The article describes design features of sectional BB4 and double case BB5 pumps according to the API 610 requirements applied in water injection systems in order to maintain the reservoir pressure during oil production. The pumps considered are CNSp240-1422 and CNSDp240-1422 produced by HMS Group. Design optimization of casing parts is conducted by means of Finite Element Analysis in order to minimize the mass. The optimization criteria are a static strength and stiffness, and the corresponding results of strength calculation are presented.