API 5L Grade B - also designated L245 - is the standard-strength line pipe grade. It sits at the lower end of the API 5L strength spectrum, which actually works in its favor: the moderate strength means excellent weldability, predictable field performance, and lower cost compared to higher grades like X52 or X65. That combination makes it the go-to choice for general oil, gas, water transmission, and structural piping.
This guide covers the manufacturing process, chemistry, specification data, and unit-weight table for large-diameter Grade B seamless pipe.
1. Chemical Composition and Mechanical Properties
Grade B chemistry is controlled to balance weldability with the required strength. API 5L offers two product specification levels - PSL1 (basic) and PSL2 (stricter, with supplementary requirements).
Chemical Composition (Heat Analysis)
|
Element |
Grade B PSL1 (max %) |
Grade B PSL2 (max %) |
|
Carbon (C) |
0.28 |
0.22 |
|
Manganese (Mn) |
1.20 |
1.20 |
|
Phosphorus (P) |
0.030 |
0.025 |
|
Sulfur (S) |
0.030 |
0.015 |
|
Carbon Equivalent (CEV) |
Not mandatory |
≤ 0.42 |
Mechanical Properties
|
Property |
Grade B (PSL1) |
Grade B (PSL2) |
|
Min. yield strength |
245 MPa (35 ksi) |
245 MPa (35 ksi) |
|
Min. tensile strength |
415 MPa (60 ksi) |
415 MPa (60 ksi) |
|
Yield-to-tensile ratio |
Not specified |
≤ 0.93 |
|
Charpy V-notch impact |
Not mandatory |
Mandatory at specified temp. |
The lower carbon content in PSL2 (0.22% vs 0.28%) directly improves weldability, while the mandatory CEV limit ensures consistent weld performance. Choose PSL2 for higher-pressure or critical service; PSL1 is adequate for general transmission duties.
Sour service note: Resistance to sulfide stress cracking (SSC) is not an inherent property of Grade B. For sour gas field development, the pipe must meet PSL2 requirements and the supplementary sour-service provisions of NACE MR0175 / ISO 15156 - including hardness limits and SSC testing. These must be specified at the time of ordering.
2. Specification
| Item | Specification |
|---|---|
| Product | API 5L Gr B large-diameter low-carbon steel pipes |
| Material | API 5L Grade B (L245) |
| Standard | API Spec 5L; equivalent supply to ASTM A53M / A106M on request |
| Surface | Black paint, varnish, oiled or galvanized |
| Pipe length | Fixed length, random length, or as required |
| Pipe ends | Plain ends or beveled ends |
| End protection | Plastic caps (small OD) or iron protectors (large OD) |
| Application | Fluid, oil, gas, structure and boiler piping |
| Testing | Chemical component analysis, mechanical and technical property tests, exterior and size inspection, hydrostatic test, X-ray examination |
| Productivity | 20,000 tons per month |
| Min. order | 10 tons |
| Remark | Special designs available on request |
3. Unit Weight Table (kg/m)
The theoretical unit weight of seamless pipe is calculated as (OD - WT) x WT x 0.02466 kg/m, where OD and WT are in millimetres. The table below lists the nominal unit weights for the common large-diameter range (values in kg/m).
| Nominal OD (mm) / WT (mm) | 5.0 | 5.5 | 6.0 | 7.0 | 8.0 | 9.0 | 10.0 | 11.0 | 12.0 | 13.0 | 14.0 | 15.0 | 16.0 | 18.0 | 20.0 | 22.0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 273 | 33.04 | 36.28 | 39.51 | 45.92 | - | - | - | - | - | - | - | - | - | - | - | - |
| 323.9 | 39.32 | 43.18 | 47.04 | 54.70 | 62.32 | 69.89 | - | - | - | - | - | - | - | - | - | - |
| 355.6 | 43.23 | 47.48 | 51.73 | 60.18 | 68.57 | 76.92 | - | - | - | - | - | - | - | - | - | - |
| 406.4 | 49.44 | 54.32 | 59.24 | 68.94 | 78.60 | 88.20 | 97.75 | - | - | - | - | - | - | - | - | - |
| 457 | 55.73 | 61.24 | 66.73 | 77.69 | 88.58 | 99.43 | 110.23 | 120.98 | 131.60 | 142.34 | - | - | - | - | - | - |
| 508 | - | - | 74.28 | 86.48 | 98.64 | 110.75 | 122.81 | 134.82 | 146.78 | 158.69 | - | - | - | - | - | - |
| 610 | - | - | 89.37 | 104.09 | 118.76 | 133.39 | 147.96 | 162.48 | 176.96 | 191.39 | - | - | - | - | - | - |
