Section 2 Piping Design Requirements

2.1.1 All pipe systems, whether inside or outside the pressure hull, are to conform to the requirements of Pt 5 Main and Auxiliary Machinery of the Rules and Regulations for the Classification of Ships, July 2022. All pipes and fittings are to be of approved type. Where quick release couplings are permitted they are to be permanently connected to the flexible pipes. For general requirements for piping system fittings see Pt 5, Ch 3, 3.1 General Requirements for Piping Systems Fittings.

2.1.2 Piping systems are to be designed, constructed and tested in accordance with Rules for the Manufacture, Testing and Certification of Materials, July 2022 and Rules and Regulations for the Classification of Ships, July 2022 Pt 5 Main and Auxiliary Machinery, as applicable. However, piping systems for life support systems are to be designed, constructed, and tested in accordance with the requirements for Class I piping systems.

2.1.3 Piping systems are to be so designed that protuberances are faired to reduce the possibility of damage, for example, when alongside support craft or during work operations.

2.1.4 Where necessary external pipes may be protected against corrosion by suitable bonding or coatings.

2.1.5 Piping systems should be so designed as to minimize the noise inside the diving bell and surface compression chamber during normal operation.

2.1.6 Piping systems which could be subjected to higher pressures than their design pressure are to be fitted with a pressure relief valve.

2.1.7 Piping systems carrying mixed gas or oxygen under high pressure are not to pass through accommodation spaces, engine rooms or similar compartments.

2.1.8 High pressure gas systems are to be reduced in pressure as close as possible to the gas storage.

2.1.9 All pipes penetrating pressure chambers including diving bells are to be provided with internal and external isolating values. These valves are to have positive means of indication to show whether they are open or shut and are to be capable of being secured in either position. The securing arrangements are to be such that the valves can be operated in an emergency. Where appropriate, one valve should be of the non-return type. Where it is not practicable to fit isolating valves direct to the shell, distance pieces of short rigid construction may be fitted between the valves and shell plating. The number of screwed fittings, if employed for this purpose, should be kept to a minimum.

2.1.10 Any components fitted between the shell penetrations and isolating valves are to be designed for an internal and external pressure of not less than that equivalent to the maximum diving depth.

2.1.11 All high pressure piping should be well protected against mechanical damage.

2.1.12 All piping is to be approved metallic construction suitable for the service intended, except where flexibility is essential in which case flexible hoses of approved type having integral closely woven wire braid reinforcement with properly attached end fittings of swaged crimped or similar type are acceptable as short joining lengths between permanent piping.

2.1.13 All connections to instrumentation and pressure gauges are to be provided with suitable isolating valves, see Pt 5, Ch 3, 3.1 General Requirements for Piping Systems Fittings 3.1.5.

2.1.14 Mechanical components such as valves and fittings, which are procured from recognized suppliers may, with the prior agreement of LR, be accepted on the evidence of manufacturers full documentation supplemented by final system testing to the satisfaction of LR’s Surveyors. See also Ch 1, 2 Approval and survey requirements of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

2.1.15 All valves, fittings, controls, indicators and warning devices are to be provided with identification plates made of a material which is at least flame retardant. The identifying marks are to be clear and unmistakable (e.g. stating the short designation and/or the function of the item concerned).

2.1.16 Means must be provided for the complete evacuation, drainage and venting of piping systems.

2.1.17 Compression chambers and diving bells are to have suction guards on exhaust line openings inside each compartment.

2.1.18  Gas lines and electrical cables are to be routed separately.

2.1.19 Expansion in piping systems is to be compensated by pipe bends or compensators. Attention is to be given to the suitable sizing of fixed points.

2.1.20 Materials used in the breathing gas system shall not produce noxious, toxic or flammable products under specified design conditions.

2.1.21 In oxygen pressure systems, all the materials in contact with this gas shall be shock tested according to EN 738-1, -2 and - 3:1997/1998 “Pressure regulators for use with medical gases” or equivalent standard applicable to the particular component. (See also EN 849:1996, EN ISO 11114-3:1997 and EN ISO 2503:1998 in informative references)

2.1.22 For piping systems of copper, corrosion resistant alloys and austenitic steels with chromium-nickel content above 22%, the test can be waived.

2.1.23 Precautions shall be taken to avoid galvanic corrosion.

2.1.24 Non-metallic materials retaining pressurised gas shall be considered for gas-permeability.

2.2.1 For general design requirements of piping system fittings see Pt 5, Ch 3, 2.3 Pipe fittings.

2.2.2 Wherever possible, pipes should be joined by full penetration butt welds.

2.2.3 Flanged connections and flange bolts conforming to a recognized standard may be used.

2.2.4 Other types of connections may be submitted for consideration.

2.2.5 Screwed pipe connections are to be of an LR approved type.

2.3.1 All surface compression chambers and diving bells are to be equipped at a centralized position outside the chamber with such valves, gauges and other fittings as necessary to control and indicate the internal pressure and safe environment of each compartment. The external pressure on the diving bell is also to be indicated inside the bell.

