Shipbuilding Steels: Part One

Abstract:

Various shipbuilding requirements, such as reduction in welding man-hours, shortening of welding lines, elimination of cutting steps, stabilization of fabricated part quality and reduction in control costs, have been met by developing TMCP high-strength steels that require no preheating for welding, irregular-section plates and plates with close dimensional tolerances, and by increasing the stringency of pre-shipment plate quality control.

A demand for heavy thick plates with a good combination of high strength, toughness, and weldability has been widely growing in recent years for large container ship building. Because of this, e tra high-strength termomechanically processed steels TMCP have been developed to be more user friendly than the traditional steels.

E cellent handling properties are based on thermomechanical treatment that reduces the need for e cessive use of alloying elements to strengthen the steel. TMCP plates are thermomechanically controlled rolled, and with greater plate thicknesses, also accelerated cooled after rolling.

Generally, TMCP steels are supplied as heavy plates, surface treated plates and plate components. Due to the very low carbon equivalent, TMCP steels are easily weldable using all common processes. In addition, they are easy to form, bend and edge.

TMCP steels give many monetary advantages to the shipbuilder:

Reduced plate thickness

Saving weight in the final structure

Greater effective loads during use

Cost savings in welding and fabrication.

The successful application of thermo-mechanical control process (TMCP) with the recent innovative technology has induced the development of EH36, EH40, and EH47 grade steel plates. The alloying elements such as boron, copper, and nickel were added and the rolling and cooling processes were strongly and precisely controlled to improve the strength and toughness at the same time. EH36 steel plate for high heat input welding was successfully developed with good toughness at the heat affected zone (HAZ) by increasing the thermal stability of TIN particles at the high temperature.

The quality of shipbuilding steels has an e tremely large impact on the quality, efficiency and cost of ships built from those steels. Many steel producers established a system to supply wide and long plates to the shipbuilding industry.

Various shipbuilding requirements, such as reduction in welding man-hours, shortening of welding lines, elimination of cutting steps, stabilization of fabricated part quality and reduction in control costs, have

been met by developing TMCP high-strength steels that require no preheating for welding, irregular-section plates and plates with close dimensional tolerances, and by increasing the stringency of pre-shipment plate quality control. Table 1 shows the common steel grades for shipbuilding.

Table 1: Steel for Ship Building

LloydsNorskeVeritas

GermanischerLloyds

BureauVeritas

American Bureauof Shipping

USSRRegister

NipponKaigi Kyoka

A A A A A A A

B B B B B B B

D D D D SS D D

CD/DS

NV A27S

NV D27S

AH 32 NV A32 A 32 AH 32 AH 32 A 32

DH 32 NV 32 D 32 DH 32 DH 32 D 32

EH 32 NV E32 E 32 EH 32 EH 32 E 32

AH 34S

DH 34S

EH 34S

AH 35 NV A36 A 36 AH 36 AH 36 A 36

DH 36 NV D36 D 36 DH 36 DH 36 D 36

EH 36 NV E36 E 36 EH 36 EH 36 E 36

NV A40

NV D40

NV E40

NV A420

NV D420

NV E420

Steel in shipbuilding

Shipbuilding traditionally uses structural steel plate to fabricate ship hulls. Modern steel plates have much higher tensile strengths than their predecessors, making them much better suited to the efficient construction of large container ships.

A particular type of plate is available with a designed-in resistance to corrosion, ideal for building oil tankers. Such steels make possible much lighter vessels than before, or larger capacity vessels for the same weight, offering significant opportunities to save on fuel consumption and hence CO2 emission.

The advanced steels used in these steel-plate applications also find uses in a number of related industries. Offshore oil rigs, bridges, civil engineering and construction machines, rail carriages, tanks and pressure vessels, nuclear, thermal and hydroelectric plants – all these applications benefit from the attributes of modern steels.

