Hydrogen Blistering

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Hydrogen Blistering is a form of wet H2S damage generally characterized by internal blisters (i.e., planar cavities that result in physical bulges) in steel that are caused by the accumulation of molecular hydrogen. Physically, these cavities appear as subsurface “bubbles” or “blisters.”

Blisters form as a result of atomic hydrogen diffusing through metal and accumulating in voids. Being highly reactive, hydrogen atoms combine with each other inside of voids and form hydrogen gas (H2). The buildup of hydrogen gas then increases the pressure beneath the surface of the metal to form blisters.

This form of hydrogen damage typically occurs in low-strength metals and cannot be reversed. Additionally, hydrogen blistering permanently decreases the mechanical strength of the metal and may lead to failure (i.e. rupture) even under light loads.

Factors that cause Hydrogen Blistering

The main sources of hydrogen blistering depend on the following conditions:

Material Type. Low-strength metals are the most common type of material that are susceptible to hydrogen blistering. Hydrogen is able to collect in material that contains inclusions (i.e. impurities).

Chemical Environment. In the petroleum industry, exposure to impurities and corrosive elements found in crude oil is inevitable. The most common corrosives in crude oil include carbon dioxide, chlorides, sulfur, and sulfate reducing bacteria. Hydrogen is a byproduct of many corrosion reactions.

Thermal Environment. If not controlled, high temperature operations and weld repairs are also environments that facilitate hydrogen damage.

Preventative Measures

Hydrogen blistering can be mitigated by:

  1. Using metals that are chemically resistant to corrosion, such as nickel-containing steels or austenitic stainless steels, rather than ferritic or martensitic steels.
  2. Controlling inclusions (impurities) that may be found in steels during processing.
  3. Using coatings that are resistant to hydrogen penetration and nonreactive with the parent metal.
  4. Using inhibitors that reduce the rate of hydrogen induced corrosion.
  5. Improving equipment design where necessary (e.g. eliminating the need for welded joints).
  6. Applying a proper post weld heat treatment (PWHT) in order to diffuse hydrogen out of the surface of the metal.


  1. Prueter, P., 2021, “Damage Control: Wet H2S Damage Detection,” Inspectioneering Journal, 27(5), pp. 45-52.

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Articles about Hydrogen Blistering
January/February 2022 Inspectioneering Journal

This edition of Damage Control will offer practical steps to mitigate different forms of wet H2S damage and help to minimize long-term inspection and maintenance costs related to wet H2S damage.

November/December 2021 Inspectioneering Journal

This issue of Damage Control offers a perspective on how to assess the different forms of wet H2S damage using modern FFS and computational analysis techniques with the safe operation of damaged pressure vessels, piping, and associated components.

September/October 2021 Inspectioneering Journal

This article summarizes the fundamentals of wet H2S-related damage mechanisms, offers some practical inspection guidance, and reviews a notable industry failure caused by different forms of wet H2S damage.

May/June 2006 Inspectioneering Journal

As noted in the discussion on delayed cracking, when the steel contains hydrogen as a result of service exposure (or corrosion, or high temperature - high pressure hydrogen processing) then a hydrogen bake out may be needed to avoid cracking...

Authors: John Reynolds
May/June 1995 Inspectioneering Journal

Exposure of carbon steel equipment to wet H2S service environments can lead to various forms of attack, e.g. hydrogen blistering and hydrogen induced cracking (HIC), stress oriented hydrogen induced cracking (SOHIC) and sulfide stress cracking...

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Traditional inspection methods used to detect internal corrosion and corrosion under insulation (CUI) in piping and pipeline assets can be time-consuming and costly. With ART, you’ll discover CUI detection best practices that can help save you up...

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