Tube trailers with large capacity glass fiber wrapped composite cylinders with steel liners have entered the Chinese market to deliver compressed gases since 2011. The tube trailers with the composite cylinders can carry more gases than those with full steel cylinders, and are welcomed by the market. However, the outer surfaces of the composite layers of the cylinders are susceptible to abrasion damages as resin-based glass fiber composites have low surface hardness. Effect of outer surface defects on the large capacity composite cylinders for tube trailers was investigated in this paper using finite element analysis. First, a mesh model of the large capacity composite cylinder without any defects was built according to its actual geometrical dimensions, in which each layer of the composite overwrap was modeled using a layer of solid elements. Second, the meshes corresponding to surface defects with different surface sizes and different depths were killed using element birth and death method to generate surface defects. Then, the models under internal pressure were solved to obtain stress distribution and predict burst pressure. Numerical results show that the surface defects decrease the burst pressure of the cylinders, and the defect depth has a more important effect on the burst pressure than the surface sizes of the defects. Based on the numerical results, three suggestions to deal with the surface defects were proposed: 1) the cylinders having surface defects with depths less than 1 mm can be acceptable, 2) those having surface defects with depths greater than 3 mm should be condemned, and 3) those having surface defects with depths between 1 mm and 3 mm may be repaired but the inspection interval of the cylinders must be shortened.

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