Refinaries...photos

Welding Operation...................

PARETO ANALYSIS / ABC ANALYSIS

PARETO ANALYSIS / ABC ANALYSIS Pareto analysis (sometimes referred to as the 80/20 rule and as ABC analysis) is a method of classifying items, events, or activities according to their relative importance. It is frequently used in inventory management where it is used to classify stock items into groups based on the total annual expenditure for, or total stockholding cost of, each item. Organisations can concentrate more detailed attention on the high value/important items. Pareto analysis is used to arrive at this prioritisation. Taking inventory as an example, the first step in the analysis is to identify those criteria which make a significant level of control important for any item. Two possible factors are the usage rate for an item and its unit value. Close control is more important for fast moving items with a high unit value. Conversely, for slow moving, low unit value items the cost of the stock control system may exceed the benefits to be gained and simple methods of control should be substituted. These two factors can be multiplied to give the annual requirement value (ARV) - the total value of the annual usage. If the stock items are then listed in descending order of ARV, the most important items will appear at the top of the list. If the cumulative ARV is then plotted against number of items then a graph known as a Pareto curve is obtained. The precise shape of a Pareto curve will differ for any analysis but the broad shape remains similar - following 'the 80/20 rule'. Vilfredo Pareto was a 19th century economist who observed that 80% of Italy's wealth was owned by 20% of the population. In this case, typically, the first 20% of items in the list will account for approximately 80% of cumulative ARV. For a company with a stock list of 1,000 different items this means that paying more attention to the top 200 items (with a sophisticated stock control system) will give close control of about 80% of total stock investment. The next, say, 40% of items, will, typically, account for a further 15% of cumulative ARV. These can be subject to less precise control methods. The last 40% of (low value of low usage) items then account for a mere 5% of ARV and can be controlled with a simple system. The alternative term ABC analysis stems from the fact that the first 20% of important items are known as Category A items, the next, typically 40% are Category B items and the relatively unimportant, though larger in number, 40% are Category C items. Other examples Control of travel costs : again, typically, 20% of journeys will account for 80% of total travel costs - and should be closely monitored and controlled. Quality control : failure modes can be prioritised depending on their impact on a system's performance.

BEAMS

MS Beams are o f 2 types:-

1) I-BEAM

2) H-BEAM (Column) I- BEAM: - It is represented by dimensions of Web & Flange. For e.g. 150x75 beam means, Width of Web = 150mm Width of Flange = 75mm H - BEAM: - In H-Beam generally the sizes of the Web & Flange are almost equal. When we say, 254 x 254 beam means Web = 254mm & Flange = 254mm kg/m shows on third  and m2 /m shows fourth ISMB100x75   0.100 0.075 11.5 0.50 ISMB125x70   0.125 0.070 13.4 0.53 ISMB125x75   0.125 0.075 13.0 0.55 ISMB150x80   0.150 0.080 14.9 0.62 ISMB175x90   0.175 0.090 19.3 0.71 ISMB200x100   0.200 0.100 25.4 0.80 ISMB225x110   0.225 0.110 31.2 0.89 ISMB250x125   0.250 0.125 37.3 1.00 ISMB300x140   0.300 0.140 44.2 1.16 ISMB350x140   0.350 0.140 52.4 1.26 ISMB400x140   0.400 0.140 61.6 1.36 ISMB450x150   0.450 0.150 72.4 1.50 ISMB500x180   0.500 0.180 86.9 1.72 ISMB550x190   0.550 0.190 103.7 1.86 ISMB600x210   0.600 0.210 122.6 2.04

ANGLES

An ANGLE is a structural shape whose cross section resembles the letter L. Two types, are commonly used: an equal-leg angle and an unequal-leg angle. The angle is identified by the dimension and thickness of its legs; for example, angle 50 mm  x 50mm x 6mm thick. The dimension

of the legs should be obtained by measuring along the outside of the backs of the legs. When an angle has

unequal legs, the dimension of the wider leg is givenfirst, as in the example just cited. The third dimension

applies to the thickness of the legs, which always have equal thickness. Angles may be used in combinations o

  wight / m shows third item and m2/m is forth one in the table 

                                                                                       

