c11_pressure_system_hazards_and_controls_COMPLETE Flashcards
Saturation temperature is…
When the number of molecules leaving the liquid surface is more than those re-entering, the water freely evaporates. At this point it has reached boiling point, or its saturation temperature, as it is saturated with heat energy.
Enthalpy is…
the amount of heat content used or released in a system at constant pressure.
A steam explosion is…
a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or heated by interaction with molten metals.
Condensation induced water hammer occurs when…
large quantities of condensate lying inside a pipe are pushed along the pipe at steam velocities. This can result in damage when the water impacts with an obstruction in the pipe, for example a control valve.
Mounded pressurised torpedoes offer a safer option and eliminate the possibility of
BLEVE
Refrigeration systems are designed around two key principles:
(1) Liquids absorb heat when changed from liquid to gas. (2) Gases give off heat when changed from gas to liquid.
A new, self-contained air compressor is to be installed in a workshop. Identify THREE protective devices that may be necessary to control the risk of over-pressurisation AND for EACH device outline its purpose. 6 marks
(a) Protective devices include: a pressure gauge to identify the receiver pressure a safety valve which would relieve excess pressure when the maximum safe working pressure of the receiver is attained a pressure cut-out or unloading device which cuts off the compressor when the working pressure is reached a fusible metal plug which prevents over-heating and in turn over pressurisation if external heat sources are applied by melting and thus again relieves the pressure.
PER divides pressure equipment into four major categories on the basis of two fundamental hazards:
(1) The degree of danger from failure of the equipment (expressed by the product of the pressure of the fluid and the volume of the equipment or DN value for piping products). (2) The degree of danger from the release of the fluid contained (based on classifications adopted in the directives on dangerous substances).
As per the Simple Pressure Vessels (Safety) Regulations 1991 (SPV), simple pressure vessels have the following characteristics or limitations: 5
Intended to contain air or nitrogen at a gauge pressure >0.5 bar, but less than or equal to 30 bar. Not intended to be exposed to flame (i.e. ‘unfired’). Manufactured in series, i.e. more than one vessel of the same type is manufactured during a given period by the same continuous manufacturing processes, in accordance with a common design of welded non-alloy steel, or non-alloy aluminium construction, or non-age hardening aluminium alloy. A maximum working pressure (PS) of not more than 30 bar, and a PS.V (the product of PS and the vessel’s capacity expressed in litres) of not more than 10,000 bar litres. A minimum working temperature of not lower than -50°C, and a maximum working temperature of not >300°C for steel vessels, and not >100°C for aluminium or aluminium alloy vessels.
Schedule 1 of SPV details the essential safety requirements that qualifying vessels must satisfy. It also gives details of how the vessels should be categorised, the technical requirements to be satisfied, and the conformity assessment procedures to be followed. The ESR’s are presented in four parts:
Part 1: Materials Part 2: Vessel design Part 3 Manufacturing Process Part 4: Definitions and symbols
The air receiver should either be constructed to withstand the compressor’s maximum pressure safely, or
be fitted with a safety valve and a pressure-reducing valve to prevent the receiver’s safe working pressure from being exceeded.
Since air receivers are typically constructed out of carbon steel, they are subject to internal corrosion from water, which has condensed from the compressed air. Consequently air receivers are fitted with
automatic condensate drains or a manually operated drain valve to eliminate accumulated moisture.
With reference to the Pressure Systems Safety Regulations 2000, explain what is meant by a ‘pressure system’. 4 marks
(a) A ‘pressure system’ is a system comprising one or more pressure vessels of rigid construction, any associated pipe work and protective devices; the pipe work with its protective devices to which a transportable pressure receptacle is, or is intended to be connected; or a pipeline and its protective devices which contains or is liable to contain a relevant fluid, but does not include a transportable pressure receptacle. Examples of a ‘relevant fluid’ include: steam; a liquid which has a pressure 0.5 bar above atmospheric at the temperature of the liquid or at 17.5º C; a fluid or mixture of fluids which is at a pressure greater than 0.5 bar above atmospheric pressure when in equilibrium with its vapour at either the actual temperature of the liquid or at 17.5 degrees Celsius; or a gas dissolved under pressure in solvent contained in a porous substance at ambient temperature and which could be released from the solvent without the application of heat.
The Pressure Equipment Regulations 1999 (PER) apply to
the design, manufacture and conformity assessment of pressure equipment, and assemblies of pressure equipment with a maximum allowable pressure greater than 0.5 bar.
The PER do not apply to excluded pressure equipment and assemblies. Excluded equipment and assemblies are listed at Schedule 1 of the Regulations (Annex A of the Directive). The list is extensive and includes: 4
Simple pressure vessels Aerosol dispensers Blast furnaces Radiators and pipes in warm water heating systems.