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The cylinder shall be of welded construction having a cold or how drawn cylindrical portion with hemispherical, ellipsoidal or tori-spherical ends welded to it, or two halves of cold or hot drawn and circumferentially welded together, or any other construction approved by the statutory authority.

The calculation of the thickness of pressure parts of the gas cylinder is related to the minimum value of yield strength guaranteed by the cylinder manufacturer for the finished cylinder and the test pressure.

2 MANUFACTURE

2.1 The number of longitudinal scams in the welded cylinder shall not exceed one and the number of circumferential seams shall not exceed two.

2.2 When the welded cylinder contains a longitudinal seam, the edges of the plate forming the longitudinal joint of the shell shall be rolled or formed by pressure not by blows, to the required curvature.

2.3 The end or dished part shall be hemispherical, semi-ellipsoidal or tori-spherical shape. The end shall have a cylindrical skirt or parallel portion of minimum length 20 mm or three times the shell thickness, whichever is greater.

2.4 Agreed Finished Thickness - The agreed finished thickness shall not be less than the minimum calculated wall thickness at any transverse section of the cylindrical portion. Additional thickness may also have to be provided to cover corrosion allowance and stresses due to horizontal acceleration and retardation during transportation. The amount of the allowance shall be as agreed to between the manufacturer and the purchaser.

2.5 Examination of Cylinders Before Closing in Operation - Cylinders shall be examined for wall thickness, before the closing-in operation, circularity of the cylindrical shell and the skirt portion of ends, external and internal surface defects, the profile regularity of the ends, offset at the joints, and straightness. The manufacturer shall assure himself that the wall thickness is not less than the agreed finished thickness at any point. The eccentricity of bung hole centre line with respect to centre line of half/body of cylinder shall not be more than one percent of the nominal diameter of cylinder subject to a maximum of 2 mm.

2.5.1 Circularity - The out-of-roundness of the cylindrical shell shall be limited to such a value that the difference between the maximum and the minimum outside diameter in the same cross section is not more that one percent of the mean of these diameters.

2.5.2 Surface Defects - The internal and external surfaces of the cylindrical shall be free from defects which will adversely affect the safe working of the cylinder.

2.5.3 Profile Regularity - The contour of dished end shall not deviate from the approved dimensions by more than 1.25 percent of the nominal diameter in respect of radial dimensions and by more than one percent in respect of axial dimensions. Such deviations shall not be abrupt changes and shall be outside the specified shape.

2.5.4 Offset at the Joint - The misalignment measure at the surface of the plates shall not exceed 10 percent of the nominal plate thickness. Where the thickness of the ends exceeds the shell thickness by more than 25 percent, the abutting edges shall be reduced by a smooth taper extending for a distance of four times the offset between the abutting edges.

2.5.5 Straightness - Unless otherwise shown in the drawing, the maximum deviation of the shell from a straight line shall not exceed 0.3 percent of the cylindrical length.

3 VALVES AND VALVES PAD

3.1 The valve connection shall consist of a welded pad/bung, and shall be threaded to suit the type of valve specified in IS 8737 (Part 2) : 1978. Two runs of welding shall be employed for bungs which have a backing pad (either on the outside or one on the outside and one on the inside). In the case of bungs without backing pad, one run of welding shall be given on the inside and one on the outside. If the positive projection of a bung inside the cylinder is 4 mm or more, the same may be welded only on the outside with two runs of weld.

3.1.1 Any other valve connection may be provided as agreed to between the manufacturer and the purchaser and approved by the statutory authority.

3.2 Valve Protection

3.2.1 Cylinder shall have their valves protected against damage by the provision of a stout metal cap or round or metal cover or protective metal ring or grill of an approved design. Where the design of the cylinder provides for the valve lying wholly below the level of the body of the cylinder such a protection is not necessary.

3.2.2 In the case of non-vented valve protection the cap shall be provided with a suitable device which will allow any pressure that has accumulated inside the valve cap to be slowly released before removal of the cap.

3.2.3 The metal cap or metal cover shall be screwed on to the neck of the cylinder.

3.2.4 The protective metal ring or grill shall be welded to the upper end of the cylinder concentric with the neck.

3.2.5 In case the protective ring is made out of tube/pipe the dimensions of tube/pipe may be as agreed between the purchaser and the manufacturer.

3.2.6 The protective device shall be of adequate construction to prevent such damage to the valve as would cause the escape of the product. When a water filled container with quantity being half the nominal water capacity is dropped from a height of 1.2 m, so that the protective device struck a hard flat surface, there shall be no damage to the valve.

4 FITTINGS OTHER THAN VALVES

4.1 Handle or other suitable arrangement for lifting the cylinder shall be provided. It shall be capable of withstanding static loading in any direction equal to twice the weight of the cylinder when filled with water.