Figure 1: Ships: Navy, Cargo and Cruise

In recent years, more attention has been paid to the safety and durability of ships and environment protection of sea, which have lead to the development of new structural steel plates. One of them is the development of more corrosion resistant plates for double-hull tankers. Crude oil carriers are now required to have double hulls to prevent oil spill, and an increase in temperature in oil tanks with the double hull structure increases the likelihood of corrosion of upper deck steel plates exposed to the vapor space in the tanks. To prevent the corrosion and to increase the life time of the ships, different corrosion resistant steel palates have been developed.

The development of new steel plates has also been made to increase construction efficiency and thereby to decrease construction cost. Longitudinally profiled (LP) steel plates were developed in this context. Thickness change within a plate was achieved by controlled rolling, which made it possible to replace the plates which had been made by welding steel plates of different thickness, and therefore to reduce the welding time and cost.

Another development is concerned with residual stress retaining in steel plates. TMCP steel plates are likely to possess residual stresses from their production, and this often results in distortion in different ways after cutting and welding of the plates. In order to achieve residual stress-reduced steel plates, temperature differences over the large surface area in a wide and long plate and through the thickness should be minimized and cold levering is also used for the purpose of reducing inhomogeneous stress for block shape accuracy.

A number of research projects are currently being carried out on the European and national levels to improve the application of lasers and optical technologies in shipbuilding. In laser beam welding, centre line solidification cracks in the fused zone are in issue and can limit the travel speed and hence productivity.

The fused zones are typically of the same composition as the steel being welded and whilst there are several welding procedural factors which can be used to minimize the risk of cracking, the problem hinges on the steel composition. Lower S and P levels may thus be required as shown in Table 2.

Table 2: Classification society guidelines for laser welding of ship hull

C 0.12% max (lower speeds ≤ 0.15%)

S 0.005% max (≤ 0.010% for ≤ 12 mm, 0.6 m/min)

P 0.010% max (≤ 0.015% for ≤ 12 mm, 0.6 m/min)

CE 0.38% max

Weld hardness ≤ 380 HV5 max (≤ 400 HV5 isolated)

LR Grade A shipbuilding steel plate

LR Grade A, LR/A steel, LR/A steel plate, LR/A steel sheet, LR/A shipbuilding steel price, LR/A steel supplier and manufacturer

LR Grade A shipbuilding Steel Description:LR grade A steel is a kind of hot rolled general tensile strength steel. LR steels come 4 grades in ordinary-strength steel for shipbuilding and grade A is the lowest one of them. The LR A grade steel plates have yield strength of 34,100 psi (235 MPa), and ultimate tensile strength of 58,000 - 75,500 psi (400-520 MPa). All the LR/A shipbuilding Steel offered by Katalor Industry can be certificated by Lloyd’s Register of Shipping (LR).

LR Grade A shipbuilding Steel Application: LR A grades of steel plate are almost exclusively used in the Shipbuilding Industry for the construction of structural parts of ships, barges and marine equipment. LR A Shipbuilding steel plates also can be used for ship repairing, the offshore oil drilling platform, the platform pipe joints and other components.

LR Grade A Steel Grade Specification:Thickness: 4mm to 260mm, Width: 1200mm to 4000mLength: 3000mm to 18000mm.

LR Grade A Shipbuilding Steel Chemical Composition Heat Analysis:

ElementLR Grade A Max % Element LR Grade A Max %

C 0.21 Ni -

Mn 2.5*C min Mo -

Si 0.50 Al -

S 0.035 Nb -

P 0.035 V -

Cu - Ti -

Cr - N -

LR Grade A Ship Steel Mechanical Properties:

Grade

Thickness Yield Strength Tensile Strength Elongation Impact Energy

(mm) MPa (min) MPa % (min) (KV J) (min)

20 degree

LR Grade A 4-260 235 400-520 22

Note: the impact energy under less 50mm thickness

Katalor Industry is a professional LR/A shipbuilding steel supplier and exporter. Katalor Industry has been in steel industry for many years and can offer every kind of shipbuilding steel plates and steel sheets to worldwide shipyard and ship building company.