ISA20x20x4		0.020	0.020	1.1	0.08
ISA25x25x4		0.025	0.025	1.4	0.10
ISA25x25x5		0.025	0.025	1.8	0.10
ISA30x30x4		0.030	0.030	1.8	0.12
ISA30x30x5		0.030	0.030	2.2	0.12
ISA35x35x4		0.035	0.035	2.1	0.14
ISA35x35x5		0.035	0.035	2.6	0.14
ISA35x35x6		0.035	0.035	3.0	0.14
ISA40x40x4		0.040	0.040	2.4	0.16
ISA40x40x5		0.040	0.040	3.0	0.16
ISA40x40x6		0.040	0.040	3.5	0.16
ISA45x45x4		0.045	0.045	2.7	0.18
ISA45x45x5		0.045	0.045	3.4	0.18
ISA45x45x6		0.045	0.045	4.0	0.18
ISA50x50x4		0.050	0.050	3.0	0.20
ISA50x50x5		0.050	0.050	3.8	0.20
ISA50x50x6		0.050	0.050	4.5	0.20
ISA55x55x5		0.055	0.055	4.1	0.22
ISA55x55x6		0.055	0.055	4.9	0.22
ISA55x55x8		0.055	0.055	6.4	0.22
ISA55x55x10		0.055	0.055	7.9	0.22
ISA60x60x5		0.060	0.060	4.5	0.24
ISA60x60x6		0.060	0.060	5.4	0.24
ISA60x60x8		0.060	0.060	7.0	0.24
ISA60x60x10		0.060	0.060	8.6	0.24
ISA65x65x5		0.065	0.065	4.9	0.26
ISA65x65x6		0.065	0.065	5.8	0.26
ISA65x65x8		0.065	0.065	7.7	0.26
ISA65x65x10		0.065	0.065	9.4	0.26
ISA70x70x5		0.070	0.070	5.3	0.28
ISA70x70x6		0.070	0.070	6.3	0.28
ISA70x70x8		0.070	0.070	8.3	0.28
ISA70x70x10		0.070	0.070	10.2	0.28
ISA75x75x5		0.075	0.075	5.7	0.30
ISA75x75x6		0.075	0.075	6.8	0.30
ISA75x75x8		0.075	0.075	8.9	0.30
ISA75x75x10		0.075	0.075	11.0	0.30
ISA80x80x6		0.080	0.080	7.3	0.32
ISA80x80x8		0.080	0.080	9.6	0.32
ISA80x80x10		0.080	0.080	11.8	0.32
ISA80x80x12		0.080	0.080	14.0	0.32
ISA90x90x6		0.090	0.090	18.2	0.36
ISA90x90x8		0.090	0.090	10.8	0.36
ISA90x90x10		0.090	0.090	13.4	0.36
ISA90x90x12		0.090	0.090	15.8	0.36
ISA100x100x6		0.100	0.100	9.2	0.40
ISA100x100x8		0.100	0.100	12.1	0.40
ISA100x100x10		0.100	0.100	14.9	0.40
ISA100x100x12		0.100	0.100	17.7	0.40
ISA110x110x8		0.110	0.110	13.4	0.44
ISA110x110x10		0.110	0.110	16.5	0.44
ISA110x110x12		0.110	0.110	19.6	0.44
ISA110x110x15		0.110	0.110	24.2	0.44
ISA130x130x8		0.130	0.130	15.9	0.52
ISA130x130x10		0.130	0.130	19.0	0.52
ISA130x130x12		0.130	0.130	23.4	0.52
ISA130x130x15		0.130	0.130	28.9	0.52
ISA150x150x10		0.150	0.150	22.8	0.60
ISA150x150x12		0.150	0.150	27.2	0.60
ISA150x150x15		0.150	0.150	33.6	0.60
ISA150x150x18		0.150	0.150	39.9	0.60
ISA200x200x12		0.200	0.200	36.6	0.80
ISA200x200x15		0.200	0.200	45.4	0.80
ISA200x200x18		0.200	0.200	54.0	0.80
ISA200x200x25		0.200	0.200	73.6	0.80

NDT -ULTRASONICMETHODS

ULTRASONICMETHODS
Ultrasonic methods utilize sound waves to inspect the interior of materials. Sound waves are mechanical
or elastic waves and are composed of oscillations of discrete particles of the material. The
process of inspection using sound waves is quite analogous to the use of sonar to detect schools of
fish or map the ocean floor. Both government and industry have developed standards to regulate
ultrasonic inspections. These include, but are not limited to, the American Society for Testing and
Materials Specifications 214-68, 428-71, and 494-75, and military specification MIL-1-8950H.
Acoustic and ultrasonic testing takes many forms, from simple coin-tapping to transmission of sonic
waves into a material and analyzing the returning echoes for the information they contain about its
internal structure. Reference 15 provides an exhaustive treatment of this inspection technique.
Instruments operating in the frequency range between 20 and 500 kHz are usually defined as
sonic instruments, while above 500 kHz is the domain of ultrasonic methods. In order to generate
and receive the ultrasonic wave, a piezoelectric transducer is usually used to convert electrical signals to sound wave signals and vice versa. This transducer usually consists of a piezoelectric crystal
mounted in a waterproof housing that facilitates its electrical connection to a pulsar (transmitter)
receiver. In the transmit mode, a high-voltage, short-duration pulse of electrical energy is applied to
the crystal, causing it to change shape rapidly and emit a high-frequency pulse of acoustic energy.
In the receive mode, any ultrasonic waves or echoes returning from the acoustic path, which includes
the coupling media and part, compress the piezoelectric crystal, producing an electrical signal that
is amplified and processed by the receiver.

Sound Waves

Ultrasonic waves have several characteristics, such as wavelength (A), frequency (/), velocity (i>),
pressure (P), and amplitude (a). The following relationship between wavelength, frequency, and sound
velocity is valid for all types of waves For example, the wavelength of longitudinal ultrasonic waves of frequency 2 MHz propagating in steel is 3 mm and the wavelength of shear waves is 1.6 mm.

Ultrasonic waves are reflected from all interfaces/boundaries that separate media with different
acoustic impedances, a phenomenon quite similar to the reflection of electrical signals in transmission
lines. The acoustic impedance Z of any medium capable of supporting sound waves

NONDESTRUCTIVE TESTING-LIQUIDPENETRANTS

Nondestructive evaluation (NDE) encompasses those physical and chemical tests that are used to
determine if a component or structure can perform its intended function without the test methods
impairing the component's performance. Until recently, NDE was relegated to detecting physical
flaws and estimating their dimensions. These data were used to determine if a component should be
scrapped or repaired, based on quality-acceptance criteria. Such traditional definitions are being expanded
as requirements for high-reliability, cost-effective NDE tests are increasing. In addition, NDE
techniques are changing as they become an integral part of the automated manufacturing process .The NDE methods reviewed here consist of the five classical techniques—penetrants, ultrasonic
methods, radiography, magnetic particle tests, and eddy current methods. Additionally, we have briefly
covered thermal-inspection methods.

