GB/T 18248 34CrMo4 Seamless Steel Pipe for Gas Cylinders
GB/T 18248 34CrMo4 Seamless Steel Tube for Gas Cylinders – Composition, Properties & Equivalent Grades
Detailed material data for 34CrMo4 seamless steel tubes per GB/T 18248 for air bottle and high-pressure gas cylinder applications. Includes chemical composition, mechanical and physical properties, international equivalents, similar alternative materials, and application guidance.
Hot rolling or cold drawing + quench and temper heat treatment; machining, welding (with proper filler), expanding, necking-down
- Phone : +8618037372205
- Email : [email protected]
- WhatsApp: Contact via Whtsapp
- WeChat: +8618037372205
GB/T 18248 34CrMo4 Seamless Steel Pipe for Gas Cylinders Introduction
34CrMo4 under GB/T 18248 is a quenched and tempered chromium-molybdenum alloy steel intended for seamless tubes used in the fabrication of refillable gas cylinders (air bottles). The steel offers an optimised balance of high tensile strength (980–1180 MPa), excellent low-temperature toughness (impact energy ≥27 J at -50 °C), and good ductility. Key characteristics include:
- Precise control of harmful elements (P ≤0.020 %, S ≤0.015 %) and low residuals (As, Sn, Sb, Bi) to ensure cleanliness.
- Fine-grained microstructure after heat treatment, providing reliable performance under cyclic pressure loading.
- Superior weldability for neck ring and base assembly, consistent with international cylinder standards.
The grade is a preferred choice for light-weight, high-pressure gas storage in automotive (CNG), industrial, medical, and breathing apparatus sectors. Delivery condition is quenched and tempered (QT), with mandatory non-destructive testing to guarantee defect-free tube quality.
GB/T 18248 34CrMo4 Seamless Steel Pipe for Gas Cylinders Chemical Composition
The chemical requirements for 34CrMo4 according to GB/T 18248 are strictly controlled to achieve the desired hardenability and toughness. Special limits are applied to tramp elements (As, Sn, Sb, Bi) to avoid temper embrittlement and ensure high cleanliness for gas cylinder safety.
| Element | Specified Value (wt%) | Remarks |
|---|---|---|
| C | 0.30 – 0.37 | |
| Si | 0.10 – 0.40 | |
| Mn | 0.60 – 0.90 | |
| P | ≤ 0.020 | |
| S | ≤ 0.015 | |
| Cr | 0.90 – 1.20 | |
| Mo | 0.15 – 0.30 | |
| Ni | ≤ 0.30 | |
| Cu | ≤ 0.20 | |
| As | ≤ 0.020 | Residual element limit |
| Sn | ≤ 0.020 | Residual element limit |
| Sb | ≤ 0.010 | Residual element limit |
| Bi | ≤ 0.010 | Residual element limit |
| N | ≤ 0.012 | If not otherwise agreed |
| H | ≤ 0.0002 | For product analysis, when specified |
GB/T 18248 34CrMo4 Seamless Steel Pipe for Gas Cylinders Thermal and Electrical Physical Properties
Physical properties are representative for 34CrMo4 in the quenched and tempered condition. Values vary slightly with exact tempering temperature and heat treatment parameters.
| Property | Typical Value | Unit | Test Condition / Reference |
|---|---|---|---|
| Density, ρ | 7.85 | g/cm³ | 20 °C |
| Modulus of elasticity, E | 210 | GPa | 20 °C |
| Shear modulus, G | 81 | GPa | 20 °C |
| Poisson's ratio, ν | 0.30 | – | Elastic range |
| Thermal expansion coefficient, α | 11.1 | 10⁻⁶/K | 20 – 100 °C |
| Thermal expansion coefficient, α | 12.0 | 10⁻⁶/K | 20 – 200 °C |
| Thermal expansion coefficient, α | 12.7 | 10⁻⁶/K | 20 – 300 °C |
| Thermal conductivity, λ | 42 | W/(m·K) | 20 °C |
| Specific heat capacity, c | 460 | J/(kg·K) | 20 °C |
| Electrical resistivity, ρₑ | 0.25 | 10⁻⁶ Ω·m | 20 °C |
GB/T 18248 34CrMo4 Seamless Steel Pipe for Gas Cylinders Mechanical Properties
Mechanical properties are determined on test specimens taken from the quenched and tempered tube. Both longitudinal and transverse properties are specified to ensure integrity. Low-temperature toughness at -50 °C is mandatory for gas cylinder service.
