SHIPBUILDINGSHIPBUILDING

INTRODUCTIONThere is a wide range of materials used in

shipbuilding comprising ferrous metals, non- ferrous metals, plastics, GRP (Glass Reinforced Plastics/ fiber glass) and wood.

The most widely used material in ship building remains steel especially plan carbon or mild steel approximately 90%.

Properties of SteelGood metallurgical properties – to

overcome Brittle fracture and fatigueReasonable good mechanical properties

Low carbon steel (mild steel) have tensile strength of 400 to 490 MN/m2 and Yield strength of 235 MN/m2, and elongation of 15 to 20 %

Susceptibility ease to join process by welding with good control over weld defects

Cont-

Reasonable costReasonably ease to castAbility to be heat treated. Alloy elements

can also be use to change the character of steel:- Carbon (0.18% to 0.28%) increases hardness and strength but reduces ductility.- Manganese (0.6% to 15%) increase tensile strength, ductility and notch toughness- Silicon (< 0.5%) increase hardness and tensile strength without making welding difficult.- Sulphur (>0.04 or 0.05%) improves weldability and welding stresses- Phosphorus (> 0.04 or 0.05%) reduces ductility and toughness

Grades of steelGrade A - White

Grade B - Green

Grade D - Red

Grade E - Yellow

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Grade A

A mild steel used in the majority of the ship structures of less than 20 mm thickness such as bulkheads, tank top, non strength decks and superstructures

Grade B

A mild steel used for strength members of 20 to 25 mm thickness

Grade D

A ‘Notch-tough’ steel which resists the spread of cracks and has higher strength.

It is used for structure greater than 25 mm thick

Grade E

An ‘Extra Notch tough’ steel because this is a heat treated Grade D steel used for very thick plating in excess of 50mm thick.

It is used for sheer strakes, bilge strakes, keels I.e. all high stress regions of the ship

Artic DA special grade of steels used where part of

the structure is subject to extremely low temperature.

The Ultimate tensile strength is 435 to 510 NM/m2, yield stress is 310 NM/m2 – 80% of UTS and absorbs 40 Joules of energy at - 55oC in a Charpy Impact test. Normally used for icebreakers

Stainless steel

1. Suffers from deep pitting in stagnant waters-if cleaned

regularly this pitting can be reduced

Expected life spans of some materials in sea water:

Galvanised steel- 6 to 9 yearsCopper- Maximum velocity (water flow) 4ft/sec90/10 Cupro-Nickel- 10yrs+70/30 Cupro-Nickel- 22 yrs+