Technical Term in Design Steam Boiler

Operating pressure: The actual pressure that be operated in steam pressure parts.
Design Pressure: The pressure used for calculating the minimum thickness requirement for steam boiler parts.
Maximum Allowable Working Pressure (MAWP): The maximum gage pressure or the pressure above the atmospheric pressure that is permitted in the steam boiler. It’s based on the lowest design pressure of any steam boiler part.

Operating temperature: The actual temperature that be operated in steam boiler parts.
Design temperature: Maximum mean wall temperature of pressure parts (tube, pipe, header and drum) that is to say the sum of the outside and inside pressure parts surface temperatures divided by two. A steam boiler is designed for design metal temperature which influence allowable stress values. The design metal temperature of an individual component may be much higher than the design steam temperature of the steam boiler.

Design margin: This is also known as safety factor. Design margin is defined as

The design margin was 4 until 1999. It was changed to 3.5 by introducing a code case by ASME Boiler and Pressure Vessel Committee in mid 1998

Corrosion allowance: A designer shall consider whether to add corrosion allowance when designing thickness of steam boiler parts.
Structural stability: This allowance is provided for pipes and tubes to consider threading and mechanical loads.
Allowable stresses. The stress values to be used in the design are temperature-dependent.
Thermal shock: Thermal shock is caused by temperature difference when cold water is directly introduced on hot surfaces of a steam boiler parts.
Hydrostatic head: This is the load caused by the weight of steam boiler part and its content.
Local loads: Local loads can result from steam boiler mountings, lugs, external piping, and the like.
Wind loads: General effects of wind loads fall into two categories: bending due to moments imposed and dynamic effects due to vibration.
Seismic loads: General effects of seismic loads fall into two categories: bending due to moments imposed and dynamic effects due to vibration.
Thermal loads: this Type of load occurs when steam boilers are used in cyclic service, with frequent start-ups and shutdowns that causes high thermal stress.
Effective Projected Radiant Surface (EPRS): Total projected area surface which is contacted by radiant heat of the flame plus added by total area surface of superheater which is exposed because the first convection heat transfer from flue gas.

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