The determination of the hardness of 5, after heat treatment, the hardness of the elbow part shall not exceed the prescribed value of parent material hardness.

Heat treatment after welding, pipe two:
1, pipeline welding, according to the steel hardenability, considering the thickness of welding and using conditions, according to the requirements of the drawings or specified in Table 3 of post weld heat treatment.
2, pipeline welding joints of heat treatment after welding, the general should be timely after welding, for easy to produce welding welded joint crack delayed, if post weld heat treatment is not timely, cooled to 300-350 DEG C after welding (interval or heating to the temperature of heat preservation), 4 - 6h slow cooling, heating range and heat treatment after welding the same.
3, post weld heat treatment by crawler or ceramic heater, temperature detection according to different requirements, using pencil and thermocouple, heat preservation material used for aluminum silicate needled insulation blanket, thermal insulation in the weld width from R date on each side of not less than 5 times of the pipe wall thickness.
The heating range 4, heat treatment after welding to weld center; as a benchmark, each side should not be less than 3 times the width of the weld, and not less than 60mm.
5, post weld heat treatment heating rate, time of constant temperature and cooling rate, shall comply with the following provisions.
(1) the heating rate. Heating to 3O0 deg.c, heating rate should not exceed 220 * 25.4/ delta C / h (Delta as the wall thickness, mm), and not more than 220 DEG C / h.
(2) the time of constant temperature, carbon per mm wall thickness is 2 - 2.5mm; alloy steel per mm wall thickness is 3min, and not less than 30min.
(3) cooling (cooling) rates drop; constant temperature, cooling rate shall not exceed 275 * 25.4/ delta C / h and not more than 275 DEG C / h. 300 degrees below the natural cooling.
Heat treatment 6, dissimilar metal welded joints after welding, determined by the composition of the alloy is lower side of the metal, the heat treatment temperature does not exceed the critical point of AC1 steel under the.
7, after postweld heat treatment, the hardness value of welding heat affected zone of the weld and base material: steel should not be more than the parent material of carbon steel l20% cable, Taiwan should not be more than the parent material of l25%, when the hardness more than regulations, should be re heat treatment, and must make the determination of the hardness. Hardness test position. Each weld is not less than l, the test of weld and heat affected zone and base metal each three points, when the tube diameter is larger than 57 mm, check the heat treatment weld number more than 10%, when the tube diameter is less than or equal to 57mmS, check the heat treatment weld number more than 5%.
Heat treatment conditions Table 4 common elbow
Table 5 common pipe hot bending temperature and day treatment conditions