The use of electroslag welding of circular joints in large-diameter thick-walled vessels without zone normalizing has been limited because of the low cold resistance of the welded joints.Various methods of increasing the cold resistance of electroslag welded joints without normalizing are known [I-4], but the development and introduction of means and methods for zone normalizing [5][6][7][8] has significantly broadened the prospects for the use of electroslag welding, particularly in petrochemical equipment construction.The most rational, from the point of view of productivity and energy costs, is the method of combining the operations of electroslag welding and heat treatment in making a single joint, especially when the heat treatment is done in a single rotation of the part at a speed equal to the electroslag welding speed. Under plant conditions it is convenient to use heaters which are located on the outer side of the part. The temperature drop across the wall thickness is the limiting factor in practical use of one-sided heating~ It has been established [7,8] that this requirement is satisfied most fully by induction heating at a line frequency of 50 Hz. Using the known method [9] of calculating throughinduction heating of stee] plates, it may be shown that for the hottest points in local heating the temperature dropA is the depth of penetration of the current into the part metal in cm; h is the ?art wall thickness in cm; X is the averaged coefficient of thermal conductivity of the metal being heated in W/cm-deg; po is the unit power transmitted from the heater to the metal in W/cm2; and ql and q2 are the unit values of thermal losses from the inner and outer surfaces, respectively, of the part being heated, in W/cm 2.The coefficient k h with h/A ~ 1.2, which corresponds to a wall thickness of 80 mm, does not exceed 0.08 (Fig. l). This coefficient characterizes the influence of distribution of internal sources of heat on the temperature drop across the wall thickness.With surface heating, for example, with gas flame heaters or with a sharply expressed surface effect with induction heating, kh = 0.5.The influence of thermal losses may be evaluated having considered two limiting cases. The maximum value of the second term in Eq. (I) corresponds to the case where the outer surface of the heated part is thermally insulated (q2 ~ 0) and the inner does not have thermal insulation (is open), with ql ~ 8 W/cm 2. The second term in Eq. (|) will have a minimum value with q~ = q2, that is, when both surfaces are either thermally insulated or or similarly open.Normally the outer surface is not insulated, but as a result of reflection of energy from the inductors, losses of heat from the outer surface are less than from the inner. The inner surface is difficult to insulate in normalizing a closing joint since access to the inner cavity of the part is difficult.As many measurements under production and laboratory conditions showed, in this case the temperature drop does not exceed ]00~ with a wall thickness up to 70 mm....

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