In offshore structural fabrication, welding of S690 high-strength steel is typically carried out under the supervision of major classification societies such as DNV, Lloyd's Register, Bureau Veritas, and ABS.
These organizations have established comprehensive rule systems with minimum technical thresholds to ensure structural integrity and operational safety in harsh marine environments.
Although the core requirements defined by these classification bodies are largely harmonized, achieving compliance in real-world production demands substantial welding experience, strict process control, and suitable consumable selection-especially for S690 offshore steel structures.
Minimum Mechanical Requirements for Weld Metal
All welding consumables used for S690 steels in offshore service must meet or exceed the mechanical properties listed below:
| Property | Minimum Requirement | Typical Offshore Expectation |
|---|---|---|
| Tensile Strength | ≥ 770 MPa | 770–860 MPa |
| Yield Strength | ≥ 690 MPa | ≥ 690 MPa |
| Elongation | ≥ 17% | 17–22% |
| Charpy V-Notch Impact (-40°C) | ≥ 69 J | 70–90 J |
These values are critical to ensure sufficient load-bearing capacity, crack resistance, and toughness under low-temperature offshore conditions.
Welding Consumable Solutions for S690 Steel
Rutile Flux-Cored Wire – CEWELD AA R690
CEWELD AA R690 is a seamless rutile flux-cored wire specifically designed for S690 and HY100 offshore steels. Flux-cored wires are widely favored by welders due to their stable arc characteristics and wide spray transfer range.
Key characteristics:
Excellent arc stability and smooth metal transfer
Optimal welding current range: 180–270 A
Suitable for high-current positional welding
Typical PF position current: ~240 A (vs. ~120 A for solid wire)
Integrated slag system supporting vertical and positional welds
This makes AA R690 particularly suitable for complex offshore structures where repositioning large components is impractical.
Metal-Cored Wire (MCAW) – CEWELD AA M690
CEWELD AA M690 is a seamless metal-cored welding wire developed for S690 high-strength offshore steels. The primary advantage of metal-cored wire lies in its superior deposition efficiency.
Technical advantages:
10–20% higher deposition rate compared to solid wire
Improved current density due to easily melting metal powder
Enhanced weld pool wetting behavior
Enables higher travel speeds
Facilitates control of T8/5 cooling times, which are critical for maintaining toughness in S690 welds
AA M690 is often selected when productivity and precise heat input control are equally important in offshore fabrication.
Solid GMAW Wire – CEWELD ER 110 Ti
With the advancement of modern inverter-based power sources and digitally controlled arc characteristics, the performance gap between solid wires and cored wires has narrowed.
CEWELD ER 110 Ti (ER 110 S-1) offers:
Improved arc stability through digital arc control
Enhanced wetting behavior compared to conventional solid wires
Significantly reduced risk of lack-of-fusion defects
Mechanical properties suitable for S690–HY100 steels
Despite these improvements, solid wires are still less dominant in offshore welding due to approval limitations and positional welding challenges.
Comparison of Welding Wire Types for S690 Offshore Steel
| Wire Type | Deposition Rate | Positional Welding | Arc Stability | Offshore Approvals | Typical Usage |
| Flux-Cored (FCAW) | Very High | Excellent | Excellent | Widely Approved (DNV/LR) | ~95% offshore welding |
| Metal-Cored (MCAW) | High (+10–20%) | Good | Very Good | Commonly Approved | Productivity-focused |
| Solid Wire (GMAW) | Moderate | Limited | Good (digital arc) | Limited | Controlled environments |
Why Flux-Cored Wire Dominates Offshore S690 Welding (≈95%)
Flux-cored welding wires remain the preferred choice for offshore S690 steel fabrication due to the following factors:
Large offshore structures are difficult or impossible to rotate into down-hand welding positions
Offshore quality and toughness requirements are demanding and difficult to achieve consistently with solid wires
Flux-cored wires show significantly fewer bonding and fusion defects
Most solid wires lack full offshore approvals (DNV, Lloyd's, etc.)
Higher productivity:
Up to 200% deposition efficiency in positional welding
~120% efficiency in down-hand welding
Improved arc behavior increases welder duty cycle by ≥5%, reducing fatigue and rework
For offshore construction involving S690 high-strength steel, flux-cored and metal-cored welding consumables provide the optimal balance between mechanical performance, toughness, productivity, and compliance with classification society requirements.
While solid wires have improved with digital arc technology, flux-cored wires remain the industry standard for offshore S690 welding due to their superior positional capability and proven reliability.
Q: Heat input control is critical when welding S690 steel.
A: Because S690 steel is supplied in the quenched and tempered condition, excessive heat input during welding can lead to softening of the heat-affected zone (HAZ).
If not properly controlled, this softening may reduce the effective yield strength near the weld, undermining the original design assumptions. Therefore, strict limits on heat input, interpass temperature, and cooling rate are commonly specified in welding procedures.
Q: Hydrogen-induced cracking is a key risk in S690 welding.
A: Although S690 has relatively low carbon content, its high strength level increases susceptibility to hydrogen-assisted cold cracking. To mitigate this risk, low-hydrogen welding consumables are mandatory, and preheating may be required depending on plate thickness, joint restraint, and ambient conditions. In offshore and heavy-duty structures, hydrogen control is often more critical than preheat temperature alone.
Q: S690QL and S690QL1 differ mainly in low-temperature impact requirements.
A: The primary distinction between S690QL and S690QL1 lies in their Charpy V-notch impact test temperatures. S690QL typically requires impact testing at −40 °C, while S690QL1 is tested at −60 °C.
This makes S690QL1 more suitable for arctic, offshore, or cold-region applications, where fracture toughness at low temperatures is a critical design parameter.
Q: Using S690 allows weight reduction but increases fabrication discipline.
A: From a structural design perspective, S690 enables significant plate thickness and overall weight reduction compared with S355 or S460 steels. However, these savings come at the cost of stricter fabrication control.
Welding procedures, inspection levels, and operator qualification often need to be upgraded to fully realize the benefits of high-strength steel without compromising safety.
