Section 5 Hull construction

5.1.1 The hull structure is to comply with the relevant requirements of Vol 1, Pt 3 Design Principles and Constructional Arrangements, Vol 1, Pt 4 Military Design and Special Features, Vol 1, Pt 5 Environmental Loads and Vol 1, Pt 6 Hull Construction in Steel, except where stated otherwise in this Section.

5.1.2 Independent substance and effluent tanks are to be protected from mechanical damage. This may be achieved either by installation in spaces where there are no cargo or vehicle movements and where no heavy lifting operations are expected, or by mechanical protection if installed in spaces where such operations may take place.

5.1.3 Where necessary, the probable temperature variations during operations and the thermal stress considerations are to be stated. Where it is necessary either to heat or cool chemical storage tanks, the arrangements are to utilise either active pipe coils or ducts for circulating a heating or cooling medium within the chemical storage tank or a heat exchanger through which the chemical and a heating or cooling medium are circulated. Active heating and cooling systems are to have capacity such that the chemical in the designated tanks can be maintained within the specified temperature limits, see Vol 2, Pt 12, Ch 1, 3.3 Chemical substances 3.3.3, Vol 2, Pt 12, Ch 1, 3.4 Mechanical equipment 3.4.4 and Vol 2, Pt 12, Ch 1, 7.1 General 7.1.10, under the following conditions:

Heating or cooling media are to be suitable for use with the specific chemical and consideration is to be given to the surface temperature of heating coils or ducts to avoid dangerous reactions from localised overheating or overcooling of chemicals. Heating or cooling systems are to be provided with valves to isolate the system for each tank and to allow manual regulation of flow along with a means for measuring the cargo temperature.

5.1.4 Where independent tanks are used for chemical substances, these are to be arranged so as to contain leakage. This may be achieved by using a double skinned storage tank, by means of a spill containment bund or by placing the tank in a dedicated compartment. Where a bund is to be used, it is to comply with the following:

1. the bund is dimensioned so as to contain 1,5 times the maximum contents of the tank, ensuring that consideration has also been given to the angle of inclination requirements for main and auxiliary machinery in Table 3.4.2 Inclinations inVol 2, Pt 1, Ch 3, 4 Operating conditions; or

2. there is a drain arrangement meeting the requirements of Vol 2, Pt 12, Ch 1, 5.1 General 5.1.6; or

If the tank is located in a dedicated compartment then the compartment is to contain no equipment other than that required by the tank with permanent access and floor plates positioned above the liquid level if the tank were to discharge its full contents into the compartment. Any valves, equipment and emergency stop functions are to be operable from outside this compartment and are to meet the requirements of Vol 2, Pt 12, Ch 1, 5.2 Location service and control spaces.

Tanks and spill containment arrangements are to be fitted with alarms and safeguards, in accordance with Table 1.9.1 Machinery emissions to air abatement plant: alarms and safeguards.

5.1.5 Proposals are to be made for the dimensioning of containment arrangements, relative to the potential leakage which may require containment. Where it is not practicable to contain fully the potential leakage and where this leakage can pose a hazard to personnel, proposals are to be submitted, demonstrating that leakage will be transferred to a suitable retention tank, and the means of transfer shall be capable of operating in a dead ship condition and shall be fitted with a flow detection alarm, in accordance with Table 1.9.1 Machinery emissions to air abatement plant: alarms and safeguards.

5.1.6 Tanks are to be arranged such that any residues and slops can be pumped out, drained or otherwise removed from the tank without exposing personnel to these residues and slops.

5.1.7 Chemical tanks containing substances which are categorised as a safety hazard in Chapter 17 of the Rules for Ships for Liquid Chemicals (designated by letter “S” in column d) are not to be located in the same space as essential machinery and equipment.

5.1.8 Arrangements for venting and gas-freeing chemical tanks required by emissions abatement plant are to meet the requirements of Vol 2, Pt 7, Ch 1 Piping Design Requirements, Vol 2, Pt 7, Ch 2 Ship Piping Systems, Vol 2, Pt 7, Ch 3 Machinery Piping Systems as applicable and are to be independent of the air pipes and venting systems of other tanks and/or compartments of the ship. Tank venting systems are to minimise the possibility of chemical vapour accumulating about the decks, entering accommodation, service and machinery spaces and control stations and, in the case of flammable vapours, entering or collecting in spaces or areas containing sources of ignition. Tank venting systems are to be arranged to prevent entrance of water into the chemical tanks. The venting systems shall be connected to the top of each chemical tank and as far as practicable are to be self-draining back to the chemical tanks under all normal operational conditions of list and trim.

5.1.9 Tank vent piping connected to cargo tanks of corrosion-resistant material, or to tanks which are lined or coated to provide corrosion resistance, are to be similarly lined or coated or constructed of corrosion-resistant material.

5.2.1 Where flammable or toxic chemicals, gases or vapours are present, as identified inVol 2, Pt 12, Ch 1, 3.3 Chemical substances 3.3.1 and Vol 2, Pt 12, Ch 1, 3.3 Chemical substances 3.3.2, service and control stations essential to the operation of the plant are to meet the requirements of Vol 2, Pt 12, Ch 1, 9.1 General 9.1.4, and should, wherever possible, be located so that access thereto is from a defined safe space. If such a location is not possible, the station is to be specially ventilated.

5.2.2 Arrangements are to be made in spaces occupied by emissions abatement plant so that substances which are flammable, corrosive, toxic or are likely to present a hazard due to reaction when mixed are kept separate unless they are fully contained within a part of the emissions abatement system which has been designed for the safe mixing of such substances.

5.3.1 Where integrity of water or gastightness is required between compartments containing the plant, it is to be maintained in way of pipe tunnels or duct keels where these traverse such compartments.

5.3.2 Installations and the spaces in which they are installed are to be, in all cases, compliant with applicable National and International requirements for prevention, detection and extinction of fire.

5.4.1 Decks and other structures supporting the plant are, in general, to comply with the requirements of Vol 1 Ship Structures. Such structures can, however, be considered on the basis of an agreed uniformly distributed loading in association with local loads at plant support points, provided that adequate transverse strength of the ship is maintained.

5.4.2 Where the nature and dispositions of heavy plant items are such that forces on the ship and support structure due to ship motions are significant (whether underway with or without working fluids, or moored with working fluids), calculations of the loading and the structural response are to be submitted.

5.5.1 In cases where the mass distribution of large columnar equipment items is such that the centre of action of the dynamic force differs significantly from the centre of gravity of the item, due account of this is to be taken in the calculation of the forces and moments at the support positions.

5.6.1 The integrity of the weather deck is to be maintained. Where items of plant penetrate the weather deck and are intended to constitute the structural barrier to prevent the ingress of water to spaces below the freeboard deck, their structural strength is to be equivalent to the Rule requirements for this purpose. Otherwise, such items are to be enclosed in superstructures or deckhouses fully complying with the Rules.