Material Identification, Handling, and Storage

Why Material Identity Matters in Ship Construction

A shipyard receives hundreds of tons of steel and aluminum plate every month. If the wrong grade reaches the cutting table, the hull can fail classification inspection — or worse, fail at sea. Every piece of structural material used on a vessel must be traceable from the steel mill to the finished weld. That traceability starts with the Certified Mill Test Report and ends with a legible heat number on the plate.

The Certified Mill Test Report (CMTR)

A CMTR is the manufacturer's official document proving that a batch of material meets a specific standard. For shipbuilding you will commonly see:

• ASTM A36 — a common structural carbon steel used in many fabrication applications.
• ABS Grade A — a hull structural steel certified to American Bureau of Shipping rules; it carries tighter chemical and mechanical requirements than plain ASTM A36 and is required wherever ABS classification governs the vessel.
• 5083 aluminum — a non-heat-treatable alloy with excellent corrosion resistance, widely used for hull plating and structural members in saltwater service.
• 6061 aluminum — a heat-treatable alloy used where higher strength and machinability are needed, though it is less corrosion-resistant than 5083 in marine environments.

A CMTR contains: the material specification and grade, the heat number (the identifier tied to a single melt at the mill), chemical composition (elements and percentages), mechanical test results (yield strength, tensile strength, elongation, and — for ABS grades — impact test results where required), and the certifying signature. Your job is to confirm that every value on the report meets the minimum requirements stated on the engineering drawing or the applicable standard.

Locating the Heat Number on the Plate

The mill stamps or stencils the heat number directly onto the plate surface, typically near one edge. When plate is cut into smaller pieces, the fabricator must transfer the heat number to every resulting piece before cutting — this is called material traceability. Use paint marker or low-stress steel stamps approved for the material. Never use a standard steel stamp on aluminum; the sharp indentations can initiate cracks.

To match a plate coupon to its CMTR: (1) find the heat number stenciled on the plate, (2) locate the same heat number in the CMTR header, (3) confirm the grade designation printed on the plate (for example, "ABS-A" or "5083-H116") matches the grade called out on the drawing.

Segregating and Storing Steel and Aluminum

Steel and aluminum must never be stored in contact with each other. Steel particles — from grinding, brushing, or simply resting steel on aluminum — embed in the softer aluminum surface and cause galvanic corrosion in a marine environment. Follow these rules:

• Separate storage areas: Use clearly marked bays or racks. Color-coded tags (for example, yellow for carbon steel, blue for aluminum) applied to each piece make the separation visible at a glance.
• Dunnage: Lay plates flat on timber or rubber-padded dunnage. Space dunnage supports close enough to prevent the plate from sagging under its own weight — a sagged plate that is later force-straightened can carry residual stress. For long structural sections such as T-bars or angle, support at multiple points along the length to prevent camber.
• Environmental protection: Store aluminum away from chloride-heavy environments where possible. Keep both materials off bare ground to prevent moisture wicking.
• FIFO: First-in, first-out rotation prevents older material from being buried and forgotten.

Surface Preparation: Steel

Before layout lines can be scribed and before welding, plate surfaces must be free of mill scale, rust, oil, and moisture. For steel:

1. Wire brush loose scale and rust by hand, or use a wire-wheel attachment on an angle grinder.

2. Follow with a flap disc on the angle grinder to smooth the surface and remove remaining scale in the weld area. Move the grinder at a consistent angle (typically 5–15 degrees from the surface) to avoid gouging.

3. Wipe with an approved solvent — acetone is common — using clean, lint-free rags. Work in the direction of the metal grain. Discard solvent-soaked rags in a covered, labeled flammable-waste container.

Surface Preparation: Aluminum

Aluminum forms a tough oxide layer quickly. It must be removed just before welding:

1. Use a dedicated stainless-steel wire brush — one that has never touched steel. A contaminated brush deposits iron particles that cause weld porosity.

2. Wipe with acetone or another approved cleaner. Follow the SDS for ventilation requirements and flash-point precautions.

3. Weld within the time window specified by your procedure; the oxide begins reforming immediately.

Do not use grinding discs on aluminum that have been used on steel.

Safety Essentials

• PPE: Safety glasses at all times in the shop. Add a face shield when grinding. Chemical-resistant gloves when handling solvents. Leather gloves for material handling.
• Lockout/Tagout: Before changing a grinding disc or clearing a material jam in any powered equipment, follow your site's LOTO procedure.
• SDS awareness: Before opening any solvent container, read the SDS. Note the flash point, required ventilation, first-aid measures, and disposal instructions. Acetone is highly flammable — eliminate ignition sources.
• Lifting: Use mechanical assists (forklifts, cranes, vacuum lifters) for plate over the weight limit for manual handling. Rig properly; plate edges are sharp.
• Housekeeping: Keep aisles clear of dunnage scraps and off-cuts. Steel swarf from grinding is a puncture and fire hazard.