The Fe-Ni-Cr 800 series alloys, which are commonly used materials of construction in the petrochemical industry, were examined following high-temperature isothermal exposure. Mill annealed alloys were cold worked prior to welding to simulate fabrication conditions. Weldments were tested in the as produced and stress-relieved conditions to evaluate the effect of stress-relief. The levels of alloying additions within the specified chemical composition and variation in grain size were found to greatly influence the properties. Data is presented on the tensile, stress rupture, and microstructural analysis. Further response of various materials to stress relaxation crocking and the remedial heat treatment to avoid potential fabrication related failures are presented.