In structures with a wall thickness of more than 150 mm with single -pass welding, residual stresses with a multi -axis field with a significant value of the components occur. Under these conditions, welded joints can turn into a fragile state.
For such structures, high vacation is necessary to eliminate residual stresses and ensure the performance of products.
In the global practice of the construction of welded boilers and other thick -walled structures, high vacation is considered mandatory in the manufacture of structures with a small wall thickness when laying not only single -pass, but also multi -pass seams. In this case, high vacation is prescribed regardless of maintaining the constancy of geometric forms. Very strict requirements are imposed, in this regard, to welded boiler structures in the GDR, Germany and other countries.
High vacation when welding thick -walled structures, in our opinion, should be considered justified in many cases, but not only to eliminate residual stresses, but also to maintain resistance to fragile destruction, which is not equivalent. In the zones of concentrators when welding elements of large thicknesses, as a rule, the plastic properties of the metal are exhausted. The presence of double -axle and three -axle fields of residual stresses enhances the effect of exhaustion, as a result of which fragile destruction is formed. The use of high leave in thick -walled welded structures in most cases is caused not so much by the desire to eliminate residual stresses, but to increase the plastic properties of the metal to improve its resistance to external forces.
