Steel X70-MO (Offshore service, X70MO)
Grade
ASTM API 5L X70 · GB L485
For subsea/offshore risers and flowlines: tighter yield-to-tensile ratio, strain-ageing and through-thickness (Z-direction) requirements plus DWTT and CTOD testing.
Values for the MO condition
Other X70 tempers and conditions
X70 is listed in 3 conditions; see the grade overview at X70.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
MDefault Thermomechanically controlled processed | Default modern condition for large-diameter gas transmission line pipe: best combination of low carbon equivalent, high low-temperature toughness and tight yield range. | 520 | 610 | 28 | 200 HB | — |
MOThis page Offshore service, X70MO | For subsea/offshore risers and flowlines: tighter yield-to-tensile ratio, strain-ageing and through-thickness (Z-direction) requirements plus DWTT and CTOD testing. | 525 | 620 | 28 | 200 HB | 10 % IACS |
quenched and tempered, X70Q / L485Q | Choose for heavy-wall seamless or thick plate where TMCP through-thickness properties are hard to achieve, e.g. risers, induction bends and fittings. | 540 | 630 | 25 | 215 HB | — |
What is X70-MO?
X70-MO is X70 in the MO grade — for subsea/offshore risers and flowlines: tighter yield-to-tensile ratio, strain-ageing and through-thickness (Z-direction) requirements plus DWTT and CTOD testing. X70-MO has a yield strength of 525 MPa (76.1 ksi) and a tensile strength of 620 MPa (89.9 ksi) — stronger than 68% of steel grades. Elongation at break is 28% and the elastic modulus is 207 GPa (30 Msi). X70-MO has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,490°C (2,714 °F). M is the default condition FabDigit quotes; MO is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 210 MPa·√m (191.1 ksi·√in), better than 100% of steel grades
- Ductile — tolerates forming and impact — 28%, better than 89% of steel grades
- Readily welded — 88/100, better than 87% of steel grades
- High electrical conductivity — 10 % IACS, better than 83% of steel grades
- Forms and bends easily — 65/100, better than 81% of steel grades
Limitations
- Limited service temperature — 250°C (482 °F), worse than 85% of steel grades
- Hard to polish — 45/100, worse than 84% of steel grades
X70-MO properties
Typical room-temperature values for X70-MO; 23 are specific to this condition. Other listed values are X70 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
X70-MO has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,490°C (2,714 °F).
Mechanical16
X70-MO has a yield strength of 525 MPa (76.1 ksi) and a tensile strength of 620 MPa (89.9 ksi) — stronger than 68% of steel grades. Elongation at break is 28% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
X70-MO is rated for continuous service to 250°C (482 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
X70-MO conducts electricity at 10 % IACS, better than 83% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of X70-MO takes about 25 MJ of energy and emits 2.1 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 20%.
Manufacturability6
X70-MO's machinability is fair (52/100, better than 52% of steel grades); weldability excellent (88/100); formability good (65/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with X70-MO
Is X70 easy to machine?
Machines like a tough C-Mn steel at roughly 60 % of AISI 1212; sharp positive-rake carbide, generous feed and rigid setup avoid work-hardened glazing on bevels and counterbores.
Can X70 be welded?
Excellent weldability with CE_IIW ≤0.43 and Pcm ≤0.25 — cellulosic or low-hydrogen SMAW, GMAW/FCAW and multi-wire SAW all standard; keep heat input moderate (≈0.5–2.5 kJ/mm) so TMCP HAZ does not soften, and preheat 50–100 °C for heavy wall or damp conditions.
Can X70 be formed, bent or molded?
Cold formed by UOE/JCOE/spiral (HSAW) routes with cold expansion 0.8–1.3 %; avoid hot forming or normalizing of TMCP material, which permanently loses strength — heavy induction bends should use Q-condition or be re-quenched and tempered.
What surface finishes work on X70?