Property Grade A Grade B Grade D Grade E

% of Carbon 0.21 max 0.21 max 0.21 max 0.18 max

% of Manganese2.5 times %C min

0.8 times %C min

0.6 times %C min

0.7 times %C min

% of Silicon 0.5 max 0.35 max 0.1 – 0.35 0.1 – 0.35

% of Phosphorous 0.035 max 0.035 max 0.035 max 0.035 max

% of Sulphur 0.035 max 0.035 max 0.035 max 0.035 max

% of Aluminum - - 0.015 min -

Ultimate Tensile Strength (N/mm2)

400-520

Yield Strength (N/mm2) 235

% Elongation 22

Temperature at which Impact test is done (deg Cel)

NA 0 -20 -40

High Tensile Steels (HTS)

HTS can be used effectively in highly stressed areas of the ship.

They have less thickness for same strength compared to normal steel.

Strength is increased by adding grain refining elements such as (% Al: 0.015 min, % Nb: 0.02 – 0.05, % V: 0.05 – 0.10, % Ti: 0.02)

High tensile steels are expressed as AH 36, BH 40, etc.

AH stands for High tensile steel of Grade A

The number represents minimum yield strength in N/mm2 (32 means minimum 315 N/mm2, 36 means minimum 355 N/mm2, 40 means minimum 390 N/mm2)

Ultimate Tensile Strength for the above three numbers are: 32 —-> 440 – 590 N/mm2, 36 —-> 490 – 620 N/mm2 and 40 —-> 510 – 650 N/mm2

It should be noted that for Grade A steel temperature for impact test is not applicable. At the same time for Grade AH steel impact test to be carried out at zero degree Celsius.

Standard ASTM A 131M covers structural steel-shapes, plates, bars, and rivets intended primarily for use in ship construction. Material under specification A 131M is available in the following categories:

Ordinary Strength — Grades A, B, D, DS, CS, and E with a specified minimum yield point of 235Mpa, and

Higher Strength — Grades AH, DH, and EH with specified minimum yield points of either 315 MPa or 350 MPa.

Shapes and bars are normally available as Grades A, AH32, or AH36. Other grades may be furnished by agreement between the purchaser and the manufacturer.

When the steel is to be welded, it is presupposed that a welding procedure suitable for the grade of steel and intended use or service will be utilized.

The parts of a ship vary, depending on what kind of boat it is, but a few general parts are common to all types. Knowing the parts will increase your understanding when reading about boating related topics, and will also help you orient yourself when on board a ship. Many of the terms used are very old, as humans have been building, sailing, and talking about ocean going vessels for thousands of years.

The core of a ship is the structural keel, a heavily reinforced spine which runs along the bottom, in the middle. The keel supports the structure of the ship, and is the first part to be built, since it serves as a foundation. Some ships also have a hydrodynamic keel designed to increase their performance efficiency, which takes the form of a streamlined projection from the bottom of the boat to help it move quickly and smoothly through the water. The framework for the hull or shell, the body, is attached to the keel.

The hull is the most visible part of a ship, because it is the body of the watercraft. The hull makes the ship buoyant while providing shelter to those on board, and is divided by bulkheads and decks, depending on its size. Bulkheads are compartments which run across the ship from side to side, creating isolated areas, while decks are analogous to the floors of a house. A small boat may only have one primary deck, while larger ones may have over 10 decks, stacked from top to bottom.

The very bottom is known as the bilge, and the top is usually called the top deck. The top deck is broken up by the bridge, a covered room which serves as the command center. On larger ships, the top deck may have several levels, designed to isolate various parts. There may also be several deck areas topside, including the poop deck, the deck in the rear of the ship, and the afterdeck, located directly behind the bridge. The rig, including masts, rigging, and sails, rises up from the top deck.

