API 5L X65 Steel
A line pipe steel for oil and gas transmission
Typical values for the temper in the title
X65 is a grade in the API 5L standard for line pipe. The number gives the minimum yield strength: 65 ksi (448 MPa). In the international standard ISO 3183 it is called L450. It is a microalloyed carbon-manganese steel, low in carbon, so it is strong and still welds well in the field.
The standard has two requirement levels: PSL1 and PSL2. PSL2 is stricter, including a maximum yield, impact testing and a carbon-equivalent limit. For "sour" service (with H2S) there are additional requirements per NACE MR0175.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 530 MPa min | minimum |
| Yield strength Rp0.2 | 448 MPa min | minimum (65 ksi) |
| Elongation A | 18% | |
| Hardness | 210-240 HB | |
| Modulus of elasticity E | 207 GPa | |
| Density ρ | 7.85 g/cm³ | |
| Machinability | 55% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| C carbon | low (limited in PSL2) | weldability |
| Mn manganese | limited per the standard | |
| Nb / V / Ti | microalloying | strength without extra carbon |
| Fe iron | balance |
Descriptive composition. Exact limits are in API 5L and depend on the PSL and pipe type (welded or seamless).
Conditions and heat treatment
Structural, pressure and pipeline steels are selected by minimum yield strength and impact toughness at a given temperature, not by a heat treatment the user performs. The delivery condition is defined by the standard.
| Condition | Properties | When to choose it |
|---|---|---|
| PSL1 | minimum yield 448 MPa | basic requirements |
| PSL2 | minimum and maximum yield, impact testing, CE limit | common in transmission pipelines |
| Sour service | additional requirements per NACE MR0175 | for H2S presence |
Applications
- Oil and gas transmission pipelines
- Subsea pipelines
- Compressor station piping
- High-pressure water lines
- Petrochemical piping
Fabrication
Welding
In the field, per qualified procedures. Preheat is set by CE and thickness.
Sour service
Requires hardness control in welds and the weld zone.
Corrosion
Buried or subsea pipe is protected by coating and cathodic protection.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| A516 Gr.70 | 485-620 / 260 MPa | Excellent | a plate steel for pressure vessels · material page |
| S355 | 470–630 / 355 MPa | Good | a structural steel · material page |
| A572 Gr.50 | 450 / 345 MPa | Excellent | an HSLA structural steel · material page |
Common mistakes
Ordering PSL1 when the project requires PSL2
Testing and composition requirements differ.
Ignoring sour service requirements
With H2S, hydrogen cracking may occur in pipe not intended for it.
Confusing X65 with tensile strength
65 ksi is the minimum yield strength.
Equivalents, standards and supply
| EN | L450 (ISO 3183) |
|---|---|
| Standards | API 5L / ISO 3183 |
| Forms | pipe only (seamless/welded) |
| Producers | Tenaris · Vallourec · EVRAZ · Nippon Steel |
Learn more
Values are typical and for comparison only, and depend strongly on condition and diameter. For design, rely on the standard and on the mill certificate. Sources: SAE J403 and J404, ASTM A29, A322 and A519 (composition), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026