Hydrogen Induced Cracking (HIC) is a type of wet H2S cracking caused by a high hydrogen concentration in metals. Atomic hydrogen diffuses into a metal structure as part of the procedure. HIC cracking occurs parallel to the surface in the hoop stress direction. Because of the presence of moist H2S, hydrogen-induced cracking is more common in sour service settings. Other components may also contribute to hydrogen-induced cracking. Arsenic, antimony, selenium, and cyanides are examples of these elements. However, in the oil and gas sector, H2S is regarded as the most significant contributor to hydrogen-induced cracking damage. Many metals and alloys get blistered as a result of HIC.
Hydrogen-induced cracking is more common in ferrous alloys due to the limited-slip capabilities of the BCC structure. At relatively low temperatures, HIC affects steels with Rockwell C harnesses of 22 or above.
HIC can also arise during high-temperature processes such as electroplating, pickling, phosphating, cathodic protection, arc welding, and so on. HIC = Hydrogen Induced Cracking = Cracking caused by the impact of hydrogen on metal.
Some terminology for Hydrogen-induced cracking are:
- Hydrogen Damage
- Hydrogen Embrittlement
- Hydrogen Blistering
- Delayed Cracking
- Lamellar Tearing
- Underbead Cracking
- Stepwise Cracking
Hydrogen Induced Cracking Process
The HIC process in a wet H2S environment begins with the creation of atomic hydrogen, which diffuses throughout the metal or alloy and gathers at voids or cracks within the metal structure. When these hydrogen atoms merge to create a hydrogen molecule, they generate a lot of pressure inside the cavity. The H2S drives these hydrogen atoms into the metal structure, reducing the metal’s ductility and tensile strength. This mechanism decreases metal ductility, resulting in the formation of successive internal cracking, a procedure is known as hydrogen-induced cracking.
Exhibit: Hydrogen Induced Cracking
HIC is usually visible as a horseshoe-shaped pattern on the metal surface. Regular examination and testing are required to minimize the chance of hydrogen-induced corrosion. HIC damage can be detected through wet fluorescent magnetic particle inspection. The most commonly used and effective non-destructive approach for broken components is Phased Array Ultrasonic Testing.
Hydrogen-induced cracking is more common in low alloy steels and high-strength titanium and nickel steels. Low-strength steels having tensile strengths of less than 1000 MPa are typically resistant to HIC. The materials most resistant to HIC include copper, aluminum, and their alloys.
Hydrogen Induced Cracking Resistant Materials Needs
- Carbon and Low Alloy Steels Needs
- The parent material’s hardness is less than 22 HRC (237 BHN).
- The steel must be completely destroyed (silicon/aluminum).
- Heat treating the material by normalizing, annealing, or Q & T.
- The carbon content must be less than 0.23 % and carbon equivalent (CE) must be less than 0.43 %.
- Sulfur and phosphorus concentrations of below 0.002 %
- Calcium Treated and Inclusion Control Requirements
- Austenitic Stainless Steel Needs
- Hardness of Parent Materials below 22HRC (237 BHN).
- Heat Treated by Solution Annealing.
- Duplex and Super Duplex Stainless Steel Needs
- Hardness on parent Material below 25 HRC.
- Heat Treated by Solution Annealing.
- Ferrite shall be 35% to 65%.
Testing of Hydrogen Induced Cracking
The HIC test is carried out in accordance with NACE TM0284. For the standard test, the unstressed HIC test specimen is subjected to the appropriate process environment saturated with hydrogen sulfide gas at 1 bar pressure for 96 hours (4 days). Fitness for testing is achieved by utilizing lower partial pressures of hydrogen sulfide for a period of up to 30 days.
When the exposure period is over, the test specimen is inspected and any cracks that have formed are measured. The Crack Sensitivity Ratio, Crack Length Ratio and Crack Thickness Ratio are the most frequently utilized ratios for hydrogen-induced cracking studies.
Another HIC test technique is the Stress Oriented Hydrogen-induced Cracking (SOHIC) test method. SOHIC tests are carried out in accordance with NACE MR0175 or ISO 15156, utilizing the whole ring test technique specified in BS 8701, the tensile test method specified in NACE TM0177-Method A, or the four-point bend method specified in NACE TM0316.
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