Rectangular hollow sections (RHS) are produced in diverse locations internationally to various specifications, predominantly by cold-forming. RHS cold-formed by different techniques have different material and residual stress properties. Hot-dip galvanizing and heat treatment are commonly applied post-cold-forming processes. A comprehensive literature review showed that dedicated research on the effects of these processes on the performances of tubular steel members and connections is insufficient. Also, there is no definitive published guidance on this topic from structural steel associations. In particular, further research on the effects of heat treatment at various temperatures for various durations is needed to ensure a fit-for-purpose process (e.g. improvement of compressive member behaviour) which consumes less energy. This paper reports a comprehensive experimental investigation on the residual stress properties of 26 RHS specimens with different grades (nominal yield strengths from 350 to 690 MPa), cold-formed by different techniques, and subsequently subjected to post-production galvanizing and heat treatments to different degrees.