precrack loading is the lesser of 70% of expected K Iapplied and 27 ksi in 0.5  Crack should be sharpened at 2/3 of the max loading at final stage.  API 5CT  Max. K I for fatigue loading < 18.6 ksi in 0.5 Feasible ??? MaterialEnvironment Arm Disp. (in) a i (in) 0.7*K iapplied (ksi in 0.5 ) Max. Fatigue Load (lb) Final Fatigue Load (lb) C110100% H2S C1107% H2S ‒ ›

12 Effects of Fatigue Precracking on K ISSC 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 (Houston, TX, 1995) Scatter  What Happens if Fatigue Precrack Loading Is too High?

13 Fatigue Precracking: Recommendation  Fatigue Loading for Precrack  Max. K I for precrack loading is less than 90% expected K Iapplied MaterialEnvironment Arm Disp. (in) a i (in) 0.9*K iapplied (ksi in 0.5 ) Max. Fatigue Load (lb) C110100% H2S C1107% H2S 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. K I for fatigue precrack to be less than 90% of expected K iapplied.

15  Questions?  Thank you!