GB 6479 Carbon Steel Seamless Steel Tube for Chemical Fertilizer Equipment
Product Overview
GB/T 6479 seamless steel tubes are designed for pressure-bearing pipelines and equipment used in fertilizer production and other chemical-processing systems. The specification covers carbon steel, low-alloy steel and chromium-molybdenum alloy grades manufactured by hot rolling, hot extrusion, cold drawing or cold rolling.
Compared with general-purpose seamless tubing, GB/T 6479 tubes require tighter control of chemical composition, mechanical properties, heat treatment, dimensional accuracy, surface quality and non-destructive examination. Typical service positions include high-pressure process piping, ammonia synthesis systems, urea production units and chemical-fluid transfer lines.
GB/T 6479-2013 specifies dimensions, shape, mass, technical requirements, testing, inspection, marking and certification for seamless tubes used in high-pressure fertilizer equipment, pipelines and other chemical equipment.
Specifications
| Item |
Available Specification |
| Product Type |
Seamless pressure-bearing steel tube |
| Standard |
GB/T 6479-2013 |
| Main Grades |
10, 20, Q345B, Q345C, Q345D, Q345E, 12CrMo, 15CrMo, 12Cr2Mo, 12Cr5Mo |
| Material Category |
Carbon steel, low-alloy steel and Cr-Mo alloy steel |
| Manufacturing Method |
Hot rolled, hot extruded, cold drawn or cold rolled |
| Outside Diameter |
10-1,200 mm, subject to production route and grade |
| Wall Thickness |
1-200 mm, subject to OD, grade and heat-treatment capability |
| Standard Length |
Normally 4-12 m |
| Customized Length |
1-12 m fixed length or multiple length |
| Cross Section |
Round |
| End Condition |
Plain ends, cut ends, bevelled ends or machined ends |
| Surface Condition |
Hot-finished, cold-finished, pickled, shot-blasted, oiled or anti-rust coated |
| Heat Treatment |
Normalized, normalized and tempered, annealed, or quenched and tempered according to grade |
| Hydrostatic Testing |
According to GB/T 6479 or purchaser-approved NDT substitution |
| Inspection Documents |
Mill Test Certificate with heat number and batch traceability |
| Optional Inspection |
UT, eddy-current testing, magnetic-flux-leakage testing, PMI and third-party inspection |
Dimensional Tolerances
The exact permissible deviation depends on whether the tube is hot-finished or cold-finished and whether ordinary or advanced accuracy is ordered.
| Manufacturing Condition |
Dimension |
Size Range |
Ordinary Accuracy |
Advanced Accuracy |
| Hot-finished |
Outside diameter |
≤159 mm |
±1.0%, minimum ±0.5 mm |
±0.75%, minimum ±0.3 mm |
| Outside diameter |
>159 mm |
±1.0% |
±0.90% |
| Hot-finished |
Wall thickness |
≤20 mm |
+15% / −10% |
±10% |
| Wall thickness |
>20 mm |
+12.5% / −10% |
±10% |
| Cold-finished |
Outside diameter |
14-30 mm |
±0.20 mm |
±0.15 mm |
| Outside diameter |
>30-50 mm |
±0.30 mm |
±0.25 mm |
| Outside diameter |
>50 mm |
±0.75% |
±0.60% |
| Cold-finished |
Wall thickness |
≤3 mm |
+12.5% / −10% |
±10% |
| Wall thickness |
>3 mm |
±10% |
±7.5% |
The selected tolerance class should be written into the purchase specification. A statement such as "GB/T 6479" alone may not define whether ordinary or advanced dimensional accuracy is required.
Straightness
| Tube Type |
Recommended Control |
| General hot-finished tube |
Local straightness controlled in accordance with GB/T 6479 |
| Cold-drawn precision tube |
Tighter local and full-length straightness available by agreement |
| Tubes for automatic welding |
Full-length straightness and end alignment should be stated separately |
| Tubes for machining |
Straightness, ovality and wall-thickness eccentricity should be included in the purchase order |
For tubes used in prefabricated high-pressure spools, dimensional inspection should cover not only OD and wall thickness, but also ovality, local straightness, full-length bow and end squareness.
