Fabrication

WELDING

  1. The welding consumable shall be controlled as per the manufacturer’s recommendation.
  2. Welding shall be as per the applicable AFC WPS, and the same shall be performed only by a qualified welder.
  3. Work shall not be performed when the weather or degree of protection does not permit satisfactory workmanship. For site welding, adequate shelters shall be provided to protect from wind, rain and moisture. In windy conditions, the pipe ends shall be sealed to prevent through draught.
  4. Weld surfaces shall be thoroughly cleaned and dried before welding. Moisture shall be removed to a minimum width of at least 75 mm on either side of the joint by means of blowers, or in exceptional cases, a torch as specified in the AFC WPS may be used.
  5. Shielding and purging gas shall be as required in the AFC WPS.
  6. Back purging shall be done as given in the AFC WPS. Prior to setup, all hoses and connections shall be checked for leakages. The weld groove containing the purging gas in the chamber between the dams must be sealed from outside.
  7. Minimum preheat temperature shall be in accordance with the design code. Where preheating is not required, the actual minimum ambient temperature expected shall be indicated on the WPS.
  8. Preheating and inter-pass temperature control requirement shall be as per the AFC WPS. Under no circumstances shall inter-pass temperatures exceed 300°C for the carbon steel or 150°C for the stainless steel. The inter-pass temperature shall be monitored by means of thermos sticks or infrared thermometer.
  9. Arc strikes shall be avoided, and if found, shall be ground and the area shall be DPI/MPI examined to ensure defects are removed.
  10. Earthing clamps used for the SS welding in direct contact with the SS materials shall have SS contact surface.
  11. Proper earthing shall be ensured and condition of cables and attachments shall be periodically examined. Any arcing from the poor connection shall be treated as an arc strike.
  12. Welds shall be left as welded and shall not be treated with a flame torch or other mechanical means to change their appearance other than the cleaning and dressing operations specified in the AFC WPS. Welds shall not be peened.
  13. After completion of welding, all surfaces shall be cleaned of spatter, burrs and other imperfections.
  14. Welding of each weld shall be a continuous operation, with the exception of manually welded root runs for submerged arc welding. In case the welding is to be discontinued, this shall take place after the hot pass is completed.
  15. The maximum time that a production weld will remain part welded is 48 hours. The maximum number of heat cycles that will be used in a production weld shall be two. Slow cooling of the weld area shall be ensured. Before continuation of welding, the weld shall be inspected for cracks visually and by MPI. Upon resumption of welding, preheating shall be done in accordance with the approved WPS.
  16. Root penetration of welds on orifice flanges shall be ground flush and smooth.

22 Handbook of oil and gas piping

The following shall be ensured during welding activity:

DOs

DON’Ts