Hydrogen Induced Cracking


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This is a presentation on hydrogen induced cracking ,sulfide stress cracking and test procedure for HIC resistant steel


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  • Hydrogen embrittlement: Hydrogen combines with carbon within the alloy and forms methane. The methane molecules create a pressure which leads to embrittlement and even cracking of the metal.
  •   HIC IN WELDING Cold cracking/ HAZ cracking – moisture n org compounds r primary sources of H. may be present on steel and electrode , shielding material, atm. Flux absorb hydrogen from atm .so proper selection must be done. Occurs 72 hrs later of welding At 450 F H diffuse at rate of 1 inch /hr At 220 F1 inch / 48 hr Room temp 2 weeks PREVENTION Weld surface free of moisture ( preheat min requirement 20 degree C at distance 6 times thickness of base metal) PWHT can be applied to reduce conc of H at a place .400-450 F holding for 1 hr. will redistribute the H thru diffusion. thus reducing risk of H cracking
  • Hydrogen Blistering A special case of hydrogen damage is known as hydrogen blistering. Hydrogen blistering occurs when hydrogen atoms diffuse into the steel, and hydrogen gas nucleates at internal defects and inclusions, forming voids which eventually generate enough pressure to locally rupture the metal
  • Hydrogen ions are a product of many corrosion processes .These ions pick up electrons from the base material producing hydrogen atoms. At that point, two hydrogen atoms may combine to form a hydrogen molecule. Most molecules will eventually collect, form hydrogen bubbles, and float away harmlessly. Some percentage of the hydrogen atoms will diffuse into the base metal and embrittle the crystalline structure. When the concentration of hydrogen becomes critical and the tensile stress exceeds the threshold level, SSC occurs. H 2 S does not actively participate in the SSC reaction; sulfides promote the entry of the hydrogen atoms into the base material.
  • Increasing strength and applied stress, increasing H2S concentrations and increasing acidity (decreasing pH) increase SSC susceptibility The presence of CO 2 reduces the pH of the solution to approximately 3, aggravating the corrosion problem and breaking down any protective films that may form during the corrosion reaction. Sulfide stress cracking is most severe at ambient temperature, 20° to 120°F (-7° to 49°C). Below 20°F (-7°C) the diffusion rate of the hydrogen is so slow that the critical concentration is never reached. Above 120°F (49°C) the diffusion rate is so fast that the hydrogen passes through the material in such a rapid manner that the critical concentration is not reached. The occurrence of stress corrosion cracking above 120°F (49°C) is still likely and must be carefully considered when selecting material.
  • The cracks are usually non-branching and fast growing, and are more often transgranular (through the grains) rather than intergranular (through the grain boundaries).
  • Hydrogen Induced Cracking

    2. 2. Contents <ul><li>What is HIC/SSC ? </li></ul><ul><li>How it occurs? </li></ul><ul><li>Where is occurs? </li></ul><ul><li>Standards used b ARAMCO </li></ul><ul><li>Test Method to check HIC resistance steel </li></ul><ul><li>Acceptance criteria </li></ul>
    3. 3. <ul><li>What is HIC </li></ul><ul><li>HIC is internal cracks caused in material by trapped nascent hydrogen atoms. </li></ul><ul><li>Atomic hydrogen , and not the molecule, is the smallest atom and it is small enough to diffuse readily through a metallic structure. When the crystal lattice is in contact or is saturated with atomic hydrogen, the mechanical properties of many metals and alloys are diminished </li></ul>
    4. 4. <ul><li>2H (atoms)  H 2 (gas) </li></ul><ul><li>If the formation of molecular hydrogen is suppressed, the nascent atomic hydrogen atom can diffuse into the interstices of the metal instead of being harmlessly evolved as a gaseous reaction product thus producing a crack in the material. </li></ul><ul><li>Residual and applied tensile stress not necessary for HIC </li></ul><ul><li>Certain chemical species poison this recombination (e.g. cyanides, arsenic, antimony, or selenium compounds). However, the most commonly encountered species is hydrogen sulfide (H2S), formed in many petrochemical process. </li></ul>
