This paper presents the results of laboratory tests which simulated the effect of repeated cycles of heating and cooling of a spot on a catalytic-cracker regenerator shell. A specimen was made to resemble in all feasible respects a 6-ft-square piece of a cylindrical shell of a regenerator, including welded seams and vapor stops. After 50 cycles of heating to 900 F at the center of the spot for 1 or 2 days, then cooling to near room temperature, the plate was radiographed, its microstructure examined, and its mechanical properties determined. No evidence of cracking or of deterioration of the metallic structure was observed. Some distortion was produced by the first few cycles of heating but continued cycling did not produce further distortion.