Section 9 Piping for LPG/LNG carriers, gas fuelled ships and classed refrigeration systems

9.1.1 This Section is applicable to piping systems installed in LPG/LNG carriers, gas fuelled ships and classed refrigeration systems for the following pipes and piping system components:

1. Pipework – stainless steel, carbon steel and copper.

2. Valves – normal and cryogenic service (below minus 55°C).

3. Bellows – normal and cryogenic service (below minus 55°C).

4. Pipe fittings – elbows, reducers, tee connections, etc.

5. Ancillary fittings – weldolets, threadolets, thermopockets.

9.1.2 The following piping systems are covered by this Section:

1. LPG/LNG cargo systems – normal cargo operations.

2. LPG/LNG cargo systems – cargo gas to reliquefaction system.

3. LNG cargo systems – gas burning and use of cargo as fuel.

4. LNG Regasification system – high and low pressure.

5. Cargo Reliquefaction system – nitrogen or mixed refrigerant.

6. Refrigeration – independent plant used in cascade systems.

7. Gas storage and supply systems for gas fuelled ships.

9.2.1 The requirements of this Section apply to pipes and piping system components, such as valves, elbows and bellows, which are to be used on gas carriers, gas fuelled ships or classed refrigeration/reliquefaction systems. The requirements are also applicable to other gas cargo services such as regasification systems and gas combustion units, and are in addition to those contained in both the Rules for Ships for Liquefied Gases and relevant Sections of this Chapter where appropriate.

9.3.1 The material requirements for piping systems vary depending on the Class of the piping system. The Class of the piping system is dependent on the design pressure or temperature of the system and the pipe material used, see Pt 5, Ch 12, 1.6 Classes of piping systems and components.

9.3.2  Table 12.1.1 Maximum pressure and temperature conditions for Class II and III piping systems shows piping systems containing LPG/LNG, cargo or fuel gas as the conveyed medium are to be treated as 'Flammable liquids'. These piping systems are to be categorised as Class II. Vapour lines are also to be categorised as Class II systems but the upper limit on pressure may be increased to 4 MPa gauge in accordance with the ‘Other media’. Where higher design pressures are applied, such as in a regasification system, liquid lines above 1,6 MPa gauge and vapour lines above 4 MPa gauge are to be categorised as Class I. All open ended pipes, such as vent lines and pipes inside the cargo tanks may be categorised as Class III, provided that the temperature of the cargo at the pressure relief valve setting is not colder than minus 55°C.

9.3.3 For reliquefaction and refrigeration systems the requirements of Pt 5, Ch 12, 1.6 Classes of piping systems and components are to be applied. Nitrogen and non-toxic or nonflammable refrigerants are to be considered under the ‘Other media’ heading. Refrigeration systems containing ammonia are to be considered as Class I systems irrespective of the operational pressure.

9.4.1 Stainless steel pipes, valves and fittings for welded fabrication are to be grades 304L, 316L, 321 or 347 in accordance with Ch 6, 5 Stainless steel pressure pipes of the Rules for the Manufacture, Testing and Certification of Materials, July 2022. For non-welded fabrications the grades 304 and 316 may be accepted.

9.4.2 The materials used in Class I and Class II systems are to be produced at a works approved by LR. Testing is to be in accordance with the Rules for the Manufacture, Testing and Certification of Materials, July 2022 and Tables LR 6.1 and 6.4 in chapter 6 of the Rules and Regulations for the Construction and Classification of Ships for the Carriage of Liquefied Gases in Bulk, July 2022 or Table LR 7.1 and LR 7.4 in Chapter 7.4 Regulations for materials of the Rules and Regulations for the Classification of Ships using Gases or other Low-flashpoint Fuels, July 2022.

9.4.3 For stainless steel pipes, valve castings and forgings, a manufacturer’s certificate is acceptable where the intended service temperature is not colder than minus 55°C and:

• DN <50 or
• DN ≤150 and DN x P <250

  Where:

  DN = nominal diameter, mm

  P = design pressure, in MPa gauge

In all other cases, an LR materials certificate is required.

9.5.1 For valves and piping components fitted in the cargo piping system of LPG/LNG gas carriers, each type of valve and piping component is to have evidence of satisfactory type testing.

9.6.1 Each size and type of valve intended to be used at a working temperature below –55°C shall be approved. Approval is based upon prototype testing and assessment of the design for compliance with a recognised national or international standard acceptable to LR.

9.6.2 The tightness test required by Process Pressure Vessels and Liquid, Vapour and Pressure Piping Systems of the Rules for Ships for Liquefied Gases is to be conducted in accordance with a recognised National or International Code or Standard.

9.7.1 For valves intended for installation in a refrigeration system with a nominal diameter equal to or less than 150 mm, a manufacturer’s certificate is acceptable. The certificate is to include details of the maximum working pressure and test pressure, and sufficient information for the LR Surveyor to assess the suitability of the equipment for the intended use. Each size and type of valve is to be supplied with its own certificate and is to be signed by a responsible person in the manufacturer’s quality control department.

9.7.2 Valves with nominal diameters above 150 mm are to be supplied with a LR materials certificate in accordance with the Rules for Materials.