The front region is called the bow, and the rear is the stern. When someone is forward, they are in the front of the boat, while a sailor located amidships would be in the middle, and a person to the rear is aft. The right hand side is starboard, and the left is port.

A” class divisions (fire divisions)

‘A’ Class divisions are those divisions formed by bulkheads and decks which comply with the following criteria:

(a) They are to be constructed of steel or other equivalent material.

(b) They are to be suitably stiffened.

(c) They are to be so constructed as to be capable of preventing the passage of smoke and flame up to the end of the one-hour standard fire test.

(d) They are to be insulated with approved non-combustible materials such that the average temperature of the unexposed side will not rise more than 140°C above the original temperature, nor will the temperature, at any one point, including any joint, rise more than 180°C above the original temperature, within the time listed below:

Class ‘A-60’ – 60 minutes

Class ‘A-30’ – 30 minutes

Class ‘A-15’ – 15 minutes

Class ‘A-0’ – 0 minutes

(e) In accordance with the Fire Test Procedures Code, a test of a prototype bulkhead or deck may be required to ensure that it meets the above requirements for integrity and temperature rise

B” Class Divisions

“B” class divisions are those divisions formed by bulkheads, decks, ceilings or linings which comply with the following criteria:

.1 they are constructed of approved non-combustible materials and all materials used in the construction and erection of “B” class divisions are non-combustible, with the exception that combustible veneers may be permitted provided they meet other appropriate requirements of this chapter;.2 they have an insulation value such that the average temperature of the unexposed side will not rise more than 140ºC above the original temperature, nor will the temperature at any one point, including any joint, rise more than 225ºC above the original temperature, within the time listed below:class “B-15″ 15 minclass “B-0″ 0 min.3 they are constructed as to be capable of preventing the passage of flame to the end of the first half hour of the standard fire test; and.4 the Administration has required a test of a prototype division in accordance with the Fire Test Procedures Code to ensure that it meets the above requirements for integrity and temperature rise. <Chapter II-2, part A, regulation 3>.

Source: IMO Resolution MSC.99(73), amendments to the International Convention for the Safety of Life at Sea, 1974, as amended, 5 December 2000, International Maritime Organization. Legislation

“B” Class Divisions (fire divisions)

‘B’ Class divisions are those divisions formed by bulkheads, decks, ceilings or linings which comply with the following criteria:

(a) They are to be so constructed as to be capable of preventing the passage of flame to the end of the first half hour of the standard fire test.

(b) They are to have an insulation value such that the average temperature of the unexposed side will not rise more than 140°C above the original temperature, nor will the temperature at any one point, including any joint, rise more than 225°C above the original temperature, within the time listed below:

Class ‘B-15’- 15 minutes

Class ‘B-0’ – 0 minutes

(c) They are to be constructed of approved noncombustible materials and all materials used in the construction and erection of ‘B’ Class divisions are to be non-combustible, with the exception that combustible veneers may be permitted, provided they meet other appropriate requirements of this Chapter.

(d) In accordance with the Fire Test Procedures Code, a test of a prototype division may be required to ensure that it meets the above requirements for integrity and temperature rise.

C” class divisions (fire divisions)

‘C’ Class divisions are divisions to be constructed of approved non-combustible materials. They need meet neither requirements relative to the passage of smoke and flame nor limitations relative to the temperature rise. Combustible veneers are permitted provided they meet the requirements of this Chapter.

‘H’ Class Divisions (fire divisions)

‘H’ Class divisions are those divisions formed by fire walls and decks which comply with the construction and integrity requirements for ‘A’ Class divisions, 2.6.1(a) and (b) and with the following:

(a) They are to be so constructed as to be capable of preventing the passage of smoke and flame up to the end of the one hour hydrocarbon fire test. (Note that some administrations may require the ‘H’ Class division integrity to be maintained for 120 minutes).