4.2 FOOTRING - The footring, where fitted as a separate fixture to the bottom end of the cylinder, shall be at least 20 mm away from the circumferential weld. The thickness of the sheet from which the footring is made shall not be less than the calculated wall thickness of the cylinder body. The footring may be intermittently welded. In case, the bottom edge is curled, the curling shall be inwards to facilitate safe handling. It shall be provided with holes for ventilation, and if curled, drainage holes to be provided to avoid corrosion. The maximum permissible deviation from the vertical shall not exceed 1°. Footring shall be sufficiently strong and made of steel compatible with that of the cylinder prescribed in IS 1079 :1988 or of other steel, having equivalent properties. The bottom of the footring shall not be less than 8 mm below the outside bottom of the cylinder shell for cylinder upto 34 liters nominal water capacity. For cylinders of more than 34 liters nominal water capacity and up to 50 liters nominal water capacity, this value shall be minimum 15mm and for cylinders exceeding 50 liters nominal water capacity, this value shall be minimum 25 mm.

4.3 Bung - The requirements of bungs shall be in accordance with Annex-B.

5 HEAT TREATMENT

All cylinders shall be efficiently normalized, or stress relieved in accordance with the steel maker’s recommendation, after manufacture and completion of all welding (including that of attachments) and before hydrostatic test is applied. A complete record of the heat treatment cycle shall be maintained.

6 HYDROSTATIC TEST

6.1 Each heat treated cylinder shall be subjected to hydrostatic test. During the hydrostatic test, the pressure shall be increased gradually till the required test pressure is reached. After the test pressure is reached and the external surfaces of the cylinder are dried, it shall be retained for a period of not less than 30 seconds. Any reduction in pressure noticed during this retention period or any leakage, or visible bulge or deformation shall be treated as a case of failure in the test.

6.1.1 The value of hydrostatic test pressure for LPG shall be in accordance with IS 8867 : 1978.

6.1.2 Hydrostatic test shall be carried out according to 7 of IS 3196 (Part 3) : 1991.

7 PNEUMATIC LEAKAGE TEST

7.1 Each cylinder, after it has been dried, and fitted with valve using a suitable jointing material as agreed to between the purchaser and the manufacturer, shall be tested for leakage by subjecting to air pressure of not less than 980 kPa (10kgf/cm²) for a period of one minute while immersed in water and shall show no leakage from the body of the cylinder and valve pad joint. This test shall be carried out after fixing the safety cap on the valve.

7.1.1 Alternatively any other method approved by the statutory authority may be used.

7.1.2 Pneumatic leakage test shall be carried out according to 8 of IS 3196 (Part 3) : 1991.

8 HYDROSTATIC STRETCH TEST AND BURSTING TEST

8.1 Hydrostatic Stretch Test - One cylinder taken at random from each lot of 483 or less shall be subjected to a hydrostatic stretch test. No pressure greater than 80 percent of the test pressure shall have been applied to the cylinder before the test.

8.1.1 Hydrostatic stretch test shall be carried out according to 6 of IS 3196 (Part 3) : 1991.

8.1.2 Permanent stretch suffered by the cylinder due to application of test pressure shall not exceed the following limits:

- In the case of cylinders below 20 liter water capacity for non-corrosive gases, 10 percent of the total stretch suffered during test; and

- In other case, 10% of the total stretch suffered during the test or 1/5000 of the original volume of the cylinder, whichever is less.

8.2 The cylinder which has passed the hydrostatic stretch test under 17.1 or alternatively one cylinder selected at random from those which have passed the hydrostatic test shall then be subjected to a hydrostatic pressure till its bursts.

8.2.1 Bursting test shall be carried out according to 9 of IS 3196 (Part 3) : 1991.

8.2.2 The nominal hoop stress value of (f_b) shall be not less that 0.95 of the minimum specified tensile strength of the material of the cylinder.

The cylinder shall burst without fragmentation. During burst test in case leakage starts from any welding before fracture or before achieving required hoop stress, the specimen shall be discarded and fresh test specimen shall be taken. Fracture shall not occur in the weld in the direction of the seam nor parallel to it within 10 mm from its edge. Fracture at bung welding shall be treated as a failure irrespective of its meeting hoop stress requirements.

9 ACCEPTANCE TESTS

9.1 For every batch of 202 or less heat-treated and finished cylinders, one test cylinder shall be selected at random, and the various acceptance tests shall be carried out on test specimens taken from this cylinder.

9.1.1 Number of test specimen and method of testing shall be in accordance with 5 of IS 3196 (Part 3) : 1991.

9.1.2 The percentage elongation and yield strength, wherever applicable, and tensile strength thus determined shall not be less than the respective requirements for the material specified.

9.1.3 The bend test specimen having cracks or any other open defects, which exceed 3 mm, measured in any direction on the convex surface of the specimen, shall be treated as a failure.

9.1.4 The weld shall show a good penetration and absence of lack of fusion.

9.1.5 The thickness shall not be less than the calculated thickness.

Governing Specifications