Composite materials are resistant to a lot of chemical products such as acids, hydroxides, crude oil, etc. Corrosion resistance against salt and seawater is excellent.
Steel structures typically require periodic maintenance such as conservation and paint systems to prevent corrosion. Composites are not susceptible to corrosion resulting in lower Life-cycle costs.
Though composite materials themselves are slightly more expensive than metals, combining properties such as insulation and weight savings often results in a cost effective product.