Section 3 Corrosion protection

3.1.1 Where bimetallic connections are made, measures are to be incorporated to mitigate galvanic corrosion.

3.2.1 Prefabrication primers are to be approved in accordance with Ch 15 Corrosion Prevention of the Rules for Materials.

3.2.2 Aluminium coatings intended for oil tankers and chemical tankers used in way of the cargo oil tanks, cargo tank deck areas, pumprooms, cofferdams or any other area where oil vapour may accumulate are to be coated using systems containing less than 10 per cent aluminium by weight in the dry film.

3.3.1 The requirements for cathodic protection of internal tanks in Ch 15 Corrosion Prevention of the Rules for Materials are to be complied with. When a cathodic protection system is to be fitted in tanks for the carriage of liquid cargo with flash point not exceeding 60°C, a plan showing details of the locations and attachment of anodes is to be submitted. The arrangements will be considered for safety against fire and explosion aspects only. Impressed current cathodic protection systems are not permitted in any tank.

3.3.2 Particular attention is to be given to the locations of anodes in relation to the structural arrangements and openings of the tank.

3.3.3 Anodes are to be of approved design and sufficiently rigid to avoid resonance in the anode support. Steel cores are to be fitted, and these are to be so designed as to retain the anode even when the latter is wasted.

3.3.4 Anodes are to be attached to the structure in such a way that they remain secure both initially and during service. The following methods of attachment would be acceptable:

1. Steel core connected to the structure by continuous welding of adequate section.

2. Steel core bolted to separate supports, provided that a minimum of two bolts with lock nuts is used at each support. The separate supports are to be connected to the structure by continuous welding of adequate section.

3. Approved means of mechanical clamping.

3.3.5 Anodes are to be attached to stiffeners, or may be aligned in way of stiffeners on plane bulkhead plating, but they are not to be attached to the shell. The two ends are not to be attached to separate members which are capable of relative movement.

3.3.6 Where cores or supports are welded to the main structure, they are to be kept clear of the toes of brackets and similar stress raisers. Where they are welded to asymmetrical stiffeners, they are to be connected to the web with the welding kept at least 25 mm away from the edge of the web. In the case of stiffeners or girders with symmetrical face plates, the connection may be made to the web or to the centreline of the face plate but well clear of the free edges. However, it is recommended that anodes are not fitted to face plates of higher tensile steel longitudinals.

3.4.1 Aluminium and aluminium alloy anodes are permitted in tanks which can contain explosive or flammable vapour, or in tanks adjacent to tanks which can contain explosive or flammable vapour, but only at locations where the potential energy of the anode does not exceed 275 J. The weight of the anode is to be taken as the weight at the time of fitting, including any inserts and fitting devices. The height of the anode is, in general, to be measured from the bottom of the tank to the centre of the anode. Where the anode is located on a horizontal surface (such as a bulkhead stringer) not less than 1 m wide, provided with an upstanding flange or face plate projecting not less than 75 mm above the horizontal surface, the height of the anode can be measured above that surface.

3.4.2 Aluminium anodes are not to be located under tank hatches or Butterworth openings unless protected by adjacent structure.

3.4.3 Magnesium or magnesium alloy anodes are not permitted in tanks which can contain explosive or flammable vapour, or in tanks adjacent to tanks which can contain explosive or flammable vapour. Where permitted for other tanks, adequate venting must be provided.

3.5.1 Suitable protection of the underwater portion of the hull is to be provided.

3.5.2 Where a cathodic protection system is fitted, plans showing the proposed layout of anodes and hull penetrations are to be submitted in accordance with Ch 15 Corrosion Prevention of the Rules for Materials.

3.5.3 All equipment is to be suitable for its intended location.

3.5.4 The arrangements for glands, where cables pass through the shell, are to include a small cofferdam.

3.5.5 Cables which pass through ballast tanks are to be enclosed in a steel tube of at least 10 mm thickness.

3.5.6 Cables to anodes are not to pass through tanks intended for the storage of low flash point products; including, but not limited to, oils.

