Steel X65-MO (TMCP, offshore service)
Grade
ASTM API 5L X65 · GB L450
Reel-lay / deep-water offshore pipe: narrow yield band, controlled Y/T ratio and tight ovality for strain-based design and welding productivity.
Values for the MO condition
Other X65 tempers and conditions
X65 is listed in 5 conditions; see the grade overview at X65.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
As-rolled (hot-rolled, no special heat treatment), PSL1 | Lowest-cost PSL1 option for non-critical, ambient-temperature service where no impact-energy requirement is imposed. | 480 | 565 | 25 | 178 HB | 8.6 % IACS |
Normalized | Choose for seamless or normalized-plate pipe where uniform through-thickness properties and post-forming heat treatment tolerance matter more than peak toughness. | 485 | 590 | 28 | 185 HB | — |
MDefault Thermomechanically controlled processed | Default condition for LSAW/HSAW/HFW line pipe from TMCP coil or plate — best combination of strength, low-temperature toughness and low carbon equivalent for field welding. | 495 | 570 | 32 | 180 HB | — |
MOThis page TMCP, offshore service | Reel-lay / deep-water offshore pipe: narrow yield band, controlled Y/T ratio and tight ovality for strain-based design and welding productivity. | 500 | 580 | 32 | 182 HB | 8.6 % IACS |
Quenched and tempered, PSL2 | Heavy-wall seamless or thick plate pipe for deep-water/high-pressure lines — tempered martensite/bainite gives the most uniform strength and toughness in thick sections. | 515 | 615 | 26 | 195 HB | — |
What is X65-MO?
X65-MO is X65 in the MO grade — reel-lay / deep-water offshore pipe: narrow yield band, controlled Y/T ratio and tight ovality for strain-based design and welding productivity. X65-MO has a yield strength of 500 MPa (72.5 ksi) and a tensile strength of 580 MPa (84.1 ksi) — stronger than 63% of steel grades. Elongation at break is 32% and the elastic modulus is 207 GPa (30 Msi). X65-MO has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). M is the default condition FabDigit quotes; MO is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 230 MPa·√m (209.3 ksi·√in), better than 100% of steel grades
- Ductile — tolerates forming and impact — 32%, better than 95% of steel grades
- Readily welded — 90/100, better than 90% of steel grades
- Forms and bends easily — 72/100, better than 88% of steel grades
Limitations
- Hard to polish — 40/100, worse than 96% of steel grades
- Limited service temperature — 250°C (482 °F), worse than 85% of steel grades
X65-MO properties
Typical room-temperature values for X65-MO; 23 are specific to this condition. Other listed values are X65 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
X65-MO has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
X65-MO has a yield strength of 500 MPa (72.5 ksi) and a tensile strength of 580 MPa (84.1 ksi) — stronger than 63% of steel grades. Elongation at break is 32% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
X65-MO is rated for continuous service to 250°C (482 °F). It conducts heat at 47 W/m·K (27.2 BTU/hr·ft·°F), better than 75% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
X65-MO conducts electricity at 8.6 % IACS, better than 66% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of X65-MO takes about 25 MJ of energy and emits 2 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 20%.
Manufacturability7
X65-MO's machinability is fair (54/100, better than 54% of steel grades); weldability excellent (90/100); formability very good (72/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with X65-MO
Is X65 easy to machine?
Machines like normalized C-Mn steel (~60 % of AISI 1212): carbide tooling, moderate speeds; bevel ends by machining rather than flame cutting where CVN in the HAZ matters.
Can X65 be welded?
Excellent field weldability at CE_IIW ≤0.43 / Pcm ≤0.25 — SMAW cellulosic or mechanized GMAW with E/ER 8xx-class consumables; control heat input (≈0.7–2.0 kJ/mm) to avoid HAZ softening of TMCP material, low-hydrogen practice and preheat 50–100 °C for heavy wall.
Can X65 be formed, bent or molded?
