04f Hydrogen Damage.ppt
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The document discusses various forms of hydrogen damage that can occur in steel, including hydrogen blistering, hydrogen induced cracking, stress oriented hydrogen induced cracking, and sulfide stress cracking. The general mechanism involves penetration of atomic hydrogen generated from wet corrosion reactions into steel, where it can then recombine and form bubbles or collect at defects and cause cracking, especially under stress. Methods to prevent hydrogen damage include minimizing corrosion, controlling steel composition and inclusions, and heat treating welds.
04f Hydrogen Damage.ppt
- 1. uop Corrosion and Fouling Hydrogen Damage Jun 2002 1 Hydrogen Damage
- 2. uop Corrosion and Fouling Hydrogen Damage Jun 2002 2 Low Temp Hydrogen Damage • Several terms applied – Hydrogen blistering – Hydrogen induced cracking (HIC) – Stress oriented hydrogen induced cracking (SOHIC) – Sulfide stress cracking (SSC) or hydrogen stress cracking • All variations of same phenomenon
- 3. uop Corrosion and Fouling Hydrogen Damage Jun 2002 3 General Mechanism • Penetration of atomic hydrogen (Ho) into steel • At low temperatures (<400 F or 204C) molecular hydrogen does not react with steel and does not penetrate • Atomic hydrogen comes from any wet corrosion reactions which makes H2 – Often associated with H2S
- 4. uop Corrosion and Fouling Hydrogen Damage Jun 2002 4 General Mechanism Cont. • Atomic Hydrogen generated by corrosion normally combines to form molecular hydrogen and escapes into solution • Some doesn’t • Recombination poisons promote penetration – CN-, As, S2- – CN- also forms soluble complex with Fe
- 5. uop Corrosion and Fouling Hydrogen Damage Jun 2002 5 Hydrogen Blistering • Low tensile strength steel (high ductility) • Voids and inclusions – Particularly MnS stringers • Atomic hydrogen finds void and recombines to molecular hydrogen
- 6. uop Corrosion and Fouling Hydrogen Damage Jun 2002 6 Hydrogen Blistering S2- H+ H+ H+ H+ H0 H0 H0 H0 H2 H2 Void or Inclusion Steel Solution
- 7. uop Corrosion and Fouling Hydrogen Damage Jun 2002 7 Hydrogen Induced Cracking • Starts at elongated MnS inclusions • Cracks start at tips of blisters and grow parallel to steel surface • Link by growing perpendicular • Want low Mn and S steel with shape controlled inclusions
- 8. uop Corrosion and Fouling Hydrogen Damage Jun 2002 8 Hydrogen Induced Cracking H2 H2 H2 H2
- 9. uop Corrosion and Fouling Hydrogen Damage Jun 2002 9 Stress Oriented Hydrogen Induced Cracking (SOHIC) • Starts from wet corrosion producing H0 which diffuses in • H0 collect at lattice defects but don’t necessarily form voids • Cracks form in plane of inclusions and link in plane perpendicular to stress • Often at hard spots near welds
- 10. uop Corrosion and Fouling Hydrogen Damage Jun 2002 10 Stress Oriented Hydrogen Induced Cracking Stress Stress
- 11. uop Corrosion and Fouling Hydrogen Damage Jun 2002 11 Sulfide Stress Cracking • High strength steel or hard welds • Stress or residual stress • Temperature and hydrogen flux affect cracking • Unlike other types of hydrogen damage significant wet corrosion is not required • Heat treat steel, welds < HRc 22 (HV 248)
- 12. uop Corrosion and Fouling Hydrogen Damage Jun 2002 12 Sulfide Stress Cracking, Hydrogen Stress Cracking Stress Stress High Strength Steel
- 13. uop Corrosion and Fouling Hydrogen Damage Jun 2002 13 Examples • HF units • Sour water strippers • FCC – HP and LP separators – Stripper tower overhead
- 14. uop Corrosion and Fouling Hydrogen Damage Jun 2002 14 What to do about it • Minimize wet corrosion (generates H0) • Minimize recombination poisons (H2S etc.) • Use low Mn, S steels with inclusion shape control • Avoid high strength steels • Heat treat welds to below HRc 22