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Gas cylinder steel is a clean, low-carbon hot-rolled steel made for welded pressure containers rather than for general fabrication. The requirement the whole grade family is built around is a balancing act: keep the carbon low, hold sulphur and phosphorus to tight limits, and still meet the specified strength together with good toughness and impact energy.
That combination is why this is treated as a speciality product. The plate has to be deep drawn into hemispherical halves, welded along the seam, and then hold pressure through years of filling, transport and temperature cycling — so formability, weldability and toughness are specification requirements, not extras. Everything else on this page follows from that: the grades in section 03, the minimum properties in section 04, and the applications in section 05.
11Grade Designations6 linked pages
3Standard FamiliesJIS · GB/T · BQB
1.5–12 mmRolling ThicknessWidth and length to programme
500 LJIS G3116 ScopeWelded containers up to this capacity
What “special steel” means here: low carbon with sulphur and phosphorus strictly controlled, so the plate meets its strength requirement while keeping good toughness and impact energy. The practical consequence for a buyer is that you cannot simply swap in a general structural grade of matching yield strength — the cleanliness, the inclusion control and the deep-drawing and seam-welding behaviour that follow from them are what you are actually buying. The figures that apply to your delivery are the ones printed on the MTC for the standard and grade you ordered.
02Thickness Range, Product Form & Processing
Thickness is the dimension published for this product. Width, length and coil parameters are confirmed against the rolling programme for the grade you order.
Product Form
Item
Range / Standard Specification
Remarks
Gas Cylinder Steel Plates
Thickness
1.5 mm – 12 mm
The rolling window published for this product; outside it is rolled to order
Width & Length
Confirmed per rolling programme
Send the width, length and coil dimensions you run and we confirm what the mill can roll
Product Form
Hot-rolled plate, sheet and strip
Coil supply with decoiling and slitting for press-line feed
Blanks and circles cut to the press requirements of the cylinder line
On sizes: not every thickness is available in every width, and the combination depends on the grade and the rolling programme. Two further points matter when you specify: mechanical properties are thickness-dependent, so the elongation and strength combination a grade can meet at 3 mm is not the one it meets across the whole window, and thin-gauge requirements are often given their own limits in the standard. Both are stated on the MTC for your heat.
03Available Grades & Standards
11 designations across 3 specifications. Click any linked grade to open its own page with composition, mechanical properties and supply detail.
Reading the designations: in JIS G3116, SG marks steel for welded gas cylinders and the number is the specified minimum yield strength in MPa — SG295 calls for at least 295 MPa yield. In GB/T 6653, HP is the welded-cylinder series and the number does the same job — HP295 calls for at least 295 MPa. BQB 321 is a mill specification using the same HP suffix with its own strength numbers. Published equivalence tables routinely pair SG255 with HP265 and SG295 with HP295, but they remain separate specifications with their own chemistry and testing requirements — see FAQ Q2 before substituting one for the other, and quote both the standard and the edition you design to.
Why the composition is controlled the way it is, and the minimum mechanical values each grade has to meet.
Low carbon is what keeps the seam weld sound. Welded cylinders are joined by automatic processes with little margin for a hard, cracking heat-affected zone, so carbon is held down and strength is recovered with manganese and, where the grade calls for it, microalloying.
Sulphur and phosphorus are held to very low limits because of what they do rather than what they add. Sulphur forms manganese sulphide inclusions that stretch out during rolling and give the plate directional properties — a deep-drawn cup with poor through-thickness ductility tears at the earing zone. Phosphorus raises strength but embrittles, costing precisely the impact energy the cylinder needs when it is dropped or filled cold. Across the grades listed here the two elements are typically limited to the order of 0.025–0.030% phosphorus and 0.012–0.030% sulphur, depending on standard and grade — the exact figure that applies is the one in the standard edition you buy to.
Standard
Grade
Yield Strength min (MPa)
Tensile Strength (MPa)
Elongation min (%)
JIS G3116
SG255
255
400 min
28
JIS G3116
SG295
295
440 min
26
JIS G3116
SG325
325
490 min
22
JIS G3116
SG365
365
540 min
20
GB/T 6653
HP235
235
380–500
29
GB/T 6653
HP265
265
410–520
27
GB/T 6653
HP295
295
440–560
26
GB/T 6653
HP325
325
490–600
22
GB/T 6653
HP345
345
510–620
21
BQB 321
B440HP
—
—
—
BQB 321
B490HP
—
—
—
How to read this table: the values above are the published minimum requirements of the respective standards for the grades as normally quoted, and they are the floor a heat has to clear — not the values your MTC will necessarily show, and not limits fixed for every thickness. GB/T 6653 in particular gives separate elongation minima for thin gauges, and Charpy energy, bend testing and any impact requirement come from the applicable cylinder design code rather than from the base steel specification. BQB 321 is a mill specification supplied to its own schedule; we confirm those values against the mill datasheet when you enquire. Higher strength is not automatically better: moving up the series buys pressure capability and costs elongation, so the grade is chosen against the cylinder design, not picked for its yield figure alone.
05Typical Applications
One product family, one job — welded pressure containers for compressed and liquefied gas. These are the container types this plate goes into.
