34CrMo4A Air Bottle Pipe
34CrMo4A Seamless Steel Pipe: GB/T 18248 Gas Cylinder Material Data
Comprehensive data for 34CrMo4A alloy steel pipe according to GB/T 18248 standard for gas cylinder applications.
Hot rolling, cold drawing, quenching and tempering (Q+T), machining, welding (with proper procedure)
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34CrMo4A Air Bottle Pipe Introduction
34CrMo4A is a chromium-molybdenum alloy steel grade specified in GB/T 18248 for seamless steel pipes used in high-pressure gas cylinders (air bottles). This quenched and tempered steel offers an excellent combination of high tensile strength, good yield strength, and reliable low-temperature impact toughness. The material is designed to withstand repeated pressurization cycles and is widely applied in the production of CNG, hydrogen, oxygen, and other industrial gas storage vessels. Its narrow chemical composition limits and strict purity control (low phosphorus and sulfur) ensure consistent mechanical properties and weldability. Typical delivery condition is quenched and tempered, providing a microstructure of tempered martensite or bainite. The steel demonstrates good hot and cold formability for pipe manufacturing and reliable performance in safety-critical applications across the energy, chemical, and medical industries.
34CrMo4A Air Bottle Pipe Chemical Composition , Heat Analysis
The chemical composition of 34CrMo4A is strictly controlled to achieve the desired balance of strength and toughness after quenching and tempering. The alloy design relies on chromium and molybdenum for hardenability and high-temperature strength, while low phosphorus and sulfur contents ensure cleanliness and resistance to temper embrittlement. Residual elements such as nickel and copper are limited to avoid adverse effects on toughness.
| Element | Content (wt%) | Remarks |
|---|---|---|
| Carbon (C) | 0.30 ~ 0.37 | |
| Silicon (Si) | 0.10 ~ 0.40 | |
| Manganese (Mn) | 0.60 ~ 0.90 | |
| Phosphorus (P) | ≤ 0.020 | |
| Sulfur (S) | ≤ 0.010 | |
| Chromium (Cr) | 0.90 ~ 1.20 | |
| Molybdenum (Mo) | 0.15 ~ 0.30 | |
| Nickel (Ni) | ≤ 0.30 | Residual element |
| Copper (Cu) | ≤ 0.20 | Residual element |
| Nickel + Copper (Ni+Cu) | ≤ 0.50 | Combined limit |
34CrMo4A Air Bottle Pipe Physical Properties
These physical properties are typical for a quenched and tempered Cr-Mo alloy steel similar to 34CrMo4A. They are not specified in GB/T 18248 but are provided for engineering calculations. Values such as density, modulus of elasticity, thermal expansion, and thermal conductivity are essential for design, heat transfer analysis, and welding procedure development.
| Property | Typical Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.82 | g/cm³ | 20 °C |
| Modulus of elasticity (E) | 210 | GPa | 20 °C |
| Shear modulus (G) | 80 | GPa | Calculated from E and ν |
| Poisson's ratio (ν) | 0.3 | — | 20 °C |
| Thermal expansion coefficient (α) | 11.1 | 10⁻⁶/K | 20–100 °C |
| Thermal conductivity (λ) | 44 | W/(m·K) | 20 °C |
| Specific heat capacity (c) | 460 | J/(kg·K) | 20 °C |
| Electrical resistivity (ρ_e) | 0.22 | Ω·mm²/m | 20 °C |
34CrMo4A Air Bottle Pipe Mechanical Properties
The mechanical properties of 34CrMo4A seamless pipes are guaranteed after quenching and tempering. The steel must exhibit high tensile strength in the range of 980–1180 MPa and a minimum yield strength of 835 MPa to withstand high internal pressures. Adequate elongation ensures formability, and impact toughness at -50°C is critical for low-temperature service and safety against brittle fracture. Tests are carried out on longitudinal specimens unless otherwise specified.
