GAS CYLINDER
A gas cylinder or tank is a pressure vessel used to store gases at high pressure. Gases stored this way are called bottled gases.
DESIGN PROCESS
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MANUFACTURING PROCESS OF TRANSPORTABLE REFILLABLE WELDED STEEL CYLINDERS FOR LIQUEFIED PETROLEUM GAS (LPG)
SPECIFICATION :
EN 1442 : 1998 / A2
“Transportable refillable welded steel cylinders for liquefied Petroleum Gas (LPG) – Design and construction.”
PRODUCT :
Two-piece transportable refillable welded steel cylinders for liquefied Petroleum Gas (LPG) of water capacity 26.2 litres as per EN 1442 : 1998 / A2 (latest)
RAW MATERIAL
a) Body (shells & end pressings)
The steel used in the manufacture of LPG cylinders shall conform to EN 10120 latest (steel P265NB or P245NB). It may either be in coil form or sheets of required size.
The manufacturer provides a test certificate covering all applicable requirements (ladle analysis and mechanical properties) of EN 10120 for each cast of material supplied. Alternatively check analysis is got done from NABL approved laboratory for chemical and mechanical properties.
b) Footring
The steel used in the manufacture of footrings shall be of weldable quality and compatible to the body material and shall conform to IS: 1079 latest or equivalent.
c) Bung / Valve boss or pad
The steel used in the manufacture of bung / valve boss or pad shall be of weldable quality and compatible to the body material and shall conform to EN 10028-3 latest or equivalent.
d) Valve Protection Collar
The steel used in the manufacture of valve protection collar shall be of weldable quality and compatible to the body material and shall conform to IS: 1079 latest or equivalent.
DECOILING & ROTARY SHEARING (For Steel in Coil Form)
Prior to cutting, a batch no. and colour code is assigned to each cast of steel from same supplier and a record is maintained indicating details of cast, quantity, weight, production & rejection details on stage-wise basis.
The coil is decoiled and circles of desired diameter are directly sheared on the automatic decoiling & rotary shearing line in a continuous and automatic manner. Colour code of batch assigned is marked for identification. 100% visual examination of circles is carried out for any surface irregularities and randomly checked for dimensions and recorded.
SHEARING (For Steel in Sheet Form)
The sheets are cut on the shearing machine to form squares of desired size. Colour code of batch assigned is marked for identification. 100% visual examination of squares for any surface irregularities is carried out and 5 pieces are checked for dimensions and recorded.
CIRCLE CUTTING (For Steel in Sheet Form)
The squares so obtained are cut into circles of desired diameter. Colour code of batch assigned is marked for identification. 100% visual examination of circles is carried out for any surface irregularities and 5 pieces are checked for dimensions and recorded.
DEEP DRAWING OF HALVES / DOMED ENDS
The circles are cold deep drawn on 200+100 T double action hydraulic press to form halves / domes.
TRIMMING
Immediately after draw, the irregular edge of the halves is trimmed to desired height to suit the water capacity. 100% visual inspection of halves is carried out and 5 pieces are checked for height and water capacity at the start of production. Colour code of batch assigned is marked for identification.
BUNG HOLE PIERCING
A hole of diameter suitable to the bung / valve boss or pad size is pierced on the upper half in its centre on a hydraulic press.
DEGREASING / WASHING
The halves are fed on the conveyorised washing line and water is sprayed through jets to wash them.
HALVES INSPECTION
The washed halves are inspected visually (100%) for surface irregularities and dimensional checks (5 pieces at the start of production & randomly) and records are maintained. Colour code is maintained for the batch for identification and segregation.
BUNG WELDING
A clean and inspected bung is inserted in the upper half and mounted on the automatic bung welding fixture and welding is done by MIG / MAG process using 1.2 mm copper coated mild steel wire and Ar-CO2 mixture (92:8) or CO2 with single/two runs of welding with overlap. The bung welded halves are checked visually for any welding defects.
Welding Procedure Specification (WPS) No.: 02/2005 is followed for welding parameters.
JOGGLING
The bung welded halves are joggled on the hydraulic joggling machine.
FOOTRING WELDING
Clean and inspected footring is welded to the lower half by MIG / MAG welding process using 1.2 mm copper coated mild steel wire and Ar-CO2 mixture (92:8) or CO2 on automatic footring welding machine. Alternatively, footring welding may be carried by MMAW process. The footring welded halves are checked visually for any welding defects.
Welding Procedure Specification (WPS) No.: 03/2005 is followed for welding parameters.
ASSEMBLY
The upper (bung welded & joggled) and lower (footring welded) halves are assembled together to form assembled cylinders on the assembly fixture. Care is taken to ensure proper cleaning of halves from inside and that the assembly is free of offset all around.
CIRCUMFERENTIAL WELDING
Prior to circumferential welding, the joint of the assembled cylinder is cleaned / buffed by motorized wire brush to remove any dirt or rust on the area to be welded to avoid defects in welding.
