Seawater-cooled metallic heat exchangers used in natural gas processing are prone to corrosion and fouling, resulting in increased operational and maintenance costs. A lab-scale polymer composite gas-liquid webbed tube bank heat exchanger is designed and evaluated for application in conditions representative of a fielded natural gas processing application. The heat exchanger thermal performance and structural integrity are investigated numerically using computational fluid dynamics (CFD) and finite element (FE) models, respectively. For polymer composite thermal conductivities above 20 W/m-K, in forced gas-side convection, the exchanger heat transfer rate is comparable to that of a high conductivity conventional metallic heat exchanger having the same geometry, at reduced materials, manufacturing and operational costs. In addition, the prototype heat exchanger would be structurally reliable at the maximum envisaged gas-side operating pressure for the application considered.