The premature failure of a high strength low alloy steel (HSLA) pressure chamber has been analysed using standard metallographic and failure analysis techniques. The chamber used in the upper stage of a satellite launch vehicle had a premature failure during routine proof pressure testing. The failure occurred in the welded portion at an internal pressure of 110 bar against a design proof pressure of 165 bar. Investigations revealed welding defects as the origin of failure. The welding defect had grown into a semi-elliptical surface crack during the fabrication process of the pressure chamber, resulting not only in a localised reduction of the wall thickness of the chamber, but also acting as a stress raiser, due to which the chamber had failed at a pressure much below its design level.