Operators often have to make field attachment of weld neck flanges to pipe in order to complete field assembly of pressure systems. To facilitate the fit-up of field welded, flanged equipment, flanges must have parallel orientation at the time of attachment. And, unless engineering considerations require otherwise, flanges at opposite ends of pipe should have the same bolt hole orientation as well. See the illustration below for a suggested setup for installing or checking the installation of weld neck flanges on straight pipe using a carpenter’s level. 

The following outline of steps supported by the above illustration will provide a useful guide to set-up or check field-fabricated units of straight pipe with 2 weld neck flanges.

  1. Obtain a good quality carpenter’s level that can check vertical as well as horizontal orientation.
  2. Position the pipe (or body) in a stable, level orientation. Check with the carpenter’s level as illustrated.
  3. Position, or check, vertical orientation of both end flanges using the carpenter’s level, as illustrated.
  4. Using two equal diameter pins located in two adjacent bolt holes, orient the flange on one end so that the carpenter’s level resting on the pins indicates level. Move the pins and level to the opposite flange and, without any rotation of the pipe (or body), position or check the orientation of the holes in the second flange in the same manner as the first. The level should indicate level while resting on the pins on both flanges without any rotation of the body.
  5. Rotate the pipe (or body) 90°, check both flanges again for vertical orientation. This step will assure parallel flange faces.
  6. Visually inspect the external weld surface for uniform appearance, and inspect the internal area for excessive burn through or lack of full penetration.

All  checks made with a level in the field have an approximate nature, so fabricators must take care to execute careful craftsmanship.1

Operators should always use Qualified Welding Procedures, supported by Procedure Qualification Records, performed by Qualified Welders, on flanges and pipe of known material chemistries. Flange weld necks and pipe diameters, O.D. and I.D., should match. Successful, safe use of API Weld Neck Flanges requires sound full penetration welds. 

For more information see: About Weld Neck Flanges. 

1 Words in bold italic indicate they have subjective meaning and persons using this information must use experience to improve the reliability of their judgement when the meaning of these words can have impact on performance

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