Hot rolled steel used in cylinder manufacturing for low pressure liquefiable gases

Steel is the prominent choice for cylinder manufacturing due to its unmatched durability, affordability, and safety in high-pressure applications.

Strength and Durability – Steel cylinders can withstand high pressure and rough handling. They are more impact-resistant compared to other materials.

Cost-Effectiveness – Steel is more economical in terms of manufacturing, maintenance and recycling.

In the present scenario, for the manufacturing of cylinders used in storing low pressure liquefiable gases, the Bureau of Indian Standards (BIS) has specified two steel standards that can be used.

 

The two BIS standards for steel used in cylinder manufacturing are:

IS 6240: One of the applicable standards for the manufacturing of welded low carbon steel cylinders with a water capacity exceeding 5 litres, designed for  storing low-pressure liquefied gases.

This standard covers cylinders intended for:

• LPG (Liquefied Petroleum Gas)

• Non-toxic gases (Other than LPG)

• Toxic and corrosive gases

 

IS 15914: This is also an applicable standard for the manufacturing of welded low carbon steel cylinders with a water capacity exceeding 5 litres, designed for  storing low-pressure liquefied gases.

This standard covers cylinders intended for LPG (Liquefied Petroleum Gas) only.

These standards define the chemical composition, mechanical properties, and testing requirements to ensure the steel meets the necessary performance criteria for gas storage.

The key properties required for manufacturing cylinders for low pressure  liquefiable gases, as per the relevant BIS codes include:-

Tensile test

It involves straining a test piece by tensile force, generally to fracture, for the  determination of one or more of the mechanical properties. A uniaxial force is  applied to a steel specimen until it fractures, measuring how the material  responds under tension.

 

Bend Test

This method is used for determining the ability of metallic materials to  undergo plastic deformation in bending.

It consists of submitting a test piece of round, square, rectangular, or polygonal  cross-section to plastic deformation by bending, without changing the  direction of loading, until a specified angle of bend is reached.

 

Strainage Embrittlement Test

Strainage embrittlement refers to the loss of ductility and toughness in steel  due to plastic deformation (strain) followed by aging at elevated temperatures.  This embrittlement occurs due to the precipitation of impurity elements (such  as phosphorus, nitrogen, or carbon) along grain boundaries, leading to  reduced fracture resistance.

 

Erichsen Cupping Test

A standard test method for determining the ability of metallic sheets and strips  having a thickness from 0.1 mm up to 2 mm and a width of 90 mm or greater  to undergo plastic deformation in stretch forming.

Forming an indentation by pressing a punch with a spherical end against a  clamped test piece between a blank holder and a die until a through crack  appears. The measured depth of the indentation is the result of the test based  on the movement of the punch.

Standard	Chemical Composition (Ladle analysis as per IS 228)					Tensile Testing (IS1608 & EI% as per IS 3803)					Normalizing (⁰C)
	C%	Mn%	Si%	S%	P%	Al%	YS (MPa)	TS (MPa)	EI% 5.65√S0	Bend
IS 6240 Gr 240	Max. 0.16	Min 0.30	Max. 0.25	Max. 0.025	Max. 0.025	Min 0.020	Min 240	350-450	25	t	670±20
IS 15914 HS235	Max. 0.16	Min 0.30	Max. 0.25	Max. 0.025	Max. 0.025	Min 0.015	Min 235	360-460	25	-	920-960
IS 15914 HS265	Max. 0.18	Min 0.40	Max. 0.30	Max. 0.025	Max. 0.025	Min 0.015	Min 265	410-510	22		890-930
IS 15914 HS295	Max. 0.19	Min 0.50	Max. 0.35	Max. 0.025	Max. 0.025	Min 0.015	Min 295	450-560	20		890-930
IS 15914 HS345	Max. 0.20	Min 0.70	Max. 0.45	Max. 0.025	Max. 0.025	Min 0.015	Min 345	490-610	18		880-920

A. Earlier, LPG cylinders were manufactured using raw materials conforming to IS 6240.

However, with recent advancements, cylinder manufacturers are  now promoting IS 15914 as the preferred material. Cylinders made from IS 15914 are lighter compared to those manufactured under IS 6240, offering improved  efficiency.

 

Please refer to the table below for a detailed comparison.

Gas Weight (Kg)	IS6240 Gr 240  (RM Thk.)	IS15914 HS 345  (RM Thk.)
5	2.2 mm	2 mm
14.2	2.9 mm	2.20/2.30 mm
19	2.9 mm	2.5 mm

 

 

B. Use of composite material for household LPG Cylinder

These cylinders have a three-layered construction. It is made up of a blow molded High-Density Polyethylene (HDPE) inner liner, covered with a  Composite layer of polymer-wrapped fiber glass and fitted with a HDPE outer  jacket.

 

These new age composite cylinders have multiple advantages over the existing steel cylinders:

• They are light weight: the tare weight of a composite cylinder is half of its steel counterpart.

• They have a translucent body which helps customers to accurately check the LPG level against light. This will help customers plan their next refill easily.

• They are rust-free, and do not corrode. This reduces the chances of  leaving stains and marks on surfaces.

• They are aesthetically designed which makes them visually appealing  and ideal for modern kitchens of today.

• They are safer to use than being explosion proof.