FAILURE ANALYSISFAILURE ANALYSIS

Sources of failureSources of failure  

-        -       -        -       •Material Related Failures.

•Deficiency in Design.

•Service Related Failures. •Environmental Related Failures.

Material Related FailuresMaterial Related Failures

1.   Deficiency in Selection of Materialsa)   Inadequacy of Mechanical PropertiesStandard Specifications for :Tensile test data (Yield, U.T.S., E%)

Hardness (or microhardness)Impact strength (toughness)

Types of loadingStatic Repeated Impact

Types of stressTension Compression Shear

Material Related Failures Contd.Material Related Failures Contd.Chemical Composition

Carbon content (for ferrous materials)

alloying elements

b)  Heat treatment

Secure removal of residual stress.

1.   Imperfection in Material

Segregation Lamination

Inclusions Porosity

Voids

1.   Deficiency in Fabrication of PartsCold forming Machining and grindingIdentification markingImproper heat treatmentAcid pickling or cleaningWelding and joiningCasting

Deficiency in Design Deficiency in Design

Upgrading of a part to a new application

local over-stressing.

Sudden or severe change in direction corrosion related deficiency

Operation (Service) Related FailuresOperation (Service) Related Failures1.   Errors in Assembly•-        Operator negligence•-         Misalignment•-         Inadequate procedure• Insufficient tightening• Non-uniform tightening• Over tightening

2.   Thermal DamageOver heating

3.   Inadequate Maintenance

4.   Start-up

5.   Shut-Down

Environmental Related Failures Environmental Related Failures

Corrosion

Atmosphere

Environment

FAILURE ANALYSIS

MODE OF FRACTURE

OPERATING CONDITIONS

FAILURE IDENTIFICATION

CONTRIBUTING FACTORS

FAILURE ANALYSIS FAILURE ANALYSIS GGeneral Practice1.     Collection of background information.2.     Record & keep.3.     Selection of samples.4.     Visual and macroscopic examination5.     Mechanical testing.6.     Microscopic (Metallographic) examination7.     Chemical analysis: bulk, local, surface, corr. Product etc.8.     Non-destructive testing.9.     Testing under simulated condition (special test).10.    Determination of failure mechanism.11.    Conclusions.12.     Report writing.

Collection of Background Information Collection of Background Information -        Service History.

-        Material specification.

-        System descriptive information.

-        Operation details.

-        Manufacturing and fabrication data-        Mechanical-        Thermal-        Chemical

Record Keeping Record Keeping

By writing, sketches or photograph

•-        The system (contg. the failed part)

•-        Position of the part.

•-        Features and shape (color, corr. product).

•-        Dimensions.

Selection of SamplesSelection of Samples

-        Represent failure characteristics.

-    Compare with unfailed samples.

-      Sample of fluid, deposits.

Visual and Macroscopic ExaminationVisual and Macroscopic Examination

-        Unaided eye, hand lens, portable microscope.

-        Detect changes of color and texture.

-        Search for cracks and branches.

-        Inspect fracture surface.

-        Asses basic design.

Mechanical TestingMechanical Testing

HHardness-        evaluate heat treatment-        Approx. value to tensile strength.-        Detect hardening (softening) by overheating

or decarburization.

Tensile or impact.-        Conform specification.

Failure MechanismFailure Mechanism        If the failure involved Cracking or Fracture: determine-        Crack initiation site.-        Stress concentration points-        Intensity and type of load :SStatic / cyclic / intermittent       If temp. Contribute to failure : determine -        Approx. service temp. at time of failure.       If wear contribute to failure : determine-        Flow speed.-        Direction of flow.       If Corrosion contribute to failure : determine-        Form of corrosion.

CHECK :

-        Specification of material composition.

-        Cross section : adequate ?

-        Mechanical properties : suitable ?

-        Heat treatment : proper ?

-        Fabrication : proper ?

-        Assembly and installation : proper ?

-        Repair (if any) : proper?

-        Operation : proper ?

-        Maintenance : proper ?

CONTRIBUTING FACTORS CONTRIBUTING FACTORS االنهيار االنهيار أسباب أسباب

DESIGN

•Bad geometry•Wrong Material• Under Estimate of Stress

MANUFACTURE

MachiningCasting DefectsMetal working Rolling Drawing ForgingFaulty Heat Treatment

ASSEMBLY & MAINTENANCE

Faulty joining Reviting Welding

Faulty fitting

Screw threads

REPORT WRITING REPORT WRITING 1.               Description of the failed component.2.               Operating condition at the time of failure.3.               Service History.4.               Manufacturing and processing history of component.5.               Material Specification.6.               Visual and macroscopic examination.7.               Metallurgical examination.8.               Mechanical testing.9.               Chemical analysis.10.         Other tests : N.D.T. or simulated.11.         Mechanism of failure.12.         Recommendation : correction of similar component prevention of similar failure.13.         Abstract.