3.5.7 Cables which pass through cofferdams of storage tanks which may contain low flash point products are to be enclosed in a steel tube of at least 10 mm thickness. See also Pt 6, Ch 2, 14 Electrical equipment for use in explosive gas atmospheres or in the presence of combustible dusts.

3.5.8 Where an *IWS (In-water Survey) notation is to be assigned, see Pt 1, Ch 2, 2.3 Class notations (hull) 2.3.11, protection of the underwater portion of the hull is to be provided by means of a suitable high resistance paint applied in accordance with the manufacturer’s requirements. Details of the high resistance paint are to be submitted for information in accordance with Ch 15 Corrosion Prevention of the Rules for Materials.

3.6.1 For ships that are required to comply with IMO Resolution MSC.215(82) - Performance Standard for Protective Coatings for Dedicated Seawater Ballast Tanks in all Types of Ships and Double-Side Skin Spaces of Bulk Carriers - (Adopted on 8 December 2006), all dedicated sea-water ballast tanks of all types of ships and double-side skin spaces of bulk carriers are to comply with all of the requirements of the Resolution, see ShipRight Procedure Anti-Corrosion Systems Notation and Ch 15 Corrosion Prevention of the Rules for Materials.

3.6.2 For ships that are required to comply with IMO Resolution MSC.288(87) – Performance Standard for Protective Coatings for Cargo Oil Tanks of Crude Oil Tankers – (Adopted on 14 May 2010) , all cargo oil tanks are to comply with all of the requirements of the Resolution, see ShipRight Procedure Anti-Corrosion System Notation and Ch 15 Corrosion Prevention of the Rules for Materials.

3.6.3 For ships that are required to comply with the IMO Resolution MSC.289(87) – Performance Standard for Alternative Means of Corrosion Protection for Cargo Oil Tanks of Crude Oil Tankers – (Adopted on 14 May 2010) , by application of corrosion resistant steel, see Ch 3, 1.3 Corrosion resistant steels for cargo oil tanks of crude oil tankers of the Rules for Materials, all cargo oil tanks are to comply with all of the requirements of the Resolution, see ShipRight Procedure Anti-Corrosion System Notation and Ch 15 Corrosion Prevention of the Rules for Materials.

3.6.4 For ships that are required to comply with IMO Resolution MSC.244(83) - Adoption of Performance Standard for Protective Coatings for Void Spaces on Bulk Carriers and Oil Tankers - (Adopted on 5 October 2007), all void spaces are to comply with all of the requirements of the Resolution, see ShipRight Procedure Anti Corrosion System Notation and Ch 15 Corrosion Prevention of the Rules for Materials.

3.6.5 For ships that are not required to comply with the IMO Resolution MSC.215(82) - Performance Standard for Protective Coatings for Dedicated Seawater Ballast Tanks in all Types of Ships and Double-Side Skin Spaces of Bulk Carriers - (Adopted on 8 December 2006), all sea-water ballast spaces having boundaries formed by the hull envelope are to have an efficient protective coating, epoxy or equivalent, applied in accordance with the manufacturer’s recommendations, see ShipRight Procedure Protective Coatings in Water Ballast Tanks (PCWBT) andCh 15 Corrosion Prevention of the Rules for Materials.

3.6.6 The following tanks are not considered to be dedicated sea-water ballast tanks and are therefore exempted from the application and requirement of the IMO PSPC:

1. ballast tanks identified as ‘Spaces included in Net Tonnage’ in the 1969 ITC Certificate;

2. sea-water ballast tanks in passenger vessels also designated for the carriage of grey water or black water; or

3. sea-water ballast tanks in livestock carriers also designated for the carriage of the livestock dung.

Alternative provisions are to be made for the protection of these tanks.