| Property | Required Value | Unit | Test Condition |
|---|---|---|---|
| Tensile strength, Rm | 980 – 1180 | MPa | Ambient temperature, longitudinal sample |
| Yield strength, ReH (Rp0.2) | ≥ 835 | MPa | Ambient temperature, 0.2% offset, longitudinal |
| Elongation after fracture, A | ≥ 12 | % | Longitudinal, gauge length 5.65√S₀ |
| Elongation after fracture, A | ≥ 10 | % | Transverse, gauge length 5.65√S₀ |
| Impact energy, KV₂ | ≥ 27 | J | Charpy V-notch, -50 °C, longitudinal |
| Impact energy, KV₂ | ≥ 20 | J | Charpy V-notch, -50 °C, transverse |
| Hardness | Not specified; typical 300 – 360 HBW | HBW | For reference only in QT condition |
GB/T 18248 34CrMo4 Seamless Steel Pipe for Gas Cylinders Fully Equivalent Material Standards and Alternative Designations
| Country/Region | Standard | Designation | Remarks |
|---|---|---|---|
| European Union | EN 10297-1 | 34CrMo4 | Seamless circular steel tubes for mechanical and general engineering purposes; same chemical and very similar mechanical requirements |
| International | ISO 9809-1 | 34CrMo4 | Refillable seamless steel gas cylinders – tube material; directly aligned with GB/T 18248 requirements |
| Germany | DIN EN 10297-1 | 34CrMo4 | Identical to EN 10297-1, widely used for pressure vessel tubing |
| China | GB/T 18248 | 34CrMo4 | Original standard – the base reference |
GB/T 18248 34CrMo4 Seamless Steel Pipe for Gas Cylinders Application Introduction
GB/T 18248 34CrMo4 tubes are engineered for the fabrication of seamless refillable gas cylinders operating at high pressures (typically up to 30 MPa or more). The combination of high strength, good low-temperature toughness, and reliable fatigue performance makes the material suitable for weight-optimised storage solutions. The tubes are used after appropriate heat treatment (quenching and tempering) at the cylinder manufacturer and are subject to stringent quality verification.
Product Applications: Seamless steel CNG cylinders (Type I), Industrial gas cylinders (high-pressure O₂, N₂, H₂ bottles), SCBA and SCUBA breathing air cylinders, Seamless accumulator shells, High-pressure storage tubes for tube trailers
Processed into products: Cylinder body (drawn or spun from seamless tube), Neck ring (welded or integral with hot necking), Base cap or foot ring, Boss and valve port area, Reinforcing sleeves
Application industries: Compressed natural gas (CNG) vehicle fuel systems, Industrial gas packaging (oxygen, nitrogen, argon, hydrogen), Breathing air and diving apparatus, Firefighting SCBA cylinders, Medical gas storage, Aerospace accumulators and emergency gas bottles
GB/T 18248 34CrMo4 Seamless Steel Pipe for Gas Cylinders Similar or Closely Comparable Material Recommendations
| Country/Region | Standard | Designation | Remarks |
|---|---|---|---|
| USA | ASTM A519 | 4130 | Similar Cr-Mo steel; typical C 0.28–0.33 %, Cr 0.80–1.10 %, Mo 0.15–0.25 %; strength range often lower; requires additional evaluation for gas cylinder compliance |
| China | GB/T 3077 | 35CrMo | Closest Chinese structural alloy steel; C 0.32–0.40 %; used for hollow bars, but not specifically formulated for gas cylinder tubing; impact toughness may differ |
| European Union | EN 10083-3 | 34CrMo4 | Quenched and tempered steel for general engineering; same nominal composition but not covered by the same cylinder-specific quality requirements as GB/T 18248 |
| International | ISO 9809-2 | 34CrMo4 | If produced to the alternative gas cylinder standard, can be equivalent but differs in detailed testing scope |
Notes:
- The tubes are normally supplied with mill test certificates according to EN 10204 Type 3.1 or 3.2, including chemical analysis, mechanical test results, and non-destructive testing reports (ultrasonic testing per GB/T 5777 or eddy current).
- Surface quality: free from cracks, laps, and other detrimental imperfections; internal and external surface finish as agreed.
- Dimensional tolerances for outer diameter and wall thickness are specified in GB/T 18248; typically D ±1% and wall thickness +10%/-0%.
- For manufacturing of cylinders, the material is required to demonstrate a minimum 5% lateral expansion after an acid pickling test (or notch-free surface by magnetic particle inspection).
- Weld repairs on base material are not permitted; the tube must be seamless.
- Share