9.7.3 Where valves are fitted to pressure vessels, the requirements of Pt 5, Ch 10 Steam Raising Plant and Associated Pressure Vessels and Pt 5, Ch 11 Other Pressure Vessels are applicable for the Class of pressure vessel. Mountings for liquefied gas pressure vessels are to comply with the Rules for Ships for Liquefied Gases. Any acceptance of manufacturer's certification in other Sections of this Chapter is not applicable to the valves fitted to pressure vessels in Ch 10 Electrical Installations and 11 of the Rules for Ships for Liquefied Gases.

9.7.4 Any valve fitted directly onto a pressure vessel is to be considered a mounting and is required to be hydraulically pressure tested to twice the approved design pressure. See Pt 5, Ch 11, 10.2 Mountings 10.2.1.

9.8.1 The following plans and particulars are to be submitted:

1. Dimensioned drawings of each type of bellows.

2. Design calculations to show that the bellows are suitable for the intended design conditions, carried out to EJMA (Expansion Joint Manufacturers Association) standards (latest edition) or equivalent.

3. A proposed type test program covering the tests detailed in Process Pressure Vessels and Liquid, Vapour and Pressure Piping Systems of the Rules and Regulations for the Construction and Classification of Ships for the Carriage of Liquefied Gases in Bulk, July 2022.

4. Calculations to EJMA standards may be accepted, together with sample testing detailed above, in order to cover the entire size range for the type.

5. Thermal insulation protection, if applicable.

9.8.2 In accordance with 5.3 Type tests on piping components of the Rules for Ships for Liquefied Gases, the requirements for type testing in Pt 5, Ch 12, 9.8 Expansion bellows 9.8.3 are to be performed on each type of expansion bellows intended for use on LPG/LNG piping.

9.8.3 For each type of expansion bellows, an element of the bellows, not pre-compressed, is to be pressure tested at not less than five times the design pressure without bursting. This test is to be conducted at room temperature on each ‘type’ of element and need not be the complete bellows unit. A test on one element can cover other sized bellows with the same cross-sectional bellows form. The design pressure is to be at least 1 MPa gauge; bellows fitted to safety valves and vent lines may have a minimum design pressure of not less than the lower of 0,5 MPa gauge or 10 times the relief valve set pressure in accordance with Process Pressure Vessels and Liquid, Vapour and Pressure Piping Systems of the Rules for Ships for Liquefied Gases. The required test duration is not to be less than 5 minutes.

9.8.4 A pressure test is to be performed on each type of expansion joint complete with all the accessories such as flanges, stays and articulations, at twice the design pressure at the extreme displacement conditions recommended by the manufacturer without permanent deformation. The test is to be undertaken at the minimum design temperature, unless the bellows material is stainless steel for which this test may be carried out at ambient temperature. The test duration is to be 30 minutes unless otherwise agreed with LR.

9.8.5 A cyclic thermal movement test, replicating the cooling down and warming up cycle which occurs during cargo loading and discharge, is to be performed on a complete expansion joint, by the application of representative external deflection resulting in bellow movement. This is to successfully withstand at least as many cycles, under the conditions of pressure, temperature, axial movement, rotational movement and transverse movement, as it will encounter in actual service. The number of cycles is to be estimated by the builder and depends on the ship’s intended trading pattern and life expectancy. As a minimum, testing to 7000 cycles is to be carried out. The test is to be carried out at between 2-5 cycles per second. Testing at ambient temperature is permitted when this testing is at least as severe as testing at the service temperature. The maximum movements on the horizontal and vertical axis are to be provided by the builders and obtained from their stress analysis; however, the test can be extended to any value which is greater than that expected, or to the maximum deflection for which the bellows unit is suitable. Movements in the test need not be in both horizontal and vertical directions; but the horizontal-vertical box diagonal distance may be used. NDE testing is required after cyclic testing.

9.8.6 A cyclic fatigue test, representing ship deformation, is to be performed on a complete expansion joint (inclusive of its thermal insulation when fitted, where the thermal insulation is an integral part of the joint; however, this test could be performed without insulation where the thermal insulation is completely independent of the bellows movement), without internal pressure, by simulating the bellows movement corresponding to a compensated pipe length, for at least 2,000,000 cycles at a frequency not higher than 5 Hz. NDE is required after cyclic testing. This test is only required when, due to the piping arrangement, ship deformation loads are actually experienced.

9.9.1 Pressure testing is to be undertaken in accordance with specific Rule requirements relating to the system in which the component is to be located.

9.9.2 The duration for which pressure tests are to be held is to be in conjunction with an applicable and recognised code or standard acceptable to LR.

9.10.1 A certificate is required for each piping component supplied to be fitted in a Class I or Class II system. This certification is required for each size and type of equipment delivered. A single certificate may cover a number of valves, provided that they are of the same type and size, and serial numbers have been included on the certificate. If the piping components are part of a system fitted to a skid or packaged unit, then the complete skid may be supplied with a single certificate stating that the package has been constructed using approved materials, approved and tested in accordance with LR Rule requirements.

9.11.1 Relief valves fitted to cargo tanks and deck tanks are to be of a type tested design. Type testing is to include:

• flow or capacity verification to a recognised Standard acceptable to the Administration;
• cryogenic testing when operating at design temperatures colder than minus 55°C;
• seat tightness testing to a recognised Standard or manufacturers’ procedure acceptable to the Administration; and
• pressure testing of pressure-containing parts to at least 1,5 times the design pressure.

9.11.2 The materials used for construction of relief valves fitted to cargo tanks and deck tanks are to be produced in a works approved by LR and be provided with a Clasifications Register Material Certificate.