Section 2 Carbon and low alloy steels

2.1.1 Materials for Class I and Class II piping systems, also for ship-side valves and fittings and valves on the collision bulkhead, are to be manufactured and tested in accordance with the appropriate requirements of Pt 5, Ch 12, 1.7 Materials of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

2.1.2 Materials for Class III piping systems are to be manufactured and tested in accordance with the requirements of acceptable national specifications. Pipes having forge butt welded longitudinal seams are not to be used for fuel oil systems, for heating coils in oil tanks, or for pressures exceeding 0,4 MPa. The manufacturer's certificate will be acceptable and is to be provided for each consignment of material. See Ch 1, 3.1 General 3.1.3.(c) of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

2.1.3 Steel pipes, valves and fittings may be used within the temperature limits indicated in Table 12.2.1 Carbon and carbon-manganese steel pipes and Table 12.2.2 Alloy steel pipes. Where rimming steel is used for pipes manufactured by electric resistance or induction welding processes, the design temperature is limited to 400°C, see Ch 6, 3 Welded pressure pipes of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

2.2.1 The maximum permissible design stress, σ, is to be taken as the lowest of the following values:

Values of the maximum permissible design stress, σ, obtained from the properties of the steels specified in Ch 6 Steel Pipes and Tubes of the Rules for Materials are shown in Table 12.2.1 Carbon and carbon-manganese steel pipes and Table 12.2.2 Alloy steel pipes. For intermediate values of specified minimum strengths and temperatures, values of the permissible design stress may be obtained by interpolation.

2.2.2 Where it is proposed to use, for high temperature service, alloy steels other than those detailed in Table 12.2.2 Alloy steel pipes particulars of the tube sizes, design conditions and appropriate national or proprietary material specifications are to be submitted for consideration.

2.2.3 The minimum thickness, t, of straight steel pipes is to be determined by the following formula:

For pipes passing through tanks, an additional corrosion allowance is to be added to take account of external corrosion; the addition will depend on the external medium and the value is to be in accordance with Table 12.2.3 Values of c for steel pipes . Where the pipes are efficiently protected, the corrosion allowance may be reduced by not more than 50 per cent.

2.2.4 The minimum thickness, t _b, of a straight steel pipe to be used for a pipe bend is to be determined by the following formula, except where it can be demonstrated that the use of a thickness less than t _b would not reduce the thickness below t at any point after bending:

2.2.5 Where the minimum thickness calculated by Pt 5, Ch 12, 2.2 Wrought steel pipes and bends 2.2.3 or Pt 5, Ch 12, 2.2 Wrought steel pipes and bends 2.2.4 is less than that shown in Table 12.2.4 Minimum thickness for steel pipes, the minimum nominal thickness for the appropriate standard pipe size shown in the Table is to be used. No allowance is required for negative tolerance, corrosion or reduction in thickness due to bending on this nominal thickness. For larger diameters, the minimum thickness will be considered. For threaded pipes, where permitted, the minimum thickness is to be measured at the bottom of the thread.

2.2.6 For sounding pipes, except those for cargo tanks with cargo having a flash point of less than 60°C, the minimum thickness is intended to apply to the part outside the tank.

2.2.7 For air, bilge, ballast, fuel, overflow, sounding and venting pipes as listed in Table 12.2.4 Minimum thickness for steel pipes, where the pipes are efficiently protected against corrosion, the thickness may be reduced by not more than 1 mm.

2.2.8 The internal diameter for bilge, venting and overflow pipes listed in Table 12.2.4 Minimum thickness for steel pipes is to be not less than 50 mm. The internal diameter for sounding pipes is to be not less than 32 mm.

2.2.9 Reinforced thickness of ballast and cargo oil piping. Ballast piping passing through cargo tanks and cargo oil pipes passing through segregated ballast tanks, as permitted by Regulation 19.3.6 of MARPOL Annex I, are to comply with the following requirements.

