Difference between BV D550 and BV D690

BV D550 and BV D690 are high-strength, fine-grained structural steel plates classified by Bureau Veritas (BV) for critical marine and offshore applications. These grades are utilized in areas demanding exceptional performance, such as highly stressed hull components, offshore wind turbine foundations, and heavy-lift vessel construction, where a superior strength-to-weight ratio and good low-temperature toughness are essential.

Key Differences:

The primary distinction is their specified minimum yield strength. BV D550 provides a yield strength of 550 MPa, while BV D690 offers a substantially higher yield strength of 690 MPa. This makes D690 the superior choice for ultra-high-strength applications, enabling maximum weight reduction and payload optimization through thinner, lighter structural designs.

To achieve this highest strength grade, D690 necessitates a more advanced and precisely controlled manufacturing process. It is exclusively supplied in a quenched and tempered (Q&T) condition. While D550 can also be Q&T, the chemical composition for D690 is more rigorously optimized. Consequently, the fabrication complexity increases significantly with D690. It demands extremely strict welding protocols-including specific filler metals, precise preheating and interpass temperature controls, and often mandatory post-weld heat treatment-to mitigate the risk of cold cracking and to ensure the weld zone maintains adequate toughness and strength. The selection is a key engineering decision: D690 offers the pinnacle of strength for weight-critical designs, while D550 provides a more manageable balance of high strength and relative fabrication ease.

 Chemical Composition

Mechanical Property