(b) They are to be insulated with approved non-combustible materials such that the average temperature, on the unexposed side, when exposed to a hydrocarbon fire test, will not rise more than 140°C above the original temperature, nor will the temperature at any one point, including any joint, rise more than 180°C above the original temperature within the time listed below:

Class ‘H-120’ – 120 minutes

Class ‘H-60’ – 60 minutes

Class ‘H-0’ – 0 minutes.

(c) A test of a prototype fire wall or deck may be required to ensure that it meets the above requirements for integrity and temperature rise.

Class B Fire Division

A division manufactured in incombustible materials that satisfies the following criteria:a) it prevents the spread of flames for at least half an hour of the standardised fire test,b) it is designed so that the average temperature on the unexposed side does not rise more than 140°C above the original temperature. In addition, the temperature at any single point shall not rise more than 225°C above the original temperature within the following timeframes:– class B-30: 30 minutes,– class B-15: 15 minutes,– class B- 0: 0 minutes.

Class A Fire Division

A division manufactured in incombustible materials that satisfies the following criteria:a) it is sufficiently reinforced,b) it prevents the spread of flames and smoke for at least one hour of the standardised fire test,c) it is designed so that the average temperature and the temperature of any single point on the unexposed side do not rise more than 140°C and 180°C, respectively, above the original temperature within the following timeframes:– class A-60: 60 minutes,– class A-30: 30 minutes,– class A-15: 15 minutes,– class A- 0: 0 minutes,d) any insulation materials are fire-tested at an institution that is internationally or nationally recognised in the specific discipline.

Class H Fire Division

A division manufactured in incombustible materials that satisfies the following criteria:a) it is sufficiently reinforced,b) it prevents the spread of flames and smoke for at least two hours of the standardised fire test,c) it is designed so that the average temperature and the temperature of any single point on the unexposed side do not rise more than 140°C and 180°C, respectively, above the original temperature within the following timeframes:– class H-120: 120 minutes,– class H-60: 60 minutes,– class H-0: 0 minutes,d) any insulation materials are fire-tested at an institution that is internationally or nationally recognised in the specific discipline.

Class A-60 division” means a division formed by a bulkhead or deck that is

1. constructed of steel or an equivalent material and suitably stiffened,

2. constructed to prevent the passage of smoke and flame after 60 minutes of exposure to a standard fire test, and

3. insulated with non-combustible materials so that, if either side is exposed to a standard fire test, after 60 minutes the average temperature on the unexposed face will not increase by more than 139°C above the initial temperature and the temperature at any point on the unexposed face, including any joint, will not increase by more than 180°C above the initial temperature;

Class H-120 Division

“Class H-120 division” means a division formed by a bulkhead or deck that is

1. constructed of steel or an equivalent material and suitably stiffened,

2. constructed to prevent the passage of smoke and flame after exposure to a hydrocarbon

fire test for 120 minutes, and

3. insulated with non-combustible material so that, if either face is exposed to a

hydrocarbon fire test, after 120 minutes the average temperature on the unexposed face

will not increase by more than 139°C above the initial temperature, and the temperature

at any point on the unexposed face, including any joint, will not increase by more than

180°C above the initial temperature; cloisonnement de classe H-120.

Class A-0 Division

Class A-0 division

“Class A-0 division” means a division formed by a bulkhead or deck that is constructed

1. of steel or an equivalent material and suitably stiffened, and

2. to prevent the passage of smoke and flame after 60 minutes of exposure to a standard fire test; cloisonnement de classe A-0.

A class bulkhead or deck

A class bulkhead or deck means a bulkhead or deck that

1. Is made of steel or other equivalent material; and

2. Prevents the passage of flame and smoke for 60 minutes if subjected to the standard

fire test.

Bulkhead Deck

Bulkhead deck is the uppermost deck up to which the transverse watertight bulkheads are carried. <Chapter II-2, part A, regulation 3>.

Weather Deck

Weather deck is a deck which is completely exposed to the weather from above and from at least two sides. <Chapter II-2, part A, regulation 3>.

