1. Womic Steel: Manufacturing Capabilities & Company Strength
Womic Steel Group holds DNV GL approval for manufacturing SAWL pipes per DNV-OS-F101. This standard has more stringent requirements than API 5L for offshore pipelines, including:
● Tighter dimensional tolerances (ovality ≤ 0.2% for UOE, ≤ 0.3% for JCOE)
● Mandatory fracture toughness testing (CTOD – Crack Tip Opening Displacement)
● Higher impact energy requirements (often 50J min at -20°C)
● Strict weld hardness limits (typically ≤ 85 HRB for sour service, ≤ 90 HRB for non-sour)
● Full traceability from plate to finished pipe
● Third-party survey by DNV or other recognized classification society
Production processes: UOE (preferred for deepwater due to superior roundness and low residual stress) and JCOE. Womic’s UOE line includes hydraulic O-press (6,000t) and mechanical expander (72 segments) achieving ovality ±0.15%.
Annual DNV-certified LSAW capacity: 40,000 tons.
Production Flexibility for DNV-OS-F101 L450:
● UOE: 508–1,220mm OD × 6.0–40.0mm WT × ≤ 24m (preferred for deepwater)
● JCOE: 406–1,422mm OD × 6.0–50.8mm WT × ≤ 18m (for shallow water and shore approaches)
● All pipes receive 100% UT with TOFD, hydrotest, and CTOD testing as required.
2. DNV-OS-F101 L450: Material Composition & Performance Characteristics
DNV-OS-F101 L450 is equivalent to API 5L X65 but with additional requirements for offshore use. The “L” designation indicates line pipe, and “450” is the minimum yield strength in MPa.
Chemical Composition (max % by mass, typical for L450):
| Element | DNV-OS-F101 L450 (typical) | Sour Service (optional) |
| C | ≤ 0.12 (typical 0.06-0.10) | ≤ 0.10 |
| Mn | ≤ 1.60 | ≤ 1.40 |
| P | ≤ 0.025 | ≤ 0.020 |
| S | ≤ 0.015 | ≤ 0.003 |
| Si | ≤ 0.45 | 0.20-0.40 |
| Nb+V+Ti | ≤ 0.12 | ≤ 0.10 |
| CEV | ≤ 0.43 | ≤ 0.40 |
Mechanical Properties (Room Temperature):
| Property | DNV-OS-F101 L450 |
| Yield Strength (min) | 450 MPa (65,300 psi) |
| Yield Strength (max) | 575 MPa (83,400 psi) |
| Tensile Strength (min) | 535 MPa (77,600 psi) |
| Elongation (min) | 18% (for 50mm gauge) |
| Hardness (max) – non sour | 90 HRB |
| Hardness (max) – sour service | 85 HRB (typical) |
Fracture Toughness Requirements (DNV-OS-F101):
| Test | Temperature | Acceptance |
| Charpy V-Notch (full size) | 0°C or -20°C | Average ≥ 50J, single ≥ 38J (typical) |
| CTOD (weld metal and HAZ) | -20°C or lower | δ ≥ 0.25mm (weld), δ ≥ 0.30mm (HAZ) |
| DWTT (for fracture propagation) | -20°C | Shear area ≥ 85% |
These values are project-specific. Womic can qualify to client requirements.
3. Dimensional Range & Standards Compliance
| Item | Specification |
| Standard | DNV-OS-F101 (Offshore Standard) – SAWL pipes |
| Manufacturing Processes | UOE (preferred), JCOE |
| Outside Diameter Range | 508mm – 1,220mm (20″ – 48″) for UOE; 406mm – 1,422mm for JCOE |
| Wall Thickness Range | 6.0mm – 40mm (UOE); up to 50.8mm (JCOE) |
| Length Range | Standard: 12m, 18m, 24m (UOE); up to 18m (JCOE) |
| End Finish | Beveled End (BE) per DNV-OS-F101 |
| Surface Finish | 3LPE, 3LPP, FBE, or bare (with temporary corrosion protection) |
| Tolerances (DNV) | OD: ±0.2% (UOE), ±0.5% (JCOE); Ovality: ≤ 0.2% (UOE), ≤ 0.3% (JCOE); WT: -0% / +12.5% (stricter than API); Length: +50mm / -0mm |
4. Available Dimensions & Specifications – DNV-OS-F101 L450 SAWL Steel Pipe
| OD (mm) | WT Options (mm) | Process | Approx Weight (kg/m) | Standard Length | Typical Offshore Application |
| 508 | 10.0, 12.5, 14.0, 16.0, 19.0 | UOE | 122.8 – 229.1 | 12m / 18m / 24m | Subsea flowline |
| 610 | 12.5, 14.0, 16.0, 19.0, 22.0, 25.4 | UOE | 184.2 – 366.2 | 12m / 18m / 24m | Gas export line |
| 711 | 14.0, 16.0, 19.0, 22.0, 25.4, 28.0 | UOE | 240.7 – 471.7 | 12m / 18m | Deepwater riser |
| 813 | 16.0, 19.0, 22.0, 25.4, 30.0, 32.0 | UOE/JCOE | 314.4 – 616.2 | 12m / 18m | Main export |
| 914 | 19.0, 22.0, 25.4, 30.0, 35.0, 38.0 | JCOE | 419.5 – 820.9 | 12m / 18m | Large diameter |
| 1,016 | 22.0, 25.4, 30.0, 35.0, 40.0 | JCOE | 539.2 – 963.9 | 12m | Ultra deepwater |
| 1,220 | 25.4, 30.0, 35.0, 40.0 | JCOE | 748.4 – 1,164.6 | 12m | Deepwater trunk |
For deepwater (water depth > 1,000m), UOE is strongly recommended due to tight ovality tolerance (≤ 0.2%). For shallower water (< 500m), JCOE is acceptable.
