Bulging is generally
an indication of overheating. Continuing under the same temperature and stress
conditions will eventually lead to creep and stress rupture. The amount of
bulging varies with the specific metal and the type of damage, creep or overstress.
If the bulge is attributed to overstress (short-term overheating), and the
temperature and stress have been returned to normal, typically the life of the
tube has not been reduced. Creep life will be reduced, if the bulge is the
result of creep damage (long-term overheating). Bulging is considered more
serious than sagging or bowing.
Showing posts with label Mechanical. Show all posts
Showing posts with label Mechanical. Show all posts
Sunday, July 6, 2014
Bowing of a tube
Excessive bowing is generally caused by uneven metal temperatures, which may be due to flame impingement or coke accumulation inside the tube. Heating on one side of the tube causes greater thermal expansion on the hotter side and bowing toward the heat source. Bowing may also be caused by binding of the tube in the tube sheets or improper suspension of the tube so that longitudinal expansion is restricted or by the use of improper tube lengths when individual tube replacements are made.
Sagging of a tube
Excessive sagging is usually because of a decrease in the structural strength of the tube caused by overheating. It may also be caused by improper spacing of hangers, uneven metal temperatures, or failure of one or more tube supports or hangers.
Thursday, December 5, 2013
Turbine
A rotor-machine that is used to extract
energy from high pressure, high temperature fluids via expansion
across the turbine blades.
Sunday, October 20, 2013
Sunday, September 15, 2013
Specific heat(cp) of the substance
The
heat capacity of a substance per unit mass is called the specific
heat(cp) of the substance.
Heat Capacity (Cp) of the substance.
The
ratio of the heat (Q) added to or removed from a substance to the
change in temperature (∆T)
produced is called the heat capacity (Cp)
of the substance.
Latent heat of vaporization
Latent
heat of vaporization is the amount of heat added or removed to change
phase between liquid and vapor.
Latent heat of fusion
Latent
heat of fusion is the amount of heat added or removed to change phase
between solid and liquid.
Latent heat
Latent
heat is the amount of heat added to or removed from a substance to
produce a change in phase.
Sensible heat
The
heat added to or removed from a substance to produce a change in its
temperature is called sensible heat.
Work
Work is
defined for mechanical systems as the action of a force on an object
through a distance.
A
positive value for work indicates that work is done by the system on
its surroundings; a negative value indicates that work is done on the
system by its surroundings.
Specific enthalpy
Specific
enthalpy (h) is defined as h=u+Pν,
where u is the specific internal energy (Btu/lbm) of the system being
studied, P is the pressure of the system (lbf/ft2
), and ν is the specific
volume (ft3 /lbm) of the
system.
Monday, September 9, 2013
Potential energy; Kinetic energy; Specific internal energy
Potential
energy (PE) is defined as the energy of position.
Kinetic
energy (KE) is the energy of motion.
The
specific internal energy (u) of a substance is its internal energy
per unit mass.
Absolute Pressure & Gauge Pressure
When
pressure is measured relative to a perfect vacuum, it is called
absolute pressure (psia).
When
pressure is measured relative to atmospheric pressure (14.7 psi), it
is called gauge pressure (psig).
Pressure
Pressure
is a measure of the force exerted per unit area on the boundaries of
a substance (or system). It is caused by the collisions of the
molecules of the substance with the boundaries of the system.
Rankine (R) scale
The
absolute scale that corresponds to the Fahrenheit scale is called the
Rankine (R) scale.
Kelvin (K) scale
The
absolute temperature scale that corresponds to the Celsius scale is
called the Kelvin (K) scale.
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