Published: Jan 1993
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Fracture-mechanics methods have been used to provide a basis for assessing the structural integrity of the all-steel (AISI 4130 grade, 31 HRC) compressed natural gas cylinders used as storage fuel tanks on vehicles. A leak-before-break (LBB) failure mode of the cylinders in the event of fatigue crack growth has been established from the cylinder tests as well as from the analysis. Results indicated a safety factor of 1.3 on the materials' fracture toughness for the LBB performance in the worst operating condition. Length of the leaks varied from 2.6 to 3.5 times the cylinder wall thickness for the single-crack-initiated fatigue cracks. Average growth for internal cracks, pressurized with water, was found to be 1.5 times faster than that of external cracks. Flaws shallower than the 30% of wall thickness were not critical for the subsequent five-year service period.
compressed natural gas, steel on-board cylinders, leak-before-break failure, fatigue crack growth, crack shape development, fracture toughness, allowable flaw size, fracture mechanics, fatigue (materials)
Fracture mechanics specialist, Powertech Labs, Surrey, British Columbia