Flange Processing and Connection

① Flange pressure contact surface should be gold processing, in order to prevent welding deformation, flange contact surface depth should be recessed into h = (0.10 ~ 0.20) t, to provide the amount of deformation. 

② Steel pipe intersecting line weld seam fillet weld, multi-layer welding, welding should be continuous, each weld surface should be promptly cleaned, if found to be defective in quality, should be eradicated after welding.

③ Flange pressure contact surface unevenness should be less than or equal to ± 0.20mm, in order to ensure the flange connection, the contact surface fit rate greater than or equal to 75%, with 0.4mm feeler inspection, the depth of the insertion area and the sum of not more than 25% of the total area, the maximum connection gap shall not be greater than 0.8mm. 

④ Outer diameter of flange plate machining ovality less than or equal to 0.03 ~ 0.1mm (according to 11 tolerances) considering the influence of oval tolerance of steel pipe, flange diameter machining amplification allowance is + 0.4 ~ 1.0mm, ID angle weld groove greater than or equal to 45o, groove height h ≥ 0.7t.

Flange bolt hole diameter greater than or equal to less than or equal to M16, 1 ~ 1.5mm, greater than M16, 2mm. Screw hole indexing tolerance should be less than ± 0.2mm, to ensure 100% perforation rate. Flange plate reinforcement in the pipe and flange on the weld, the ribs should be made into a chamfer, when the chamfer into 45o, the chamfer width of 1.2hf (hf for the weld height), that is cut angle for welding foot. High 1.2 times. Flange connection using ordinary bolts or high strength bolts, ordinary bolts with a single nut plus spring pad locking.