Not anodizable; standard protection is grit blast plus fusion-bonded epoxy, 3-layer PE/PP or coal-tar coating with cathodic protection, and internal flow-efficiency epoxy for gas lines.
X70 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CPSL2 M/Q; PSL1 allows up to 0.28 | ≤ 0.12 | 0.06 |
| Si | ≤ 0.45 | 0.25 |
| Mn | ≤ 1.7 | 1.55 |
| P | ≤ 0.03 | 0.01 |
| S≤0.002 typical for MS sour grades | ≤ 0.02 | 0 |
| Nbmicro-alloy; Nb+V+Ti ≤0.15 | ≤ 0.06 | 0.05 |
| V | ≤ 0.1 | 0.03 |
| Ti | ≤ 0.06 | 0.02 |
| Cu | ≤ 0.5 | 0.1 |
| Ni | ≤ 0.5 | 0.15 |
| Cr | ≤ 0.5 | 0.1 |
| Mo | ≤ 0.5 | 0.15 |
| Alacid-soluble Al | ≤ 0.06 | 0.03 |
| N | ≤ 0.01 | 0.01 |
| BM condition | ≤ 5×10⁻⁴ | 2×10⁻⁴ |
| Fe | balance | — |
X70-MO — frequently asked
What is X70-MO used for?
X70-MO is typically used for long-distance gas pipelines, large-diameter welded pipe and arctic pipelines. In short: standard large-diameter gas grade; TMCP strength with weldability; arctic toughness options.
What is the yield strength of X70-MO?
X70-MO has a typical yield strength of 525 MPa (76.1 ksi) and a tensile strength of 620 MPa (89.9 ksi) — stronger than 68% of steel grades. Strength varies by condition: see the 3 listed tempers.
Is X70-MO easy to machine?
Reasonably — machinability is rated fair (52/100, better than 52% of steel grades). Machines like a tough C-Mn steel at roughly 60 % of AISI 1212; sharp positive-rake carbide, generous feed and rigid setup avoid work-hardened glazing on bevels and counterbores.
Can X70-MO be welded?
Yes — weldability is rated excellent (88/100). Excellent weldability with CE_IIW ≤0.43 and Pcm ≤0.25 — cellulosic or low-hydrogen SMAW, GMAW/FCAW and multi-wire SAW all standard; keep heat input moderate (≈0.5–2.5 kJ/mm) so TMCP HAZ does not soften, and preheat 50–100 °C for heavy wall or damp conditions.
What surface finishes work on X70-MO?
Not anodizable; standard protection is grit blast plus fusion-bonded epoxy, 3-layer PE/PP or coal-tar coating with cathodic protection, and internal flow-efficiency epoxy for gas lines.
Can X70-MO be formed, bent or molded?
Cold formed by UOE/JCOE/spiral (HSAW) routes with cold expansion 0.8–1.3 %; avoid hot forming or normalizing of TMCP material, which permanently loses strength — heavy induction bends should use Q-condition or be re-quenched and tempered.
What is the maximum service temperature of X70-MO?
X70-MO is rated for continuous use to about 250°C (482 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between X70-M and X70-Q?
M is the default condition — default modern condition for large-diameter gas transmission line pipe: best combination of low carbon equivalent, high low-temperature toughness and tight yield range. Q: choose for heavy-wall seamless or thick plate where TMCP through-thickness properties are hard to achieve, e.g. risers, induction bends and fittings. Yield strength is 520 MPa in M versus 540 MPa in Q.
Sources
- API 5L Specification for Line Pipe, 46th edition — API (2018)
- ISO 3183 Petroleum and natural gas industries — Steel pipe for pipeline transportation systems — ISO (2019)
- EN 10208-2 Steel pipes for pipelines for combustible fluids — Requirements class B (L485MB) — CEN (2020)
- ANSI/NACE MR0175 / ISO 15156-2 — Cracking-resistant carbon and low-alloy steels — NACE/ISO (2020)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Line pipe steel grades X60–X80 (TMCP hot rolled coil and plate) — major linepipe mills (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.