S460MLO

1.8878

High-strength weldable fine-grain structural steel for fixed offshore structures · EN 10225-1:2019 — Plates · EN 10225-2:2019 — Sections · NORSOK M-120:2021 MDS Y40 — frequently specified supplementary requirements for plate

S460MLO is a 460 MPa-class, thermomechanically rolled offshore structural steel with specified Charpy toughness at −40 °C. The designation applies to both plate and rolled sections, but chemistry, thickness limits, tensile requirements and impact-test orientation depend on the applicable part of EN 10225. It is intended for welded fixed offshore structures—not subsea pipelines, risers or process piping—and commonly requires project-specific options such as Z35 through-thickness properties, enhanced ultrasonic testing, weldability qualification, PWHT simulation or NORSOK MDS Y40.

Thermomechanically rolled, MDelivery condition · The required property set depends on the controlled rolling and cooling route and cannot necessarily be restored by later heat treatment.
460 MPa minimum yield strength at t ≤ 16 mmNominal strength class · The EN 10225 minimum decreases with increasing product thickness unless a supplementary specification such as NORSOK MDS Y40 modifies it.
Specified at −40 °CLow-temperature toughness · Plate: 60 J minimum average, transverse. Section: 50 J minimum average, longitudinal.
Plate ≤120 mm; section ≤63 mmStandard thickness scope · Greater thicknesses require agreement and demonstration that the applicable standard requirements are maintained.
CEV ≤0.43; Pcm ≤0.22Plate weldability limits · EN 10225-1 limits for S460MLO plate through 120 mm; Pcm up to 0.23 is permitted for t ≤15 mm.
Base grade does not automatically include Z35, CTOD, enhanced UT or NORSOK Y40Offshore quality is option-sensitive · These requirements must be stated in the enquiry, order and inspection documentation.

Overview

Designation system: EN 10027 steel name and steel number system
Product forms: Plate to EN 10225-1, Rolled H, I, Z and T sections, channels and angles to EN 10225-2
Condition: Thermomechanically rolled condition M (TMCP)
Density: 7850 kg/m³ (Reference density used by EN 10225 for calculated mass; not a heat-specific measured property.)

Meaning and scope of the designation

The name identifies structural steel (S), a minimum specified yield strength of 460 MPa for thicknesses not exceeding 16 mm, thermomechanical rolling (M), specified impact properties at −40 °C (L), and intended use in offshore structures (O). Steel number 1.8878 applies to the current designation.

EN 10225 is written for weldable steel used in fixed offshore structures, primarily with North Sea practice in mind. It does not qualify the steel for subsea pipelines, risers, process equipment, process piping or other utility systems. The project design temperature, structural category, fatigue demand, joint detail and governing offshore rules remain separate design considerations.

Product standard determines the actual requirement set

Product form	Governing part	Standard thickness range	Former 2009 designation	Important distinction
Plate	EN 10225-1:2019	Up to 120 mm	S460G1+M	Transverse Charpy testing; plate-specific chemistry, tensile ranges, mandatory UT and optional through-thickness testing.
Rolled sections	EN 10225-2:2019	Up to 63 mm	S460G3+M	Longitudinal Charpy testing; section chemistry permits higher C, P, S and weldability indices than plate.

S460MLO should never be specified or compared without identifying the product standard and product form.

Mechanical requirements in the delivery condition

S460MLO plate — EN 10225-1:2019

Nominal thickness t	Minimum yield strength ReH	Tensile strength Rm	Minimum elongation A	Maximum Re/Rm
t ≤16 mm	460 MPa	520–700 MPa	17%	0.93
16 < t ≤25 mm	440 MPa	520–700 MPa	17%	0.93
25 < t ≤40 mm	420 MPa	520–700 MPa	17%	0.93
40 < t ≤63 mm	415 MPa	500–675 MPa	17%	0.93
63 < t ≤80 mm	405 MPa	500–675 MPa	17%	0.93
80 < t ≤120 mm	400 MPa	500–675 MPa	17%	0.93

Tensile specimens are transverse to the principal rolling direction. Values are specification requirements, not typical mill data.

S460MLO plate impact requirement

Test temperature	Orientation	Minimum average energy	Sampling
−40 °C	Transverse	60 J	Subsurface specimens; for plate over 40 mm, additional verification at mid-thickness is required.

The requirement is the average of three Charpy V-notch specimens. One individual result may be below the specified average but not below 70% of it, subject to the standard's retest rules.

