S9074-AR-GIB-010/278
8.5.3 Temperature variation during heating and cooling cycles. During the heating and cooling period, the portion of the weldment being heated shall not vary more than 250°F between the highest and lowest reading. 8.5.4 Holding temperature variation. Holding temperature shall be considered the mean between the highest and the lowest thermocouple readings. Thermocouple readings shall be within the temperature ranges specified for the materials involved: table VI for a ferrous materials, nickel alloys (see 6.4.1). and other alloys as approved. During the holding time at the specified stress-relieving temperature, the maximum temperature difference between any two points on the weldment shall not exceed 100°F. 8.5.5. Preventing oxidation and distortion. During the heating and holding periods the furnace atmosphere shall be controlled to minimize surface oxidation. Flame shall not impinge directly on the weldment for which support shall be provided if required to minimize sagging due to its weight and the effect of high temperatures. 8.5.6 Rate of furnace cooling. Except for materials that are quenched from post-weld heat treatment temperatures, cooling above 800°F shall be done in a closed furnace or cooling chamber at a rate not greater than 200°F per hour. From 800°F, vessel or component may be cooled in still air provided it is protected from inclement conditions and drafts (see 8.5.7). 8-5.7 Special considerations (heating or cooling rates). The rates of heating and cooling need not be less than 100°F per hour. However, consideration of closed chambers and complex structures may indicate the need to reduce loading temperatures and rates of heating and cooling to avoid structural damage due to excessive thermal gradients.
8.5.8 Post-weld heat treatment of titanium and titanium alloys shall be performed in accordance with MIL-H-81200 and the additional requirements of 8.8.
8.6 Post-weld heat treatment procedures (local).
8.6.1 Heating method. Post-weld heating shall be accomplished by electric inductance or electrical resistance devices, or other approved local heating methods.
8.6.2 Heating rate. Holding temperature variation, and cooling rate. The heating rate of localized heating shall not exceed 40*F per 5-minute period. Holding temperature variation and rate of cooling shall be in accordance with 8.5.4 and 8.5.6 respectively. 8.6.3 Postheating piping welds. The width of the circumferential band to be heated shall be at least equal to 3 times the wall thickness, but in no case less than 1-1/2 times the width of the weld face, on each side of the joint. Where a pipe is welded to a valve, the width of the heated zone may be decreased on the value side to a minimum distance, measured from the edge of the weld, equal to the width of the weld face.
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