LIQUIDPENETRANTS

Liquid penetrants are used to detect surface-connected discontinuities in solid, nonporous materials.
The method uses a brightly colored penetrating liquid that is applied to the surface of a clean part.
The liquid in time enters the discontinuity and is later withdrawn to provide a surface indication of
the flaw.

The Penetrant Process

Technical societies and military specifications have developed classification systems for penetrants.

Society documents (typically ASTM E165) categorize penetrants into two methods (visible and fluorescent)

and three types (water washable, post-emulsifiable, and solvent removable). Penetrants, then,

are classified by type of dye, rinse process, and sensitivity. 

The first step in penetrant testing (PT) or inspection is to clean the part .

Many times this critical step is the most neglected phase of the inspection. Since PT detects only

flaws that are open to the surface, the flaw and part surface must, prior to inspection, be free of dirt,

grease, oil, water, chemicals, and other foreign materials. Typical cleaning procedures use vapor

degreasers, ultrasonic cleaners, alkaline cleaners, or solvents.

After the surface is clean, a penetrant is applied to the part by dipping, spraying, or brushing.

 shows the penetrant on the part surface and in the flaw. In the case of tight

surface openings, such as fatigue cracks, the penetrant must be allowed to remain on the part for a

minimum of 30 minutes to enhance the probability of complete flaw filling. Fluorescent dye penetrants

are used for many inspections where high sensitivity is required.

At the conclusion of the minimum dwell time, the penetrant on the surface of the part is removed

by one of three processes, depending on the characteristics of the inspection penetrant. Ideally, only

the surface penetrant is removed and the penetrant in the flaw is left undisturbed 

The final step in a basic penetrant inspection is the application of a developer, wet or dry, to the

part surface. The developer aids in the withdrawal of penetrant from the flaw and provides a suitable

background for flaw detection. The part is then viewed under a suitable light source; either ultraviolet

or visible light. White light is used for visible penetrants while ultraviolet light is used for fluorescent

penetran

Categories of Penetrants

Once the penetrant material is applied to the surface of the part, it must be removed before an
inspection can be carried out. Penetrants are often categorized by their removal method. There are
generally three methods of removing the penetrant and thus three categories. Water-washable penetrants
contain an emulsifier that permits water to wet the penetrant and carry it from the part, much
as a detergent removes stains from clothing during washing. The penetrant is usually removed with
a water spray. Post-emulsifiable penetrants require that an emulsifier be applied to the part to permit
water to remove the excess penetrant. After a short dwell time, during which the emulsifier mixes
with the surface penetrant, a water spray cleans the part. For solvent-removable penetrants, the excess
material is usually removed with a solvent spray and wiping. This process is generally used in field
applications where water-removal techniques are not applicable.

 Reference Standards

Several types of reference standards are used to check the effectiveness of liquid-penetrant systems.
One of the oldest and most often-used methods involves chromium-cracked panels, which are available
in sets containing fine, medium, and coarse cracks. The panels are capable of classifying penetrant
materials by sensitivity and identifying changes in the penetrant process.

Limitations of Penetrant Inspections

The major limitation of liquid-penetrant inspection is that it can only detect flaws that are open to
the surface. Other methods are used for detecting subsurface flaws. Another factor that may inhibit
the effectiveness of liquid-penetrant inspection is the surface roughness of the part being inspected.
Very rough surfaces are likely to produce excessive background or false indications during inspection.
Although the liquid-penetrant method is used to inspect some porous parts, such as powder metallurgy
parts, the process generally is not well suited for the inspection of porous materials because the
background penetrant from pores obscures flaw indications.

figure Shows

1. Section of material with a surface-breaking crack that is not visible to the naked eye.
2. Penetrant is applied to the surface.
3. Excess penetrant is removed.
4. Developer is applied, rendering the crack visible.

MECHANICAL FAILURE CONSIDERATIONS

Any change in the size, shape, or material properties of a structure, machine, or machine part that

renders it incapable of performing its intended function must be regarded as a mechanical failure of

the device. It should be carefully noted that the key concept here is that improper functioning of a

machine part constitutes failure. Thus, a shear pin that does not separate into two or more pieces

upon the application of a preselected overload must be regarded as having failed as surely as a drive

shaft has failed if it does separate into two pieces under normal expected operating loads Failure of a device or structure to function properly might be brought about by any one or a

combination of many different responses to loads and environments while in service. For example,

too much or too little elastic deformation might produce failure. A fractured load-carrying structural

member or a shear pin that does not shear under overload conditions each would constitute failure.

Progression of a crack due to fluctuating loads or aggressive environment might lead to failure after

a period of time if resulting excessive deflection or fracture interferes with proper machine function.

A primary responsibility of any mechanical designer is to ensure that his or her design functions

as intended for the prescribed design lifetime and, at the same time, that it be competitive in the

marketplace. Success in designing competitive products while averting premature mechanical failures

can be achieved consistently only by recognizing and evaluating all potential modes of failure that

might govern the design. To recognize potential failure modes a designer must be acquainted with

the array of failure modes observed in practice, and with the conditions leading to these failures. The

following section summarizes the mechanical failure modes most commonly observed in practice,

followed by a brief description of each one.A failure mode may be defined as the physical process or processes that take place or that combine

their effects to produce a failure, as just discussed. In the following list of commonly observed failure

modes it may be noted that some failure modes are unilateral phenomena, whereas others are combined

phenomena. For example, fatigue is listed as a failure mode, corrosion is listed as a failure

mode, and corrosion fatigue is listed as still another failure mode. Such combinations are included

because they are commonly observed, important, and often synergistic. In the case of corrosion

fatigue, for example, the presence of active corrosion aggravates the fatigue process and at the same

time the presence of a fluctuating load accelerates the corrosion process.