2.3.2 Valves in oxygen systems where the system pressure is above the exemption pressure as defined in IGC13/12/E, are to be screw down type and slow opening except that ball valves may be used as emergency shut-off valves fitted directly to the shell.

2.3.3 Gas valves, including pressure-reducing valves and their systems, are to be tested to 1,5 times design pressure. It is to be demonstrated that they are capable of delivering the specified quantity of gas at a pressure equivalent to the intended maximum diving depth.

2.3.4 All valves are to be constructed as to prevent the possibility of valve covers or glands being loosened when the valves are operated.

2.3.5 All valves are to be clearly labelled and provided with open/shut indication.

2.3.6 Shutoff devices must conform to a recognized standard. Valves with screw-down bonnets or spindles are to be protected against unintentional unscrewing of the bonnet.

2.3.7 Manually operated shutoff devices are to be closed by turning in the clockwise direction.

2.3.8  Hose fittings are to be made of corrosion resistant material and are to be so designed that they cannot be disconnected accidentally.

2.4.1 Except for umbilicals, non-metallic hoses are to be reduced to a minimum and are only to be installed in short lengths.

2.4.2 Hose lines, including their connectors, must be of proven suitability for the media, pressures and temperatures concerned. When selecting the material, special attention is to be paid to toxicity, incombustibility, gas permeability, and where applicable, compatibility with oxygen. Only types approved by LR may be used.

2.4.3 Hose lines for liquids/gases are to be designed for a bursting pressure equivalent to at least 4 and 5 times respectively the maximum permissible working pressure, see Pt 5, Ch 5, 4.6 Resistance to burst.

2.4.4 Hoses are to be permanently coupled to their connectors.

2.4.5 Systems with hose lines are to be fitted with a device for relieving the pressure before the hoses are disconnected.

2.4.6 Unless equipped with load cables, umbilical hose lines must be fitted with load relieving devices.

2.4.7 Umbilicals must be protected against abrasion and damage. Where protective sheathing is used, care is to be taken to ensure that minor leaks cannot lead to an internal pressure build-up. Metal inserts are to be avoided.

2.4.8 Electrical cables in the umbilical must conform to the requirements stated in Pt 6 Electrical Installations and Control Engineering Systems.

2.5.1 Equipment and piping systems which may be subjected to pressures higher than the design pressure must be fitted with overpressure protection.

2.5.2 All compression chambers and diving bells shall be provided with pressure relief valves or overpressure alarms. Where pressure relief valves are proposed these may be fitted on the chamber or bell or, alternatively on each gas pressurizing line. Where relief valves are fitted on a chamber a quick operating manual shut-off valve should be installed between the chamber and the pressure relief valve which should be wired open with a frangible wire. This valve should be readily accessible to the diving supervisor monitoring the operation of the chamber.

2.5.3 Heat exchangers and heaters in life support system are to be protected by suitably sized safety relief devices set at a pressure not exceeding their maximum allowable working pressure (MAWP) and they are to be installed with no intervening valves between the pressure container and the safety relief device with the exception of PVO's. The maximum allowable working pressure is the maximum pressure permissible at the top of the pressure vessel, heat exchanger or heater in its normal operating condition and at the designated concurrent temperature specified for that pressure. If the safety devices are mounted outside the main pressure hull, they are to be constructed of suitable non-corrosive materials and are to be inspected on a regular basis in accordance with the procedure outlined in the approved Maintenance Manual. For these safety devices, the designer is to consider the effect of seawater back-pressure acting on the downstream side of the safety device.

2.5.4 If the safety devices are mounted on equipment or piping within PVHO, then it is to be demonstrated by calculations that the release of the fluid contained in the pressure vessel will not increase the pressure within the main pressure hull by more than 1 atmosphere, nor raise the partial pressure of the atmospheric gases above their maximum allowable levels. Special consideration will be given to the equivalent alternative arrangements.

2.6.1 Ballast systems should be designed to operate under all specified angles of heel and trim including maximum anticipated damage conditions.

2.6.2 In an autonomous or free-swimming submersible where pumps are required for the transfer or discharge of ballast a stand-by pump should be provided.

2.6.3 On passenger submersibles, pumps are to be provided which are capable of quickly transferring ballast and altering trim according to the number of passengers embarked on each trip.

2.6.4 Internal ballast or trim systems which may be subjected to the dive pressure should be suitable for the maximum design diving depth and are to be tested to 1,5 times this pressure.

2.6.5 Ballast control and tank flow valves are to be of a failsafe design or, alternatively provided with stand-by facilities.

2.6.6 Where compressed air is used to discharge ballast or to trim tanks the capacity should be sufficient to discharge all the tanks at the maximum diving depth with a reserve of 50 per cent. On passenger submersibles the reserve should be 100 per cent.

