D1 & D2 = ± 1%
D3 = ± 1 mm
D4 = 0/-0.4 mm
L = ± 0.1 mm
N = see note 6
P = ± 0.1 mm
S = ± 0.1 mm
T = see note 2
The Upstream side of the orifice tab shall be stamped at the indicated locations with:
- the word UPSTREAM
- the Tag Number
- the ASME flange class, followed by RF
- the nominal pipe size (NPS)
- the measured orifice D1 (in mm)
- the material of the orifice plate
- the type of orifice plate (Square, Restriction etc.)
Letter height approx. 4 mm
- Welding of tab
Tab may be integral with orifice plate up to and including 7 mm plate thickness.
In other cases full penetration joint to be applied.
- Finish of plate
The upstream and downstream faces of the orifice plate to a diameter equal to D3 shall have a surface roughness Ra ≤ 0.8 µm according to ASME B46.1.
The remaining annular part (between D4 and D3) of upstream and downstream faces shall have a surface roughness Ra between 3.2 and 3.6 µm according to ASME B46.1. This finish shall be obtained by machining with a round nosed cutting tool having a 0.8 mm radius at a feed rate between 0.35 and 0.45 mm per revolution.
The centre of the orifice shall not differ from the centre of the plate by more than 0.1 mm for ≤ NPS 8 and 0.2 mm for > NPS 8.
- Finish of throat
The throat and outlet cone shall have a surface roughness Ra ≤ 0.4 µm according to ASME B46.1.
All edges shall be sharp and free from burrs, so that when viewed with the naked eye no light is reflected by the corners.
- Plate thickness
The difference between any two measurements of plate thickness, for annular part D1-D3, shall not differ by more than 0.001 DN in mm.
The plate shall not depart from flatness along any diameter by more than 0.01 D3.
Tolerance for N shall be:
N ≤ 6 mm +0.1/-0.25 mm
N > 6 mm +0/-1.5 mm
Thickness for annular part D3-D4, may be slightly less, max 0.05 mm, due to surface finishing difference between D1-D3 and D3-D4. (see note 3)
- Dimensions are in millimeters unless otherwise indicated.
- Allowable pressure difference 20 bar for temperatures up to 400 °C and D1/D3 ≥ 0.1. The thickness of the plate needs to be verified for strength in case the pressure difference is higher than 20 bar and/or the temperature is beyond 400 °C. Based on the outcome of the calculation the thickness of the plate needs to be adjusted.
- DIA D1 & DIA D2 - to be specified by purchaser.
- Material to be specified by purchaser.