Hydrogen blistering refers to the physical description of a metal with subsurface cavities that were created by accumulated hydrogen gas. 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.
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.
Hydrogen blistering can be mitigated by:
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May/June 2006 Inspectioneering Journal
By John Reynolds at Intertek
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 problems during or after welding. |
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May/June 1995 Inspectioneering Journal
By Dr. Russell D. Kane at CLI International Inc., and Dr. Michael S. Cayard at Flint Hills Resources
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 (SSC). Documented cases of leaks and failures of pressure containing equipment have been attributed to these forms of corrosive damage. |
