Fatigue - Progressive cracking in the base material, weld, or weld zone that is caused by pressure cycling or oscillatory stresses associated with the operation of the system. Girth Weld - Cracks in the weld or weld zone of the butt welds that connect sections of pipe. Seam Weld - Cracks in the weld or weld zone of the longitudinal seam weld of the pipe. Selective Corrosion - A localized corrosion attack along the bond line of electric resistance welds (ERW) and flash welds (FW), that leads to the development of a wedge shaped groove that is often filled with corrosion products.