Bulb Flat Steel — Factory Direct Supplier | Huaxia-Steel

Bulb flat steel (bulb plate) is the asymmetric stiffener profile that dominates modern shipbuilding and offshore construction: a flat web with a bulb-shaped flange on one edge, designed to be welded flush against deck, side shell, and bulkhead plating. Compared with flat bars of equal weight, the bulb profile gives 20–30% higher section modulus per kilogram, resists buckling better, and makes continuous welding faster because the web sits flat against the plate. Huaxia-Steel supplies bulb flats from 80×5 to 430×12.5 mm across the full range of ship-classification grades, with class society certification and EN 10204 3.1/3.2 documentation.

Product Overview

Profile: web height × bulb thickness (e.g., 200×9 mm); rolled on specialized mills, hot-rolled finish.

Size range: 80×5 to 430×12.5 mm; lengths 6–12 m, cut-to-length by cutting plan.

Grades: A, B, D, AH32/36, DH32/36, EH32/36 per class societies (CCS, ABS, LR, DNV, BV, NK, KR).

Key advantage: higher section modulus per kg than flat bar — lighter structures for the same stiffness, and weld-backing geometry that speeds panel line production.

Surface: hot-rolled mill scale; blast + shop primer (zinc silicate) on request.

Specification Table

Parameter	Range / Value
Web height (h)	80 – 430 mm
Bulb thickness (t)	5 – 12.5 mm
Mass range	3.95 – 47.9 kg/m (by size)
Height tolerance	±2.0 mm (h ≤ 200); ±3.0 mm (h > 200)
Web thickness tolerance	−0.4 / +0.8 mm typical
Straightness	≤ 0.25% of length (web flatness & bow)
Lengths	6–12 m; fixed length ±50 mm; nest-cut per panel plan
Steel grades	CCS A–EH36, ABS A–EH36, LR A–EH36, DNV, BV, NK, KR equivalents

Common Sizes and Section Data

Size (h×t, mm)	Mass (kg/m)	Typical Use
120×6	6.71	Small craft frames, secondary stiffeners
160×7	10.20	Deck longitudinals, bulkhead stiffeners
200×9	16.30	Main deck/side shell stiffening
240×10	21.60	Primary framing, cargo hold structures
300×11	29.10	Hull longitudinals, transverse frames
430×12.5	47.90	Large vessel primary structure, offshore

Available Grades and Certification

Class Grade	Yield min (MPa)	Tensile min (MPa)	Impact Test
A / B / D	235	400–520	20°C / 0°C / −20°C
AH32 / DH32 / EH32	315	440–570	0°C / −20°C / −40°C
AH36 / DH36 / EH36	355	490–630	0°C / −20°C / −40°C

All material is supplied with class society works approval and per-heat certificates: Z-marking (Z25/Z35 through-thickness ductility) available for DH36/EH36 where the design requires it. For offshore projects, EN 10225 S355 grades and EN 10204 3.2 third-party certification can be arranged. Every bundle carries heat-number tagging matching the certificates, and class surveyor witness of testing is welcome at the mill.

Manufacturing Standards and Process Control

Bulb flats are rolled on universal/profile mills from continuously cast blooms under each classification society’s material rules (aligned with IACS UR W11/W31 for hull structural steel). Chemistry follows the standard hull-grade bands (e.g., DH36: C ≤ 0.18%, Mn 0.90–1.60%, Nb/V/Ti microalloyed), with grain refinement and normalized or thermomechanical (TM) delivery for higher-toughness grades. Straightness and web-flatness are checked hot and cold before bundling; each order ships with a class surveyor-stamped certificate listing chemistry, tensile, and impact results at the grade’s test temperature.

Applications

Hull longitudinals and transverse frames — deck, side shell, bottom, bulkheads

Bulk carrier, container ship, tanker stiffening systems

Offshore platform decks, FPSO modules, jack-up legs’ secondary framing

Ro-ro ramp structures and port equipment framing

Ship repair and conversion — cut-to-length supply by cutting plan

Quality Assurance

Class society certification (CCS/ABS/LR/DNV/BV/NK/KR) per shipment

EN 10204 3.1 standard; 3.2 with surveyor witness for offshore orders

Z15/Z25/Z35 through-thickness options on higher grades

Dimensional report: height, thickness, straightness per lot

Packaging and Shipping

Bundles 2–5 t with steel strapping, size-tagged, heat-number stenciled

Nest-cut bundles per panel plan with piece marking for yard workflow

Break-bulk and flat-rack for long lengths; container for ≤ 5.8 m

Blast + shop primer 15–25 µm zinc silicate available for yard efficiency