The following list is not presented in any special order but it includes all commonly observed

modes of mechanical failure:

1. Force and/or temperature-induced elastic deformation.2. Yielding.3. Brinnelling.4. Ductile rupture.

5. Brittle fracture.6. Fatigue:a. High-cycle fatigueb. Low-cycle fatiguec. Thermal fatigued. Surface fatiguee. Impact fatiguef. Corrosion fatigueg. Fretting fatigue7. Corrosion:a. Direct chemical attackb. Galvanic corrosionc. Crevice corrosiond. Pitting corrosione. Intergranular corrosionf. Selective leachingg. Erosion corrosionh. Cavitation corrosioni. Hydrogen damagej. Biological corrosionk. Stress corrosion

8. Wear:a. Adhesive wearb. Abrasive wearc. Corrosive weard. Surface fatigue weare. Deformation wearf. Impact wearg. Fretting wear9. Impact:a. Impact fractureb. Impact deformationc. Impact wear

d. Impact frettinge. Impact fatigue10. Fretting:a. Fretting fatigueb. Fretting wearc. Fretting corrosion

11. Creep.12. Thermal relaxation.13. Stress rupture.14. Thermal shock.15. Galling and seizure.16. Spalling.

17. Radiation damage.18. Buckling.19. Creep buckling.20. Stress corrosion.21. Corrosion wear.

22. Corrosion fatigue.23. Combined creep and fatigue.

As commonly used in engineering practice, the failure modes just listed may be defined and

described briefly as follows. It should be emphasized that these failure modes only produce failure

when they generate a set of circumstances that interferes with the proper functioning of a machine

or device.

Force and I or temperature-induced elastic deformation failure occurs whenever the elastic (recoverable)

deformation in a machine member, brought about by the imposed operational loads or temperatures,

becomes large enough to interfere with the ability of the machine to perform its intended

function satisfactorily.

Yielding failure occurs when the plastic (unrecoverable) deformation in a ductile machine member,

brought about by the imposed operational loads or motions, becomes large enough to interfere with

the ability of the machine to perform its intended function satisfactorily.

Brinnelling failure occurs when the static forces between two curved surfaces in contact result in

local yielding of one or both mating members to produce a permanent surface discontinuity of

significant size. For example, if a ball bearing is statically loaded so that a ball is forced to indent

permanently the race through local plastic flow, the race is brinnelled. Subsequent operation of the

bearing might result in intolerably increased vibration, noise, and heating; and, therefore, failure

would have occurred.

Ductile rupture failure occurs when the plastic deformation, in a machine part that exhibits ductile

behavior, is carried to the extreme so that the member separates into two pieces. Initiation and

coalescence of internal voids slowly propagate to failure, leaving a dull, fibrous rupture surface.Brittle fracture failure occurs when the elastic deformation, in a machine part that exhibits brittle

behavior, is carried to the extreme so that the primary interatomic bonds are broken and the member

separates into two or more pieces. Preexisting flaws or growing cracks form initiation sites for very

rapid crack propagation to catastrophic failure, leaving a granular, multifaceted fracture surface.

Fatigue failure is a general term given to the sudden and catastrophic separation of a machine

part into two or more pieces as a result of the application of fluctuating loads or deformations over

a period of time. Failure takes place by the initiation and propagation of a crack until it becomes

unstable and propagates suddenly to failure. The loads and deformations that typically cause failure

by fatigue are far below the static failure levels. When loads or deformations are of such magnitude

that more than about 10,000 cycles are required to produce failure, the phenomenon is usually termed

high-cycle fatigue. When loads or deformations are of such magnitude that less than about 10,000

cycles are required to produce failure, the phenomenon is usually termed low-cycle fatigue. When

load or strain cycling is produced by a fluctuating temperature field in the machine part, the process

is usually termed thermal fatigue. Surface fatigue failure, usually associated with rolling surfaces in

contact, manifests itself as pitting, cracking, and spalling of the contacting surfaces as a result of the

cyclic Hertz contact stresses that result in maximum values of cyclic shear stresses slightly below the surface. The cyclic subsurface shear stresses generate cracks that propagate to the contacting

surface, dislodging particles in the process to produce surface pitting. This phenomenon is often

viewed as a type of wear. Impact fatigue, corrosion fatigue, and fretting fatigue are described later. Corrosion failure, a very broad term, implies that a machine part is rendered incapable of performing

its intended function because of the undesired deterioration of the material as a result of

chemical or electrochemical interaction with the environment. Corrosion often interacts with other

failure modes such as wear or fatigue. The many forms of corrosion include the following. Direct

chemical attack, perhaps the most common type of corrosion, involves corrosive attack of the surface

of the machine part exposed to the corrosive media, more or less uniformly over the entire exposed

surface. Galvanic corrosion is an accelerated electrochemical corrosion that occurs when two dissimilar

metals in electrical contact are made part of a circuit completed by a connecting pool or film of

electrolyte or corrosive medium, leading to current flow and ensuing corrosion. Crevice corrosion is

the accelerated corrosion process highly localized within crevices, cracks, or joints where small

volume regions of stagnant solution are trapped in contact with the corroding metal. Pitting corrosion

is a very localized attack that leads to the development of an array of holes or pits that penetrate the

metal. Intergranular corrosion is the localized attack occurring at grain boundaries of certain copper,

chromium, nickel, aluminum, magnesium, and zinc alloys when they are improperly heat treated or

welded. Formation of local galvanic cells that precipitate corrosion products at the grain boundaries

seriously degrades the material strength because of the intergranular corrosive process. Selective

leaching is a corrosion process in which one element of a solid alloy is removed, such as in dezincification

of brass alloys or graphitization of gray cast irons. Erosion corrosion is the accelerated

chemical attack that results when abrasive or viscid material flows past a containing surface, continuously

baring fresh, unprotected material to the corrosive medium. Cavitation corrosion is the accelerated

chemical corrosion that results when, because of differences in vapor pressure, certain

bubbles and cavities within a fluid collapse adjacent to the pressure-vessel walls, causing particles

of the surface to be expelled, baring fresh, unprotected surface to the corrosive medium. Hydrogen

damage, while not considered to be a form of direct corrosion, is induced by corrosion. Hydrogen

damage includes hydrogen blistering, hydrogen embrittlement, hydrogen attack, and decarburization.

