Guidelines for Fabrication of Pressure Vessels

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Guidelines for Fabrication of Pressure Vessels

In this post, we are discussed what are the guidelines for fabrication of pressure vessels. we listed some guidelines or general notes on the fabrication of pressure vessels, So let’s learn,

  1. The Code of Construction of pressure vessels should be noted on the Mechanical Datasheet of Drawing.
  2. The latest applicable Code of Construction Shall be made in all aspects.
  3. Design and fabrication drawing should be approved by the client before starting of fabrication of pressure vessels
  4. Thickness Indicated on fabrication Drawing hall be minimum thickness and shall be achieved after fabrication or Machining
  5. Any change in thickness on higher side shall be acceptable but written approval shall be taken by the client before commencing further work
  6. Tolerance for fabrication shall be maintained within limits given by the client or as per approved tolerance sheet of the client
  7. Tested material should be used in the fabrication of pressure vessels
  8. All external weld should be wire brushed and weld spatter should be removed.
  9. The vessel shall be completely cleaned from inside and all dirt, dust, slag, etc should be removed before hydro-testing of Vessels.
  10. Vessels shall be dried after hydro-testing.
  11. All internal shall be preferable of removable type and the maximum weight of individual piece shall not exceed 20 kg. unless noted otherwise on the mechanical datasheet.
  12. Only qualified welders should be deployed for the fabrication of pressure vessels.
  13. Whenever spot radiography specified on drawing it means a minimum of 10% radiography of longitudinal and circumferential seam joints and full radiography of all ‘T” Joints.
  14. Nozzle neck shall be from seamless pipe and Nozzles fabricated from plates shall be 100% radiography of Weld seams.
  15. Dish ends generally be made from a single plate, a large size dish end may be fabricated by joining plates then these joints shall be 100% radiography after forming, Joint location, and details indicated on fabrication drawing & “T” Joints re to be avoided.
  16. Internal Coils, Suction heater, and external limpet coil shall be separately hydro-tested hen main vessel is not under hydro-tested.
  17. All manhole Cover or blind flange weighing more than 30 kg shall be provided with davits and hinges.
  18. All Stainless steel surfaces shall be acid pickling and passivation from both side s per applicable code. the external surface of the SS vessel shall be of jacketed equipment shall be pickled and passivated before the assembly of the jacket.
  19. All pressure parts shall be full penetration welded and shall be back-chipped to sound metal and re-welded from the other side whenever back chipping is not accessible root run shall be done by TIG Welding.
  20. All sharp corners shall be rounded up to 1/8″ or 3 mm radius minimum.
  21. All Nozzle neck of size greater than or equal to 50 NB shall be stiffened by 2 nos. of 40 mm wide and 5 mm thick gusset located at 90 Degree apart.
  22. All Nozzles reinforcement pads and SORF flanges shall be provided with 1/8″ NPT “T/T” holes at the lowest location and shall be tested pneumatically t 1.05 kg/cm2 using soup solution for leak detection.
  23. Vent holes shall be plugged with hard grease after testing.
  24. weld seam in the vessel shall be located so as to be clear of other attachments and shall be clearly visible from the inside after fixing internals.
  25. All horizontal manholes shall be provided a suitable handgrip just above the manholes inside the vessels.
  26. The backing strip used for welding shall be completely removed from inside the vessels.
  27. All plates/forging having thickness greater than 20 mm shall be 100% Ultrasonically tested as per the applicable standards.
  28. For Tongue and Grooved flanges, Groove shall be on nozzle flanges attached to vessels.
  29. When Vessel is dispatched in section or pieces. the pieces shall be perfectly match marked for ease of assembly at site.
  30. Corrosion allowance shall be provided on all wetted surfaces of nonremovable internals only, corrosion allowance may not be provided on removable internals.
  31. Only Clean Potable water shall be used for hydro-testing.
  32. Water used for hydro-testing of Stainless steel equipment shall not contain more than 20 ppm of chlorides.
  33. All bolt hole shall straddle to principle center lines of pressure vessels or a line parallel to them unless otherwise stated.

These all are Guidelines for fabrication pressure vessels and it should be followed by all fabricators during pressure vessel fabrications in day to day fabrication activity.

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Imran Pinjara

Author of Book " Master in Fabrication Layout Development " Published worldwide. Founder and CEO of Let'sFab Educational Services. More than 8 Years of Professional Experience in Field of Pressure Vessel, Heat Ex changer, Storage Tanks, Piping and other Process Equipment Fabrication Industry. He had worked in many Fabrication Industry from small workshop to MNC Company. He had Completed PGDM in Process Piping Design and Engineering as per ASME B31.3 and Bachelor of Mechanical Engineering.