2.2.10 The thicknesses shown in the above table refer to carbon steel.

2.3.1 Joints in pressure pipelines may be made by:

• Screwed-on or welded-on bolted flanges, see Pt 5, Ch 12, 2.5 Screwed-on flanges and Pt 5, Ch 12, 2.6 Welded-on flanges, butt welded joints and fabricated branch pieces.
• Butt welds between pipes or between pipes and valve chests or other fittings, see Pt 5, Ch 12, 2.6 Welded-on flanges, butt welded joints and fabricated branch pieces.
• Socket weld joints, see Pt 5, Ch 12, 2.8 Socket weld joints.
• Welded sleeve joints, see Pt 5, Ch 12, 2.9 Welded sleeve joints.
• Threaded sleeve joints, see Pt 5, Ch 12, 2.10 Threaded sleeve joints and threaded couplings
• Threaded connections, see Pt 5, Ch 12, 2.11 Fittings having threaded end connections
• Mechanical couplings, see Pt 5, Ch 12, 2.12 Other mechanical couplings
• Special types of joints that have been shown to be suitable for the design conditions. Details are to be submitted for consideration.

2.3.2 The dimensions and materials of flanges, gaskets and bolting, and the pressure − temperature rating of bolted flanges in pressure pipelines, are to be in accordance with National or other established Standards.

2.3.3 With the welded pressure piping systems referred to in Pt 5, Ch 12, 2.3 Pipe joints - General 2.3.1 it is desirable that a few flanged joints be provided at suitable positions to facilitate installation, cold `pull up' and inspection at Periodical Surveys.

2.3.4 Piping with joints is to be adequately adjusted, aligned and supported. Supports or hangers are not to be used to force alignment of piping at the point of connection.

2.3.5 Pipes passing through, or connected to, watertight decks are to be continuous or provided with an approved bolted or welded connection to the deck or bulkhead.

2.3.6 Consideration will be given to accepting joints in accordance with a recognised National Standard which is applicable to the intended service and media conveyed.

2.4.1 Flanges may be cut from plates or may be forged or cast. The material is to be suitable for the design temperature. Flanges may be attached to the pipes by screwing and expanding or by welding. Alternative methods of flange attachment may be accepted provided details are submitted for consideration.

2.4.2 Flange attachments to pipes and pressure − temperature ratings in accordance with National or other approved Standards will be accepted.

2.5.1 Where flanges are secured by screwing, as indicated in Figure 12.2.1 Screwed-on flange, the pipe and flange are to be screwed with a vanishing thread and the diameter of the screwed portion of the pipe over the thread is not to be appreciably less than the outside diameter of the unscrewed pipe. After the flange has been screwed hard home the pipe is to be expanded into the flange.

2.5.2 The vanishing thread on a pipe is to be not less than three pitches in length, and the diameter at the root of the thread is to increase uniformly from the standard root diameter to the diameter at the top of the thread. This may be produced by suitably grinding the dies, and the flange should be tapered out to the same formation.

Figure 12.2.1 Screwed-on flange

2.5.3 Such screwed and expanded flanges may be used for steam for a maximum design pressure of 3 MPa and a maximum design temperature of 370°C and for feed for a maximum design pressure of 5 MPa.

2.6.1 The types of welded-on flanges are to be suitable for the pressure, temperature and service for which the pipes are intended.

2.6.2 Typical examples of welded-on flange attachments are shown in Figure 12.2.2 Typical welded-on flanges, and limiting design conditions for flange types (a) to (f) are shown in Table 12.2.6 Limiting design conditions for flange types.

Figure 12.2.2 Typical welded-on flanges

2.6.3 Butt welded joints are generally to be of the full penetration type and are to meet the requirements of Pt 5, Ch 13 Ship Piping Systems of the Rules for Materials.

2.6.4 Welded-on flanges are not to be a tight fit on the pipes. The maximum clearance between the bore of the flange and the outside diameter of the pipe is to be 3 mm at any point, and the sum of the clearances diametrically opposite is not to exceed 5 mm.