Biological corrosion is a corrosion process that results from the activity of living organisms, usually

by virtue of their processes of food ingestion and waste elimination, in which the waste products are

corrosive acids or hydroxides. Stress corrosion, an extremely important type of corrosion, is described

separately later.Wear is the undesired cumulative change in dimensions brought about by the gradual removal of

discrete particles from contacting surfaces in motion, usually sliding, predominantly as a result of

mechanical action. Wear is not a single process, but a number of different processes that can take

place by themselves or in combination, resulting in material removal from contacting surfaces through

a complex combination of local shearing, plowing, gouging, welding, tearing, and others. Adhesive

wear takes place because of high local pressure and welding at asperity contact sites, followed by

motion-induced plastic deformation and rupture of asperity functions, with resulting metal removal

or transfer. Abrasive wear takes place when the wear particles are removed from the surface by the

plowing, gouging, and cutting action of the asperities of a harder mating surface or by hard particles

entrapped between the mating surfaces. When the conditions for either adhesive wear or abrasive

wear coexist with conditions that lead to corrosion, the processes interact synergistically to produce

corrosive wear. As described earlier, surface fatigue wear is a wear phenomenon associated with

curved surfaces in rolling or sliding contact, in which subsurface cyclic shear stresses initiate microcracks

that propagate to the surface to spall out macroscopic particles and form wear pits. Deformation

wear arises as a result of repeated plastic deformation at the wearing surfaces, producing a

matrix of cracks that grow and coalesce to form wear particles. Deformation wear is often caused

by severe impact loading. Impact wear is impact-induced repeated elastic deformation at the wearing

surface that produces a matrix of cracks that grows in accordance with the surface fatigue description

just given. Fretting wear is described later Impact failure results when a machine member is subjected to nonstatic loads that produce in the

part stresses or deformations of such magnitude that the member no longer is capable of performing

its function. The failure is brought about by the interaction of stress or strain waves generated by

dynamic or suddenly applied loads, which may induce local stresses and strains many times greater

than would be induced by the static application of the same loads. If the magnitudes of the stresses

and strains are sufficiently high to cause separation into two or more parts, the failure is called impact

fracture. If the impact produces intolerable elastic or plastic deformation, the resulting failure is

called impact deformation. If repeated impacts induce cyclic elastic strains that lead to initiation of

a matrix of fatigue cracks, which grows to failure by the surface fatigue phenomenon described

earlier, the process is called impact wear. If fretting action, as described in the next paragraph, is

induced by the small lateral relative displacements between two surfaces as they impact together,

where the small displacements are caused by Poisson strains or small tangential "glancing" velocity

components, the phenomenon is called impact fretting. Impact fatigue failure occurs when impact loading is applied repetitively to a machine member until failure occurs by the nucleation and propagation

of a fatigue crack.Fretting action may occur at the interface between any two solid bodies whenever they are pressed

together by a normal force and subjected to small-amplitude cyclic relative motion with respect to

each other. Fretting usually takes place in joints that are not intended to move but, because of

vibrational loads or deformations, experience minute cyclic relative motions. Typically, debris produced

by fretting action is trapped between the surfaces because of the small motions involved.

Fretting fatigue failure is the premature fatigue fracture of a machine member subjected to fluctuating

loads or strains together with conditions that simultaneously produce fretting action. The surface

discontinuities and microcracks generated by the fretting action act as fatigue crack nuclei that propagate

to failure under conditions of fatigue loading that would otherwise be acceptable. Fretting

fatigue failure is an insidious failure mode because the fretting action is usually hidden within a joint

where it cannot be seen and leads to premature, or even unexpected, fatigue failure of a sudden and

catastrophic nature. Fretting wear failure results when the changes in dimensions of the mating parts,

because of the presence of fretting action, become large enough to interfere with proper design

function or large enough to produce geometrical stress concentration of such magnitude that failure

ensues as a result of excessive local stress levels. Fretting corrosion failure occurs when a machine

part is rendered incapable of performing its intended function because of the surface degradation of

the material from which the part is made, as a result of fretting actionCreep failure results whenever the plastic deformation in a machine member accrues over a period

of time under the influence of stress and temperature until the accumulated dimensional changes

interfere with the ability of the machine part to perform satisfactorily its intended function. Three

stages of creep are often observed: (1) transient or primary creep during which time the rate of strain

decreases, (2) steady-state or secondary creep during which time the rate of strain is virtually constant,

and (3) tertiary creep during which time the creep strain rate increases, often rapidly, until rupture

occurs. This terminal rupture is often called creep rupture and may or may not occur, depending on

the stress-time-temperature conditions.

Thermal relaxation failure occurs when the dimensional changes due to the creep process result

in the relaxation of a prestrained or prestressed member until it no longer is able to perform its

intended function. For example, if the prestressed flange bolts of a high-temperature pressure vessel

relax over a period of time because of creep in the bolts, so that, finally, the peak pressure surges

exceed the bolt preload to violate the flange seal, the bolts will have failed because of thermal

relaxation.

