Inspectioneering Journal

99 Diseases of Pressure Equipment: Hydrogen Assisted Cracking or Hydrogen Embrittlement

By John Reynolds, Principal Consultant at Intertek. This article appears in the November/December 2003 issue of Inspectioneering Journal.

Hydrogen Embrittlement (HE) is an insidious form of degradation that can strike during equipment fabrication, cleaning, repairs or while in-service. It stems from the infusion of atomic hydrogen into some higher strength steels that then leads to embrittlement, cracking or catastrophic brittle fracture. During welding, the hydrogen can come from wet electrodes or moisture on the steel. Underbead cracking, hydrogen cold cracking, and delayed cracking are all forms of HE that are fairly well known, and usually the right precautions (heated electrodes, preheat, etc.) are taken to prevent such HE. However, during service, the hydrogen can come from common aqueous corrosion reactions or from hot hydroprocess environments. Great care must be taken to start-up and shut-down heavy wall hydroprocess equipment that might be susceiptible to HE. Catastrophic brittle failure could occur if such equipment had a flaw that became a critical defect when the metal is saturated with atomic hydrogen.

Another form of HE cracking happens when flange bolts are exposed to leaking process fluids that cause corrosion. Bolting material is usually higher strength and will fail brittlely from just a very small amount of the wrong kind of exposure to process fluids. When too many bolts fail brittlely in a bolted joint, the remaining bolts in the joint can overload and fail suddenly and catastrophically.

Do your operators know about hydrogen embrittlement and how to help avoid it? Do they know what could happen to themselves if they don't follow slow heat up and cool down procedures on heavy wall hydroprocess equipment?

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