The Effects of Induction Heating Conditions on Controlling Residual Stresses in Welded Pipes

Abstract

Induction heating for stress improvement (IHSI) is a method for reducing the tensile weld induced stresses on the inner surfaces of the girth welded pipes. The process entails inductively heating the outside of a welded pipe while cooling the inner surface with flowing water. A 10-in. Schedule 80 Type 304 stainless steel pipe was selected for this study. Residual stresses due to welding were first determined using a finite element computational model. Several IHSI treatments subsequent to welding are then examined computationally to determine the effect of induction coil length and maximum outer surface temperatures on the final residual stress state. All IHSI treatments gave reduced inside surface tensile weld induced stresses on the inner surface. Longer coils and higher outer surface temperatures led to inner surface stresses that were more compressive.

Heat Effects of Welding

“…This is verified by Rybicki and McGuire [423] in continuation of Ref. Provided the process parameters are appropriately selected, it is possible with this method to reduce the longitudinal and transverse tensile stresses at the weld root which enhance the risk of crack initiation or to transform them into compressive stresses.…”

“…146). A further investigation [423] deals with the stress reduction as a result of inductive post-weld heat-treatment (see Section 4.4.3.3.4). The circumferential shrinkage force causes a contraction of the circumferential weld to a reduced diameter, i.e.…”

Characteristics of Residual Stresses Generated by Induction Heating on Steel Plates

“…It is worth noting that induction heating (IH) has been used for localized heat treatment in welded steel pipes to control tensile residual stresses [16][17][18]. Heat treatment with IH commonly is used for pipelines and pressure vessels, which are basically made of thick plates, and it is not generally applied to civil engineering structures, for example, steel bridges.…”

Untersuchung einer mehrlagigen Schweißnaht eines dickwandigen Rohres aus dem austenitischen Stahl X6 CrNiNb 18 10

“…Für die Diskussion der Eigenspannungsverläufe im Bereich der inneren Rohroberfläche der mehrlagigen Einseiten-Rundnaht ist grundsätzlich davon auszugehen, dass sich im Wurzelund engeren Nahtnebenbereich Zugeigenspannungen in Axial-und Umfangsrichtung ausbilden [5,7,17,18]. Dabei geht die etwas größer anzusetzende Umfangsspannung in der WEZ mit zunehmendem Abstand von der Schmelzlinie in Druckeigenspannungen über.…”