General Notes for Fabrication of Pressure Vessels

Guideline for Fabrication of Pressure Vessel

  1. Code of Construction of pressure vessels should be noted on Mechanical Datasheet of Drawing.
  2. 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 client before commencing further work
  6. Tolerance for fabrication shall be maintain within limits give by client or as per approved tolerance sheet of client
  7. Tested material should be used in fabrication of pressure vessels
  8. All external weld should be wire brushed and weld spatter should be removed.
  9. Vessel shall be completely cleaned from inside and all dirt,dust,slag etc should be remove before hydro-testing of Vessels.
  10. Vessels shall be dried after hydro-testing.
  11. All internal shall be preferably of removable type and maximum weight of individual piece shall not exceeds 20 kg. unless noted otherwise on mechanical datasheet.
  12. Only qualified welders should be deployed for fabrication of pressure vessels.
  13. Whenever spot radiography specified on drawing it means minimum 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 single plate, large size dish end may be fabricated by joining a plates then this 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 that 30 kg shall be provided with davits and hinges.
  18. All Stainless steel surface shall be acid pickling and passivation from both side s per applicable code. external surface of SS vessel shall be of jacketed equipment’s shall be pickled and passivated before assembly of jacket.
  19. All pressure parts shall be full penetration welded and shall be back-chipped to sound metal and re welded from other side whenever back chipping is not accessible root run shall be done by TIG Welding.
  20. All sharp corner 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 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 vessel shall be located so as to be clear of other attachment and shall be clearly visible from inside after fixing internals.
  25. All horizontal manhole shall be provided suitable hand grip just above the manholes inside the vessels.
  26. 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 surface of non removable internals only, corrosion allowance may not 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’s shall not be contains more than 20 ppm of chlorides.
  33. All bolt hole shall be straddle to principle center lines of pressure vessels or line parallel to them unless otherwise stated.

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.

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