Stress rupture failure is intimately related to the creep process except that the combination of

stress, time, and temperature is such that rupture into two parts is ensured. In stress rupture failures

the combination of stress and temperature is often such that the period of steady-state creep is short

or nonexistent.

Thermal shock failure occurs when the thermal gradients generated in a machine part are so

pronounced that differential thermal strains exceed the ability of the material to sustain them without

yielding or fracture.

Galling failure occurs when two sliding surfaces are subjected to such a combination of loads,

sliding velocities, temperatures, environments, and lubricants that massive surface destruction is

caused by welding and tearing, plowing, gouging, significant plastic deformation of surface asperities,

and metal transfer between the two surfaces. Galling may be thought of as a severe extension of the

adhesive wear process. When such action results in significant impairment to intended surface sliding

or in seizure, the joint is said to have failed by galling. Seizure is an extension of the galling process

to such severity that the two parts are virtually welded together so that relative motion is no longer

possible. 

Spalling failure occurs whenever a particle is spontaneously dislodged from the surface of a

machine part so as to prevent the proper function of the member. Armor plate fails by spalling, for

example, when a striking missile on the exposed side of an armor shield generates a stress wave that

propagates across the plate in such a way as to dislodge or spall a secondary missile of lethal potential

on the protected side. Another example of spalling failure is manifested in rolling contact bearings

and gear teeth because of the action of surface fatigue as described earlier.

Radiation damage failure occurs when the changes in material properties induced by exposure to

a nuclear radiation field are of such a type and magnitude that the machine part is no longer able to

perform its intended function, usually as a result of the triggering of some other failure mode, and

often related to loss in ductility associated with radiation exposure. Elastomers and polymers are

typically more susceptible to radiation damage than are metals, whose strength properties are sometimes

enhanced rather than damaged by exposure to a radiation field, although ductility is usually

decreased.

Buckling failure occurs when, because of a critical combination of magnitude and/or point of

load application, together with the geometrical configuration of a machine member, the deflection of

the member suddenly increases greatly with only a slight change in load. This nonlinear response results in a buckling failure if the buckled member is no longer capable of performing its design

function.

Creep buckling failure occurs when, after a period of time, the creep process results in an unstable

combination of the loading and geometry of a machine part so that the critical buckling limit is

exceeded and failure ensues.

Stress corrosion failure occurs when the applied stresses on a machine part in a corrosive environment

generate a field of localized surface cracks, usually along grain boundaries, that render the

part incapable of performing its function, often because of triggering some other failure mode. Stress

corrosion is a very important type of corrosion failure mode because so many different metals are

susceptible to it. For example, a variety of iron, steel, stainless-steel, copper, and aluminum alloys

are subject to stress corrosion cracking if placed in certain adverse corrosive media.

Corrosion wear failure is a combination failure mode in which corrosion and wear combine their

deleterious effects to incapacitate a machine part. The corrosion process often produces a hard,

abrasive corrosion product that accelerates the wear, while the wear process constantly removes the

protective corrosion layer from the surface, baring fresh metal to the corrosive medium and thus

accelerating the corrosion. The two modes combine to make the result more serious than either of

the modes would have been otherwise.

Corrosion fatigue is a combination failure mode in which corrosion and fatigue combine their

deleterious effects to cause failure of a machine part. The corrosion process often forms pits and

surface discontinuities that act as stress raisers which in turn accelerate fatigue failure. Furthermore,

cracks in the usually brittle corrosion layer also act as fatigue crack nuclei that propagate into the

base material. On the other hand, the cyclic loads or strains cause cracking and flaking of the corrosion

layer, which bares fresh metal to the corrosive medium. Thus, each process accelerates the other,

often making the result disproportionately serious.

Combined creep and fatigue failure is a combination failure mode in which all of the conditions

for both creep failure and fatigue exist simultaneously, each process influencing the other to produce

failure. The interaction of creep and fatigue is probably synergistic but is not well understood.

ALUMINUM AND ITS ALLOYS

Aluminum is the most abundant metal and the third most abundant chemical element in the earth's
crust, comprising over 8% of its weight. Only oxygen and silicon are more prevalent. Yet, until about
150 years ago aluminum in its metallic form was unknown to man. The reason for this is that
aluminum, unlike iron or copper, does not exist as a metal in nature. Because of its chemical activity
and its affinity for oxygen, aluminum is always found combined with other elements, mainly as
aluminum oxide. As such it is found in nearly all clays and many minerals. Rubies and sapphires
are aluminum oxide colored by trace impurities, and corundum, also aluminum oxide, is the second
hardest naturally occurring substance on earth—only a diamond is harder.
It was not until 1886 that scientists learned how to economically extract aluminum from aluminum
oxide via electrolytic reduction. Yet in the more than 100 years since that time, aluminum has become
the second most widely used of the approximately 60 naturally occurring metals, behind only iron.

