[vcx]

considering taken in selection and design of materials for a practical application. for example choices leading to selection of  metal as the appropriate type of material for construction of a commercial gas cylinder are strength, ductility and cost of the material, what other criteria have to think about before use it for practical application? what other example of practical application?

[Bakegaku]

Reactivity/resistance to corrosion would be important and depending on the application of the gas cylinder (I.E. whether it's being used just to store the gas or to transport it) density may be an issue.  Appart from that I'm not sure what other main properties would be taken into account.  How did you come up with ductility?