S355MLO vs S355ML EN 10025-4 Structural Supplier

 

 

S355MLO vs S355ML EN 10025-4 Structural Supplier

Gangsteel – China's Leading Mill-Direct Supplier & Exporter of S355MLO and S355ML EN 10025-4 Structural Steel Plates

Gangsteel is the professional supplier for both S355ML (standard EN 10025-4) and S355MLO (offshore enhanced) structural steel plates, with the largest combined stock in Asia – over 6,000 tons ready for immediate delivery in thickness 6–200 mm, width 1500–4200 mm, length up to 18 m. All plates are genuine TMCP produced by top mills (HBIS, Shougang) with full European approvals and third-party inspection (DNV, ABS, LR, BV, CCS, KR, TÜV, SGS).

We supply S355MLO with full offshore certification package (CTOD, strain ageing, Z35 mandatory) in stock, alongside standard S355ML.

 

S355MLO vs S355ML – The Real Difference Explained

In the EN 10025-4 standard, S355ML is the official grade.

S355MLOis not a separate grade in the published EN 10025-4 standard.

"S355MLO" is a market designation used by mills and suppliers (especially for offshore applications) to indicate S355ML with additional offshore requirements, typically:

• Z35 through-thickness quality mandatory
• Higher impact energy (often ≥50 J average at –40 °C or –50 °C)
• CTOD (Crack Tip Opening Displacement) toughness testing
• Strain ageing test (impact after 5 % strain + ageing)
• PWHT (post-weld heat treatment) simulation testing
• Compliance with offshore standards like DNV-OS-B101, Norsok M-120, or API 2W

The base material is identical – same chemistry, same strength, same TMCP process.

The difference is only in the additional testing and guarantees required by offshore classification societies.

In short: S355ML = standard EN 10025-4 grade S355MLO = S355ML + offshore package ("O" for offshore)

Most modern offshore wind projects (Hornsea, Borkum Riffgrund, Formosa, Baltica) now specify S355MLO instead of plain S355ML to get the extra safety margin in welded joints.

Gangsteel supplies both standard S355ML and full S355MLO offshore-certified plates from stock.

 

For the grade meaning, see S355ML Meaning EN 10025-4 Structural Steel Supplier.

 

Chemical Composition – Identical for Both

Both S355ML and S355MLO have exactly the same chemical requirements per EN 10025-4.

Element	C	Si	Mn	P	S	Nb	V	Al min	Ti	Cr	Ni	Mo	Cu	N	CEV max
S355ML / S355MLO	0.14	0.50	1.60	0.025	0.020	0.05	0.10	0.020	0.05	0.30	0.50	0.10	0.55	0.015	0.39

Typical Gangsteel actual values: C 0.09–0.12 %, CEV 0.34–0.37.

For S355MLO offshore packages, we can offer tighter controls (e.g., P+S ≤0.025 %, Ni 0.30–0.50 %) if required by the project specification.

Full chemical data: S355ML Chemical Composition EN 10025-4 Supplier

 

Mechanical Properties – Standard vs Enhanced Requirements

Base mechanical properties are identical, but S355MLO has additional guarantees.

Property	S355ML (Standard)	S355MLO (Offshore Enhanced)	Notes
Yield Strength ReH (MPa)	355 (≤16 mm) → 285–295 (>150 mm)	Same + higher actual values (typically +20 MPa)	Same EN 10025-4 requirement
Tensile Strength Rm (MPa)	470–630	Same	Identical
Elongation A5 (%)	≥22	Same	Identical
Impact Toughness (long.)	≥27 J at –50 °C	≥50 J average at –40 °C or –50 °C + CTOD testing	The main enhancement
Z-quality	Z25 standard, Z35 optional	Z35 mandatory + higher RA (reduction of area)	Critical for offshore welds
CTOD Toughness	Not required	Required (≥0.25 mm at –10 °C or –40 °C typical)	Fracture mechanics for offshore
Strain Ageing Test	Not required	Often required (impact after strain + ageing)	Simulates fabrication effects

S355MLO plates from Gangsteel routinely achieve:

• Impact values 100–200 J at –50 °C
• CTOD 0.4–0.6 mm at –40 °C
• Z35 with ≥40 % reduction of area

Full mechanical tables: S355ML Mechanical Properties EN 10025-4 Plate Supplier

 

Weldability – Both Excellent, S355MLO Superior in HAZ

Both grades have the same low CEV, but S355MLO's additional testing guarantees superior HAZ properties after high heat input welding.

No preheating required up to 80 mm for both grades. Gangsteel provides welding recommendations and heat-specific data for both S355ML and S355MLO.

 

Price Difference and Market Reality

Grade	Price Level (November 2025)	When to Choose
S355ML	Baseline	Standard structural, onshore, mild cold
S355MLO	+120–220 USD/ton	Offshore wind, oil & gas, Arctic, high-risk welds

The extra cost of S355MLO is easily justified by the additional safety margin and reduced risk of weld failure in offshore environments.

 

Why Choose Gangsteel for S355ML and S355MLO Plates

• Largest stock of both S355ML and S355MLO in Asia (6,000+ tons combined)
• Factory-direct price – 60–120 USD/ton lower than traders
• Full offshore certification packages for S355MLO in stock
• Z35 quality always available
• Immediate delivery worldwide
• Exported to 90+ countries

 

FAQ

Q1: Is S355MLO a separate grade in EN 10025-4?

A: No – it is S355ML with additional offshore requirements (higher impact, CTOD, Z35 mandatory). The base material is identical.

Q2: Can I use S355ML instead of S355MLO?

A: Only if the project specification allows. Most offshore wind projects now require S355MLO package for extra safety in welded joints.

Q3: Price difference?

A: S355MLO is 120–220 USD/ton higher than standard S355ML.

Q4: Do you have S355MLO in stock?

A: Yes – large stock of S355MLO with full offshore certification ready.

Q5: Additional testing for S355MLO?

A: CTOD toughness, strain ageing test, higher impact energy, Z35 mandatory – all included in our S355MLO stock plates.

Contact Gangsteel

For S355ML or S355MLO plates, quote now.

 

Email: admin@gangsteel.com WhatsApp/WeChat/Mobile: +86 135 9887 9167 Website: https://gangsteel.net/

Gangsteel – Your Expert for Both Standard and Offshore S355ML Plates.

 

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