Engineering tool
High tensile steel replacement estimate
Enter the plates you have in normal strength steel and the higher strength grade you are considering. The estimate scales the thickness by the IACS UR S4 material factor k where the thickness is set by hull girder section modulus, rounds to a thickness you can order under UR W13, and compares weight and cost.
Settings
Prices are optional. Use the same currency for both. Nothing here is a quote.
Material factor k = 0.72 (UR S4)
Plates in normal strength steel
This is an example, not your data. Replace it or clear it.
- Required thickness × k
- 14.4 mm
- Order thickness, normal strength
- 20.5 mm
- Order thickness, higher strength
- 15 mm
- Weight, normal → higher strength
- 19.311 → 14.130 t
- Saved
- 5.181 t (26.8 %)
- Required thickness × k
- 12 mm
- Order thickness, normal strength
- 12.5 mm
- Order thickness, higher strength
- 12.5 mm
- Weight, normal → higher strength
- 8.478 → 8.478 t
- Saved
- 0.000 t (0.0 %)
Result
All plates
- Total weight, normal strength
- 27.789 t
- Total weight, higher strength
- 22.608 t
- Weight saved
- 5.181 t (18.6 %)
The higher strength option costs less overall while its price per tonne stays less than 22.9 % above normal strength steel.
What this estimate does not check
The UR S4 condition that the midship section moment of inertia is not less than 3 × Wmin × L (cm⁴), the society's minimum plate thickness, buckling, fatigue and the hull girder strength calculation. The scaling by k assumes the plate's share of the section modulus is proportional to its thickness.
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What this estimate covers
The UR S4 material factor k for 315, 355 and 390 N/mm² steel, order thickness and weight under UR W13, and a break-even price premium: how much dearer per tonne the higher strength steel can be before the saving in weight is lost.
What it does not check
UR S4 does not apply to CSR bulk carriers and oil tankers. The estimate does not check the UR S4 condition on the midship moment of inertia, the society's minimum plate thickness, buckling, fatigue or the hull girder strength calculation itself. Plates whose thickness is set by anything other than section modulus keep their thickness.
Questions about the estimate
- Why is the thickness multiplied by k?
- For members that carry hull girder bending, the section modulus the rules require goes with k. A higher strength steel with k of 0.72 needs about 72 % of the section modulus, and the estimate assumes the plate's share of it is proportional to its thickness. That is only an approximation for a real stiffened section, which is why the result is an estimate.
- Why does AH40 have two values of k?
- UR S4 gives k = 0.66 for 390 N/mm² steel when a fatigue assessment of the structure is made to the society's requirements, and 0.68 otherwise. Tick the box if one is made.
- What does the break-even premium mean?
- It is the weight of the normal strength plates divided by the weight of the higher strength plates, less one. If the higher strength steel costs less than that percentage more per tonne, the total steel bill is lower even though each tonne costs more. It leaves out welding, handling and any other change.
Source
The material factors and the moment of inertia condition are from IACS Unified Requirement S4 (Rev.4, 2017), read in full. Original: IACS UR S4 (PDF)
This is a first estimate for comparing options, not a design calculation. The thickness on your class-approved drawings governs. For plate ready to ship, contact us. Request a quote