Hydrogen-Induced Cracking (HIC)

🔹 What is HIC?

Hydrogen-Induced Cracking is a type of internal cracking that occurs in metals, especially carbon steel, due to the absorption and accumulation of atomic hydrogen.

🔹 How It Happens:

1. Hydrogen atoms enter the metal (e.g., during corrosion in sour service environments containing H₂S).

2. Hydrogen atoms diffuse into the steel and accumulate at trap sites like inclusions or laminations.

3. This leads to the formation of internal pressure from molecular hydrogen (H₂), which creates micro-cracks.

4. Cracks typically form parallel to the rolling direction of the steel.

🔹 Key Characteristics:

• Cracks are blister-like or stepwise.

• Occurs below the surface, not on external welds.

• Common in wet H₂S environments (e.g., pipelines, pressure vessels).

• No external stress is needed — it can occur even without applied load.

🔹 Commonly Affected Materials:

• Carbon and low-alloy steels, especially with high sulfur content or non-metallic inclusions.

🔹 Prevention Methods:

• Use HIC-resistant materials (e.g., low-sulfur steels, vacuum-degassed steel).

• Apply inhibitors in corrosive environments.

• Use cladding or coating (e.g., stainless steel overlays).

• Conduct NACE TM0284 testing to assess HIC susceptibility.

🔹 Testing & Detection:

• Ultrasonic Testing (UT).

• Metallography on test samples.

• Hydrogen permeation tests.

• NACE standards guide testing protocols.