Narrow Gap Submerged Arc Welding (NG-SAW): A High-Efficiency Solution for Thick-Section Welding

In the field of modern welding technology, Narrow Gap Submerged Arc Welding (NG-SAW) has become a key process for heavy engineering and thick-section structures. Since its introduction in the 1980s, NG-SAW has been widely adopted in industries such as pressure vessel manufacturing, shipbuilding, bridge construction, and offshore engineering.

Technical Overview and Basic Forms

NG-SAW utilizes an extremely narrow groove design (with single-side angles as small as 1°) to achieve high-quality welds through multi-layer and multi-pass welding. Depending on plate thickness, the following configurations are commonly used:

l Single Layer Single Pass (SLSP) : Suitable for materials 70–150 mm thick. It offers high efficiency but requires strict control over groove accuracy and welding parameters due to sensitivity to thermal cracking.

l Single Layer Double Pass (SLDP) : Recommended for plates 150–300 mm thick. It ensures better penetration, easier slag removal, and wider allowable parameter tolerances.

l Single Layer Triple Pass (SLTP) : Applied for plates exceeding 300 mm. This method ensures uniformity and structural integrity across the entire weld section.

Key Advantages of NG-SAW

1. High Efficiency and Cost Savings

l Compared with conventional wide-groove submerged arc welding, NG-SAW improves productivity by 50–80%.

l Reduces filler wire consumption by 38–50% and flux usage by 56–64.7%.

2. Superior Weld Quality

l High weld shape factor ensures excellent side-wall fusion without spatter.

l Multi-layer welding allows grain refinement and improved toughness in both the weld metal and heat-affected zone (HAZ), enhancing resistance to cold cracking.

3. Process Stability and Reliability

l The high arc power of SAW makes it less sensitive to fluctuations in current or voltage.

l The slag-wall drop transition eliminates spatter, ensuring stable wire feeding and torch movement—critical in deep, narrow grooves.

Critical Welding Parameters

To ensure optimal performance, the following parameters should be carefully controlled:

l Wire Diameter : Typically between 2–5 mm. A 3 mm diameter is most common; 4 mm is recommended for plates >140 mm; 5 mm is used for plates >670 mm.

l Welding Current : Up to 800A (for straight wire).

l Arc Voltage : Recommended range: 25–32V. Below 25V may cause excessive convexity; above 32V increases risk of undercutting and slag inclusion.

l Wire-to-Wall Distance (Wire-Wall Spacing) : Ideally equal to the wire diameter (±0.5 mm). Typically set at 5–6 mm to ensure proper sidewall fusion and HAZ control.

l Twin-Wire Sequence : In twin-wire NG-SAW, the front wire initiates the arc and travels 30–50 mm before the rear wire starts on the still-molten pool. The rear wire completes the crater filling before extinguishing.

Groove Design Considerations

l Groove width: 18–50 mm

l Single-wire NG-SAW groove angle: Minimum 1° per side

l Twin-wire NG-SAW groove angle: Minimum 1.5° per side

Flux Requirements and Development Needs

Due to the limited accessibility and difficulty in interpass slag removal, fluxes used in NG-SAW must offer excellent slag detachability. While standard or slightly modified fluxes are widely used in multi-pass configurations, self-releasing fluxes are preferred for single-pass applications—particularly in Japan.

Industry Applications and Future Outlook

NG-SAW is especially suited for large-scale welded structures requiring high productivity, low distortion, and excellent mechanical properties. Its adoption is growing rapidly in sectors including energy equipment, marine engineering, and heavy machinery.

As automation and new flux technologies continue to evolve, NG-SAW is expected to expand into more complex and demanding applications, offering even greater efficiency and reliability in extreme environments.

If you're seeking a cost-effective, high-performance solution for thick-section welding, Narrow Gap Submerged Arc Welding is an ideal choice. Contact us today to learn more about our NG-SAW systems and how they can enhance your production capabilities.