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.