2.6.5 Where butt welds are employed in the attachment of flange type (a), in pipe-to-pipe joints or in the construction of branch pieces, the adjacent pieces are to be matched at the bores. This may be effected by drifting, roller expanding or machining, provided that the pipe wall is not reduced below the designed thickness. If the parts to be joined differ in wall thickness, the thicker wall is to be gradually tapered to the thickness of the thinner at the butt joint. The welding necks of valve chests are to be sufficiently long to ensure that the valves are not distorted as the result of welding and subsequent heat treatment of the joints.

2.6.6 Where backing rings are used with flange type (a) they are to fit closely to the bore of the pipe and should be removed after welding. The rings are to be made of the same material as the pipes or of mild steel having a sulphur content not greater than 0,05 per cent.

2.6.7 Branches may be attached to pressure pipes by means of welding provided that the pipe is reinforced at the branch by a compensating plate or collar or other approved means, or, alternatively, that the thickness of pipe and branch is increased to maintain the strength of the pipe. These requirements also apply to fabricated branch pieces.

2.6.8 Welding may be carried out by means of the shielded metal arc, inert gas metal arc, oxy-acetylene or other approved process, but in general oxy-acetylene welding is suitable only for flange type (a) and is not to be applied to pipes exceeding 100 mm diameter or 9,5 mm thick. The welding is to be carried out in accordance with the appropriate paragraphs of Pt 5, Ch 17 Requirements for Fusion Welding of Pressure Vessels and Piping.

2.7.1 Loose flange designs as shown in Figure 12.2.3 Loose flange arrangements may be used provided they are in accordance with a recognised National or International Standard.

Figure 12.2.3 Loose flange arrangements

2.7.2 Loose flange designs where the pipe end is flared as shown in Figure 12.2.3 Loose flange arrangements(b) are only to be used for water pipes and on open ended lines.

2.8.1 Socket weld joints may be used in Class III systems with carbon steel pipes of any outside diameter. Socket weld fittings are to be of forged steel and the material is to be compatible with the associated piping. In particular cases, socket weld joints may be permitted for piping systems of Class I and II having outside diameter not exceeding 88,9 mm. Such joints are not to be used where fatigue, severe erosion or crevice corrosion is expected to occur or where toxic or asphyxiating media are conveyed, other than for carbon dioxide fire-extinguishing distribution piping, see also Pt 5, Ch 10, 14.4 Welded-on flanges, butt welded joints and fabricated branch pieces 14.4.9.

2.8.2 The thickness of the socket weld fittings is to meet the requirements of Pt 5, Ch 12, 2.2 Wrought steel pipes and bends 2.2.3 but is to be not less than 1,42 times the nominal thickness of the pipe or tube in order to satisfy the throat thickness requirement in Pt 5, Ch 12, 2.8 Socket weld joints 2.8.3. The diametrical clearance between the outside diameter of the pipe and the bore of the fitting is not to exceed 0,8 mm, and a gap of approximately 1,5 mm is to be provided between the end of the pipe and the bottom of the socket. See also Ch 13, 5.2 Manufacture and workmanship 5.2.9 of the Rules for Materials.

2.8.3 The leg lengths of the fillet weld connecting the pipe to the socket weld fitting are to be such that the throat dimension of the weld is not less than the nominal thickness of the pipe or tube.

2.8.4 As an alternative to the general dimensional requirements in Pt 5, Ch 12, 2.8 Socket weld joints 2.8.2 and Pt 5, Ch 12, 2.8 Socket weld joints 2.8.3, consideration will be given to socket weld joints in accordance with a recognised National or International Standard.

2.8.5 Socket weld joints may be used in carbon dioxide fire-extinguishing system distribution piping only as permitted by Pt 5, Ch 12, 2.14 Carbon dioxide (CO2) fire-extinguishing system piping.

