In shipbuilding, SS490 is used for secondary and non-critical structural components, where high impact toughness and specialized marine corrosion resistance are not primary requirements. It is not used for the primary hull or highly stressed, critical parts.
Here's a breakdown of its typical applications and the important limitations:
Typical Components Made from SS490 in Shipbuilding
| Component Category | Specific Examples | Why SS490 is Suitable Here |
|---|---|---|
| Internal Supporting Structures | • Deck girders and floors (in non-critical areas) • Bulkhead stiffeners (non-watertight) • Platforms, walkways, and staircases inside the hull • Foundation beds for non-critical machinery |
These are statically loaded and housed within the protected internal environment of the ship, shielded from direct seawater impact and extreme low temperatures. |
| Superstructure & Accommodation Blocks | • Upper deck houses • Cabin walls and roof framing • Interior partitions |
Subject to lower stresses and a relatively mild environment (protected from direct sea spray). |
| Outfitting & Auxiliary Items | • Storage racks and shelves • Workshop tables and frames • Non-critical ducting supports • Miscellaneous brackets and hangers |
Non-structural or lightly loaded items where cost-effectiveness is key. |
Critical Limitations & What SS490 is NOT Used For
SS490 is prohibited or highly discouraged for critical marine applications due to two major shortcomings:
Lack of Guaranteed Toughness: SS490 has no mandatory Charpy impact test. This makes it unfit for:
Primary Hull Structure: Plating, longitudinals, and frames that absorb dynamic wave loads and must resist brittle fracture, especially in cold waters.
Critical Stress Areas: Zones of high stress concentration (e.g., hatch corners, sheer strake).
Poor Corrosion Resistance: As a carbon steel, it has no inherent resistance to marine corrosion. It is not used for:
External Hull Plating
Ballast Tanks (highly corrosive environment)
Sea Chests or Overboard Components
Marine-Grade Steel Alternatives for Critical Parts
For components where SS490 is unsuitable, shipbuilders use specialized marine-grade steels with strict toughness and chemistry controls:
General Hull Structure: Grade A, B, D, E steels per ship classification society rules (e.g., ABS, LR, DNV, NK).
Example (JIS): KA, KB, KD, KE grades (JIS G 3106, with added requirements). These have defined impact tests at temperatures down to -40°C for KE grade.
Higher Strength & Thicker Plates: AH32/DH32/EH32, AH36/DH36/EH36 (high-strength hull structural steel).
Extreme Low-Temperature Service (e.g., LNG carriers): Nickel-alloyed steels or special low-temperature steels (JIS G 3127).
These grades guarantee the necessary weldability, impact toughness at service temperature, and through-thickness properties (Z-quality) for safety and reliability.
Summary
SS490's role in shipbuilding is limited to cost-effective, secondary internal structures and outfitting within the hull's protected environment. Its use is governed by classification society rules and the ship's design specifications, which will explicitly list approved steel grades for each component.
Always, the primary hull, exposed structures, and critical stress members require certified marine-grade steels with guaranteed impact toughness-not SS490.