Example:
In the flanges of this equipment, a 1 mm tolerance and 1 mm corrosion margin have been indicated, but in the calculations, the thickness "corroded dimensions" only subtracts 1 mm, for example, flange 20.04, nominal thickness 40 mm, calculation thickness 39 mm (should be 40 - 1 - 1 = 38mm).
On the other hand, the body is made of tube and the 7/8 (12.5%) tolerance is applied in the calculation of the cylinder but not in the nozzles, for example, in the calculation of N4, diameter of the opening is 60.3 mm, thickness 5.54 mm and 1 mm corrosion margin so in the dimensions of the table the UG-40, the diameter "d" should be 60.3 - 2*(5.54*7/8-1) = 52,605 mm but in the calculation it appears 60.3 - 2(5.54 - 1) = 51.22 mm.
Also, shouldn’t the software take into consideration the corrosion allowance? Since the flange will have corrosion before the gasket, its like when the detail has a male-female face and the software subtracts the thickness of the face from the thickness on the bolt.
Answer:
- For a flange there is no corrosion at the level of the bolt circle since it is above the gasket, only the tolerance is applied in this part.
- As per ASME UG-37(a) the tolerance is not applicable
- Furthermore,
See below the thickness of the flange (e) to consider for the stresses checking as per Pressure Vessel codes.The local reduction in thickness under the gasket is ignored, the thicknesses are always those measured under the gasket and at the level of the bolting.