Main Characteristics
Pressure-Bearing Seamless Construction
The tube is manufactured without a longitudinal weld seam. This eliminates weld-line geometry and weld heat-affected-zone variation from the tube body, which is important for components subjected to internal pressure, cyclic loading and elevated temperatures.
Grade-Specific Strength Levels
The standard provides several material families rather than one universal grade:
- Grade 10 is selected for lower-strength applications requiring good formability
- Grade 20 provides higher carbon-steel strength for general chemical pressure piping
- Q345B offers a minimum nominal yield-strength class of 345 MPa for thinner-wall sections
- 12CrMo and 15CrMo contain chromium and molybdenum for improved high-temperature strength and microstructural stability
Controlled Impurity Content
Modern GB/T 6479 grade requirements impose relatively low phosphorus and sulfur limits. For many commonly supplied grades, phosphorus is limited to 0.025% and sulfur to 0.015%. Lower impurity levels support improved toughness, weldability and resistance to brittle failure.
Mandatory Heat-Treatment Control
The final properties depend on grade-specific heat treatment. Carbon grades are commonly normalized, while Cr-Mo grades may require normalization and tempering or another specified heat-treatment cycle. The heat-treatment condition must be recorded in the quality certificate.
Pressure and Non-Destructive Testing
Tubes are normally subjected to hydrostatic testing or an approved non-destructive examination route. Eddy-current or magnetic-flux-leakage testing may be used where permitted by the standard and agreed in the order.
Our Technical Advantages
1. Grade and Heat-Treatment Verification Before Production
A frequent procurement problem is ordering the correct chemical grade but failing to define the delivery heat-treatment condition. This is especially important for 12CrMo, 15CrMo and other Cr-Mo grades because tensile properties and elevated-temperature performance depend on the complete thermal cycle.
Before production, the order is reviewed for:
- Design temperature and pressure
- Applicable material grade
- Tube dimensions
- Normalized, normalized-and-tempered or annealed condition
- Post-weld heat-treatment requirements
- Required impact-test temperature
- Additional hardness or metallographic requirements
The manufacturing route and furnace cycle are then linked to the heat number and recorded in the inspection documentation.
2. Dimensional Control Beyond Basic OD and Wall Thickness
Professional pressure-equipment buyers are often concerned about eccentric wall thickness, ovality, tube-end deviation and full-length straightness. These conditions may cause fit-up problems even when individual OD and wall-thickness readings comply with the nominal tolerance.
Available controls include:
- Continuous or multi-position wall-thickness measurement
- OD and ovality inspection
- Local and full-length straightness measurement
- End squareness inspection
- Fixed-length cutting tolerance
- Tube-end visual and dimensional inspection
Advanced OD and wall-thickness tolerances can be supplied when they are specified before production.
3. Traceable Testing for Pressure-Service Qualification
A chemical-pressure tube should not be accepted only on the basis of nominal grade identification. The inspection package should demonstrate that the supplied tube matches the ordered heat, batch, dimensions and heat-treatment condition.
Available documentation may include:
- Heat-number traceability
- Product chemical analysis
- Tensile-test results
- Impact-test results where required
- Flattening, flaring or bending-test results where applicable
- Hydrostatic or NDT reports
- Heat-treatment records
- Dimensional inspection reports
- EN 10204 3.1-type documentation where contractually requested
- Third-party inspection by an agreed inspection agency
Execution Standards
| Standard System |
Relevant Standard |
Typical Scope |
| GB |
GB/T 6479 |
Seamless steel tubes for high-pressure chemical fertilizer equipment |
| GB |
GB/T 5310 |
Seamless steel tubes and pipes for high-pressure boilers |
| GB |
GB/T 9948 |
Seamless steel tubes for petroleum cracking |
| ASTM/ASME |
ASTM A106 / ASME SA-106 |
Seamless carbon steel pipe for high-temperature service |
| ASTM/ASME |
ASTM A335 / ASME SA-335 |
Seamless ferritic alloy steel pipe for high-temperature service |
| ASTM/ASME |
ASTM A213 / ASME SA-213 |
Seamless ferritic and austenitic alloy-steel boiler and heat-exchanger tubes |
| EN |
EN 10216-2 |
Seamless steel tubes for pressure purposes with elevated-temperature properties |
| JIS |
JIS G3456 |
Carbon steel pipes for high-temperature service |
| JIS |
JIS G3462 |
Alloy steel boiler and heat-exchanger tubes |
| GOST |
GOST 550 |
Seamless steel tubes for petroleum-processing and petrochemical equipment |
These standards should not be treated as automatically interchangeable. Equivalent-grade selection must consider chemistry, minimum yield strength, tensile range, impact temperature, heat treatment, dimensions and testing requirements.