PROPERTIES OF ALUMINUM

Let us consider the properties of aluminum that lead to its wide use.
One property of aluminum that everyone is familiar with is its light weight or, technically, its low
specific gravity. The specific gravity of aluminum is only 2.7 times that of water, and roughly one third that of steel or copper. An easy number to remember is that 1 in.3 of aluminum weighs 0.1 Ib;
1 ft3 weighs 170 Ib compared to 62 Ib for water and 490 Ib for steel. The following are some other
properties of aluminum and its alloys that will be examined in more detail in later sections:

Formability. Aluminum can be formed by every process in use today and in more ways than
any other metal. Its relatively low melting point, 122O0F, while restricting high-temperature
applications to about 500-60O0F, does make it easy to cast, and there are over 1000 foundries
casting aluminum in this country.
Mechanical Properties. Through alloying, naturally soft aluminum can attain strengths twice
that of mild steel.
Strength-to-Weight Ratio. Some aluminum alloys are among the highest strength to weight
materials in use today, in a class with titanium and superalloy steels. This is why aluminum
alloys are the principal structural metal for commercial and military aircraft.
Cryogenic Properties. Unlike most steels, which tend to become brittle at cryogenic temperatures,
aluminum alloys actually get tougher at low temperatures and hence enjoy many cryogenic
applications.
Corrosion Resistance. Aluminum possesses excellent resistance to corrosion by natural atmospheres
and by many foods and chemicals.
High Electrical and Thermal Conductivity. On a volume basis the electrical conductivity of
pure aluminum is roughly 60% of the International Annealed Copper Standard, but pound for
pound aluminum is a better conductor of heat and electricity than copper and is surpassed
only by sodium, which is a difficult metal to use in everyday situations.
Reflectivity. Aluminum can accept surface treatment to become an excellent reflector and it
does not dull from normal oxidation.
Finishability. Aluminum can be finished in more ways than any other metal used today

ALUMINUMALLOYS

While commercially pure aluminum (defined as at least 99% aluminum) does find application in
electrical conductors, chemical equipment, and sheet metal work, it is a relatively weak material, and
its use is restricted to applications where strength is not an important factor. Some strengthening of
the pure metal can be achieved through cold working, called strain hardening. However, much greater
strengthening is obtained through alloying with other metals, and the alloys themselves can be further
strengthened through strain hardening or heat treating. Other properties, such as castability and machinability,
are also improved by alloying. Thus, aluminum alloys are much more widely used than is
the pure metal, and in many cases, when aluminum is mentioned, the reference is actually to one of
the many commercial alloys of aluminum.
The principal alloying additions to aluminum are copper, manganese, silicon, magnesium, and
zinc; other elements are also added in smaller amounts for metallurgical purposes. Since there have
been literally hundreds of aluminum alloys developed for commercial use, the Aluminum Association
formulated and administers special alloy designation systems to distinguish and classify  the alloys
in a meaningful manner

ALLOY DESIGNATION SYSTEMS

Aluminum alloys are divided into two classes according to how they are produced: wrought and cast.
The wrought category is a broad one, since aluminum alloys may be shaped by virtually every known
process, including rolling, extruding, drawing, forging, and a number of other, more specialized
processes. Cast alloys are those that are poured molten into sand (sand casting) or high-strength steel
(permanent mold or die casting) molds, and are allowed to solidify to produce the desired shape.
The wrought and cast alloys are quite different in composition; wrought alloys must be ductile for
fabrication, while cast alloys must be fluid for castability.
In 1974, the Association published a designation system for wrought aluminum alloys that classifies
the alloys by major alloying additions. This system is now recognized worldwide under the
International Accord for Aluminum Alloy Designations, administered by the Aluminum Association,
and is published as American Standards Institute (ANSI) Standard H35.1. More recently, a similar
system for casting alloys was introduced.
Each wrought or cast aluminum alloy is designated by a number to distinguish it as a wrought
or cast alloy and to categorize the alloy. A wrought alloy is given a four-digit number. The first digit
classifies the alloy by alloy series, or principal alloying element. The second digit, if different than
O, denotes a modification in the basic alloy. The third and fourth digits form an arbitrary number

Designation System for
  Wrought Aluminum Alloys
Alloy  Series                                                  Description or Major Alloying Element
Ixxx                                                                   99.00% minimum aluminum
2xxx                                                                Copper
3xxx                                                                 Manganese
 4xxx                                                                   Silicon
 5xxx                                                                Magnesium
 6xxx                                                             Magnesium and silicon
  7xxx                                                                  Zinc
  8xxx                                                             Other element
   9xxx                                                         Unused series

which identifies the specific alloy in the series.* A cast alloy is assigned a three-digit number followed
by a decimal. Here again the first digit signifies the alloy series or principal addition; the second and
third digits identify the specific alloy; the decimal indicates whether the alloy composition is for the
final casting (0.0) or for ingot (0.1 or 0.2). A capital letter prefix (A, B, C, etc.) indicates a modification
of the basic alloy.
The designation systems for wrought and cast aluminum alloys are shown in Tables

Specification of an aluminum alloy is not complete without designating the metallurgical condition,
or temper, of the alloy. A temper designation system, unique for aluminum alloys, was developed
by the Aluminum Association and is used for all wrought and cast alloys. The temper designation
follows the alloy designation, the two being separated by a hyphen. Basic temper designations consist
of letters; subdivisions, where required, are indicated by one or more digits following the letter. The
basic tempers are:

F—As-Fabricated. Applies to the products of shaping processes in which no special control
over thermal conditions or strain hardening is employed. For wrought products, there are no
mechanical property limits.
O—Annealed. Applies to wrought products that are annealed to obtain the lowest strength
temper, and to cast products that are annealed to improve ductility and dimensional stability.
The O may be followed by a digit other than zero.