    5. 5. <ul><li>Sources of hydrogen </li></ul><ul><li>In the making of steel </li></ul><ul><li>In processing parts, </li></ul><ul><li>In welding, </li></ul><ul><li>In storage or containment of hydrogen gas, </li></ul><ul><li>Hydrogen as a contaminant in the environment having low ph that is often a by-product of general corrosion </li></ul><ul><li>Hydrogen embrittlement: </li></ul><ul><li>I ngress of hydrogen into a component causing brittle failures at stresses below the yield stress of susceptible materials. </li></ul><ul><li>Methane formation </li></ul><ul><li>Reduce ductility </li></ul><ul><li>Reduce load bearing Capacity </li></ul><ul><li>Crack formation </li></ul><ul><li>Failure below Yield stress by brittle Fracture </li></ul>
    6. 6. HIC IN WELDING <ul><li>Cold cracking/ HAZ cracking </li></ul><ul><li>Source for Hydrogen entrapment </li></ul><ul><li>Moisture </li></ul><ul><li>Organic Compounds </li></ul><ul><li>Occurs 72 hrs later of welding </li></ul><ul><li>At 450 F H diffuse at rate of 1 inch /hr </li></ul><ul><li>At 220 1 inch / 48 hr </li></ul><ul><li>Room temp 2 weeks </li></ul><ul><li>Prevention </li></ul><ul><ul><li>Weld surface should free of moisture </li></ul></ul><ul><ul><li>PWHT 400-450 F holding for 1 hr. will redistribute the H thru diffusion. thus reducing risk of H cracking </li></ul></ul>
    7. 7. <ul><li>Hydrogen Blistering </li></ul><ul><li>Nucleation of Hydrogen gas at internal defects </li></ul><ul><li>Rupture of material </li></ul><ul><li>What is sour service ? </li></ul><ul><li>Sour service is a environment containing water and H 2 S( hydrogen sulfide) </li></ul><ul><li>If the presence of hydrogen sulfide i.e. sour services causes entry of hydrogen into the component, the cracking phenomenon is often termed “Sulfide Stress cracking (SSC)” </li></ul><ul><li>Electrochemical corrosion reactions produce H atoms </li></ul>
    8. 8. Chemical Reactions <ul><li>H2S(aq) + H2O(l)  H3O + (aq) + HS - (aq) ( Bisulfide ) --------1 </li></ul><ul><li>H2O(l) + H2O(l)   H3O + (aq) + OH - (aq)  -----------------------2 </li></ul><ul><li>HS - (aq) + H 2 O(l) <==> H 2 S(aq) + OH - (aq) </li></ul><ul><li>S 2- (aq)( Sulfide ) + H 2 O(l) <==> HS - (aq) + OH - (aq) --------3 </li></ul><ul><li>The sulfide ion then combines with ferrous ions to form iron sulfide. The metal surface is dissolved. </li></ul><ul><li>How are H atoms ions produced ? </li></ul>
    9. 9. <ul><li>Factors influencing SSC </li></ul><ul><ul><li>Increase in acidity ( low pH) </li></ul></ul><ul><ul><li>Carbon Dioxide </li></ul></ul><ul><ul><li>Increased stress </li></ul></ul><ul><ul><li>Ambient Temperature (-7 to 49 degree C) </li></ul></ul><ul><li>Medium strength steel are more susceptible for HIC </li></ul><ul><li>The most vulnerable are high-strength steels, titanium alloys and aluminum alloys. </li></ul>
    10. 10. <ul><li>a. Blister b. HIC c. SSC (low strength steel) d. (high strength steel) </li></ul><ul><li>Non Branching </li></ul><ul><li>Fast Growing </li></ul>
    11. 11. Standards used <ul><li>SAES-A-301 ( Materials Resistant to Sulfide Stress Corrosion Cracking ) replaced now </li></ul><ul><li>ISO 15156-2003 Petroleum and natural gas industries – Materials for use in H 2 S containing environments in oil and gas production. </li></ul><ul><ul><ul><li>It gives requirements and recommendations for the selection carbon and low alloy steels for service in equipment, used in oil and natural gas production and natural gas treatment plants in H 2 S containing environments </li></ul></ul></ul><ul><ul><ul><li>This addresses the resistance of the steel to damage that may be caused by SSC and HIC </li></ul></ul></ul>
    12. 12. <ul><li>01-SAMSS-016 - Qualification of Pipeline, In plant Piping and pressure Vessel Steels for Resistance to Hydrogen –Induced Cracking </li></ul><ul><li>SCOPE </li></ul><ul><ul><li>This specification is supplementary to current NACE TM0284 (Evaluation of pipeline and pressure vessel steels for resistance of hydrogen induced cracking) </li></ul></ul><ul><ul><li>Not Applicable to seamless pipe </li></ul></ul>
