Wednesday, August 28, 2013

General Requirements for Marine Boilers: Regulation Requirement Series!

"Regulation Requirements for Marine Boilers: Definitions and Materials Used"

1 General

1.1.1 Propulsion capability
Means shall be provided whereby normal operation of main boilers can be sustained or restored even though one of the essential auxiliaries becomes inoperative. Special consideration is to be given to the malfunctioning of:
the sources of steam supply
the boiler feed water systems
the fuel oil supply systems for boilers;
the mechanical air supply for boilers.
However, the Society, having regard to overall safety considerations, may accept a partial reduction in propulsion capability from normal operation.

1.1.2 Tests
All boilers and other pressure vessels including their associated fittings which are under internal pressure shall be subjected to appropriate tests including a pressure test before being put into service for the first time.

1.1.4 Protection against overpressure
Where main or auxiliary boilers and other pressure vessels or any parts thereof may be subject to dangerous overpressure, means shall be provided where practicable to protect against such excessive pressure.

2 Definitions

2.1 Pressure vessel
Pressure vessel is a welded or seamless container used for the containment of fluids at a pressure above or below the ambient pressure and at any temperature. Fluid power cylinders in hydraulic or pneumatic plants are also considered pressure vessels.

2.2 Boiler
Boiler is one or more fired pressure vessels and associated piping systems used for generating steam or hot water at a temperature above 120°C by means of heat resulting from combustion of fuel or from combustion gases.
Any equipment directly connected to the boiler, such as economisers, superheaters, and safety valves, is considered as part of the boiler, if it is not separated from the steam generator by means of any isolating valve. Piping connected to the boiler is considered part of the boiler.

2.3 Steam generator
Steam generator is a heat exchanger and associated piping used for generating steam.

2.4 Heat exchanger
Heat exchanger is a pressure vessel used to heat or cool a fluid with another fluid.

2.5 Design pressure/Temperature
The design pressure is the pressure/temperature used by the manufacturer to determine the scantlings of the vessel. This pressure cannot be taken less than the maximum working pressure and is to be limited by the set pressure of the safety valve, as prescribed by the applicable Rules.

2.6 Maximum steam output
Maximum steam output is the maximum quantity of steam that can be produced continuously by the boiler or steam generator operating under the design steam conditions.

3 Design Standards

For more on Design Standards, Please refer to the file here.. Click me!

Table  : Information and data to be submitted
for boilers and steam generators

1Design pressure and temperature
2Pressure and temperature of the superheated steam
3Pressure and temperature of the saturated steam
4Maximum steam production per hour
5Evaporating surface of the tube bundles and water-walls
6Heating surface of the economiser, superheater and air-heater
7Surface of the furnace
8Volume of the combustion chamber
9Temperature and pressure of the feed water
10Type of fuel to be used and fuel consumption at full steam production
11Number and capacity of burners

4 Materials

4.1 Materials for high temperatures
  1. Materials for pressure parts having a design temperature exceeding the ambient temperature are to be selected by the Manufacturer and to have mechanical and metallurgical properties adequate for the design temperature. Their allowable stress limits are to be determined as a function of the temperature.
  2. When the design temperature of pressure parts exceeds 400°C, alloy steels are to be used. Other materials are subject of special consideration by the Society.

4.2 Valves and fittings for boilers

  • Ductile materials are to be used for valves and fittings intended to be mounted on boilers. The material is to have mechanical and metallurgical characteristics suitable for the design temperature and for the thermal and other loads imposed during the operation.
  • Grey cast iron is not to be used for valves and fittings which are subject to dynamic loads, such as safety valves and blow-down valves, and in general for fittings and accessories having design pressure p exceeding 0,3 MPa and design temperature T exceeding 220°C.
  • Spheroidal cast iron is not to be used for parts having a design temperature T exceeding 350°C.Bronze is not to be used for parts having design temperature T exceeding 220°C for normal bronzes and 260°C for bronzes suitable for high temperatures. Copper and aluminium brass are not to be used for fittings with design temperature T above 200°C and copper-nickel fittings with design temperature T exceeding 300°C.

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