Section 5 Pipe joints

5.1.1 Connections in piping systems may be made by any of the methods described in this Section, or by special types of approved joints which have been shown to be suitable for the design conditions. Details of connection methods, not described in this Section are to be submitted for consideration.

5.1.2 The selection of pipe connections in piping systems is to recognise the boundary fluids, pressure and temperature conditions, external or cyclic loading and location.

5.1.3 Pipe connections in accordance with national or other established standards will be accepted where the standards are appropriate to the piping system.

5.1.4 The type and location of pipe connections are to recognise the need to facilitate Periodic Survey of piping systems and associated items of machinery and the need for cold ‘pull up’ if required.

5.1.5 Pipe connections are not to be used to compensate for pipe misalignment.

5.1.6 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.

5.1.7 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.

5.1.8 For details of non-destructive tests on piping systems, other than hydraulic tests, see Ch 13 Requirements for Welded Construction of the Rules for Materials.

5.1.9 The requirements in Vol 2, Pt 7, Ch 1, 5.2 Flange connectionsare applicable to connections in metallic piping systems.

5.2.1 The dimensions and configuration of flanges and bolting are to be selected in accordance with recognised standards. The dimensions and bolting arrangements of nonstandard flanges will be the subject of special consideration.

5.2.2 Gaskets are to be suitable for the conveyed fluids under design pressure and temperature conditions and their dimensions and configuration is to be in accordance with recognised standards. Gasket materials used in oil piping systems are to be impervious to oil and the thinnest possible as determined from manufacturer's recommendations that the flange arrangement will allow, to ensure the minimum loss of bolt stress due to gasket relaxation.

5.2.3 Flange connections having components sensitive to heat, including gaskets or isolation kits, are not to be used in spaces where leakage or failure caused by fire could result in fire spread, flooding or loss of a Mobility or Ship Type system.

5.2.4 Acceptable flange pipe connections are indicated in Figure 1.5.1 Typical welded-on flanges. Limiting applications of different types of flange connections are indicated in Table 1.5.1 Limiting design conditions for flange types depending on the size, pressure and temperature.

Figure 1.5.1 Typical welded-on flanges

5.3.1 Where flanges are secured by screwing, as indicated in Figure 1.5.2 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.

Figure 1.5.2 Screwed on flange

5.3.2 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.

5.3.3 Such screwed and expanded flanges may be used for steam for a maximum design pressure of 30 bar and maximum design temperature of 370°C and for feed for maximum design pressure of 50 bar.

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

5.4.2 Butt welded joints are generally to be of the full penetration type and are to meet the requirements of Ch 13 Requirements for Welded Construction of the Rules for Materials.

5.4.3 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.

5.4.4 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.

5.4.5 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.

5.4.6 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 are increased to maintain the strength of the pipe. These requirements also apply to fabricated branch pieces.

5.4.7 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 Vol 2, Pt 1, Ch 4 Requirements for Fusion Welding of Pressure Vessels and Piping.

5.5.1 Loose flange designs as shown in Figure 1.5.3 Loose flange arrangements may be used provided they are in accordance with a recognised National or International Standard.

Figure 1.5.3 Loose flange arrangements

5.5.2 Loose flange designs where the pipe end is flared as shown in Figure 1.5.3 Loose flange arrangements are only to be used for water pipes and on open ended lines.

5.6.1 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.

5.6.2 The thickness of the socket weld fittings is to meet the requirements of Vol 2, Pt 7, Ch 1, 6.1 Wrought steel pipes and bends 6.1.3, but is to be not less than 1,25 times the nominal thickness of the pipe or tube. 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.

5.6.3 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.

5.6.4 Socket weld joints may be used in carbon dioxide fire-extinguishing system distribution piping only as permitted by Vol 2, Pt 7, Ch 1, 5.12 Piping for gaseous fire-extinguishing systems.

5.7.1 Threaded sleeve joints, in accordance with national or other established standards, may be used with carbon steel pipes within the limits given in Table 1.5.2 Limiting design conditions for threaded sleeve joints. 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.

5.8.1 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 media are conveyed.

5.8.2 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.

5.8.3 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 Vol 2, Pt 7, Ch 3, 2.8 Temperature indication 2.8.2.

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

5.8.5 The thickness of the sleeve is to satisfy the requirements of Vol 2, Pt 7, Ch 1, 6.1 Wrought steel pipes and bends 6.1.3 and Table 1.6.4 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 Vol 2, Pt 7, Ch 1, 5.8 Welded sleeve joints 5.8.6. 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 on diameters up to 200 mm nominal size and 3 mm for larger size pipes. The pipe ends are to be separated by a clearance of approximately 2 mm at the centre of the sleeve.

5.8.6 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.

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

5.9.1 Screwed fittings, including compression fittings, of an approved type may be used in piping systems for pipes not exceeding 51 mm outside diameter. Where the fittings are not in accordance with an acceptable standard then LR may require the fittings to be subjected to special tests to demonstrate their suitability for the intended service and working conditions.

5.10.1 Pipe unions, compression couplings, or slip-on joints, as shown in Figure 1.5.4 Examples of mechanical joints (Part 1) and Figure 1.5.5 Examples of mechanical joints (Part 2), may be used if type approved for the service conditions, the pipe material 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 1.5.3 Application of mechanical joints and dependence upon the class of piping, with limiting pipe dimensions, working pressure and temperature is indicated in Table 1.5.4 Application of mechanical joints depending on class of piping.

Figure 1.5.4 Examples of mechanical joints (Part 1)

Figure 1.5.5 Examples of mechanical joints (Part 2)

Table 1.5.3 Application of mechanical joints

Systems	Type of connections
	Pipe unions	Compression coupling	Slip-on joints
Flammable fluids (Flash point <60° C)
Aircraft and vehicle fuel oil lines see Notes 2 & 4	+	+	+
Vent lines see Note 2 & 3	+	+	+
Flammable fluids (Flash point > 60° C)
Aircraft and vehicle fuel oil lines see Note 2 & 4	+	+	+
Ship’s machinery fuel oil lines see Notes 2 & 3	+	+	+
Lubricating oil lines see Notes 2 & 3	+	+	+
Hydraulic oil see Notes 2 & 3	+	+	+
Thermal oil see Notes 2 & 3	+	+	+
Sea water
Bilge lines see Note 1	+	+	+
HP sea-water and water spray (not permanently filled) see Note 3	+	+	+
Water filled fire-extinguishing systems, e.g. sprinkler systems see Note 3	+	+	+
Non-water filled fire-extinguishing systems, e.g. foam, drencher systems see Note 3	+	+	+
Ballast system see Note 1	+	+	+
Cooling water system see Note 1	+	+	+
Tank cleaning services	+	+	+
Non-essential systems	+	+	+
Fresh water
Cooling water system see Note 1	+	+	+
Chilled water systems see Note 1	+	+	+
Condensate return see Note 1	+	+	+
Made water and demineralised water system	+	+	+
Ancillary system	+	+	+
Sanitary/Drains/Scuppers
Deck drains (internal) see Note 6	+	+	+
Sanitary drains	+	+	+
Scuppers and discharge (overboard)	+	+	-
Sounding /Vent
Water tanks/Dry spaces	+	+	+
Oil tanks (f.p.>60° C) see Notes 2 & 3	+	+	+
Intakes and uptakes see Note 7
HVAC trunking see Note 7
Miscellaneous
High pressure (HP) air systems see Note 1	+	+
Medium pressure (MP) air systems (Starting air) see Note 1	+	+
Low pressure (LP) air systems (incl. Control air) see Note 1	+	+
Service air (non-essential)	+	+	+
Brine	+	+	+
CO2 system see Note 1	+	+
Nitrogen system	+	+
Steam	+	+	see Note 5
KEY
+	Application is allowed
	Application is not allowed
Note 1. Mechanical joints that include any components which readily deteriorate in case of fire, are to be of an approved fire-resistant type when fitted in machinery spaces of category A. Mechanical couplings fitted on the ‘bilge main’ in machinery spaces of category A are to be of steel, CuNi or equivalent material.
Note 2. Slip-on joints are not accepted inside machinery spaces of category A, munition stores, or accommodation spaces. Slip-on joints are accepted in other machinery and service spaces provided that the joints are located in easily visible and accessible positions.
Note 3. Mechanical joints are to be of an approved fire-resistant type, except when they are fitted on open decks having little or no fire risk as defined in SOLAS Chapter II-2, Regulation 9.2.3.3.2.2(10).
Note 4. Mechanical joints are to be of an approved fire-resistant type
Note 5. See Vol 2, Pt 7, Ch 1, 5.10 Other mechanical couplings 5.10.10.
Note 6. Mechanical joints are only permitted above the limit of watertight integrity.
Note 7. Requirements for HVAC trunking or gas turbine updates and intakes are addressed in the relevant Sections of the Rules.

