Process analysis of high-pressure upper tube box using medium frequency induction heating machine for stress relief annealing

High-pressure scrubber is one of the key equipment of large-scale urea plant. The high-pressure upper pipe box is an important component of the high-pressure scrubber. Its manufacturing process is as follows: plate re-inspection, hot pressing, scribing, turning longitudinal seam grooves, one group welding and one scribing line, and turning top grooves, one group welding the top One set of groove welding, one top flange, one scoring and boring, one set of welding manholes, etc. One first stress relief annealing, one hemisphere inner surface stack welding, one second stress relief annealing, one stack welding, one turning lining part and equator A set of welding linings for the circumferential groove, a set of upper and lower hemisphere welds, a third stress relief annealing, and a hydraulic test. The annealing process is mostly carried out by medium frequency heating furnace, and the effect is very good.

1. After the first stress relief annealing, after the welding of hemispherical longitudinal seams, flanges, manholes and other components, a medium frequency induction heating machine should be used for stress relief annealing heat treatment before surfacing of large area strips, with the heating temperature being 560°C.

2. For the second stress relief annealing, stress relief annealing is performed after the radius is overlayed, and the heating temperature is also 560°C. The heat treatment workpiece is subjected to surface sandblasting treatment, and at the same time, ultrasonic thickness measurement, coloring thickness measurement inspection, and ferrite content measurement are performed. The ferrite content (volume fraction) should be ≤3%.

3. The third stress relief annealing - circumferential seam annealing. The weld after the upper and lower hemispheres are assembled is the final weld and requires stress relief annealing. For the surface layer of X2CrNiMo25-22-2 type urea corrosion resistant stainless steel surfacing, the maximum heat treatment temperature is 570℃, otherwise the corrosion resistance will be reduced. The use of medium frequency heating furnace can reliably control the maximum temperature at (530±10 ) ℃, there will be no overheating problem of the surface layer.

This article briefly introduces the stress relief annealing process of high-pressure upper tube box. I hope it will be helpful to your work. If you don't understand anything, you can read more books on heat treatment. I believe you will gain a lot.