Fabrication

DIMENSIONS CONTROL

The following shall be ensured during dimension control activity:

  1. Distance between two weld edges
    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 shall apply to the distance between the non-pressure attachment welds and the pressure-containing weld in order to allow non-destructive inspection of the pressure-containing weld.
  2. Rotation of longitudinal welds
    Longitudinal welds in two adjacent pipes shall be 180° apart, but in any case, shall be separated by at least twice the wall thickness of the thicker pipe.
  3. Location of longitudinal weld
    If the pipe contains a longitudinal weld, this weld shall not be located at the bottom of the pipe after installation. It shall be located at least 45° from the bottom of the pipe.
  4. Dimension control in bending
    If the pipe contains a longitudinal weld, this weld shall be located in the neutral zone of the bend. If the pipe is to be installed horizontally, the longitudinal weld shall be located on the top of the pipe. If one spool is bent in various planes, the longitudinal weld shall be 45° from the top of the pipe.

    Shop butt welds shall be located no closer than the smaller of 75 mm (3 inches) or half the nominal pipe diameter to the tangent line. Shop butt welds located the smaller of 150 mm (6 inches) or one nominal pipe diameter to the tangent line shall require 100% radiographic examination unless the inside diameter is accessible for visual inspection.
  5. Dimension control in piping (corrections)
    1. For carbon steel that does not require PWHT
      The maximum temperature during the alignment corrections shall be 600°C. Temperature-indicating crayons or contact thermometers shall be used to measure the maximum temperature. If crayons are used, a margin of 50°C shall be taken to allow for inaccuracy (reading shall not exceed 550°C). Forcing may be applied if necessary. Cooling in still air shall be applied.
    2. For carbon steel that requires PWHT
      The maximum temperature during alignment corrections shall be the maximum PWHT temperature. If crayons are used, a margin of 50°C shall be taken (reading shall not exceed PWHT temperature minus 50°C). Only heating with local force shall be used, no quenching. The heated area shall either comply fully with PWHT procedure or be post-weld heat-treated.
    3. For 0.5 Mo and Cr-Mo steels
      The maximum temperature during alignment corrections shall be the maximum PWHT temperature. Preferably, contact thermometers shall be used, but crayons may also be used with a 50°C margin. Forcing may be applied if necessary. Cooling in still air shall be applied. Random hardness measurements shall be taken and shall not exceed 248 HV10.
    4. For austenitic stainless steels
      The maximum temperature during alignment corrections shall be 650°C. If crayons are used, a margin of 50°C shall be taken (reading shall not exceed 600°C). Heating duration shall be kept short, and no forcing shall be applied.
  6. Tolerances on length
    Length Distance of any two parallel or crossing centerlines
    < 1.5 m ± 1.5 mm
    ≥ 1.5 m ± 3 mm

    Center to flange face / Flange face to flange face

  7. Wrinkling tolerance
    1. All wave shapes shall blend into the pipe surface in a gradual manner.
    2. The maximum vertical height of any wave shall not exceed 3% of the nominal pipe size.
    3. The minimum ratio of distance between crests to height between crests and valley shall be 12:1.
  8. Lateral alignment of flanges
    1. For standard flanges, free insertion of bolts is sufficient to demonstrate acceptable alignment. Lateral alignment may also be checked with a straight edge at 90° intervals.
    2. The measured lateral misalignment shall not exceed:
      DNMaximum Misalignment
      ≤ 1002 mm
      > 1003 mm
    3. Bolt holes shall straddle the natural centerline unless specified otherwise. Maximum deviation along the bolt circle: 1.5 mm.
  9. Parallelism of flanges
    1. Flange face alignment shall be checked by measuring distances around the circumference at equal intervals.
    2. Parallel misalignment:
      • ASME B16.50 flanges: B – C = max 2.5 mm/m
      • ASME B16.47 flanges: B – C = max 1.75 mm (regardless of diameter)
  10. Flanged accessories
    1. The individual flange face misalignment from the design plane shall not exceed 2.5 mm/m.
    2. The misalignment of two flange faces shall not exceed 2.5 mm/m.
    3. Face alignment of flangeless components (e.g., wafer type control valves) shall be:
      • ASME B16.50 flanges: B – C = max 2.5 mm/m
      • ASME B16.47 flanges: B – C = max 1.75 mm
  11. Nozzle faces on static equipment
    Alignment of nozzle flange face with the indicated plane shall be within 0.5° in any direction.
  12. Flanges connecting to rotating equipment (pumps, compressors, etc.)
    The flange face alignment check shall be performed with the bolting inserted loosely, and the acceptance criteria shall be as follows: