Section 7 Design and construction

7.1.1  Application. This Chapter is to be read in conjunction with the requirements of Vol 2, Pt 1, Ch 1 General Requirements for Classification of Engineering Systems andVol 2, Pt 1, Ch 3 Requirements for Design, Construction, Installation and Sea Trials of Engineering Systems.

7.1.2  Basic requirements. Designs are to take account of the potential effects of system and component malfunction and variability in characteristic values.

7.1.3 The design shall account for the operating conditions specified in Vol 2, Pt 1, Ch 3, 4 Operating conditions or the ship’s ConOps, whichever is the more onerous, and is to include those for static and dynamic loads and deflections, including for relative motions between elements of the gas turbine package and with the ship and other equipment, due to thermal expansion, vibration, etc. over all normal and reasonably foreseeable abnormal operating and fault conditions, including for fault condition loadings arising in the propulsion shaft line/alternator.

7.1.4 The gas turbine unit is to be capable of operating at defined power ratings with a range of fuel compositions/grades specified by the Owner/Operator and agreed by the gas turbine manufacturer.

7.1.5 The space containing the gas turbine unit shall comply with the requirements of Vol 2, Pt 1, Ch 3, 5 Machinery space arrangements.

7.1.6 Where applicable, the mounting/support arrangements of the gas turbine system are to satisfy the shock capability requirements defined by the Naval Administration. See Vol 2, Pt 1, Ch 3, 3.3 Calculations and specifications 3.3.10.

7.1.7 The fatigue life of dynamically loaded components is to be considered with respect to defined operating conditions, expected usage and maintenance policy, see Vol 2, Pt 2, Ch 2, 12 Planned maintenance and condition monitoring procedures, and ‘upkeep by exchange’. Due account is to be taken of stress raisers and material properties.

7.1.8 Primary exhaust gas emissions abatement plant (where fitted) is to meet the requirements of this Chapter; additionally, it is to meet those of Vol 2, Pt 12, Ch 1 Emissions Abatement Plant for Combustion Machinery. Where secondary exhaust gas emissions abatement systems are fitted to gas turbines, they are to meet the requirements of Vol 2, Pt 12, Ch 1 Emissions Abatement Plant for Combustion Machinery.

7.2.1 The gas generator and power turbine rotors are not to exhibit levels of vibration within the normal speed range that exceed the requirements of the Owner or that result in a failure to meet engine design life.

7.2.2 Vibration monitoring is to form an integral part of the gas turbine control, monitoring, alert and safety system. The vibration monitoring system is to be capable of detecting the out-of-balance of major parts with means being provided to shut down the gas turbine, before an over-critical situation occurs, i.e. multiple rotor blade or disc release.

7.3.1 Gas turbines and power turbines are to be designed and installed to contain debris within the unit in the event of release of a rotor blade or other rotating component of equivalent kinetic energy on release.

7.3.2 In the event of any component failure where the engine casing may not contain the debris, fuel, lubricating oil and other potentially hazardous systems or equipment are to be located outside the planes of those high-speed rotating parts identified as a potential loss of containment hazard by the engineering safety and justification report. Where this is not possible, they are to be suitably protected. This requirement also applies to fire detection and fire-extinguishing equipment.

7.3.3 Gas turbine ancillaries containing flammable products are to be segregated or protected from high temperature areas.

7.3.4 Means are to be provided such that, in the event of a failure to a shaft or coupling, the occupants of the ship are not endangered, either directly or through damage to the ship or its systems. Where necessary, guards may be fitted to achieve compliance with these requirements.

7.4.1 The air intakes and exhausts are to be in accordance with the turbine manufacturer’s design requirements. Particular attention is drawn to the requirements on pressure and flow conditions to be achieved throughout the intake and exhaust systems. Arrangements are to comply with Vol 2, Pt 2, Ch 2, 7.4 Intake and exhaust ducts 7.4.2 to Vol 2, Pt 2, Ch 2, 7.4 Intake and exhaust ducts 7.4.13, as applicable.

7.4.2 Where multiple gas turbines are installed, each gas turbine unit is to have separate intakes and exhausts so arranged as to prevent induced circulation through a stopped gas turbine unit.