2.6.7 The compressed air storage vessels should not be used for other purposes and should be fully charged before the start of each dive.

2.6.8 In a passenger submersible two separate means of enabling the craft to return to the surface should be provided and for keeping the surfaced craft in a stable condition.

2.6.9 Sufficient instrumentation and equipment should be provided to ensure that the operator is fully aware of the ballast, heel and trim conditions at all times.

2.6.10 Water leakage monitoring devices should be provided in all compartments with audible and visual alarms at the control station. Monitoring devices for battery compartments should be suitable for use in such spaces.

2.7.1 Autonomous submersibles should be provided with an efficient bilge system capable of pumping out all watertight compartments except those containing water ballast, fuel oil, etc., under all practicable conditions of list and trim.

2.7.2 Autonomous submersibles are to be provided with at least two self-priming pumps capable of draining all compartments. Where appropriate, one pump may be driven off propulsion shafting.

2.7.3 The arrangement of valves, cocks and their connections is to be such as to prevent the possibility of one watertight compartment being placed in communication with another. For this reason screw down non-return valves are to be provided at bilge pump manifold and branch bilge suctions.

2.7.4 Where bilge pipes pass through watertight bulkheads, screw down non-return valves attached to the bulkheads capable of being closed from both sides are to be provided.

2.7.5 In addition a mud box and screw down non-return valve should be provided within the space the bilge suction serves.

2.7.6 Bilge systems which may be subjected to the dive pressure should be suitable for the maximum design diving depth and are to be tested to 1,5 times this pressure.

2.8.1 Where drainage of pressure chambers is achieved by means of pressure differential, a self-closing shut-off valve is to be provided inside the chamber close to the chamber penetration.

2.9.1 Air storage pressure vessels are to be designed and manufactured to a relevant National Standard.

2.9.2 Where compressed air is used for essential ballasting movements, not less than two means of supplying the compressed air are to be provided. Alternatively where the craft is designed for trips of short duration (for example less than 6 hours) consideration could be given to recharging the storage vessels from shore.

2.9.3 Each compressor stage must be equipped with a pressure relief valve or rupture disc, neither of which can be disabled. This safety device must be designed and set in such a way that the specified pressure in the compressor stage concerned cannot be exceeded by more than 10 per cent. The setting must be safeguarded against unauthorized alteration.

2.9.4 Each compressor stage must be provided with a suitable pressure gauge indicating clearly the final pressure of that stage.

2.9.5 Where a compressor stage comprises more than one cylinder and each cylinder can be closed off individually, a pressure relief valve and a pressure gauge must be provided for each cylinder.

2.9.6 Cooling liquid systems with a shutoff device must be so designed that the specified coolant pressure cannot be exceeded.

2.9.7 Dry-running reciprocating compressors must be equipped at each stage with a device which activates a warning signal and shuts down the drive motor if the final compression temperature stated in the operating instructions is exceeded.

2.9.8 Diaphragm-type compressors must be equipped at each stage with a diaphragm rupture indicator which shuts down the compressor as soon as damage occurs to the drive or compressor diaphragm

2.10.1 Fluids having low flash points and fluids having high viscosity at low temperatures are not to be used. Fire-resistant non-toxic fluids are recommended.

2.10.2 Materials used for all parts of hydraulic seals are to be compatible with the working fluid at the appropriate working temperature and pressure.

2.10.3 Pumps are to be accessible for maintenance and are to be mounted where they will be protected from damage and dirt.

2.10.4 Overpressure protection is to be provided on the discharge side of all pumps. Where relief valves are fitted for this purpose they are to be fitted in close circuit, i.e. arranged to discharge back to the suction side of the pump.

2.10.5 System piping is not to be used as a means of supporting equipment.

2.10.6 Provision is to be made for operation of the equipment in the event of loss of pressure in the system.

2.10.7 Hydraulic piping is to be located clear of oxygen or oxygen enriched systems.

2.11.1 The minimum thickness of piping subject to external pressure is to be the greater of the thickness determined by the following equations:

Where:

2.12.1 On completion of manufacture but before insulation or painting, all piping systems are to undergo a hydraulic pressure test at 1,5 times the design pressure.

2.12.2 The gas storage facilities, diving system and life support systems including the gas piping are to be subjected to a tightness test at the maximum permissible working pressure using Nitrogen with 10% He to facilitate locating possible leaks. The maximum permissible leakage rate is represented by a 1 per cent pressure drop in 24 hours for the entire compression chamber system taking into account any temperature change. Please also see Pt 5, Ch 4, 6.3 Oxygen System Testing and Pt 5, Ch 4, 6.4 Gas leak test for all chambers and breathing gas systems respectively.

2.12.3 Wherever possible, all butt welds in LSS piping systems are to be subjected to 100 per cent NDT for class I piping systems.

2.12.4 Piping systems for breathing gas and oxygen are to be subjected to a purity test.