Process and Servicing



To manufacture LPF Cylinders first sheet is cut to size on cutting machines to make blanks. These blanks are deep drawn on deep drawing power press to two halves of the cylinder. Other parts such as foot ring, backing strip, top ring and turned components are manufactured separately. Both the halves are joined with a backing.

LPG Cylinders are fabricated from LPG grade steel sheets.  A 2500mm X 1250mm X 2.9mm sheet is cut into square pieces as per the capacity of cylinders in a shearing machine.  A circle is cut from these squares using a circle cutting machine.  The circles are then pressed into halves, using Deep drawing hydraulic press.

A foot ring and a valve protective ring assembly, both are fabricated separately, are fixed into cylinders by welding.


As per gas cylinder rules, every cylinder is inspected before filling with LPG every time. The life of cylinder is calculated as 15 years. It is mandatory that a cylinder is to be checked once in every five years. Besides this, if a cylinder needs repair either hot repair or cold repair.

  • Quality Checks
  • Visual hydraulic
  • Pneumatic tests for pressure
  • Stretch and bursting


Cold Repair

Checking, changing of valve and painting of cylinders. It is mandatory that hot repair work can be done only who possess a manufacturing license.  If the cylinder is found to be out of shape or needs repair, it would be sent to nearest cylinder manufacturers considering the transportation cost.

Hot Repair

Hot repairing is a process has to be carried out for LPG cylinders which are:

  1. After 10 years from the date of manufacturing.
  2. If any damages found in the cylinder.

The old damaged cylinders are collecting from Oil Companies against the Work Order given for a limited period. The LPG Valve, VP Ring, 3Stay Plates and Foot Ring of the cylinder are replacing with new during the repair process. The new LPG Valve is supplying from OC’s and the old valves are returning to them with repaired cylinders. The non-repairable/ rejected cylinders are returning to the OC’s after de-shaped.

Process of Hot Repair

  1. Receipt of cylinders

    The cylinders are to be unloaded manually in the stockyard. Cylinder data such as Sl.No, Test Date, Mfr Name, Tare Weight are to be collected at the time of unloading. The unloaded cylinders are inspected by QC and non-repairable cylinders rejecting while inspection.

  2. De-gasing

    The first stage of repairing is degassing. The balance LPG gas inside the cylinders is to be released using a gas releasing adapter.

  3. Valve removal

    The valve of the cylinder is to be removed from the cylinder using an automatic valve removing adapter.

  4. Inside cleaning and washing

    The cylinders are to be filled with water, allow water to overflow until the explosives meter shows zero and remove water to empty the cylinder. Surface of the cylinders are to be washed with soap water and dry the cylinder.

  5. Tare weight checking

    The cleaned cylinders are to be weighed and inspected as per standard IS 13258. The cylinders having tare weight lesser than that in the standard are rejected during this stage.

  6. Removal of VP Ring, Stay Plates and Foot Ring

    The VP Ring, Stay Plates and Foot Ring of the cylinder are to be removed manually using chisel, hammer and hand grinder.

  7. De-denting

    The cylinders are to be de-dented by cold method by pressurizing with water for 25 Kgf/cm2 and hitting with an aluminum hammer to remove dents.

  8. Welding of FootRing on to the cylinder

    The new FootRing is to be welded on to the cylinder manually with 3.15mm welding electrode using a welding machine.

  9. Welding of Stay Plate and VP Ring on to the cylinder

    The new Stay Plate and VP Rings are to be welded on to the cylinder manually and mechanically with 3.15mm welding electrode, 0.8mm & 1.2mm CCMS wire, using a welding machine.

  10. Heat Treatment

    The cylinders are to be heat treated in a furnace as per the set parameters required and to be kept for natural cooling. Furnace oil is using as fuel for firing furnace.

  11. Hydrostatic Test

    The cylinders are to be hydrostatically tested for checking leak.

  12. Grit Blasting

    The cylinders are to be blasted for surface cleanliness in an automatic blasting machine using Steel Grits.

  13. Metallizing

    The cylinders are to be metalized manually to prevent corrosion by spraying Zinc using a metalizing gun. The Zinc used for this purpose is in the form of coiled 3.15mm wire.

  14. Bung thread cleaning & checking

    The thread of the bung is to be cleaned before valve fixing using a ¾” HSS NGT Tap and the thread to be checked with L1 & L9 gauges.

  15. Weighing

    The cylinders are to be weighed and the tare weight to be punched in the stay plates.

  16. Valve fixing

    The new valve supplied from OC’s is to be fitted in the cylinder by a automatic valve fixing machine at a set pressure of 140 lbft. The air is filled in to the cylinder at a pressure of 12 Kgf/cm2 before primer/paint application.

  17. Painting

    The cylinders are to be painted with one coat of Red Oxide Primer and one coat of Signal Red enamel.

  18. Stenciling

    Stenciling on the cylinder to be done as per the drawing given by the respective Oil Companies.

  19. Pneumatic Test

    Pneumatic test is to be carried out for each cylinder for detecting any leak in the cylinder welded joint and for final inspection. The cylinders are dipping in water after filling 12 Kgf/cm2 air inside the cylinder.

  20. BIS inspection and clearance

    The cylinders are to be kept batch wise for BIS inspection carried out by an officer from Bureau of Indian Standards. The passed and rejected cylinders are certified by issuing Test Certificates by the BIS authorities.

  21. Despatch

    The certified cylinders are to be sent back to respective bottling plants along with old valves vide necessary documents such as Delivery Challan, Invoice and Test Certificates.