    13. 13. <ul><ul><li>Applicable for following steel products </li></ul></ul><ul><ul><ul><li>High Frequency welded pipeline per 01-SAMSS-332 </li></ul></ul></ul><ul><ul><ul><li>Or / 01-SAMSS-333 </li></ul></ul></ul><ul><ul><ul><li>Submerged arc welded pipeline 01-SAMSS-035 and 01-SAMSS-038 </li></ul></ul></ul><ul><ul><ul><li>Pressure Vessel Plate per 32-SAMSS-004 </li></ul></ul></ul>
    14. 14. <ul><li>Mandatory requirements </li></ul><ul><li>The steel manufacturer shall guarantee that the pipe fabrication cold forming processes will not compromise the HIC resistance of the strip/plate. </li></ul><ul><li>Pseudo-HIC Resistant steel shall not be used to fabricate equipment intended for sour service application. Steel that passes the HIC test, but has not been initially manufactured to be HIC resistant steel shall not be used. </li></ul><ul><li>Pseudo-HIC Resistant Steel : Plate/Strip that is not fabricated utilizing the quality control/assurance and fabrication measures to intentionally produce HIC resistant steel. </li></ul><ul><li>Form 175-010200 - Inspection and testing requirements - HIC Testing </li></ul>
    15. 15. Appendix B-Test Procedure for Evaluating HIC in H 2 S Saturated Solution A <ul><li>This test procedure is described in NACE TM0284-2003 </li></ul><ul><li>Solution A- A sodium chloride, acetic acid (NaCl, CH3COOH) solution saturated with H 2 S at ambient temperature and pressure </li></ul><ul><li>Solution B- A synthetic seawater solution saturated with H2S at ambient temperature and pressure </li></ul><ul><li>As per 01 –SAMSS-016 test solution shall be Solution A </li></ul>
    16. 16. Apparatus
    17. 17. Procedure <ul><li>Each test specimen shall be 100 ±1 mm long by </li></ul><ul><li>20 ±1 mm wide. </li></ul><ul><li>The test specimen thickness shall be the full wall </li></ul><ul><li>thickness of the pipe up to a maximum of 30 mm. </li></ul><ul><li>3 test specimens shall be taken from each </li></ul><ul><li>test pipe for pipes produced by continuous casting and 6 for ingot casting </li></ul><ul><li>3 </li></ul>Sample 1 Sample 2 Sample 3 Plate Rolling Direction
    18. 18. Plate Thickness 30<T<89mm Plate Thickness T>88mm
    19. 19. pH of solution A : 2.7 ± 0.1 Concentration of H2S measured by iodometric titration, shall be min of 2300ppm Test duration :96 hrs Temperature :25 ± 3 °C
    20. 20. Evaluation of Test Specimens <ul><li>Specimen shall be Sectioned </li></ul><ul><li>Each section shall be polished metallographically and etched </li></ul><ul><li>All faces to be examined shall be subjected to either wet magnetic particle testing or macro etching prior to final metallographic polishing </li></ul><ul><li>Cracks shall be measured as illustrated in Figure </li></ul><ul><li>Definitions: </li></ul><ul><li>The &quot;Crack Length Ratio&quot;(CLR) is defined as the sum of the lengths of the individual longitudinal cracks divided by the width of the polished specimen face times 100% </li></ul><ul><li>CLR =( Σ a ∕ W ) x 100 % </li></ul>
    21. 21. The &quot;Crack Thickness Ratio&quot; (CTR) is defined as the sum of the thickness of crack arrays divided by the thickness of the polished specimen face times 100% CTR =( Σ b ∕ T ) x 100 %
    22. 22. Reporting Test Results <ul><li>The CLR and CTR results of the control sample shall be reported. </li></ul><ul><li>Longitudinal crack – Avg CLR <10% </li></ul><ul><li>Transverse crack – Avg CTR < 3% </li></ul><ul><li>pH of H2S saturated solution before addition of H2s,at the start and end of the test. </li></ul><ul><li>Chemical composition of material tested, including Al, B, C, Ca, Cr, Cu, Mn, Mo, Ni, Nb, N, P, Si, S, Ti and V. </li></ul><ul><li>Results of cracking evaluation. </li></ul><ul><li>Photomicrographs of metallographically -polished (1 micron finish) specimens </li></ul><ul><ul><li>Magnifications 100x to 500x </li></ul></ul><ul><li>Hardness shall not exceed 250 HV. ( load 5-10 kg ) </li></ul>
    23. 23. <ul><li>THE END </li></ul><ul><li> Thank You </li></ul>