LPG Cylinders
Household and commercial liquefied petroleum gas cylinders — the highest-volume use of the family, dominated by the mid-strength grades such as HP295 and SG295 that balance pressurised service against drawability.
Industrial & Permanent Gases
Oxygen, nitrogen, argon, carbon dioxide and hydrogen service cylinders, including the larger industrial sizes where the higher grades buy thinner wall for the same design pressure.
Acetylene & Dissolved Gases
Cylinders for dissolved acetylene, built with a porous filler and solvent charge. The steel still has to draw and weld cleanly, but the container has to be designed and approved to the applicable acetylene cylinder code.
Refrigerant & Specialty Gas
Refrigerant cylinders for HVAC and refrigeration service, plus specialty, calibration and instrument gas containers where cleanliness and consistency between heats matter more than the strength figure.
Fire Extinguishers & Small Containers
Extinguisher bodies, small compressed-air tanks, pneumatic receiver and accessory containers — the thin end of the thickness window, where surface quality and dimensional consistency drive the press line.
06Processing Services & Supply
Supplied as plate, sheet or coil, and prepared to feed a cylinder press line rather than a general fabrication shop.
1
Slitting, Decoiling & Cut-to-Length
Coil is decoiled, slit to the strip width the press requires and cut to length; sheet and plate are supplied cut to size as well. Coil ID, OD and weight are agreed before rolling so the material feeds the line you run.
2
Surface Condition
As-rolled, pickled and oiled, or to the surface finish your process needs. State it with the order — the surface the halves are drawn from is the surface the finished cylinder carries into pretreatment and coating.
3
Blanks for Deep Drawing
Circles and blanks cut to drawing; because the plate is drawn into hemispherical halves, earing control and wall-thinning behaviour are as important as the strength number, and thickness tolerance is agreed up front.
4
Inspection & Documentation
Mill test certificate to the ordered standard with heat-number traceability, together with chemical analysis, tensile test results and dimensional inspection. Third-party inspection can be arranged on request.
Ordering: payment terms L/C, T/T, D/P, Western Union, Paypal and Money Gram. Indicative lead time is 5 days for 1–10 tonnes, 10 days for 10–50 tonnes and negotiable above 50 tonnes, with the actual schedule confirmed against the rolling programme when you enquire. Tell us the standard and grade, thickness (and width or coil width), quantity, product form, surface condition, whether you draw and weld in-house, any inspection or certification requirement and the destination port.
07Frequently Asked Questions
Q1What makes gas cylinder steel different from ordinary structural plate?
It is made to a cleanliness specification, not just a strength one. Carbon is kept low so the seam weld stays sound, and sulphur and phosphorus are held to tight limits so the plate draws into hemispherical halves without tearing and still carries the specified impact energy at low temperature. A general structural grade with the same yield figure will meet the tensile test and may still fail you in the press or in service, because it was never made to be drawn, welded into a pressure boundary and cycled for twenty years.
Q2Are SG295 and HP295 the same material?
No. Published equivalence tables pair them — and pair SG255 with HP265 — because they sit at essentially the same strength level and are often used for the same cylinder designs, but they are separate specifications written by different bodies. Their chemistry limits differ, the GB/T series sets its own elongation values including separate figures for thin gauge, and each carries the testing and certification route of its own system. Substituting one for the other is an engineering decision that has to be checked against the cylinder design code and your approval, not just against the yield number.
Q3What sizes can you supply?
Thickness 1.5 mm to 12 mm is the rolling window published for this product, supplied as hot-rolled plate, sheet or strip. Width and length are confirmed against the rolling programme for the grade — send the dimensions or coil parameters you run and we will tell you what can be rolled. Section 02 lists the full specification.
Q4Can these grades be deep drawn and welded?
Yes — deep drawing into hemispherical halves followed by seam welding is exactly what the family exists for, with low carbon equivalent keeping the heat-affected zone stable. The caveat is that formability falls as strength rises: the elongation minima in section 04 step down from SG255 to SG365 and from HP235 to HP345, so the highest-strength grades demand more from the press and the tooling. The Welding procedure still has to be qualified for the joint, and finished cylinders are pressure-tested and approved to the applicable cylinder code.
Q5Should I choose the highest strength grade available?
Usually no. Higher yield lets you design thinner walls and lighter cylinders, which matters for large industrial containers or where weight is being optimised, but it costs elongation and asks more of the drawing and welding operations. Most domestic and commercial LPG cylinders sit in the middle of the range — HP295 or SG295 is the mainstream choice — precisely because it balances pressure capability against formability and cost.
Q6What information do you need for a quotation?
The standard with its edition plus the full grade — SG295 rather than “cylinder steel”, HP295 rather than “HP plate” — the thickness and either sheet dimensions or coil width and weight, the quantity, product form and surface condition, the pressing and welding process you run, any impact, bend or other test requirement beyond the base specification, inspection or third-party certification needed, and the destination port.
Get Your Gas Cylinder Steel Plate Quotation
Send us your standard and grade, thickness and dimensions, quantity, product form and surface condition. We will reply with available sizes, what the mill can certify at your thickness, coil or cut-to-length options, mill price and production lead time — and tell you plainly if a lower grade in the series would press and weld better for your cylinder design.
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