Marine Delta Plate – Forged vs Plate-Cut: Which to Choose?
This is the second article in our Marine Delta Plate series. In the first article, "5 Questions to Confirm Before Ordering Marine Delta Plate," we covered the key parameters to confirm before placing an order — including the two manufacturing options: forged and plate-cut.
In this article, we go deeper: What exactly is the difference between these two methods?
If you've already determined the SWL and class society requirements but are still unsure which process or material to choose, this guide will help you decide.
1. Plate-Cut vs Forged: How to Choose?
The fundamental difference between these two methods lies in how the steel is formed.
Forged Delta Plate: A solid piece of steel shaped under high heat and pressure. The grain structure flows continuously along the contours of the part — no seams, no gaps. Mechanical properties are consistent in all directions.
Plate-Cut Delta Plate: Cut and drilled from steel plate using laser cutting — fast and cost-effective. However, steel plate has inherent anisotropy — mechanical properties differ between the rolling direction (longitudinal) and transverse direction. The three holes of a delta plate experience forces in different directions, and the plate-cut piece will perform differently under tension in different directions. This is not a quality issue — it's inherent to the material itself.
| Comparison | Plate-Cut Delta Plate | Forged Delta Plate |
| Typical SWL Range | ≤ 50 tons | 50 – 150 tons |
| Material | Q355B / Q355D steel plate | CM690 forged steel |
| Process | Laser cutting + drilling | Integral forging + heat treatment + machining |
| Key Advantage | Lower cost, shorter lead time | Isotropic properties, uniform performance, higher class society acceptance |
| Key Risk | Anisotropy causes uneven strength in different directions | Longer lead time, higher cost |
| Class Society Approval | Product type approval only | System approval; smooth surveyor acceptance |
Selection Criteria:
SWL ≤ 50 tons with no class society requirement → Plate-cut is the more economical choice — lower cost, shorter lead time.
SWL > 50 tons or class society specifies forged → Forged is the safer choice.
Plate-cut delta plates are suitable when: SWL does not exceed 50 tons, no class certificate is required, and the application does not involve high loads or frequent cyclic loading. If these three conditions are met, the cost advantage of plate-cut construction is real.
50 tons is a common reference point, not an absolute rule. Always follow the project specification if the shipowner or design institute has a specific requirement.
2. Material Selection: Q355B, Q355D, and CM690
Material selection is determined by the operating environment and load requirements.
Q355B is suitable for small delta plates (SWL ≤ 20 tons), ambient temperature applications, and projects with no class society requirements. Impact test temperature is 20°C — fine for normal conditions.
Q355D is the standard choice for marine components (SWL ≤ 50 tons) and low-temperature conditions (-20°C). When vessels operate in high-latitude waters where temperatures may drop below 0°C, ordinary steel becomes brittle and may fracture suddenly under load.
CM690 is anchor chain special steel, produced and tested to classification society anchor chain standards. It matches U3 grade anchor chain, with minimum strength of 690 MPa. It is used for large delta plates (SWL ≥ 50 tons), U3 anchor chain matching, and class society projects.
Quick guide: No low-temperature requirement → Q355B. High-latitude operation → Q355D is the minimum. U3 chain matching or class society forged requirement → CM690 is the only option.
3. Why Must Large Delta Plates Use CM690?
The answer is that the uniform strength after forging meets the mechanical performance requirements and can meet the requirements of classification society certification.
Material System Matching
U3 anchor chain uses CM690. Matching delta plates and shackles must use the same material system to ensure consistency across the entire mooring system in heat treatment and mechanical properties.
Class Society Approval Threshold
The materials used in CM690 are approved by the classification society. The forgings are manufactured according to the anchor chain standard system and hold factory approval certificates. Their production process and inspection standards are fully recognized. For large projects, the classification society's surveyors can directly approve the forgings during on-site inspections.
Anisotropy
Steel plate has different mechanical properties in different directions. The three holes of a delta plate experience forces in different directions — plate-cut pieces will perform differently under tension in different directions. Forged components have consistent properties in all directions — this problem does not exist.
Conclusion
The strength of plate-cut parts is inconsistent across different angles, failing to meet the classification society's system certification requirements. For projects with a Safe Working Load (SWL) exceeding 50 tons or requiring classification society certification, forging with CM690 material is a safer and more efficient choice—consistent performance in all directions, a mature system certification, and acceptance by surveyors. Classification society system certification inherently requires traceability and verifiability throughout the entire production process. Forging has mature and standardized processes at every step from billet to finished part. For critical load-bearing components with a SWL exceeding 50 tons, forging is actually a more efficient overall solution.
SMEOCEAN has both forging and plate-cutting capabilities, capable of producing both forged and plate-cut delta plates across the full 17-ton to 150-ton SWL range. You don't need to go back and forth between multiple suppliers to confirm process capabilities — we can handle whichever option you choose.
If you have your SWL and class society requirements ready, send them over — we'll recommend the right solution directly.
More Links:
Anchor Chain Accessories: A Complete Guide