Short answer: Buy ex-ship plate by measured thickness, not by the thickness the lot is sold as. Pick plate at or just above the thickness your finished part needs, measure it with a caliper away from the edge, and check photos of both faces and a cut edge for deep pitting, laminations, heavy paint and bends. Estimate the weight of each sheet as thickness (mm) × length (m) × width (m) × 7.85 kg, and agree before loading that the weighbridge weight is billed.
This guide is for circle cutters, agricultural-implement and tool makers, and fabricators who buy used mild steel (MS) plate from ships recycled at Alang and cut it into circles, squares and parts.
What is ex-ship MS plate?
A ship's hull and decks are built from steel plate made to the rules of a classification society. The IACS unified requirement for hull steel covers "weldable normal and higher strength hot-rolled steel plates … intended for use in hull construction", up to 100 mm thick (IACS UR W11, 1.1–1.2). The normal-strength grades are A, B, D and E; higher-strength grades carry a number, such as AH32 or AH36.
When the ship is dismantled, that plate is cut into pieces and sold on. Two things follow for a buyer:
- Sizes and thickness change from lot to lot. A lot is whatever the ship was built from, cut to what could be handled.
- The grade is usually unknown. New hull plate is marked by the steelworks with the grade and the classification society's brand (UR W11, 15.1), but after years of service, painting and cutting, that marking is rarely still on the piece you buy. Treat ex-ship plate as mild steel of unknown grade unless the lot gives you proof.
If your drawing calls for a specific grade, such as IS 2062 E250 BR, with a mill test certificate, buy new mill plate for that job. Ex-ship plate suits parts where plain mild steel is enough.
What plate thickness do you need for your part?
Thickness decides what you can make from a plate, so check it first.
- Start from the finished part. For a gas-cut circle or part that will be machined, choose plate at or slightly above the finished thickness. Gas cutting does not change the thickness, so a 20 mm plate gives 20 mm parts.
- Measure, do not trust the label. Ship plate thins in service. Classification rules describe "pitting corrosion, grooving, edge corrosion" as local corrosion that surveyors measure and limit (ClassNK, CSR for bulk carriers, Ch. 13). A plate built as 12 mm can measure less today.
- Measure like the standard does. For new plate, IS 1852 measures thickness at each corner, the middle of the width and the middle of the length, "25 mm away from the edge" (IS 1852:1985, 7.3.1). Even new plate may be up to 5% under its nominal thickness under that standard (clause 7.3). Do the same on ex-ship plate with a caliper, and ask the seller for a photo of the caliper reading.
- Cutting range. Oxy-fuel cutting handles a very wide range. TWI gives it as "0.5mm to 250mm" (TWI), so for most circle and part work the limit is your torch set-up and your machining allowance, not the process.
How do you judge ex-ship plate from photos?
Most plate is bought on photos. Ask for these, and look for the faults below:
- The whole sheet with a measuring tape laid along it.
- Both faces, in daylight.
- A cut edge, close up, with a caliper on it.
Pitting. Look for craters on the face, most often on the side that was inside a tank or hold. Shallow, even rust is normal and machines off. Deep, close pits reduce the usable thickness, and a pit left on a finished face is a reject. Measure the thickness beside the deepest pits, not on the clean area.
Lamination. A lamination is a thin separation inside the plate, parallel to its faces, "flattened during the rolling process" (ispatguru). IS 2062 requires new plate to be "reasonably free from surface flaws; laminations" (IS 2062:2011, cl. 7.1), but a used plate has had no such check since it left the mill. On a cut edge, a lamination can show as a fine line or split running along the middle of the thickness (Inspection for Industry). A laminated plate can split when you cut, weld or machine it. Where it matters, plate 12.5 mm and thicker can be checked with the ultrasonic test in ASTM A435, which exists to find "gross internal discontinuities such as pipe, ruptures, or laminations" (ASTM A435/A435M-17).
Paint and coatings. Ship plate often carries several coats of paint. Paint slows the cut and gives off fumes. For toxic coatings, OSHA requires the coating to be stripped "for a distance of at least 4 inches from the area of heat application", or the worker to wear an air-line respirator (OSHA 1926.354). Old ship paints can contain lead, and OSHA lists "welding, cutting, and torch burning" on lead coatings among its high-exposure tasks (OSHA 1926.62). Ships now carry an "Inventory of Hazardous Materials" under the Hong Kong Convention (IMO). Ask how much of the lot is painted, and cut painted plate with good ventilation.