Alloy                                                      Description or Major Alloying Element
Series
Ixx.x                                                     99.00% minimum aluminum
2xx.x                                                    Copper
3xx.x                                                    Silicon plus copper and /or magnesium
4xx.x                                                    Silicon
5xx.x                                                   Magnesium
6xx.x                                                      Unused series
7xx.x                                                     Zinc
 Sxx.x                      
9xx.x                                                         Tin
                                                         Other element

H—Strain-Hardened (Wrought Products Only). Applies to products that have their strength
increased by strain hardening, with or without supplementary thermal treatments to produce
some reduction in strength. The H is always followed by two or more digits. (See Table 3.3.)
W—Solution Heat Treated. An unstable temper applicable only to alloys that spontaneously
age at room temperature after solution heat treatment. This designation is specific only when
the period of natural aging is indicated; for example: W l/2 hr.
T—Thermally Treated to Produce Stable Tempers Other than F, O, or H. Applies to products
that are thermally treated, with or without supplementary strain hardening, to produce stable
tempers. The T is always followed by one or more digits.

MECHANICAL PROPERTIES OF ALUMINUM ALLOYS

Wrought aluminum alloys are generally thought of in two categories: nonheat-treatable and heattreatable.
Nonheat-treatable alloys are those that derive their strength from the hardening effect of
elements such as manganese, iron, silicon, and magnesium, and are further strengthened by strain
hardening. They include the Ixxx, 3xxx, 4xxx, and 5xxx series alloys. Heat-treatable alloys a


First digit indicates specific sequence of treatments:
Tl—Cooled from an elevated-temperature shaping process and naturally aged to a substantially
stable condition
T2—Cooled from an elevated-temperature shaping process, cold worked, and naturally aged to a
substantially stable condition
T3—Solution heat-treated, cold worked, and naturally aged to a substantially stable condition
T4—Solution heat-treated and naturally aged to a substantially stable condition
T5—Cooled from an elevated-temperature shaping process and then artifically aged
T6—Solution heat-treated and then artifically aged
T7—Solution heat-treated and overaged/stabilized
T8—Solution heat-treated, cold worked, and then artificially aged
T9—Solution heat-treated, artificially aged, and then cold worked
TlO—Cooled from an elevated-temperature shaping process, cold worked, and then artificially
aged
Second digit indicates variation in basic treatment:
Examples:
T42 or T62—Heat treated to temper by user
Additional digits indicate stress relief:
Examples:
TX51 or TXX51—Stress relieved by stretching
TX52 or TXX52—Stress relieved by compressing
TX54 or TXX54—Stress relieved by combination of stretching and compressing strengthened by a combination of solution heat treatment and natural or controlled aging for precipitation
hardening, and include the 2xxx, some 4xxx, 6xxx, and 7xxx series alloys. Castings are not
normally strain hardened, but many are solution heat-treated and aged for added strength.
In Table 3.5 typical mechanical properties are shown for several representative nonheat-treatable
alloys in the annealed, half-hard and full-hard tempers; values for super purity aluminum (99.99%)
are included for comparison. Typical properties are usually higher than minimum, or guaranteed,
properties and are not meant for design purposes but are useful for comparisons. It should be noted
that pure aluminum can be substantially strain hardened, but a mere 1% alloying addition produces
a comparable tensile strength to that of fully hardened pure aluminum with much greater ductility
in the alloy. And the alloys can then be strain hardened to produce even greater strengths. Thus, the
alloying effect is compounded. Note also that, while strain hardening increases both tensile and yield
strengths, the effect is more pronounced for the yield strength so that it approaches the tensile strength
in the fully hardened temper. Ductility and workability are reduced as the material is strain hardened,
and most alloys have limited formability in the fully hardened tempers.
Table 3.6 lists typical mechanical properties and nominal compositions of some representative
heat-treatable aluminum alloys. One can readily see that the strengthening effect of the alloying
ingredients in these alloys is not reflected in the annealed condition to the same extent as in the
nonheat-treatable alloys, but the true value of the additions can be seen in the aged condition. Presently,
heat-treatable alloys are available with tensile strengths approaching 100,000 psi.
Again, casting alloys cannot be work hardened and are either used in as-cast or heat-treated
conditions. Typical mechanical properties for commonly used casting alloys range from 20 to 50 ksi
for ultimate tensile strength, from 15 to 50 ksi tensile yield strength and up to 20% elongation. The
range of strengths available with wrought aluminum alloys is shown graphically

WORKINGSTRESSES

Aluminum is used in a wide variety of structural applications. These range from curtain walls on
buildings to tanks and piping for handling cryogenic liquids, and even bridges and major buildings
and roof structures. In establishing appropriate working stresses the factors of safety applied to the
ultimate strength and yield strength of the aluminum alloy vary with the specific application. For
building and similar type structures a factor of safety of 1.95 is applied to the tensile ultimate strength

Typical Mechanical Properties of Representative Nonheat-Treatable Aluminum
Alloys (Not for Design Purposes)Tensile Yield  Nominal Strength Strength Elongation Hardness

Alloy    Nominal Composition Temper      Tensile stenght ( ksi)       yiled Strength ( ksi)         Elegotion(% in 2 in)             Hardness (BHN)
1199       99.9+% Al     O               6.5                        1.5                50                              —
                   H 18    17                                    16                             5                          —
1100 99+% Al O 13 5 35 23
H14 18 17 9 32
HIS 24 22 5 44
3003 1.2% Mn O 16 6 30 28
H14 22 21 8 40
HIS 29 27 4 55
3004 1.2% Mn O 26 10 20 43
1.0% Mg H34 35 29 9 63
H38 41 36 5 77
5005 0.8% Mg O 13 6 25 28
H14 23 22 6 41
HIS 29 28 4 51
5052 2.5% Mg O 28 13 25 47
H34 38 31 10 68
H38 42 37 7 77
5456 5.1% Mg O 45 23 24 70
0.8% Mn H321, H116 51 37 16 90
B443.0 5.0% Si F* 19 8 8 40
F* 23 9 10 45
514.0 4.0% Mg P 25 12 9 50

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