Carbon steel piping system of secondary side of power plant cooling systems experience severe flow accelerated corrosion (FAC) particularly at elbows where welding is done. Investigation of a number of ASTM A 106 small bore carbon steel pipes received from a power plant indicates extensive damage in the welded vicinity regions. Scanning Electron Microscopy and Fourier Transform Infrared Spectrophotomtery are used to study effects of weldinig on FAC of the carbon steel.