The assembled cylinder is circumferentially welded by MIG process using 1.2 mm copper coated mild steel wire and Ar-CO2 mixture (92:8) with single run of welding with overlap. Alternatively, submerged arc welding process with two runs of welding with overlap may also be done. The circumferentially welded cylinders are checked visually for any welding defects.
Welding Procedure Specification (WPS) No.: 01/2005 is followed for welding parameters.
VALVE PROTECTION COLLAR WELDING
Clean and inspected valve protection collar is welded on outside on the cylinder concentric to the bung by MIG / MAG process using 1.2 mm copper coated mild steel wire and Ar-CO2 mixture (92:8) or CO2. Alternatively, valve protection collar welding may be carried by MMAW process.
Welding Procedure Specification (WPS) No.: 04/2005 is followed for welding parameters.
After all the welding operations are completed, the cylinders are inspected for all welding and dimensions such as total height of cylinder, concentricity of valve protection collar with respect to bung, straightness of cylinder, etc. Defects, if any, are identified and remedial actions are taken.
Cylinders found satisfactory in all respects are allotted Serial number and these are punched at the space provided.
HEAT TREATMENT (STRESS RELIEVING OR NORMALIZED)
Cylinders are heat treated to remove the stresses developed in the parent metal due to deep drawing (forming) and welding in a oil fired continuous type furnace at a temperature of 680 ± 20° C for 42 minutes each. A record of the furnace temperature and time throughout the heat treatment cycle is maintained on graph. Cylinders may be normalized also, depending upon customer requirement, at a temperature of 910 ± 20° C in a continuous type oil fired furnace.
WATER CAPACITY
After heat treatment, 1% of the cylinders are checked for volumetric capacity requirement. Water capacity can be checked either by Difference of weight method on electronic weighing scale or by Volumetric method with the help of calibrated jars & cans.
HYDROSTATIC TEST
Hydrostatic test is essentially to be done on each and every cylinder. Each cylinder is filled with water & subjected to a hydraulic pressure of 30 bar (3 Mpa) for a period of not less than 30 seconds and checked for any leakages after drying the surface of cylinder (if required). Record of Hydrostatic test is maintained.
SHOT BLASTING
After hydrostatic test, the outer surface of the cylinders is thoroughly shot blasted to remove scales and to obtain a clean surface.
METALLIZING / ZINC COATING
One coat of zinc is sprayed uniformly on the shot blasted cylinders to provide protection against rusting. Minimum coating thickness of zinc should be 40 microns. 2% checking of coating thickness is done and records maintained.
PRIMER & PAINT COATING
One coat of zinc chromate red oxide primer followed by one coat of super synthetic enamel paint is applied on the cylinder. Minimum coating thickness after painting should be 70 microns. 2% checking of coating thickness is done and records maintained.
SCREEN PRINTING ON CYLINDERS
After painting, cylinders are screen printed as per approved drawing. The requirement of screen printing varies from customer to customer.
INTERNAL CLEANING
Each cylinder is thoroughly cleaned from inside and dried.
INTERNAL VISUAL INSPECTION
Each cylinder, after being internally cleaned and dried, is checked visually with the help of a boroscope / bulb for any defects & internal cleanliness.
TARE WEIGHT
Cylinders are weighed on electronic weighing scale having a least count of 10 grams and their weight is recorded against each serial number.
The tare weight, nett weight and date of testing of the cylinder are then accordingly punched on the cylinders at the space provided.
VALVE FITTING
The bung threads of each cylinder is cleaned, tapped and checked with L1 & L9 gauges first and then valve is fitted using teflon tape, with the help of torque wrench / automatic valve fitting machine at a torque of 145 ± 15 lb-ft. 5 cylinders are checked for torque requirements at the start of production.
AIR FILLING
Each valve fitted cylinder is filled with air to a minimum pressure of 12 kg/cm².
PNEUMATIC LEAKAGE TEST
The air pressure is checked before pneumatic test. The safety caps are firmly fixed on the valves and the cylinders are fully immersed in water for a period not less than 60 seconds and checked for joint leakness of valve and bung threads and any other leakages. Record of pneumatic testing is maintained.
VISUAL INSPECTION
After pneumatic test, the cylinders are checked visually for any surface defects, screen printing and marking details.
DE-AIRING & BATCH-WISE STACKING
The air inside the cylinders is removed using adapters and the cylinders are stacked batch-wise in the storage area.
These cylinders are ready for final inspection and dispatch subject to testing and clearance from inspection authority.
MANUFACTURE OF COMPONENTS
All components / sub-assemblies such as footring, etc are manufactured separately in the Ancillary section. Each component is inspected before its assembly with the cylinder body.
BOUGHT OUT COMPONENTS
All bought out components such as bung, valve protection collar, etc are received along with the material test certificate for conformity to the required specification and are as per approved drawing. Each component is inspected before its assembly with the cylinder body.
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