Bends, dents and cut-outs. Look along the sheet in the photo. A bent or dished plate may need straightening before it sits flat on the cutting table. Check for welded-on brackets, stiffener stubs, holes and old flame-cut openings. Each one reduces the number of good circles or parts you get from the sheet.
What should you agree before buying a mixed-thickness lot?
Ex-ship plate is often sold as a mixed lot. Before you agree a rate:
- Ask for the thickness range and a rough split, for example "mostly 10 mm, some 8 mm and 12 mm".
- Ask for photos of each thickness group with a caliper reading.
- Agree whether pieces below your useful size are part of the lot.
- If you need one thickness only, say so. Sorting by thickness costs the seller time, so expect it to affect the rate.
How much does a sheet of MS plate weigh?
The Indian standard for plate dimensions gives masses "based on density of steel = 7.85 g/cm³" (IS 1730:1989), the same density IS 2062 uses (clause 18). That works out to 7.85 kg for every square metre of plate per mm of thickness:
Weight (kg) = thickness (mm) × length (m) × width (m) × 7.85
Example: a 10 mm plate, 2.5 m × 1.2 m, weighs 10 × 2.5 × 1.2 × 7.85 = about 236 kg.
Only part of that becomes circles. A circle is about 78.5% of the square around it, so plan your offcuts. Our MS circle weight calculator gives the weight of the circles themselves. As with circles, the formula is theoretical; the weighbridge weight is what gets billed.
Which documents should come with a truck of plate?
For every truck of plate, ask for:
- a GST e-invoice;
- an e-way bill where the value requires one;
- the weighbridge slip.
Our guide to GST documents in a scrap sale explains each paper. Do not expect a grade certificate with ex-ship plate unless the seller has one for that exact lot.
How we sell plate
At J.S. STEEL we sort MS profile plates from Alang lots by thickness at our yard in Ukharala (Mamsa GIDC), Ghogha, Bhavnagar. Thickness changes with every lot. Tell us the thickness and quantity you need, and we send photos of the exact plates before loading. You can also see the plates at the yard, Monday to Saturday. If you need circles, we also sell ready gas-cut MS circles.
Frequently asked questions
Is ex-ship MS plate a known grade such as IS 2062 E250?
Usually not. The steelworks marking with the grade is rarely still on the piece after years of service, painting and cutting, so treat ex-ship plate as mild steel of unknown grade unless the lot gives you proof. If your drawing calls for a named grade with a mill test certificate, buy new mill plate for that job.
How should I measure the thickness of ex-ship plate?
Use a caliper at each corner, the middle of the width and the middle of the length, 25 mm away from the edge, and again beside the deepest pits. Ship plate thins in service, so a plate built as 12 mm can measure less today. Ask the seller for a photo of the caliper reading.
How do I spot a laminated plate?
On a cut edge, a lamination can show as a fine line or split running along the middle of the thickness. A laminated plate can split when you cut, weld or machine it. Where it matters, plate 12.5 mm and thicker can be checked with the ultrasonic test in ASTM A435.
How do I estimate the weight of a plate sheet?
Weight (kg) = thickness (mm) × length (m) × width (m) × 7.85. A 10 mm plate, 2.5 m × 1.2 m, weighs about 236 kg. The formula is theoretical; the weighbridge weight is what gets billed.
Sources
- IACS UR W11: Normal and higher strength hull structural steels (Rev. 8, 2014), via Türk Loydu
- ClassNK: Common Structural Rules for bulk carriers, Chapter 13 (amendment)
- IS 2062:2011, Hot rolled medium and high tensile structural steel (BIS), full text via Public.Resource.Org
- IS 1852:1985, Rolling and cutting tolerances for hot-rolled steel products (BIS), full text
- IS 1730:1989, Steel plates, sheets, strips and flats: dimensions (BIS), full text
- TWI: Oxyfuel cutting — process and fuel gases
- ASTM A435/A435M-17: Straight-beam ultrasonic examination of steel plates
- ispatguru: Material discontinuities and their types
- Inspection for Industry: Plate lamination defect
- OSHA 1926.354: Welding, cutting and heating in way of preservative coatings
- OSHA 1926.62: Lead in construction
- IMO: Recycling of ships