5. Common Standards for Offshore Subsea Pipelines
| Standard | Steel Grades | Typical Application |
| DNV-OS-F101 | L360, L415, L450, L485 | Subsea pipelines, risers |
| API 5L PSL2 | X52, X60, X65, X70 | Offshore (less stringent) |
| ISO 3183 | L360, L415, L450, L485 | International offshore |
| NORSOK M-120 | X65, X70 | Offshore platform piping |
| BS 7191 | L360, L450 | North Sea pipelines |
Usage summary: Deepwater gas export, subsea flowlines, dynamic risers, shore approaches, interfield pipelines.
6. Manufacturing Process – UOE (Preferred) for DNV-OS-F101 L450
DNV-OS-F101 requires tighter controls than API 5L. UOE is the preferred process.
UOE Process Steps for Offshore Pipe:
1.Plate inspection – Ultrasonic lamination check, chemical verification, tensile and Charpy testing at specified temperatures.
2.Edge milling – Precision J-bevel (±0.3mm) for consistent weld penetration.
3.U-pressing – 4,000t press forms plate into U-shape.
4.O-pressing – 6,000t press closes into cylindrical shape.
5.Tack welding – Temporary tacks to maintain shape.
6.Inner SAW welding – Heat input controlled (≤ 2.5 kJ/mm for X65/L450).
7.Back-gouging – Mechanical or air arc, followed by grinding.
8.Outer SAW welding – Multi-pass as required.
9.Mechanical expansion – 72segment expander, 0.8-1.2% OD increase. Achieves ovality ≤ 0.2%.
10.100% UT with TOFD – Automated scanning of entire weld volume.
11.Hydrostatic test – Per DNV-OS-F101 (typically 90-100% SMYS).
12.CTOD test – On weld metal and HAZ at specified temperature (e.g., -20°C).
13.DWTT – For fracture propagation control.
14.Final dimensional inspection – OD, ovality, WT, length, straightness.
15.Coating – 3LPE/3LPP applied at dedicated yard.
Key Differences from API 5L for DNV:
● Tighter ovality (0.2% vs 0.5% for API onshore)
● Mandatory CTOD (not required by API 5L)
● Higher Charpy requirements (typically 50J vs 27J)
● Stricter hardness control for sour service
● Full material traceability with surveyor witness points
7. Quality Control & Testing for DNV-OS-F101 L450 SAWL Pipe
| Stage | Inspection | DNV Requirement |
| Plate | Chemical Analysis | Verify composition per DNV-OS-F101 |
| Plate | Tensile | Yield ≥ 450 MPa, Tensile ≥ 535 MPa |
| Plate | Charpy @ -20°C | ≥ 50J average, ≥ 38J single |
| Plate | Ultrasonic | No laminations exceeding allowable |
| Weld | 100% UT with TOFD | Scan entire weld volume, record all indications |
| Weld | Radiographic Testing (spot) | Additional verification |
| Weld | Hardness (weld, HAZ, BM) | ≤ 90 HRB (non-sour) / ≤ 85 HRB (sour) |
| Finished | Hydrostatic Test | 90-100% SMYS, hold time as per standard |
| Finished | CTOD (weld and HAZ) | δ ≥ 0.25mm (weld), δ ≥ 0.30mm (HAZ) @ test temp |
| Finished | DWTT (if required) | Shear area ≥ 85% |
| Finished | Dimensional survey | Witnessed by DNV surveyor |
All testing is witnessed by DNV or client-nominated third party (SGS, BV, ABS). EN 10204 Type 3.2 certificate issued with DNV stamp.
