Effects of Post Weld Heat Treatment on Mechanical and Electrochemical Properties of Welded Carbon Steel Pipe

To prevent a failure caused by stress corrosion cracking (SCC) of welded carbon steel pipe in district heating systems within service life, the effects of post weld heat treatment (PWHT) on the mechanical, electrochemical properties and resistance of SCC were investigated. As the result of normalized treatment, Vickers hardness, yield strength and tensile strength decreased, but ductility increased. Electrochemical properties were evaluated using potentiodynamic polarization tests and electrochemical impedance spectroscopy. Uniform corrosion was observed on all specimens, although the corrosion rate was slightly increased by PWHT. The resistance of SCC was evaluated using slow strain rate test under the accelerated corrosion condition. The resistance of SCC was increased by PWHT, especially by normalized treatment. If the reduced strength by PWHT satisfies the design stress, it is possible to decrease the probability of failure within service life in welded pipeline by normalized treatment.