7.4.3 Intakes and exhausts are to include suitable means of access to carry out inspections, maintenance and/or repair of components as advised by the gas turbine manufacturer. Any access panels should be sealed suitably to maintain the desired pressure and flow conditions in the intake and exhaust.

7.4.4 Suitable intake filtration is to be provided to control the ingestion of water, particulate and corrosive marine salts within the gas turbine manufacturer’s specified limits.

7.4.5 Where an air intake enclosure forms the connection between the ship’s downtake and the gas turbine package, a suitable alarm function is to be provided to give warning when an unacceptable air intake pressure loss is reached at the air inlet (bellmouth) of the gas turbine.

7.4.6 Intakes are to be designed such that material cannot become detached due to air flow or corrosion. Fixing bolts and fastenings are to be positively locked so that they cannot work loose.

7.4.7 The exhaust system is to accommodate thermal expansion and movement of the duct due to the combined effects of operation of the gas turbine and flexure of the ship's structure.

7.4.8 The design of exhaust systems is to prevent deterioration of engine parts resulting from ingress of sea or rainwater through the exhaust ducting when the gas turbine is not in use. Drainage arrangements are to be provided and are to be led to a tank suitable for the potentially corrosive nature of any drainage.

7.4.9 The exhaust ducting is to be designed and installed to minimise the risk of unburnt fuel collecting inside the duct.

7.4.10 The arrangement of the exhaust system is to be such as to prevent exhaust gases being drawn into the manned spaces, air conditioning systems and air intakes.

7.4.11 The exhaust system is to be arranged so that hot exhaust gases are directed to avoid impingement on equipment and away from areas to which personnel have access, either on board or in the vicinity of where the craft is berthed.

7.4.12 Where the exhaust is led overboard near the waterline, means are to be provided to prevent water from being siphoned back into the gas turbine. Where the exhaust is cooled by water spray, the exhaust pipes are to be self-draining overboard. Erosion/corrosion-resistant shut-off flaps or other devices are to be fitted on the hull side shell or pipe end with suitable arrangements made to prevent water flooding the machinery space.

7.4.13 The design of exhaust systems is to take account of any noise hazards to personnel, ensuring that they are within specified requirements for the ship.

7.4.14 The design of exhaust gas waste heat recovery recuperators for combustion air heating is to be compatible with the installed engine design parameters. The parameters which influence the build up of soot deposits and overheating such as fuel, exhaust gas temperature and efflux velocity are to be considered in the design of the recuperator in order to minimise the risk of fire and breakdown during operation. The engineering safety and justification report required by Vol 2, Pt 2, Ch 2, 5.2 Documentation 5.2.8 is to also demonstrate compliance with these requirements or alternative means of preventing the accumulation of soot or overheating, such as the use of exhaust gas by-pass ducting with automatic flap valve arrangements and/or effective soot prevention and cleaning systems for installations which use recuperators. Waste heat recovery units for steam generation are to meet the requirements of Vol 2, Pt 8, Ch 1, 1.13 Exhaust gas economiser/boiler arrangements.

7.5.1 Suitable provision is to be made to protect personnel and equipment and to minimise the risk of fire from any surfaces of the gas generator, power turbine and/or exhaust volute that exceed a temperature of 220°C during operation.

7.6.1 Welding processes are to be in accordance with the requirements of the Rules for Materials.

7.7.1 Air bleed (blow off) valves and/or variable geometry mechanisms are to be fitted as required to maintain compressor surge margins throughout the operating range. Any open-ended air bleed arrangements are to be led to the uptake or atmosphere and not into the machinery space; the back pressure imposed by the ducting is to be in accordance with the turbine manufacturer’s recommendations.

7.7.2 The design of anti-surge and anti-stall systems is to take account of any noise hazards to personnel, ensuring they are within specified requirements for the ship.

7.8.1 Where a gas turbine is required for the provision of Mobility systems or Ship Type systems, it and its supporting service systems are to be capable of operation when the compartment is flooded to the level of the underside of the lowest exposed portion of the gas turbine casing.