Effect of surface roughness and coating alternatives of seawater pipes on energy efficiency of ships

Abstract

Carbon steel seawater piping in marine vessels is susceptible to corrosion resulting in the application of various coatings to reduce the corrosion rate and extend the life of the piping. Typically, coatings are selected primarily on the basis of corrosion protection without considering energy losses related to the friction of the resulting coated surface. Galvanizing is the most common method of coating seawater piping on marine vessels; however, galvanizing increases the internal pipe roughness and consequently, pressure drop, and energy consumed in pumping. This study determines the potential energy savings by comparing polyethylene coating to galvanized coating on marine vessel piping systems. The comparison was performed using both analytical and computational methods for the case of the reference vessel system. The energy savings for polyethylene coatings indicated between a 33% and 44% percent energy savings for pipe, without considering the fittings, depending on the Reynolds number of the flow. Energy saving for the pipe with fittings was obtained using CFD since there is no data for polyethylene coated fittings and found slightly lower because turbulence and eddies contribution to head losses. Results of the analytical study were further verified using Computational Fluid Dynamics (CFD). The reduction in carbon emissions per year is then quantified to be around 20 tons. In addition, when deterioration of galvanized steel pipe is considered, the amount of emission reduced increases every year till reaching 40 tons/year after five years of operation.