inherent processing in service defects

7/29/2019 Inherent Processing in Service Defects

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INHERENT PROCESSING IN SERVICE

DEFECTS


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Discontinuities

A break or gap

Lack of continuity


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Types of Discontinuities

I. Inherent Discontinuities

- They can form during the solidification of ingots or during melting,casting and solidification of metal later in the fabrication process.

Ex. CASTINGS

II. Processing Discontinuities

- Occurs during manufacturing process Ex. Rolling, Extrusion

III. Service Discontinuities- related to the various service conditions to which the material is

subjected. Fatigue cracks, Corrosion, Stress Corrosion crack


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Inherent Discontinuities


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A. Casting Process & DefectsMethod of forming metal objects of complex shapes is by pouring molten metal into mould

In which it sets to the required shape.

o Porosity

o Blowholes

o Piping

o Inclusionso Sponginess

o Shrinkage

o Hot tears

o Crack

o Cold Shuts

o Unfused Chapleto Misplaced core

o Segregation


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Processing Discontinuities


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A. Rolling

The flattening of metal between rollers is used for the production of strip, sheet, plate, barand sections.

o Spalling of the ball

oTwo sites of a corrosion rash

on the race of the outer ring.

o Crack of the inner ring

o Local wear of the inner ring

corrosion

o Pitting on the ball

o Laminations


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B. Extrusion

Similar to squeezing toothpaste from a toothpaste tube. The raw material is a heated castbillet of the required metal.

o Surface Scratch o Part Scratch o Part Dent

o Internal Cracking o Center Burst


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C. Finishing / Machining

Machining is a shape-producing process in which a power-driven device causes materialto be removed in chip form. Machine tools has been assigned to that group of equipmentdesigned to hold a cutting tool and a work piece and establish a suitable set of motionsbetween them to remove materials from the work in chip form.

TEAR

Grinding - crack


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D. Forging ProcessIs the working of metal into a useful shape by hammering or pressing and is the one oldest

of the metal forming processes. Most of forging operations are carried out hot, althoughsome metals are cold-forged. This method of shaping is therefore used in the manufactureof parts requiring good mechanical properties.Forging is a metal forming process used to produce large quantities of identical parts, as inthe manufacture of automobiles, and to improve the mechanical properties of the metalbeing forged, as in aerospace parts or military equipment.

a.Lap

b.Burst

c.Crack


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E. Heat TreatmentHeat treatment is a method used to alter the physical, and sometimes chemical,

properties of a material. The most common application is metallurgical. Heattreatments are also used in the manufacture of many other materials, such as glass.

Heat treatment involves the use of heating or chilling, normally to extreme

temperatures, to achieve a desired result such as hardening or softening of a

material. Heat treatment techniques include annealing, case hardening,

precipitation strengthening, tempering and quenching. It is noteworthy that while

the term heat treatmentapplies only to processes where the heating and cooling

are done for the specific purpose of altering properties intentionally, heating and

cooling often occur incidentally during other manufacturing processes such as hot

forming or welding.

Quenching Crack - A fracture, often termed a

hardening crack, which arises from thermalstresses induced during rapid cooling.
http://en.wikipedia.org/wiki/Physical_propertyhttp://en.wikipedia.org/wiki/Chemical_propertyhttp://en.wikipedia.org/wiki/Metallurgyhttp://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Annealing_(metallurgy)http://en.wikipedia.org/wiki/Case_hardeninghttp://en.wikipedia.org/wiki/Precipitation_strengtheninghttp://en.wikipedia.org/wiki/Temperinghttp://en.wikipedia.org/wiki/Quenchhttp://en.wikipedia.org/wiki/Quenchhttp://en.wikipedia.org/wiki/Temperinghttp://en.wikipedia.org/wiki/Precipitation_strengtheninghttp://en.wikipedia.org/wiki/Precipitation_strengtheninghttp://en.wikipedia.org/wiki/Precipitation_strengtheninghttp://en.wikipedia.org/wiki/Case_hardeninghttp://en.wikipedia.org/wiki/Case_hardeninghttp://en.wikipedia.org/wiki/Case_hardeninghttp://en.wikipedia.org/wiki/Annealing_(metallurgy)http://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Metallurgyhttp://en.wikipedia.org/wiki/Chemical_propertyhttp://en.wikipedia.org/wiki/Physical_property


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Service Discontinuities


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Material In Service Fail Due to:

Revert back, its natural state of iron oxide other revert to sulfides

and oxides or carbonates

1. Corrosion

Repeated loading and unloading over prolong periods

2. Fatigue

Removal of material from contacting surfaces by mechanical

action

3. Wear

Faulty design, extra loads applied

4. Overload

Fracture preceded by a significant amount of plastic deformation

is known as ductile fracture otherwise it is brittle fracture

5. Brittle & Ductile Fracture

inherent processing in service defects

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