Masashi Ozaki

Effect of Repair Welding on the Creep Rupture Strength of an Aged Weldment

Weldments in high-energy piping of fossil power plants are known to suffer extensive creep damage over the course of long-term operations. Repair welding after the removal of the deteriorated areas is considered as a potential method for improving the life of such weldments. Very few papers, however, are reported concerning the influence on creep rupture behaviour of repair welding performed at the end of the creep life of the weldments. In this paper, creep test of large weld specimens was carried out to create substantial numbers of creep voids, and these specimens were then repair-welded using various methods. On the basis of the results of subsequent creep rupture tests and stress analyses of these test specimens, the influence of repair welding on the creep rupture strength of deteriorated weldments was discussed.

A New Heat Treatment Technology for On-Site Life Extension of High Energy Pipe Weldments Degraded by Creep Damage

This report presents the development of technology enabling temporary countermeasures for the on-site application of life-extending induction heating to high energy pipe weldments having experienced degradation due to creep. The results of an investigation into the cross-sectional structure thus suggested that material life can be extended by the application of regenerative heat treatment. The life-extending effect of regenerative heat treatment is greatest toward the short-life vicinity of the pipes outer surface, thus providing an efficient life extension. The remaining life converted for an actual installation from the result of real scale creep burst test increased from 63,000hrs before treatment to 200,000hrs after treatment, confirming that life can be extended by approximately 130,000hrs.Copyright