Application: High-Pressure Ammonia Synthesis Pipeline
A representative application is the high-pressure process pipeline connecting the compressor section to the ammonia synthesis loop in a fertilizer plant.
The tube may be exposed to:
- High internal pressure
- Elevated operating temperature
- Pressure and temperature cycling
- Hydrogen-containing process gas
- Site welding and post-weld heat treatment
- Strict requirements for leak tightness and material traceability
For this application, material selection cannot be based solely on room-temperature tensile strength. The engineering review should consider design temperature, hydrogen service, corrosion allowance, weldability, post-weld heat treatment and applicable pressure-piping code requirements.
Chemical Composition
The following values are representative GB/T 6479-2013 ladle-analysis requirements for five frequently specified grades. Values are mass percentages.
| Grade |
C |
Si |
Mn |
P, max. |
S, max. |
Cr |
Mo |
Ni, max. |
Cu, max. |
| 10 |
0.07-0.14 |
0.17-0.37 |
0.35-0.65 |
0.025 |
0.015 |
≤0.15 |
-- |
≤0.25 |
≤0.20 |
| 20 |
0.17-0.23 |
0.17-0.37 |
0.35-0.65 |
0.025 |
0.015 |
≤0.25 |
≤0.15 |
≤0.25 |
≤0.20 |
| Q345B |
0.12-0.20 |
0.20-0.50 |
1.20-1.70 |
0.025 |
0.015 |
≤0.30 |
≤0.10 |
≤0.50 |
≤0.20 |
| 12CrMo |
0.08-0.15 |
0.17-0.37 |
0.40-0.70 |
0.025 |
0.015 |
0.40-0.70 |
0.40-0.55 |
≤0.30 |
≤0.20 |
| 15CrMo |
0.12-0.18 |
0.17-0.37 |
0.40-0.70 |
0.025 |
0.015 |
0.80-1.10 |
0.40-0.55 |
≤0.30 |
≤0.20 |
The grade-specific chemistry for 20, Q345B, 12CrMo and 15CrMo is supported by GB/T 6479 material references.
For final purchasing and inspection, the applicable edition of GB/T 6479 and the signed purchase specification should take precedence over general product literature.
Mechanical Properties
Mechanical values are measured at room temperature after the specified final heat treatment. Yield strength for Q345B varies with wall thickness.
| Grade |
Tensile Strength, MPa |
Minimum Yield Strength, MPa |
Minimum Elongation, % |
Typical Impact Requirement |
| 10 |
335-490 |
205 |
24 |
As specified by grade and order |
| 20 |
410-550 |
245 |
24 |
Commonly specified at 0°C where required |
| Q345B |
490-670 |
345 for WT ≤16 mm; 335 for WT >16-40 mm; 325 for WT >40-60 mm |
21 longitudinal; 19 transverse |
20°C impact class |
| 12CrMo |
410-560 |
205 |
21 |
According to standard and ordered test condition |
| 15CrMo |
440-640 |
295 |
21 |
According to standard and ordered test condition |
Frequently Asked Questions
Q: Are you trading company or manufacturer?
A: manufacturer, also can do trading.
Q: How long is your delivery time?
A: Generally speaking, it is 10-15 days if the goods are in stock, or it is 30-40 days if the goods are not in stock, it is according to quantity.
Q: Do you provide samples? is it free or extra?
A: Yes, we could offer the sample for free charge but need pay the cost of freight.
Q: What is your terms of payment?
A: Payment ≤ 2000 USD, 100% in advance. Payment ≥ 2000 USD, 30% T/T in advance, balance before shipment.
If you have another question, please feel free to contact with me.