8. Primary Applications – DNV-OS-F101 L450 SAWL Steel Pipe
● Deepwater gas export pipelines – Transporting natural gas from deepwater fields (> 1,000m) to onshore terminals
● Subsea oil and gas flowlines – Connecting subsea trees to manifolds and riser bases
● Dynamic and static risers – Vertical sections from seabed to platform (CTOD and fatigue critical)
● Interfield pipelines – Connecting multiple fields within a region
● Shore approaches – Pipelines crossing surf zone and tidal areas (require coating and concrete weight coating)
● Pipeline bundles – Multiple lines within a carrier pipe (L450 as carrier)
● Offshore platform tie ins – Connecting platform piping to subsea pipelines
ance
9. Packaging & Shipping – DNV Offshore Pipe
Pipes are shipped on break-bulk vessels with DNV surveyor inspection of loading. Each pipe is individually supported with rubber-padded wooden dunnage. End caps are welded steel (to prevent bevel damage). Coated pipes have additional foam wrap. Documentation includes DNV survey reports and MTC 3.2.
10. Womic Steel Advantages & FAQ – DNV-OS-F101 L450 SAWL Pipe
Why Womic Steel for DNV Offshore Pipe?
● DNV GL approved manufacturer for SAWL pipes
● UOE process with 6,000t O-press and 72-segment expander – ovality ≤ 0.15%
● In-house CTOD testing capability (CNAS accredited lab)
● Extensive track record with North Sea, Brazil, and West Africa projects
● Third-party survey by DNV, ABS, BV, or client representative
● Full compliance with DNV-OS-F101 (including Annex A, B, D as required)
Frequently Asked Questions:
Q: What is the difference between DNV-OS-F101 L450 and API 5L X65 for subsea?
A: DNV-OS-F101 is specifically written for offshore pipelines. Key differences: stricter ovality tolerance (0.2% vs 0.5%), mandatory CTOD fracture toughness testing (not required by API 5L), higher Charpy impact requirements (often 50J vs 27J), additional requirements for collapse resistance and fatigue design. For deepwater projects, DNV is the preferred standard.
Q: Do you offer CTOD testing for weld metal and HAZ?
A: Yes. We perform CTOD (Crack Tip Opening Displacement) testing per BS 7448 or ASTM E1820. We can test at -20°C, -30°C, -46°C, or as specified. Typical results: weld metal δ ≥ 0.35mm, HAZ δ ≥ 0.40mm. CTOD testing is witnessed by DNV surveyor.
Q: Can you supply L450 for sour service (H₂S)?
A: Yes. We supply L450 with sour service supplement per DNV-OS-F101 Annex A. This requires lower CEV (≤ 0.40%), Mo addition (0.15-0.25%), PWHT, hardness ≤ 85 HRB, and HIC/SSC testing. We have supplied sour service L450 to North Sea and Middle East offshore projects.
Q: What is the maximum water depth your pipes can withstand?
A: The collapse resistance depends on D/t (diameter/wall thickness) ratio, ovality, and yield strength. For a typical L450 UOE pipe with D/t = 30 (e.g., 610mm × 20mm) and ovality 0.2%, the collapse pressure exceeds 30 MPa (equivalent to 3,000m water depth). For deeper water, we can design thicker walls or tighter ovality. Please provide your water depth and design pressure for a collapse analysis.
Q: Is DNV survey required for every shipment?
A: DNV-OS-F101 requires that the manufacturer holds an approved quality system and that production is surveyed by DNV at defined witness points (e.g., hydrostatic test, CTOD, dimensional inspection). Womic’s facility is audited annually by DNV. For each order, we engage DNV surveyors to witness the required tests. We can also arrange for ABS, BV, or LR survey upon client request.
Q: What is the typical lead time for DNVcertified L450 pipe?
A: 90-120 days, including DNV survey schedule. Lead time depends on plate availability (TMCP plates for offshore have longer lead times, typically 10-14 weeks). CTOD testing adds 2-3 weeks. For repeat orders with pre qualified plates, lead time can be reduced to 60-75 days.
