Effect of laser shock processing on sulfide stress corrosion cracking of X70 pipeline steel welded joint

Laser shock processing (LSP) is a new technique for metal surface strengthening by which residual compressive stress in the superficial layer can be induced to greatly improve the stress corrosion resistance property. The effect of LSP on sulfide stress corrosion cracking (SSCC) of X70 pipeline steel welded joint has been studied in this paper. A convergent lens is used to deliver 20 J, 20 ns laser pulses by a Q switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 3 mm onto samples. The power density of laser at the surface of the sample was about 5 GW/cm2. The surface residual stress level after LSP is much higher than before. SSCC behavior of X70 pipeline steel welded joint was investigated using slow strain rate testing (SSRT) in H2S solution. Morphology of X70 pipeline steel fracture surface was observed by scanning electron microscope (SEM). It has been demonstrated that LSP is an effective surface treatment technique to improve the stress corrosion cracking (SCC) resistance properties of X70 pipeline steel welded joints.