1. Hydrogen Induced CrackingHydrogen Induced Cracking

2. • Refers to mechanical damage of metal
• Caused by the presence/Interaction with
Hydrogen
• Can be classified in to following types
1) Hydrogen Blistering
2) Hydrogen Embrittlement
3) Hydrogen Attack
4) Decarburization
Hydrogen Damage

3. Hydrogen Blistering
H+
H H2 H
H+
H
H
H
H
H
ee
H H2 H
VoidAir
Acid Electrolyte
• Occurs due to penetration of H2 in to metal
• Results in to local deformation and in extreme
cases, complete destruction of the vessel wall
H H2 H

4. Hydrogen Embrittlement
• Caused by the penetration of H2 in to a metal
• loss of ductility - Embrittlement
• Tendency increases with Hydrogen Concentration
• Catastrophic failure occurs if hydrogen
concentration > 6 ppm
• Steels with >= 75 ksi are prone to Hydrogen
Embrittlement
• Steels with >=110 ksi are very much susceptible to
Hydrogen Embrittlement

5. Hydrogen Embrittlement
• Absorption of hydrogen due to presence of H2 gas
– Hydrogen Stress Cracking
• Absorption of hydrogen due to corrosion reaction –
Stress Corrosion Cracking
• Corrosion due to the presence of H2S --
Sulfide Stress Corrosion Cracking

6. Hydrogen Attack & Decarburization
• Elevated temperature phenomenon
• Dissolved Hydrogen diffuses in to steel and reacts
with carbon or carbides to from Methane Bubble
(CH4)
C [Fe] + 4 H [Fe] = CH4
• Formation at surface is known as Surface
decarburization
• Formation within the metal is known as Internal
decarburization
• Initially CH4 forms in micro voids grows to cracks

7. • Rate of reaction depends on
(1) Amount of H2
(2) % C in the alloys
(3) Amount of CH4
Hydrogen Attack & Decarburization

8. Hydrogen Induced Cracking (HIC)
• Step Wise Cracking (Blistering)
• Hydrogen Stress Cracking
• Hydrogen Embrittlement
• Hydrogen Induced Step Wise Cracking
All are known as “Hydrogen Induced Cracking (HIC)”

9. Mechanism of Cracking
• In the Presence of H2S, the process of cracking
(HIC) can be divided in to 5 stages
1) Corrosion : Hydrogen Production
2) Hydrogen Diffusion
3) Hydrogen trapping in defaults
4) Increasing of pressure
5) Cracking
Hydrogen Induced Cracking (HIC)

10. Main external Factors:
-Acidity of the environment
-H2S content
• Metallurgical Factors :
-Susceptible Microstructure
-Inclusions in steel ( S, P, As etc)
Hydrogen Induced Cracking (HIC)
Factors leading to Cracking

11. • Inclusions in the steel (Cracking often begins near
inclusions)
-- Sulphide inclusions ( S= 0.001% Max)
-- Oxide Inclusions ( O= 0.002% Max)
Hydrogen Induced Cracking (HIC)
• Susceptible Microstructure
-- Hardened micro structure
-- No PWHT
Factors leading to Cracking

12. • Most serious type of stress corrosion cracking - due
to hydrogen (occurs in sour service)
• Hydrogen usually picked up from sulfide solutions
• Occurs in cathodically protected structures if the
level of protection is too high
• H2S poisons the oxide surface - allows Hydrogen to
diffuse in to steel
• Hardness exceeding 22HRC (appx. 248HV) 
prone to cracking
Hydrogen Induced Cracking (HIC)
Summary

13. • Link-up of cracks at different planes to form steps
across the thickness
• Cracks reduce the effective wall thickness
• The term “HIC” has been widely used and adopted
by NACE international
• Several service failures
Hydrogen Induced Cracking (HIC)
Summary

14. HIC TESTING

15. Standard Test ---- HIC
General
• NACE TM 0284 – 96
• Std Test method for evaluating HIC resistance of
pipeline and pressure vessel steels
• Provides results at simulated environment
• No acceptance or rejection criteria

16. Standard Test ---- HIC
Test Specimens – Pipeline Steels

17. Standard Test ---- HIC
Test Specimens – Pipeline Steels

18. Standard Test ---- HIC
Test Specimens – Pressure Vessel Plate

19. Standard Test ---- HIC
Reagents
Solution “A” -- Nitrogen gas for purging,
H2S gas,
5.0% Sodium Chloride (NaCl)
0.50% Acetic Acid (CH3COOH)
Solution “B” -- Nitrogen gas for purging,
H2S gas,
Synthetic Sea Water

20. Standard Test ---- HIC
Test Procedure
• Test Specimen Exposure
 Wide faces vertical
 Separated from
vessel

21. Standard Test ---- HIC
Testing Apparatus
H2S Cylinder
Flow meter
Test Specimens
Trap
Trap
10 % NaOH
Solution
Solution

22. Standard Test ---- HIC
Evaluation of Test Specimens
• Sectioning of test specimen
• Surface examination
• Section to be polished metallographically and
etched
• Include all identifiable cracks visible at 100X in
the calculations
• Measurement of cracks (Crack length and
thickness)
• Cracks separated by 0.5 mm - considered as
single crack

23. Standard Test ---- HIC
Evaluation of Test Specimens
• Crack Sensitivity Ratio (CSR) = [Σ(a x b)/ (W x T)] x 100%
• Crack Length Ratio (CLR) = (Σa / W) x 100%
• Crack Thickness Ratio = (Σb / T)x 100%
T
w
b
a
a
b

24. Standard Test ---- HIC
Reporting Test Results
• Method of testing
• Test solution used
• pH of the test solution before introduction of H2S
• pH of the test solution after completion of the test
• Individual CSR, CLR and CTR

25. Preventive Measures
Hydrogen Induced Cracking (HIC)
• Using Clean Steel -- Killed Steel
• Using Coating (Metallic, Inorganic and Organic)
• Using Inhibitors
• Removing poisons
• Substituting alloys (Ni, Cr etc.)
• Reduce corrosion rate
• Baking
•Practicing proper welding

26. Preventive Measures
Hydrogen Induced Cracking (HIC)
• Using Clean Steel -- Killed Steel
• Using Coating (Metallic, Inorganic and Organic)
• Using Inhibitors
• Removing poisons
• Substituting alloys (Ni, Cr etc.)
• Reduce corrosion rate
• Baking
•Practicing proper welding