Factors that Contribute to Pressure Vessel Failure

December 13, 2019

Engineers just have to look at the latest pressure vessel rupture alerts to see how serious this issue has become. To combat the dangers, investigative teams are assembling. They trek to the source of recent failures to examine the damage, to determine the causative factors that are shared by the various accident sites. Their goal is to compile an investigative report, one that'll eventually cause a dramatic fall-off in vessel accidents.

Pressure Vessel Failures: Frequent Root Causes

Onsite, cyclical stress is a recognized contributory factor, with fluid stresses causing metal sheets and weld seams to bulge then contract. However, modern design strategies understand cyclical stress, and they incorporate mechanisms and materials that offset this effect. Forced to track the flaw further back, perhaps as far back as the original design facility, the investigators take this opportunity to study a fabrication company's quality-assurance policies.

Assessing Design Method Shortcomings

Generally speaking, a weld has failed or a sheet metal part has developed a crack. The cracks propagate, the weld deteriorates, and then a catastrophic vessel breach ensues. An error in the heat zone welding methodology may have transpired. Perhaps the pressure vessel architecture lacks internal supports. Done with the assessment of the fabrication company, the head investigator reviews a list of possible failure factors:

• Weld metal crack initiation
• Absorbed hydrogen embrittlement
• Thermal aging
• Exposure to corrosive atmospheres
• Environmental factors

Weldment flaws and sheet metal discontinuities top the list of common pressure vessel crack-inducing determinants.

Examining Crack Qualities and Propagation Patterns

Plasticity declines occur in austenitic steels when high heat-flux regions absorb hydrogen during a welding procedure. The single-atom element is also introduced when water and chemical levels alter, to the point that acidic salts weaken a vessel's steel lining. Even a change in the pH of a pressurized container can cause hydrogen embrittlement. By closely inspecting a crack propagation pattern, we can determine whether the cause is inter-granular fracturing, corrosive or fatigue cracking, or whether the tiny fissures were abetted by a serious case of hydrogen embrittlement. In acquiring this data, it serves as a set of engineer-interpretable fingerprints.

Cracks commonly spawn catastrophic pressure vessel accidents. Consequently, investigators are trained to differentiate the various types of surface fissures so that this factor can be tagged with a likely originating fault source. Blisters are also found on the steel receptacles. They form when hydrogen decarburization occurs in austenitic steel sheets. Of course, there are weldment discontinuities to assess as well. These joints are where the bulk of the stress develops, so a hard inclusion can really give rise to a containment system weak spot.

Contact Details

Fusion - Weld Engineering Pty Ltd
ABN 98 068 987619

1865 Frankston Flinders Road,
Hastings, VIC 3915

Ph: (03) 5909 8218

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