5.10.2 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.

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

5.10.4 Mechanical joints for pressure pipes are to be tested to a burst pressure of 4 times the design pressure. For design pressures above 200 bar the required burst pressure will be specially considered.

5.10.5 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 limit of watertight integrity or tanks containing flammable fluids.

5.10.6 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.

5.10.7 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.

5.10.8 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.

5.10.9 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.

5.10.10 Restrained slip-on joints are permitted in steam pipes with a design pressure of 10 bar or less on the weather decks of oil and chemical tankers to accommodate axial pipe movement, see Vol 2, Pt 7, Ch 2, 2.7 Provision for expansion.

5.10.11 Mechanical joints are to be tested in accordance with the test requirements in 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.

5.10.12 The type or location of pipe joints may be limited by the shock policy requirements defined by the Naval Administration. The use of mechanical joints is to be considered against the shock requirements.

5.11.1 Mechanical pipe connections having sealing components sensitive to heat are not to be used in spaces where leakage or failure caused by fire could result in fire spread, flooding or loss of a Mobility or Ship Type system.

5.12.1 The requirements of Vol 2, Pt 7, Ch 1, 5.12 Piping for gaseous fire-extinguishing systems are applicable to carbon dioxide (CO2) fire-extinguishing system piping arrangements. Piping arrangements for gaseous fixed fire suppression systems using gases other than carbon dioxide are to be agreed with LR.

5.12.2 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 FSS Code is to be taken to mean LR.

5.12.3 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.

5.12.4 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 1.5.5 Minimum thickness for steel pipes for CO₂ fire-extinguishing and the manifold system is to be hydraulically tested to a pressure of 190 bar. 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 33 bar. A low pressure system is defined as a system where the carbon dioxide is stored at a working pressure in the range of 18 bar to 22 bar.

5.12.5 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 1.5.5 Minimum thickness for steel pipes for CO₂ fire-extinguishing. After installation the distribution system is to be leak tested at a pressure of 6 bar. 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 6 bar. 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 1.5.5 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 125 bar. This testing is to be carried out before installation.

5.12.6 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.

5.12.7 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 50 bar.

5.12.8 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 Vol 2, Pt 7, Ch 1, 5.12 Piping for gaseous fire-extinguishing systems 5.12.6.

2. Couplings as permitted by Table 1.5.3 Application of mechanical joints.

3. Cone connections.

4. Tapered screw joints, where allowed by Vol 2, Pt 7, Ch 1, 5.12 Piping for gaseous fire-extinguishing systems 5.12.11 and where meeting the requirements of Vol 2, Pt 7, Ch 1, 5.12 Piping for gaseous fire-extinguishing systems 5.12.11.

5. Flanged joints.

6. Socket weld joints to acceptable National Standards and where allowed by Vol 2, Pt 7, Ch 1, 5.12 Piping for gaseous fire-extinguishing systems 5.12.9 and where meeting the requirements of Vol 2, Pt 7, Ch 1, 5.12 Piping for gaseous fire-extinguishing systems 5.12.10.

5.12.9 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.

5.12.10 Where socket weld joints are utilised, the pipes in the way of the weld 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.

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