2.9.1 Welded sleeve joints may be used in Class III systems with carbon steel pipes of any outside diameter. In particular cases, welded sleeve joints may be permitted for piping systems of Class I and II having outside diameter not exceeding 88,9 mm. Such joints are not to be used where fatigue, severe erosion or crevice corrosion is expected to occur or where toxic or asphyxiating media, other than for carbon dioxide fire-extinguishing distribution piping, are conveyed.

2.9.2 Welded sleeve joints are not to be used in the following locations:

• Bilge pipes in way of deep tanks.
• Cargo oil piping outside of the cargo area for bow or stern loading/discharge.
• Air and sounding pipes passing through cargo tanks.

2.9.3 Welded sleeve joints may be used in piping systems for the storage, distribution and utilisation of fuel oil, lubricating or other flammable oil systems in machinery spaces provided they are located in readily visible and accessible positions. See also Pt 5, Ch 14, 2.9 Precautions against fire 2.9.2.

2.9.4 Welded sleeve joints may be used in carbon dioxide fire-extinguishing system distribution piping only as permitted by Pt 5, Ch 12, 2.14 Carbon dioxide (CO2) fire-extinguishing system piping.

2.9.5 Welded sleeve joints are not to be used at deck/bulkhead penetrations that require continuous pipe lengths.

2.9.6 Welded sleeve joints are not to be used below the bulkhead deck in scupper pipes as detailed in Pt 3, Ch 12, 4.2 Closing appliances 4.2.6 unless the scupper pipes are provided with an automatic non-return valve at the shell. Where this is not practical, welded sleeve joints may be accepted provided that they are kept to a minimum and located as close as possible to the underside of the bulkhead deck.

2.9.7 The thickness of the sleeve is to satisfy the requirements of Pt 5, Ch 12, 2.2 Wrought steel pipes and bends 2.2.3 and Table 12.2.4 Minimum thickness for steel pipes but is to be not less than 1,42 times the nominal thickness of the pipe in order to satisfy the throat thickness requirement in Pt 5, Ch 12, 2.9 Welded sleeve joints 2.9.8. The radial clearance between the outside diameter of the pipe and the internal diameter of the sleeve is not to exceed 1 mm for pipes up to a nominal diameter of 50 mm, 2 mm for pipes up to a nominal diameter of 200 mm and 3 mm for pipes of larger nominal diameter. The pipe ends are to be separated by a clearance of approximately 2 mm at the centre of the sleeve.

2.9.8 The sleeve material is to be compatible with the associated piping and the leg lengths of the fillet weld connecting the pipe to the sleeve are to be such that the throat dimension of the weld is not less than the nominal thickness of the pipe or tube.

2.9.9 The minimum length of the sleeve is to conform to the following formula:

2.9.10 As an alternative to the general dimensional requirements in Pt 5, Ch 12, 2.9 Welded sleeve joints 2.9.7 to Pt 5, Ch 12, 2.9 Welded sleeve joints 2.9.9, consideration will be given to welded sleeve joints in accordance with a recognised National or International Standard.

2.10.1 Threaded sleeve joints and threaded couplings, in accordance with National or other established Standards, may be used with carbon steel pipes within the limits given in Table 12.2.7 Limiting design conditions for threaded sleeve joints and threaded couplings. Such joints are not to be used where fatigue, severe erosion or crevice corrosion is expected to occur or where flammable or toxic media is conveyed.

2.11.1 Fittings such as valves, strainers and similar components having threaded end connections may be used in piping systems. Subject to the restrictions given in Pt 5, Ch 12, 2.10 Threaded sleeve joints and threaded couplings for threaded sleeve joints and threaded couplings.

2.11.2 In piping systems conveying flammable or toxic liquids, consideration will be given to instrumentation fittings having threaded connections with suitable sealing arrangements up to a size of DN15.

