What are common failure modes in welded pipes?
Fatigue cracking at stress concentration points. Corrosion-induced wall thinning and pitting. Stress corrosion cracking in specific environments. Weld defects leading to brittle fracture. Erosion-corrosion in high-velocity flow areas.
How is failure analysis conducted on welded pipes?
Visual examination documents failure characteristics. Metallurgical analysis identifies fracture mechanisms. Chemical testing verifies material composition. Mechanical testing evaluates remaining properties. NDT methods assess extent of damage.
What causes stress corrosion cracking in welded pipes?
Combination of tensile stress and corrosive environment. Sensitized microstructures in heat-affected zones. Presence of specific corrosive agents like chlorides or sulfides. Inadequate post-weld heat treatment. Improper material selection for service conditions.
How can fatigue failures be prevented in welded pipes?
Proper design to minimize stress concentrations. Controlled welding to reduce residual stresses. Post-weld improvement techniques like peening. Regular inspection of high-stress areas. Operational controls to limit pressure cycling.
What are the signs of hydrogen-induced cracking?
Step-like cracks parallel to the rolling direction. Delayed cracking after welding or service exposure. Characteristic brittle fracture appearance. Typically occurs in heat-affected zones. More prevalent in high-strength steels.