| 711 | - | - | 104.31 | 121.52 | 138.69 | 155.80 | 172.87 | 189.88 | 206.85 | 223.76 | - | - | - | - | - | - |
| 813 | - | - | - | 139.13 | 158.81 | 178.44 | 198.02 | 217.55 | 237.03 | 256.46 | 278.88 | - | - | - | - | - |
| 914 | - | - | - | 178.74 | 200.06 | 222.93 | 244.95 | 266.92 | 288.84 | 310.72 | 332.54 | 354.31 | 397.74 | 440.95 | 483.96 | - |
| 1016 | - | - | - | 198.86 | 223.49 | 248.08 | 272.62 | 297.10 | 321.54 | 345.93 | 370.27 | 394.56 | 443.02 | 491.26 | 539.30 | - |
| 1220 | - | - | - | - | 296.39 | 327.95 | 357.47 | 386.94 | 416.36 | 445.73 | 475.58 | 533.58 | 591.88 | 649.98 | - | - |
| 1420 | - | - | - | - | 347.71 | 362.21 | 416.66 | 451.06 | 485.41 | 519.71 | 553.96 | 622.36 | 690.52 | 758.49 | - | - |
| 1620 | - | - | - | - | 397.03 | 436.46 | 475.84 | 515.17 | 554.46 | 593.60 | 632.87 | 711.14 | 789.17 | 867.00 | - | - |
| 1820 | - | - | - | - | 446.35 | 490.71 | 535.02 | 579.29 | 623.50 | 667.67 | 711.79 | 799.92 | 887.81 | 975.51 | - | - |
| 2020 | - | - | - | - | 495.67 | 544.96 | 594.21 | 643.40 | 692.55 | 741.65 | 796.70 | 888.70 | 986.46 | 1084.21 | - | - |
| 2220 | - | - | - | - | 544.99 | 599.21 | 653.39 | 707.52 | 761.60 | 815.63 | 869.61 | 977.48 | 1085.11 | 1192.53 | - | - |
| 2420 | - | - | - | - | 594.34 | 635.5 | 712.62 | 771.62 | 830.20 | 889.66 | 948.05 | - | - | - | - | - |
Values are theoretical unit weights; actual weights follow the mill certificate and the permitted tolerances. For intermediate sizes, calculate with the formula above rather than interpolating.
4. Manufacturing Process
API 5L Grade B large-diameter pipe is manufactured from high-quality carbon-steel or low-alloy billets through hot-rolling or cold-drawing processes to form a seamless tubular structure. The production line runs the full process: continuous casting of round billet, ring-furnace heating, piercing, continuous rolling, sizing, cooling, straightening and non-destructive testing. Hot rolling refines the grain structure, which improves the pipe's low-temperature toughness. Compared with welded pipe, the seamless structure eliminates the weld as a potential weak point, offering superior reliability in high-pressure service (a typical working pressure range of 4-8 MPa) and in corrosive media.
API 5L GRB Large Diameter Low Carbon Steel Pipes
API 5L GRB Line pipe Packaging and shipping
API 5L Pipe MTC
FAQ
Is API 5L Grade B the same as L245?
Yes. Grade B uses the traditional designation (35 ksi minimum yield), while L245 uses the metric system (245 MPa minimum yield). They refer to the same grade in API 5L.
What's the difference between Grade B and X42 or X52?
Grade B has a lower yield strength (245 MPa / 35 ksi) compared to X42 (290 MPa / 42 ksi) or X52 (360 MPa / 52 ksi). Grade B is easier to weld and lower in cost, making it ideal for low-to-medium pressure applications. Higher grades are used when higher operating pressures require more strength.
Can Grade B seamless pipe be used for boiler piping?
No. API 5L Grade B is a line pipe grade designed for fluid transmission. For boiler tubing, use ASTM A106 Grade B or ASME SA210, which are specifically designed for high-temperature service.
What's the difference between PSL1 and PSL2 for Grade B?
PSL2 has lower carbon (0.22% vs 0.28%), tighter phosphorus and sulfur limits, mandatory Charpy impact testing, a carbon equivalent limit (CEV ≤ 0.42), and a yield-to-tensile ratio cap. Use PSL2 for critical, regulated, or sour-service applications.
How is the unit weight of seamless pipe calculated?
The formula is W = (OD − WT) × WT × 0.02466 kg/m, where OD and WT are in millimetres. The constant 0.02466 is derived from the density of carbon steel (7.85 g/cm³) and the pipe's cross-sectional geometry.
References
API Specification 5L - Specification for Line Pipe (PSL1 / PSL2)
ASTM A53 / A106 - Standard specification for seamless carbon steel pipe
NACE MR0175 / ISO 15156 - Materials for use in H₂S-containing environments
ASME B36.10M - Welded and Seamless Wrought Steel Pipe (dimension basis)