2.12.1 Pipe unions, compression couplings, and or slip-on joints, as shown in Figure 12.2.4 Examples of mechanical joints (Part 1) and Figure 12.2.5 Examples of mechanical joints (Part 2), may be used if Type Approved for the service conditions and the intended application. The Type Approval is to be based on the results of testing of the actual joints. The acceptable use for each service is indicated in Table 12.2.8 Application of mechanical joints and dependence upon the Class of piping, with limiting pipe dimensions, is indicated in Table 12.2.9 Application of mechanical joints depending on class of piping.

Figure 12.2.4 Examples of mechanical joints (Part 1)

Figure 12.2.5 Examples of mechanical joints (Part 2)

2.12.2 Where the application of mechanical joints results in a reduction in pipe wall thickness due to the use of bite type rings or other structural elements, this is to be taken into account in determining the minimum wall thickness of the pipe to withstand the design pressure.

2.12.3 Materials of mechanical joints are to be compatible with the piping material and internal and external media.

2.12.4 Mechanical joints for pressure pipes are to be tested to a burst pressure of 4 times the design pressure. For design pressures above 20 MPa the required burst pressure will be specially considered.

2.12.5 Mechanical joints, which in the event of damage could cause fire or flooding, are not to be used in piping sections directly connected to the ship’s side below the bulkhead deck of passenger ships and freeboard deck of cargo ships or tanks containing flammable fluids.

2.12.6 The mechanical joints are to be designed to withstand internal and external pressure as applicable and where used in suction lines are to be capable of operating under vacuum.

2.12.7 The number of mechanical joints in flammable fluid systems is to be kept to a minimum. In general, flanged joints are to conform to a recognised standard.

2.12.8 Generally, slip-on joints are not to be used in pipelines in cargo holds, tanks, and other spaces which are not easily accessible. Application of these joints inside tanks may only be accepted where the medium conveyed is the same as that in the tanks.

2.12.9 Usage of slip type slip-on joints as the main means of pipe connection is not permitted except for cases where compensation of axial pipe deformation is necessary.

2.12.10 Restrained slip-on joints are permitted in steam pipes with a design pressure of 1 MPa or less on the weather decks of oil and chemical tankers to accommodate axial pipe movement, see Pt 5, Ch 13, 2.7 Provision for expansion.

2.12.11 Mechanical joints are to be tested in accordance with the test requirements of LR’s Type Approval Test Specification Number 2, as relevant to the service conditions and the intended application. The programme of testing is to be agreed with LR.

2.13.1 For details of non-destructive tests on piping systems, other than hydraulic tests, see Ch 13, 5.5 Non-destructive examination of the Rules for Materials.

2.14.1 The piping for carbon dioxide fire-extinguishing systems is to comply with the requirements of Chapter 5 - Fixed Gas Fire-Extinguishing Systems of the FSS Code, as applicable. For purposes of Classification, any use of the word ‘Administration’ in the Regulation is to be taken to mean LR.

2.14.2 Where a low-pressure CO₂ system is fitted, the piping system is to be designed in such a way that the CO₂ pressure at the nozzles is not less than 1 N/mm².

2.14.3 Materials for the distribution manifolds between the carbon dioxide storage bottles and the discharge valves to each section and associated pipes, valves and fittings of high pressure systems are to be manufactured and tested in accordance with the requirements for Class I piping systems. Pipes are to meet the minimum wall thickness requirements of Table 12.2.10 Minimum thickness for steel pipes for CO2 fire-extinguishing and the manifold system is to be hydraulically tested to a pressure of 19 MPa. A high pressure system is defined as a system where the carbon dioxide is stored at ambient temperature.
Materials for the distribution manifolds between the carbon dioxide storage vessel(s) and the discharge valves to each section and associated pipes, valves and fittings of low pressure systems are to be manufactured and tested in accordance with the requirements for Class II piping systems and the manifold system is to be hydraulically tested to a pressure of 3,3 MPa. A low pressure system is defined as a system where the carbon dioxide is stored at a working pressure in the range of 1,8 to 2,2 MPa.