| Property | Required Value | Unit | Test Condition |
|---|---|---|---|
| Tensile Strength (Rm) | 980 ~ 1180 | MPa | Quenched and tempered, ambient temperature |
| Yield Strength (ReH) | ≥ 835 | MPa | Quenched and tempered, ambient temperature |
| Elongation after fracture (A) | ≥ 12 | % | Longitudinal, gauge length L₀ = 5.65√S₀ |
| Impact absorbed energy (KV₂) | ≥ 27 | J | -50 °C, Charpy V-notch, transverse or longitudinal per standard |
34CrMo4A Air Bottle Pipe Directly Equivalent Standards and Substitutable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10297-1 | 34CrMo4 (1.7220) | Seamless circular steel tubes for mechanical and general engineering; technically equivalent for gas cylinder service |
| Germany | DIN EN 10297-1 (prev. DIN 17204) | 34CrMo4 | Historically equivalent; widely used in gas cylinder manufacturing |
| International | ISO 683-2 | 34CrMo4 | Heat-treatable alloy steel with identical nominal composition |
| Japan | JIS G3441 | SCM435TK | Alloy steel tube for machine structural purposes; chemistry and strength closely aligned |
| China | GB/T 8162 | 35CrMo | Similar structural tube grade; not specifically for gas cylinders but can serve as alternative in less demanding pressure applications |
34CrMo4A Air Bottle Pipe Application Introduction
34CrMo4A seamless pipe is specifically engineered for the production of seamless high-pressure gas cylinders. Thanks to its high strength and excellent low-temperature toughness, it meets the demanding safety requirements of pressure vessel codes. The main fields of use include automotive CNG fuel storage, hydrogen energy infrastructure, industrial and medical gas transport, and fire suppression systems. The steel is suitable for hot necking and spinning operations during cylinder manufacturing. Common finished products are completely heat-treated, with strict control of wall thickness and surface integrity.
Product Applications: Seamless high-pressure gas cylinders (Type I), CNG cylinder for light and heavy-duty vehicles, Tube trailers and skid-mounted gas storage units, Stationary storage vessels for hydrogen and nitrogen, Fire extinguisher cylinders
Processed into products: Cylinder body (seamless pipe cut and formed), Neck ring and shoulder region, Boss and valve connection area, Transition pieces for multi-element gas containers (MEGC)
Application industries: Alternative fuel vehicles (CNG/Hydrogen), Petrochemical and industrial gas supply, Medical gas storage and distribution, Firefighting equipment manufacturing, Hydrogen refueling stations and energy storage
34CrMo4A Air Bottle Pipe Near-Equivalent Substitute Materials
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA | ASTM A519 | 4130 | Cr-Mo alloy steel tube with C 0.28-0.33%, Cr 0.80-1.10%, Mo 0.15-0.25%. Slightly lower carbon and chromium; similar mechanical properties after Q+T |
| Japan | JIS G4105 | SCM435 | Bolting and machine structural steel; C 0.33-0.38%, Cr 0.90-1.20%, Mo 0.15-0.30%. Excellent strength and toughness match |
| China | GB/T 3077 | 35CrMo | Alloy structural steel for general engineering with similar composition; typically used for shafts and forgings rather than tubes |
| Europe | EN 10083-3 | 34CrMo4 | Quenched and tempered steel for machinery; identical nominal chemistry, but product forms differ (bars, forgings) |
Notes:
Delivery and quality requirements: Pipes are supplied in quenched and tempered condition with guaranteed mechanical properties. Non-destructive testing (ultrasonic or eddy current) is normally required according to GB/T 18248. The internal and external surfaces shall be free from cracks, folds, and harmful defects. Additional tests such as flattening, flaring, or hydrostatic pressure tests may be specified in the purchase order. The material can be welded using low-hydrogen processes, but post-weld heat treatment is recommended for pressure-containing welds. Traceability from melt to final product is mandatory.
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