Project Reference – West Africa Deepwater Gas Export Pipeline (Gulf of Guinea)
Country: Offshore Nigeria / Equatorial Guinea border area (Gulf of Guinea)
Standard & Grade: DNV-OS-F101 L450 SAWL (UOE) with sour service supplement
Dimensions & Quantity:
l OD 610mm (24″) × WT 20.6mm – 52,000 meters (approx. 13,500 tons) manufactured by UOE process
l OD 610mm (24″) × WT 25.4mm – 8,000 meters (approx. 2,500 tons) manufactured by UOE process (riser section and shore approach)
Total: 60,000 meters (60 km), approx. 16,000 tons
Specifications: External 3LPE coating (3.2mm) with concrete weight coating (60mm, density 3,050 kg/m³) for negative buoyancy. Beveled ends 30°/1.6mm. Hydrotest at 25.0 MPa (design pressure 18.0 MPa). Water depth: 800-1,400m. Mandatory Charpy at -20°C (min 50J, achieved 120-180J). CTOD at -20°C: weld metal ≥ 0.25mm, HAZ ≥ 0.30mm (achieved 0.40-0.65mm). DWTT at -20°C: shear area ≥ 85% (achieved 90-98%). Ovality ≤ 0.2% (UOE achieved 0.08-0.15%). Hardness ≤ 85 HRB (sour service). HIC per NACE TM0284: CLR 0%, CTR 0%, CSR 0%. SSC per NACE TM0177: no cracking. 100% UT with TOFD, plus 25% RT. Third party survey by DNV GL throughout production.
Application: Deepwater gas export pipeline transporting natural gas from offshore fields (water depth 800-1,400m) to an onshore LNG terminal. The 60 km pipeline includes a deepwater mainline section (52 km, 20.6mm WT), a dynamic riser section (4 km, 25.4mm WT), and a shore approach through surf zone (4 km, 25.4mm WT with concrete coating). The gas contains trace H₂S (5-10 ppm) and CO₂ (3-5%), requiring sour service qualification.
Technical Challenges & Solutions:
1. Deepwater collapse resistance (1,400m water depth) – External hydrostatic pressure at 1,400m is approximately 14.3 MPa. Required collapse pressure with safety factor is > 25 MPa. Womic designed the 24″ × 20.6mm UOE pipe with D/t = 29.6. Using UOE process, we achieved ovality of 0.08-0.12% (well below DNV’s 0.2% limit). We performed finite element analysis (FEA) and full-scale collapse pressure testing on two samples. Collapse pressure achieved: 27.8 MPa and 28.5 MPa – both above requirement.
2. CTOD fracture toughness for dynamic riser – The riser section experiences fatigue loading due to vessel motion and waves. DNV requires CTOD testing at -20°C. Womic performed CTOD on weld metal and HAZ for the 25.4mm WT pipes. Results: weld metal δ = 0.42-0.55mm, HAZ δ = 0.48-0.65mm. We also provided S-N fatigue curves for the girth weld to assist client’s fatigue life assessment.
3. Sour service with trace H₂S – Although H₂S concentration is low (5-10 ppm), the project required full sour service qualification due to high pressure (18 MPa) and the risk of localized corrosion. Womic used low sulfur plates (S ≤ 0.0010%), CEV ≤ 0.38%, Mo addition 0.20%, and PWHT at 580°C for 1.5 hours. Hardness after PWHT: base metal 78-82 HRB, weld 80-85 HRB. HIC and SSC tests passed with zero cracks.
4. Concrete weight coating and 3LPE compatibility – The shore approach section required concrete weight coating (60mm, reinforced with steel mesh) for on-bottom stability. Concrete coating was applied over 3LPE with a bonding agent. Womic coordinated with a specialist coating yard in Angola. We provided test coupons for adhesion and impact testing. Concrete coating passed drop test (1m drop, no cracking).
5. Reel-lay installation compatibility – The pipeline was installed using reel-lay method (spooled onto a reel vessel). This requires extreme ovality control (≤ 0.2%) and weld reinforcement height ≤ 0.5mm. Womic controlled ovality to 0.08-0.15% and ground weld caps to ≤ 0.3mm height. We performed 10 full-scale spooling simulation cycles on a test pipe – no cracking or ovality degradation.
6. DNV survey and documentation – DNV surveyors witnessed hydrostatic testing, CTOD, HIC, SSC, and dimensional inspection for each batch. Womic provided a 1,500-page quality dossier (including all test reports, PWHT charts, UT logs, and surveyor sign-offs) within 4 weeks of shipment. The dossier was accepted without queries.
7. Result: The pipeline was successfully installed in Q2 2025 using the reel-lay vessel Deep Constructor. No pipe body or weld seam failures occurred during spooling, deployment, or post-lay testing. The client’s project manager stated: “Womic’s ovality control and CTOD results exceeded our expectations. The pipes welded consistently in the field with 98% first-pass acceptance rate.” Womic Steel is now on the approved supplier list for two additional deepwater gas export projects in West Africa.
Contact:
Website: www.womicsteel.com
E-mail: sales@womicsteel.com
Tel / WhatsApp / WeChat:
Victor: +86 15575100681
Jack: +86 18390957568
Womic Steel – Your reliable partner for DNV-OS-F101 L450 SAWL steel pipes for deepwater gas export, subsea flowlines, and offshore riser systems worldwide.
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