Freeboard Deck

Freeboard deck.(a) The freeboard deck is normally the uppermost complete deck exposed to weather and sea, which

has permanent means of closing all openings in the weather part thereof, and below which all openings in the sides of the ship are fitted with permanent means of watertight closing.(b) Lower deck as a freeboard deckAt the option of the owner and subject to the approval of the Administration, a lower deck may be designated as the freeboard deck provided it is a complete and permanent deck continuous in a fore and aft direction at least between the machinery space and peak bulkheads and continuous athwartships.(i) When this lower deck is stepped the lowest line of the deck and the continuation of that line parallel to the upper part of the deck is taken as the freeboard deck.(ii) When a lower deck is designated as the freeboard deck, that part of the hull which extends above the freeboard deck is treated as a superstructure so far as concerns the application of the conditions of assignment and the calculation of freeboard. It is from this deck that the freeboard is calculated.(iii) When a lower deck is designated as the freeboard deck, such deck as a minimum shall consist of suitably framed stringers at the ship sides and transversely at each watertight bulkhead which extends to the upper deck, within cargo spaces. The width of these stringers shall not be less than can be conveniently fitted having regard to the structure and the operation of the ship. Any arrangement of stringers shall be such that structural requirement can also be met.(c) Discontinuous freeboard deck, stepped freeboard deck.(i) Where a recess in the freeboard deck extends to the sides of the ship and is in excess of one metre in length, the lowest line of the exposed deck and the continuation of that line parallel to the upper part of the deck is taken as the freeboard deck (see figure 3.3).

(ii) Where a recess in the freeboard deck does not extend to the sides of the ship, the upper part of the deck is taken as the freeboard deck.(iii) Recesses not extending from side to side in a deck below the exposed deck, designated as the freeboard deck, may be disregarded, provided all openings in the weather deck are fitted with weathertight closing appliances.(iv) Due regard shall be given to the drainage of exposed recesses and to free surface effects on stability.(v) Provisions of subparagraphs (i) through (iv) are not intended to apply to dredgers, hopper barges or other similar types of ships with large open holds, where each case requires individual consideration.< Chapter I, regulation 3>.

Source: IMO Resolution MSC.143(77), amendments to Annex B to the 1988 Load Lines Protocol, 5 June 2003, International Maritime Organization. Legislation

Freeboard Deck

Freeboard deck is the deck as defined in the International Convention on Load Lines in force. <Chapter II-1, regulation 2>.

Source: IMO Resolution MSC.216(82), amendments to the International Convention for the Safety of Life at Sea, 1974, as amended, 8 December 2006, International Maritime Organization. Legislation

Freeboard Deck

The freeboard deck is normally the uppermost complete deck exposed to weather and sea, which has permanent means of closing all openings in the weather part, and below which all openings in the sides of the unit are fitted with permanent means of watertight closing. For semisubmersible units, see also 5.2.4

Flush Deck Ship

Flush deck ship. A flush deck ship is one which has no superstructure on the freeboard deck.

Superstructure Deck

Superstructure deck. A superstructure deck is a deck forming the upper boundary of a superstructure. <Chapter I, regulation 3>.

Raised Quarterdeck

Raised quarterdeck. A raised quarterdeck is a superstructure which extends forward from the after perpendicular, generally has a height less than a normal superstructure, and has an intact front bulkhead (sidescuttles of the non-opening type fitted with efficient deadlights and bolted man hole covers) (see figure 3.4). Where the forward bulkhead is not intact due to doors and access openings, the superstructure is then to be considered as a poop.

< Chapter I, regulation 3>.

Poop

Poop. A poop is a superstructure which extends from the after perpendicular forward to a point which is aft of the forward perpendicular.The poop may originate from a point aft of the aft perpendicular.

Perpendiculars

Perpendiculars. The forward and after perpendiculars shall be taken at the forward and after ends of the length (L). The forward perpendicular shall coincide with the foreside of the stem on the waterline on which the length is measured.