What is Hydrogen Induced Cracking test or HIC Test?


What is Hydrogen Induced Cracking or HIC?

HIC Cracking is a type of hydrogen embrittlement . When a steel (carbon steel, low alloy steel & Nickel alloy) is exposed in the presence of H2S, hydrogen atoms originating from the cathodic reduction reaction (driving the anodic dissolution reaction) can diffuse into the steel, resulting in various cracking mechanisms known as :

  1. Hydrogen-induced cracking (HIC),
  2. Sulphide stress cracking (SSC) and
  3. Stress-oriented hydrogen-induced cracking (SOHIC).
  4. SWC – Step Wise Cracking
  5. blistering property

The presence of liquid water mandatory for the corrosion reactions can take place even if the gas temperature in the pipeline is above the water dew point that is due to the lower temperature of the pipe wall compared to the gas temperature or where the reduction of gas temperature along the pipeline results in the water vapor in the gas condensing out. Due to the fact that such cracks can be very difficult to detect during routine pipeline inspection, this type of damage is often regarded as more dangerous than weight-loss corrosion in the industries.

MECHANISM-OF-HYDROGEN-INDUCED-CRACKING – وب سایت عصر مواد

Hydrogen induced cracks either follow a linear or stepwise path within the material, hence the term ‘stepwise cracking’. However, under certain stress and material conditions, the cracks can be arranged in a ladder-like array known as Stress Orientated Hydrogen Induced Cracking (SOHIC). This form of cracking is often seen in the low hardness Heat Affected Zone (HAZ) region of welds.

HIC Test Type and standards for HIC Test

Hydrogen Induced Cracking (HIC) test is used to assess the susceptibility of carbon and low alloy steel material to hydrogen induced cracking in wet H2S/sour service operating environments mostly found in the Oil & Gas industry. The HIC tests are normally carried out according to NACE TM0284 (Evaluation of Pipeline and Pressure Vessel Steels for Resistance to Hydrogen-Induced Cracking).

In order to evaluate the resistance to hydrogen-induced cracking of pipeline and pressure vessel steel, standard test shall be conducted in accordance with NACE TM0284. The steel specimens shall be immersed into test solutions at the temperature 25±3°C [77±5°F]. This standard describes two test solutions as,

  1. Solution A: a sodium chloride, acetic acid (NaCl, CH3COOH) solution saturated with H2S at ambient temperature and pressure and
  2. Solution B:  a synthetic seawater solution saturated with H2S at ambient temperature and pressure

NACE TM0284 includes special procedures for testing small-diameter, thin-wall, electric-resistance welded and seamless line pipe. Test is intended to evaluate resistance to hydrogen-induced (stepwise) cracking only, and not other adverse effects of sour environments such as sulfide stress cracking, pitting, or weight loss from corrosion.

HIC test method as per NACE TM0284

HIC testing is performed according to the NACE TM0284 by exposing unstressed test specimens to the specified environment saturated with hydrogen sulfide gas at 1 bar pressure & temperature of 25±3°C [77±5°F] for a duration of 96 hours for the standard test. Fitness for purpose of testing may also be performed using reduced partial pressures of hydrogen sulfide and for durations of up to 30 days. 

Note that TM0284 does not include acceptance criteria.

Following the exposure period, the specimens are metallographically prepared, optically examined, and any cracks are measured and the following ratios are reported: 

  • CSR (Crack Sensitivity Ratio)
  • CLR (Crack Length Ratio)
  • CTR (Crack Thickness Ratio) 

HIC Test specimen dimensions

HIC Specimen size for Pipe

  1. Each test specimen shall be 100 ± 1 mm (4.00 ± 0.04 in) long by 20 ± 1 mm (0.80 ± 0.04 in) wide.
  2. The test specimen thickness shall be the full wall thickness of the pipe up to a maximum of 30 mm (1.2 in). For wall thickness greater than 30 mm (1.2 in), the test specimen thickness shall be either the full wall thickness of the pipe or limited to a maximum thickness of 30 mm (1.2 in) and staggered through the thickness, as described in Section 5 of NACE TM0284. A maximum of 1 mm (0.04 in) may be removed from each of the surfaces (i.e., internal and external). Test specimen blanks shall not be flattened.

HIC Specimen size for Pipe

  1. Each test specimen shall be 100 ± 1 mm (4.00 ± 0.04 in) long by 20 ± 1 mm (0.80 ± 0.04 in) wide.
  2. A maximum of 1 mm (0.04 in) may be removed from the rolled surfaces. Test specimen blanks shall not be flattened.
  3. The test specimen thickness shall be the full thickness of the plate, up to a maximum of 30 mm (1.2 in). For plates thicker than 30 mm (1.2 in), the test specimens shall be staggered as indicated in Paragraphs 5.2.3 and 5.2.4, with the following exception: for plates thicker than 30 mm (1.2 in) that are intended to be used for manufacture of pipe, the test specimens may be full wall thickness in accordance with Paragraph 4.1.2 of NACE TM0284.

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