Controlling Mechanism of Local Rapid Cooling Heat Treatment to Reduce Internal Cladding Residual Stress of Pressure Vessels

Vollständiger Abstract

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Abstract Due to different material parameters between the cladding layer and the base metal, significant tensile residual stresses still remain within the internal cladding layer after traditional heat treatment, seriously affecting the service safety of pressure vessels. Local rapid cooling heat treatment is an effective method to reduce the tensile residual stress in the cladding layer until a compressive stress state is achieved. In this paper, the influence of local rapid cooling heat treatment process parameters on the effectiveness of residual stress reduction was analyzed. Local rapid cooling heat treatment is more effective in reducing residual stress than conventional heat treatment. As the rapid cooling start temperature increases, the cooling rate increases, and the rapid cooling end temperature decreases, the effectiveness in reducing residual stress within the welding layer of strip clad welding structure improves. A mechanical model clarified the basic mechanism that local rapid cooling heat treatment reduces residual stress in the cladding layer through the contraction effect of the base metal during the cooling process. Theoretical analysis indicated that the control effect is related to the temperature difference of the base metal. And the influence of process parameter changes on the temperature difference magnitude is consistent with the change in control effect, which confirms the validity of the conclusions derived from finite element analysis.