A method for generating steam from a feedwater inlet
stream including impurities is disclosed. The method involves receiving the feedwater inlet
stream at an inlet of a steam generator and causing the feedwater
stream to flow through a tubing circuit to an outlet of the tubing circuit, the tubing circuit having a substantially un-rifled bore defined by a
metal wall. The method also involves delivering a
heat flux to the feedwater stream through the
metal wall of the tubing circuit to generate steam by causing
evaporation of feedwater within the tubing circuit, and controlling at least one of a flow rate of the feedwater stream and the
heat flux to cause generation of an outlet stream at the outlet includes a steam portion and
liquid phase portion, the steam portion being greater than about 80% of the outlet stream by
mass. The steam portion provides sufficient cooling of the
metal wall to maintain a wall temperature at less than a
threshold temperature.