2.14.4 Piping downstream of the distribution valve(s) for high pressure systems is to be manufactured and tested in accordance with the requirements for Class II piping and is to meet the minimum wall thickness requirements of Table 12.2.10 Minimum thickness for steel pipes for CO2 fire-extinguishing. After installation the distribution system is to be leak tested at a pressure of 0,6 MPa.
Piping downstream of the distribution valve(s) for low pressure systems is to be manufactured and tested in accordance with the requirements for Class III piping. After installation the distribution system is to be leak tested at a pressure of 0,6 MPa. Class III piping may be used for open ended distribution piping downstream of the distribution valve(s) of high pressure systems where agreed by LR and where meeting the minimum wall thickness requirements of Table 12.2.10 Minimum thickness for steel pipes for CO2 fire-extinguishing and where a minimum of ten per cent of the piping is hydraulically tested at a pressure of 12,5 MPa. This testing is to be carried out before installation.

2.14.5 Any part of the carbon dioxide fire-extinguishing system piping is to be of galvanised steel or of corrosion resistant steel. Where full penetration butt welding is used, the pipe is to be protected against corrosion in the area of the weld seam after welding. The process for protecting the pipe internally against corrosion is to be of an approved type. All pipes are to be arranged to be self-draining. Where pipes are to be led into refrigerated spaces, this is subject to special consideration. The ends of distribution pipes downstream of the distribution valve(s) are to extend at least 50 mm beyond the last nozzle and are to be fitted with a dirt trap consisting of an open ended tee with a capped nipple.

2.14.6 If it is necessary for carbon dioxide pipes to pass through accommodation spaces, the pipe is to be seamless and is to meet the requirements for Class II pipes. Joints are to be made only by welding and the pipes are to be hydraulically tested after installation at a pressure of 5 MPa.

2.14.7 The following means are permitted for making joints on carbon dioxide fire-extinguishing system piping ;

1. Full penetration butt welding, where the pipe is galvanised, see Pt 5, Ch 12, 2.14 Carbon dioxide (CO2) fire-extinguishing system piping 2.14.5.

2. Couplings as permitted by Table 12.2.8 Application of mechanical joints.

3. Cone connections.

4. Tapered threaded joints , where allowed by Pt 5, Ch 12, 2.14 Carbon dioxide (CO2) fire-extinguishing system piping 2.14.11 and where meeting the requirements of Pt 5, Ch 12, 2.14 Carbon dioxide (CO2) fire-extinguishing system piping 2.14.11.

5. Flanged joints.

6. Socket weld joints to acceptable National Standards and where allowed by Pt 5, Ch 12, 2.14 Carbon dioxide (CO2) fire-extinguishing system piping 2.14.8 and where meeting the requirements of Pt 5, Ch 12, 2.14 Carbon dioxide (CO2) fire-extinguishing system piping 2.14.10.

7. Welded sleeve joints may be used where allowed by Pt 5, Ch 12, 2.14 Carbon dioxide (CO2) fire-extinguishing system piping 2.14.9 and where meeting the requirements of Pt 5, Ch 12, 2.14 Carbon dioxide (CO2) fire-extinguishing system piping 2.14.10.

2.14.8 Socket weld joints of an approved type may be used downstream of the distribution valve(s), provided that the requirements for materials and limitations on outside diameter applicable for Class II piping are applied.

2.14.9 Welded sleeve joints of an approved type may be used within the protected space, provided that the requirements for materials and limitations on outside diameter applicable for Class II piping are applied.

2.14.10 Where socket weld joints or welded sleeve joints are utilised, the pipes in way of the welded joints are to be adequately supported and the joints are to be located where they are visible. Where welding is to be carried out in situ, the piping is to be kept clear of adjacent structures to allow sufficient access for preheating and welding, which is to be carried out in accordance with approved procedures.

2.14.11 Threaded joints are only allowed inside the protected spaces and in carbon dioxide bottles storage rooms. They should have no exposed screw threads and any sealing medium should be selected as to ensure no protrusions or debris might be produced in the pipe.