Fabrication

FIT-UP

a) The fit-up activity can be performed as follows:

  1. The weld fit-up shall meet close tolerances as per the WPS.
  2. Surfaces to be welded shall be thoroughly cleaned prior to fit-up.
  3. Temporary tack welding with the suitable size and shape of small pieces (same grade of base material) in the groove may be done.
  4. Clamps, holding devices, etc., shall be used to avoid tack welding in the groove. If the type of holding device used for the fit-up requires welding onto the structural steel, such temporary attachments shall be made with the same welding procedure specification as for a permanent weld in the structural member.
  5. Alignment of equipment shall remain in use until both the root pass and hot pass are completed. Attachment welding onto the pipe, flanges or fittings is not allowed.
  6. Tack welding shall be as per the AFC WPS. The extremities of the tack welds shall be dressed by grinding. Wherever bridge tack is specified, the tack welding shall not encroach on the root area. Defective tack welding shall be removed by grinding prior to welding of the joint.
  7. All tack welds that will form part of the main weld shall be cleaned and ground down to a feather edge at both ends and visually inspected prior to welding the root pass. Tack welds shall be approximately 50 mm long and spaced so that shrinkage forces cannot cause cracking.
  8. For tack welding, the minimum preheat temperature shall be 50°C and above. Any preheat temperature specified in the WPS for actual welding shall be with a maximum temperature of 150°C.
  9. Temporary tack welds shall be removed by grinding or chipping, and the area shall be ground smooth without reduction of wall thickness.
  10. The minimum distance between the edges of two pressure-containing welds shall be twice the wall thickness of the thicker pressure part. The same requirement applies to the distance between the non-pressure attachment welds and a pressure-containing weld in order to allow the non-destructive inspection of the pressure-containing weld.
  11. Longitudinal welds in two adjacent pipes should be 180° apart, but in any case shall be separated by at least twice the wall thickness of the thicker pipe.
  12. If the pipe contains a longitudinal weld, this weld shall not be located at the bottom of the pipe after installation. It should be located at least 45° from the bottom of the pipe.
  13. Where the spool drawings indicate a “Field Weld” in the pipe, the relevant sections shall be supplied 200 mm longer (minimum) with plain ends.
  14. Misalignment of piping components shall not be more than 1.0 mm or as per the approved WPS. This may be achieved by rotating the pipe. Root misalignment may be corrected by grinding, where the nominal thickness differs. The internal diameter shall be tapered to 1:4.
  15. Where openings for branches are cut in run pipe, all materials that may drop inside the pipe shall be completely removed before the branch line is welded in place.
  16. Branch connection cutouts shall be properly beveled and accurately matched to form a suitable groove for welding, to enable and permit complete penetration of the welds at all points, resulting in a quality comparable to girth welds, in the same piping system.
  17. Weld details for branch weld shall be included in the welding procedure specification. Reference is made to the relevant section of ASME B31.3 / ASME B31.4 / ASME B31.8.
  18. The centerline of the branch connections shall intersect the centerline of the header, unless otherwise specified in the piping drawing.
  19. Nozzle joints shall be “set-on” type, so that the branch connection abuts the outside surface of the run wall.