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Grade X80

API 5L X80 · API 5L

PipelineHSLA

Grade X80 (API 5L X80) is a pipeline steel (HSLA family) to API 5L. It has a specified 0.2 % proof stress of 551 MPa and a typical tensile strength of about 621 MPa, with a uniform elongation of 21 %. Nominal carbon content is around 0.16 %. For nonlinear FEA, a bilinear model uses E = 210 GPa up to yield and a tangent modulus of 341 MPa above it. It is a general-purpose wrought steel selected on strength, cost and availability.

0.2% proof Rp0.2
551MPa
UTS Rm (typ)
621MPa
Uniform elong. εu
21.0%
Condition / basis
PSL1

Bilinear material model — nonlinear FEA

Elastic modulus E
210GPa
0.2% proof Rp0.2
551MPa
UTS Rm (typ)
621MPa
Tangent modulus Et
341MPa

Uniform elongation εu = 21.0% · conservative analysis limit ½εu = 10.5%

Bilinear (BISO) approximation. Elastic modulus E up to the 0.2% proof stress R_p0.2, then a single tangent slope Eₜ to the ultimate tensile strength: Eₜ = (Rₘ − R_p0.2) / (εu − R_p0.2/E − 0.002), where εu is the uniform elongation and Rₘ is a typical (nominal) UTS within the specified band. The half-εu figure is a conservative strain limit for the analysis. Treat these as guidance for first-pass models; for critical work use a measured true stress–strain curve for the actual product and condition.

Ratings — engineering judgement

Weldabilitygood

Low carbon (~0.16%) gives good weldability by all common processes; preheat rarely needed in thin sections.

Machinabilitymoderate

Soft and gummy at low carbon — sharp tooling helps surface finish.

Corrosion resistancepoor

No inherent corrosion resistance — protect by paint, galvanising or plating in exposed use.

Hardenabilitylow

Limited hardenability at low carbon — surface hardening is possible but through-hardening is not.

Toughnessmoderate

Adequate toughness for general use at ambient temperature.

Indicative ratings derived from composition and family — engineering guidance, not specification values.

Physical properties

Density7850kg/m³
Elastic modulus210GPa
Shear modulus80.8GPa
Poisson's ratio0.30
Thermal expansion12.0×10⁻⁶/°C
Thermal conductivity48W/(m·K)
Specific heat470J/(kg·K)
MagneticYes

Typical values for hsla steel — use the mill certificate for the specific product.

Chemical composition (wt %)

C
≤ 0.16
Mn
≤ 1.70
Si
≤ 0.45
P
≤ 0.025
S
≤ 0.015
Nb+V+Ti
≤ 0.15

Typical composition per API 5L — confirm PSL1/PSL2 and sour-service limits against the standard.

Available forms

pipeexcellent
seamless & welded line pipe
Primary form to the line-pipe standard.
plategood
for welded pipe
Coil/plate feedstock for pipe making.

Common applications

  • Oil and gas transmission line pipe
  • Water and slurry pipelines
  • Structural and pressure piping

History

API 5L is the global line-pipe standard. Its grades trace the rise of micro-alloyed, controlled-rolled steels that let cross-country oil and gas pipelines run at ever-higher pressures with the weldability and toughness needed for field girth welding. The “X” number is the minimum yield in ksi (X80 ≈ 552 MPa).

  1. 1928
    API 5L first published for line pipe
  2. 1970
    Micro-alloyed (Nb/V) controlled-rolled steels lift pipeline strength
  3. 2000
    PSL2 formalises tighter chemistry, toughness and NDE

This profile is generated from the grade's core data and family. Composition is decoded from the designation where its naming system defines it; physical properties are family-typical and ratings are indicative. Confirm critical values against the governing standard or the mill certificate. Equivalents, historical designations and hand-written expert notes are added per grade over time.