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GI Rectangular Tube โ short for Galvanized Iron (or Galvanized Steel) Rectangular Tube โ is a hollow structural steel section with a rectangular cross-section that has been coated with a protective zinc layer through the hot-dip galvanizing process. This combination of high-strength carbon steel substrate and corrosion-resistant zinc coating makes it uniquely suited to the extreme demands of shipbuilding and marine engineering.
In shipbuilding and offshore construction, materials are exposed to relentless saltwater corrosion, high humidity, mechanical stress, and fluctuating temperatures. Standard black steel sections corrode rapidly in such environments, leading to structural degradation, expensive maintenance, and safety risks. GI rectangular tubes solve this challenge by providing a long-lasting, structurally robust, and cost-effective solution that dramatically extends the service life of marine structures.
โ Key Insight: The global shipbuilding industry consumed over 35 million metric tons of steel in 2023, with galvanized hollow sections accounting for a growing share of structural components โ particularly in vessel superstructures, offshore platforms, and port infrastructure.
From container ships and bulk carriers to floating production storage and offloading (FPSO) units, naval vessels, and luxury cruise ships, GI rectangular tubes are integral to modern maritime construction. Their rectangular geometry provides superior bending resistance compared to round tubes of equivalent weight, making them the preferred choice for beams, frames, and load-bearing columns in marine environments.
Hot-dip galvanizing provides 40โ100ฮผm of zinc coating, offering decades of protection against saltwater, humidity, and chemical exposure in marine environments.
Rectangular cross-section geometry delivers excellent bending and torsional stiffness, ideal for ship frames, deck supports, and offshore load-bearing structures.
Manufactured from low-carbon or mild steel substrates, GI rectangular tubes can be cut, welded, and fabricated with standard marine welding techniques.
Tight dimensional tolerances ensure consistent fit-up during assembly, reducing fabrication time and improving overall structural integrity in shipyard production.
Lower maintenance costs and extended service life compared to painted or uncoated steel make GI rectangular tubes the most economical long-term choice for marine projects.
Available in GB, EN 10219, ASTM A500, AS/NZS, and other international standards, ensuring compatibility with global shipbuilding classification requirements.
| Size (mm) | Wall Thickness (mm) | Zinc Coating (g/mยฒ) | Steel Grade | Standard | Application |
|---|---|---|---|---|---|
| 40ร20 โ 100ร50 | 1.5 โ 4.0 | 120 โ 275 | Q235B / S235JR | GB/EN 10219 | Cabin partitions, handrails |
| 100ร50 โ 200ร100 | 3.0 โ 6.0 | 180 โ 275 | Q355B / S355J2H | GB/EN 10219 | Deck frames, superstructure |
| 200ร100 โ 400ร200 | 5.0 โ 12.0 | 275 โ 400 | Q355B / ASTM A500 | GB/ASTM | Ship hull framing, offshore columns |
| Custom sizes available | Up to 16.0 | Up to 600 | Various | As required | Offshore platforms, port structures |
* Custom dimensions, wall thicknesses, and zinc coating weights available upon request. All products comply with relevant classification society requirements.
GI rectangular tubes form the skeletal framework of ship superstructures โ bridge wings, wheelhouse frames, accommodation blocks, and funnel casings โ where corrosion resistance and weight efficiency are paramount.
Fixed and floating offshore platforms rely on GI rectangular hollow sections for secondary structural members, pipe racks, walkway grating supports, and equipment mounting frames exposed to aggressive North Sea or tropical marine conditions.
Quayside crane rails, berthing fender systems, gangway structures, and port storage buildings use GI rectangular tubes extensively due to their resistance to tidal zone corrosion and mechanical impact.
Military shipbuilders specify GI rectangular tubes for non-structural but critical components such as equipment racks, antenna mast supports, and interior framing where maintenance access is limited.
With additional coating systems, GI rectangular tubes are used in splash zone and tidal zone applications including jetty piles, wave energy converter frames, and tidal turbine support structures.
Within shipyards themselves, GI rectangular tubes construct modular scaffolding systems, ship block transport cradles, and dry dock gate frameworks โ benefiting from their dimensional consistency and ease of assembly.
Global shipbuilding order books reached record highs in 2023โ2024, driven by fleet renewal cycles, LNG carrier demand, and container ship replacements. South Korea, China, and Japan collectively account for over 90% of global tonnage, creating sustained demand for high-quality GI structural steel sections including rectangular tubes.
The IMO's 2050 net-zero carbon target is accelerating investment in LNG, ammonia, and hydrogen-fueled vessels. These new fuel systems require specialized structural components and piping supports โ areas where GI rectangular tubes provide the corrosion resistance and structural versatility needed for alternative fuel infrastructure onboard.
The global offshore wind market is projected to grow at over 15% CAGR through 2030. Installation vessels, floating wind platforms, and submarine cable-laying ships all require large quantities of galvanized structural steel. GI rectangular tubes are increasingly specified for transition piece platforms, crew transfer vessel (CTV) structures, and wind farm service operation vessels (SOVs).
Modern shipyards are adopting block-building and modular construction methodologies to reduce build times and costs. GI rectangular tubes, with their precise dimensions and excellent weldability, are ideal for prefabricated outfitting modules โ HVAC units, pipe support skids, and accommodation block panels โ that can be manufactured off-vessel and integrated efficiently.
Beyond standard hot-dip galvanizing, duplex coating systems combining zinc galvanizing with epoxy or polyurethane topcoats are gaining adoption for extreme marine environments. This trend is driving demand for higher zinc coating weight specifications (โฅ350 g/mยฒ) and surface preparation standards that GI rectangular tube manufacturers must meet to serve premium shipbuilding clients.
Post-pandemic supply chain disruptions have prompted major shipbuilders to diversify their steel sourcing. Chinese manufacturers like Baolf Steel Group โ located just 20km from Tianjin Port โ are well-positioned to serve global shipyards with competitive pricing, fast delivery, and the scale to fulfill large-volume orders reliably.
(State-Owned Holding) Founded In 1995, Located In Tianjin, China. Only 20KM Away From Tianjin Port, Save Much Cost. 800,000 Tons Annual Output Per Year.
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