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BS 3293 Carbon steel pipe flanges For the petroleum industry

BS 3293 Carbon steel weld neck flange

BS 3293 Carbon steel weld neck flange

BS 3293 Carbon steel pipe flanges Section

1 Scope
This British Standard is a material and dimensional standard only and applies to forged carbon steel slip-on and welding neck flanges of nominal sizes 26 in and larger, for use in the petroleum industry. Drilling, bolting, facing and thickness dimensions are applicable also to integral end flanges of valve and fittings.
Four classes of flanges are provided for, namely Classes 150, 300, 400 and 600.
The standard does not include pressure/temperature ratings; the flange designations quoted are for identification purposes only.

2 Designation and pressure temperature ratings
To facilitate ordering and to ensure interchangeability, flanges in this standard are designated as Classes 150, 300, 400 and 600. These class designations, however, do not imply specific pressure/temperature ratings in the same manner as flanges in accordance with BS 1560. Users shall therefore satisfy themselves that the flanges selected are adequate for the intended duty. Where it is required to use the flanges in this standard at temperatures below – 20 °F reference should be made to BS 3351.

3 Flange facings
For Class 150 flanges, raised facings only are specified. For Classes 300, 400 and 600 flanges, both raised facings and ring-joint facings are specified, and the purchaser shall specify when ordering, which type of facing is required. The 1/16 in high facing is the regular type of raised facing for flanges of Classes 150 and 300, and the 1/4 in high facing is the regular type of raised facing for flanges of Classes 400 and 600.

4 Nominal sizes
The nominal size of a flange as shown in the tables is the same as the nominal pipe size.

BS 3293 Carbon steel pipe flanges Section 2. Materials

5 Materials for flanges
Flanges shall be carbon steel forgings to the following specification, full details of which are contained in BS 1503



British Standard
Comparable A.S.T.M.
BS 1503-161 Grade 32 Class
A or B.
A105 Grade II


Material to BS 1503-161 Grade 28 Class A or B.(A.S.T.M. A105, Grade I) may be supplied if specified by the purchaser

6 Bolting materials
All bolting material shall comply with BS 17501). For pressures and temperatures above 275 psi and 450 °F, bolts shall be of alloy steel in conformity with Part 1 of the above standard, and nuts shall be of carbon or alloy steel in conformity with Part 2.
For pressures and temperatures up to and including 275 psi and 450 °F, carbon steel bolts and nuts complying with Part 3 of the above standard may be used.

BS 3293 Carbon steel pipe flanges Section 3. Dimensions and tolerances

7 Flanges
a) Flange dimensions. Flange dimensions shall conform to those given in Table 1, Table 3,
Table 5 and Table 7. In no case, regardless of the type of facing provided and the tolerances referred to in Clause 7 b), shall the minimum thickness of a flange, as specified in the tables listed above, be reduced in order to provide adequate height for a raised facing or adequate depth for a ring groove, except where a Class 150 or a Class 300 flange is provided with a 1/16 in raised facing, when the height of the facing is included in the minimum flange thickness specified.

b) Tolerances on flange dimensions. The following are the tolerances permitted on flange dimensions.

8 Flange facings and gaskets

a) Flange facing dimensions. Flange facing dimensions shall conform to those given in Table 2, Table 4, Table 6 and Table 8. Raised facings shall be finished in accordance with the requirements of BS 15602). Ring-joint grooves shall be machined true with the face and concentric with the bolt circle and the bore of the flanges. Grooves shall be finished smooth and shall be free from ridges and chatter marks.

b) Tolerances on flange facing dimensions. The following are the tolerances permitted on flange facing dimensions.

c) Gasket dimensions. Dimensions of compressed asbestos fibre gaskets for use with raised facings are given in Table 9. Dimensions of ring-joint gaskets are given in Table 10.
d) Tolerances on gasket dimensions. The following are the tolerances permitted on gasket dimensions:

9 Flange bolting dimensions
The number of bolts, their size and the bolt circle
diameter for each class and size of flange shall be as
given in Table 2, Table 4, Table 6 and Table 8.
Bolt holes shall be pitched evenly around the bolt
10 Spot-facing and back-facing of flanges
Flanges need not be spot-faced or back-faced provided that their backs are parallel, within 1°, to their faces and the fillets of their hubs do not interfere with the full bearing of the fastening nuts.

When spot-facing is required its diameter shall not be less than the dimension across the corners of the appropriate nut plus 1/8 inch.
When a spot-facing cuts into the fillet of a flange its diameter shall not exceed the dimension across the corners of the nut by more than 3/16 inch.
When a flange is back-faced the fillet may be reduced but not eliminated entirely. A sharp corner at the junction of the flange and its hub shall not be permitted.
The specified minimum thickness of any flange whether or not it is spot-faced or back-faced shall not be exceeded by more than the tolerance permitted under Clause 7, nor shall the process of spot-facing or back-facing reduce its thickness at any point to less than the specified minimum.

BS 3293 Carbon steel pipe flanges Section 4. Inspection

11 Inspection

The purchaser or his representative shall have free access, at all reasonable times, to those parts of the manufacturer’s works engaged upon his contract and shall be at liberty to inspect, at any stage of manufacture, the materials covered by this contract. He shall be at liberty to reject any material which does not comply with the requirements of this standard.
NOTE This standard does not make provision for the pressure testing of loose flanges. These may be tested after attachment to pipe or equipment. The test pressure will then depend on the requirements of the Code to which the pipe or equipment has been fabricated.
12 Repair of defects
Defects which do not impair the strength of a flange may be welded by a procedure approved by the purchaser. They shall be cleaned out to sound metal before welding and shall be submitted to the purchaser’s inspector for approval in this condition, after which they may be welded if the inspector so agrees. Such welds need not be heat treated, unless
required by the inspector. When the welding of defects is permitted the welding rod shall be such as to produce a weld having characteristics similar to the parent metal.

BS 3293 Carbon steel pipe flanges Section Section 5. Marking

13 Marking
The following markings are required on flanges covered by this standard:
a) The manufacturer’s name or trade m

b) BS 3293
c) The word “Steel”.
d) Nominal pipe size in inches.
e) On flanges provided with ring-joint facings, the letter “R” followed by the appropriate ring number, this marking being located on the flange edge.

BS 3293 Carbon steel pipe flanges Section 6. Preparation and despatch

14 Preparation
Painting of finished flanges shall be optional to the manufacturer, unless otherwise specified by the
purchaser. Machined surfaces shall be well covered with an approved rust-inhibiting composition.
15 Despatch
Flanges shall be fastened together in such a manner that they are paired and no flange facings remain
exposed. Exposed facings of single flanges shall be protected over their entire surface with a suitable close-fitting
protector securely attached at not less than four points. The type of protector and method of attachment shall be approved by the purchaser. Other methods of preparation for despatch shall be subject to agreement between the purchaser and the manufacturer.

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