It is about the ring screw thread smoke channel of the boiler shell type gas tube in the boiler field.
锅壳式烟管锅炉烟管内置水管的环形螺纹烟道，它涉及锅炉领域。
Because of the much thick wall of large capacity boiler drum, the pressed and weld longitudinal seam is used to manufacture the drum shell ring.
由于大容量电站锅炉汽包的壁较厚，所以在汽包筒节制造时常采用压制成两个半圆瓦片再焊接而成的方法。
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