S460MLO rolled sections — EN 10225-2:2019

Nominal thickness t	Minimum yield strength ReH	Tensile strength Rm	Minimum elongation A	Maximum Re/Rm
t ≤16 mm	460 MPa	520–700 MPa	17%	0.90
16 < t ≤25 mm	440 MPa	520–700 MPa	17%	0.90
25 < t ≤40 mm	420 MPa	520–700 MPa	17%	0.90
40 < t ≤63 mm	415 MPa	520–700 MPa	17%	0.90

Section impact requirement: minimum average 50 J at −40 °C in the longitudinal direction. This is not directly comparable with the transverse 60 J plate requirement.

Composition and weldability controls

S460MLO plate composition — EN 10225-1:2019

Element or sum	Requirement, mass %
C	≤0.14
Si	≤0.55
Mn	≤1.70
P	≤0.020
S	≤0.010
Cr	≤0.25
Ni	≤0.70
Mo	≤0.25
N	≤0.010
Al total	0.015–0.055
Cu	≤0.30
Nb	≤0.050
Ti	≤0.025
V	≤0.080
Nb + V	≤0.12
Nb + V + Ti	≤0.13

Maximum values unless a range is shown. Where other nitrogen-binding elements are used, the minimum aluminium value and Al/N rule may not apply. Residual-element restrictions also apply.

Product-form differences that matter for welding

Control	Plate, EN 10225-1	Section, EN 10225-2
Maximum C	0.14%	0.16%
Maximum P / S	0.020% / 0.010%	0.025% / 0.015%
Maximum N	0.010%	0.012%
Maximum CEV	0.43	0.45
Maximum Pcm	0.22	0.26

The same steel name does not mean identical weldability limits across product forms. Welding procedure development must use the actual certificate chemistry and applicable product standard.

IIW carbon equivalent

CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

All elements are mass percentages. CEV is useful for assessing hardenability and hydrogen-cracking precautions, but it does not by itself determine preheat or welding procedure limits.

Pcm carbon equivalent

Pcm = C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B

Pcm is particularly useful for modern low-carbon microalloyed steels. Heat input, combined thickness, restraint, diffusible hydrogen, consumable strength and ambient conditions must also be considered.

Fabrication consequences of the TMCP condition

S460MLO obtains its strength–toughness balance from thermomechanical rolling, microalloying and controlled cooling rather than from a conventional normalize-and-temper cycle. It is generally readily weldable when an appropriately qualified procedure is used, but the low bulk carbon content should not be interpreted as permission to ignore hydrogen control, preheat assessment, interpass temperature, heat input or HAZ toughness.

Hot forming, normalizing or other heating above 580 °C can reduce the strength of condition-M material. Such processing should not be assumed acceptable without mill guidance and appropriate property verification.

If fabrication includes PWHT, the plate or section should be ordered with the applicable simulated-PWHT testing option. EN 10225 uses 580 ±20 °C and a minimum soaking time of one hour per 25 mm, limited to four hours, unless another cycle is agreed. The actual fabrication cycle, including repair cycles and cumulative holding time, should be represented by the qualification and purchase requirements.

Cold forming capability is not defined by a single universal bend radius in the grade name. For heavily formed components, the purchaser can require the manufacturer's forming data or specific cold-forming qualification. Strain-age testing is particularly relevant where severe cold strain is introduced or plate is formed into critical welded hollow components.

Inspection, options and ordering decisions

Important EN 10225-1 plate provisions and options

Requirement or option	Basic plate specification	When it becomes important
Ultrasonic testing	All plates: EN 10160 S0/E1	Specify Option 18 for S1/E2, or a project-specific higher class where justified.
Surface condition	EN 10163-2 Class A, subclass 3 unless agreed otherwise	Confirm if stricter surface acceptance or special repair controls are required.
Inspection document	EN 10204 type 3.1 by default	Specify Option 24 for type 3.2 and identify the validating authority.
Through-thickness properties	Not included automatically	Option 12 requires EN 10164 Z35 for t ≥15 mm and through-thickness tensile strength of at least 80% of the specified minimum tensile strength.
Strain-age testing	Not included automatically	Option 11 for highly strained or critical components; S460/S500 strain-aged Charpy requirement is 46 J average at −40 °C.
Weldability data	Not included automatically	Option 17 should be requested at enquiry stage; especially relevant above 40 mm and for demanding heat-input or CTOD requirements.
PWHT simulation	Not included automatically	Option 9, with Option 10 if a cycle other than the standard 580 °C simulation is needed.
Product analysis	Not included automatically	Option 7 when verification of the finished-product composition is required.
CEV/Pcm reporting basis	Agreement may be made under Option 8	State whether CEV, Pcm or both must be reported and any project maximum below the standard limit.
Fracture mechanics or CTOD	Not a general grade guarantee	Specify the required test method, location, temperature, condition, acceptance criterion and weld procedure applicability.

Options must be invoked in the purchase order; they should not be inferred from the offshore designation alone.