Cold formed by UOE/JCOE/spiral for welded pipe and cold bent or induction bent in the field; expect ~3–5 % strain and some Bauschinger yield drop, re-check yield after cold expansion or reeling.
What surface finishes work on X65?
Not anodizable — protect with shot-blast + FBE, 3LPE/3LPP or concrete weight coating, plus cathodic protection; internal flow coating or corrosion inhibitor for wet service.
X65 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 welded pipe max 0.12 %; seamless up to 0.16 % | ≤ 0.12 | 0.06 |
| Si | ≤ 0.45 | 0.25 |
| Mnseamless PSL2 up to 1.75 % | ≤ 1.7 | 1.45 |
| Psour service ≤0.020 % | ≤ 0.03 | 0.01 |
| Ssour service (MS) ≤0.002 % | ≤ 0.02 | 0 |
| NbNb+V+Ti ≤ 0.15 % total | ≤ 0.06 | 0.05 |
| V | ≤ 0.1 | 0.04 |
| Ti | ≤ 0.06 | 0.02 |
| Cu | ≤ 0.5 | 0.15 |
| Ni | ≤ 0.5 | 0.18 |
| Cr | ≤ 0.5 | 0.12 |
| Mohigher in Q and heavy-wall grades | ≤ 0.5 | 0.08 |
| Alacid-soluble Al, grain refinement | 0.02 – 0.06 | 0.03 |
| N | ≤ 0.01 | 0.01 |
| Cainclusion shape control for sour service | ≤ 0.01 | 0 |
| Fe | balance | — |
X65-MO — frequently asked
What is X65-MO used for?
X65-MO is typically used for transmission pipelines, offshore risers and sour service pipe (select grades). In short: workhorse line pipe grade; excellent field weldability; sour-service variants available.
What is the yield strength of X65-MO?
X65-MO has a typical yield strength of 500 MPa (72.5 ksi) and a tensile strength of 580 MPa (84.1 ksi) — stronger than 63% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is X65-MO easy to machine?
Reasonably — machinability is rated fair (54/100, better than 54% of steel grades). Machines like normalized C-Mn steel (~60 % of AISI 1212): carbide tooling, moderate speeds; bevel ends by machining rather than flame cutting where CVN in the HAZ matters.
Can X65-MO be welded?
Yes — weldability is rated excellent (90/100). Excellent field weldability at CE_IIW ≤0.43 / Pcm ≤0.25 — SMAW cellulosic or mechanized GMAW with E/ER 8xx-class consumables; control heat input (≈0.7–2.0 kJ/mm) to avoid HAZ softening of TMCP material, low-hydrogen practice and preheat 50–100 °C for heavy wall.
What surface finishes work on X65-MO?
Not anodizable — protect with shot-blast + FBE, 3LPE/3LPP or concrete weight coating, plus cathodic protection; internal flow coating or corrosion inhibitor for wet service.
Can X65-MO be formed, bent or molded?
Cold formed by UOE/JCOE/spiral for welded pipe and cold bent or induction bent in the field; expect ~3–5 % strain and some Bauschinger yield drop, re-check yield after cold expansion or reeling.
What is the maximum service temperature of X65-MO?
X65-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 X65-M and X65-Q?
M is the default condition — default condition for LSAW/HSAW/HFW line pipe from TMCP coil or plate — best combination of strength, low-temperature toughness and low carbon equivalent for field welding. Q: heavy-wall seamless or thick plate pipe for deep-water/high-pressure lines — tempered martensite/bainite gives the most uniform strength and toughness in thick sections. Yield strength is 495 MPa in M versus 515 MPa in Q.
Sources
- API 5L Specification for Line Pipe, 46th ed. — American Petroleum Institute (2018)
- ISO 3183 Petroleum and natural gas industries — Steel pipe for pipeline transportation systems — ISO (2019)
- EN 10208-2 Steel pipes for pipelines — L450MB/L450NB — CEN (2020)
- NACE MR0175 / ISO 15156-2 Materials for use in H2S-containing environments — 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 plate and coil data — Baosteel / ArcelorMittal (2022)
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.