A technically complete order should identify EN 10225-1 or EN 10225-2, S460MLO or 1.8878, dimensions and dimensional standard, tolerance class, inspection certificate, applicable EN 10225 options, project or classification-society requirements, and any NORSOK MDS. Also define test frequency, testing by individual thickness, Z-quality, UT class, impact-test locations, PWHT simulation, CTOD or weldability qualification where these are design-critical.

For stock material, verify that the original mill order invoked every required option. A type 3.2 certificate or trader description cannot retrospectively create Z35, enhanced UT, NORSOK or CTOD compliance that was not included in manufacture and testing.

NORSOK MDS Y40

S460MLO plate is frequently ordered with NORSOK M-120 MDS Y40 for Norwegian offshore work. Y40 is a supplementary material data sheet, not an alternative spelling of S460MLO. Compliance must be explicitly stated and certified; EN 10225-1 compliance alone is insufficient.

Practical effect of current Y40 requirements

Characteristic	EN 10225-1 S460MLO plate	NORSOK MDS Y40 procurement
Yield strength	Minimum decreases from 460 to 400 MPa over the standard thickness range	Typically controlled to 460–580 MPa throughout the applicable thickness range.
Tensile strength	520–700 MPa through 40 mm; 500–675 MPa above 40 mm	Typically 520–700 MPa throughout the applicable range.
Carbon	Maximum 0.14%	More restrictive maximum, commonly 0.12%.
Through-thickness ductility	Optional EN 10225-1 Option 12	Y40 supply is normally associated with documented Z35 requirements for relevant plate thicknesses.
Qualification and testing	Standard EN 10225 inspection plus selected options	Adds MDS-specific qualification, testing, documentation and project controls.

The applicable revision of NORSOK M-120 and the complete MDS Y40 text must govern the order. Do not rely on a shorthand such as “S460MLO/Y40” without listing the revision and project amendments.

Selection and substitution cautions

The 460 MPa strength class can reduce plate thickness and structural mass, but design benefits depend on buckling, fatigue, stiffness, corrosion allowance and weld-detail limitations. Offshore fatigue performance is usually governed more strongly by joint geometry, weld quality, residual stress and inspection category than by base-metal yield strength alone.

S460ML to EN 10025-4 is a related thermomechanically rolled structural steel with −40 °C toughness, but it is not S460MLO. EN 10225 imposes offshore-specific chemistry, testing, inspection and optional qualification provisions. Likewise, API 2W Grade 60 and classification-society 460 MPa grades may occupy a similar application space but are not interchangeable solely on strength level.

Any substitution review should compare product form, standard edition, thickness, delivery condition, chemistry and carbon equivalents, yield and tensile ranges, Charpy orientation and sampling depth, Z-quality, UT acceptance, PWHT condition, fracture-toughness requirements, certification and project approvals.

Sources

BS EN 10225-1:2019 — Weldable structural steels for fixed offshore structures: PlatesBritish Standards Institution
BS EN 10225-2:2019 — Weldable structural steels for fixed offshore structures: SectionsBritish Standards Institution
EN 10225-1:2019 Plates — Technical data and 2009/2019 designation comparisonArcelorMittal Energy Projects
NORSOK M standards — current standards listingStandards Norway
S460MLO / NORSOK Y40 offshore structural plate dataEurope Steel Center
S460MLO material identification and predecessor designationsApplus+ Laboratories Materials Portal

ASK METALMATE

Ask MetalMate about S460MLO

Discussing: S460MLO / 1.8878

AI assistant · Responses are generated and can contain errors; verify specifications before acting.

1.8878	Steel number for S460MLO	Current EN steel number for both EN 10225-1 plate and EN 10225-2 sections.
S460G1+M	Former plate designation	Predecessor designation under EN 10225:2009 for the current EN 10225-1 S460MLO plate grade.
S460G3+M	Former section designation	Predecessor designation under EN 10225:2009 for the current EN 10225-2 S460MLO section grade.
S460G2+M	Former enhanced plate grade associated with current S460MLO plus options	Under the 2019 transition guidance, the old group-3 plate requirements correspond to S460MLO with vacuum/ladle-refining and reduced-sulfur options; it is not an unconditional one-to-one renaming.
NORSOK M-120 MDS Y40	Supplementary offshore material data sheet	Commonly applied to S460MLO plate; it modifies and adds requirements and must be explicitly ordered.
S460ML / 1.8838	Related general structural grade	EN 10025-4 grade with similar strength and low-temperature concept, but without the complete EN 10225 offshore requirement set; not automatically interchangeable.
API Specification 2W Grade 60	Approximate cross-specification counterpart	Similar TMCP offshore strength class, but chemistry, thickness-dependent properties, testing and certification differ. Engineering and purchaser approval are required for substitution.