11 - Leo Vega Bolt Failure Analysis

5/27/2018 11 - Leo Vega Bolt Failure Analysis

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Leo Vega

SEMINAR ON LEAKREDUCTION

Bolt Failure Analysis


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Topics of Discussion

Elements of a Failure Analysis Metallurgical Characterization Techniques

Types of Damage Mechanisms Case Studies Summary


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Typical Elements of a Failure

Analysis History of Component

Visual Examination PhotographicDocumentation

Sample Selection Collect Deposits Sectioning

Fractography

Metallography SEM/EDS/XRD Chemical Analysis

Mechanical Testing NDE


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Metallurgical Characterization

Techniques Visual Examination

Metallography Fractography

Scanning Electron Microscopy (SEM) and

Energy Dispersive X-ray Spectroscopy (EDS)

Hardness Testing

Non-destructive Evaluation (NDE)


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Visual Examination


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Fractography

Flat

fracture

Shear lip


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Microstructural Evaluation

Metallography To assess material

condition and features


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SEM/EDS and XRD Analysis

Deposit Analysis1000

100 m

keV

109876543210

C

o

u

n

ts

3,500

3,000

2,500

2,000

1,500

1,000

500 C

O

Si Cl Ca Mn

Fe

Fe

Fe

Ni

Ni

NiCuCu

Cu


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Hardness Testing

Rockwell tests on a failed shank

110

Hardness on Failed Shaft

No. Hardness, HRC

1 352 36

3 30

4 31

5 316 29

7 31

8 27

9 2610 19


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Micro Hardness

TestingMicrohardness Values of Sample in Longitudinal Orientation

0

100

200

300

400

500

600

700

0.003

0.05

0.008

0.01

0.013

0.015

0.018

0.02

0.023

0.025

0.028

0.03

Distance from Edge of Hole, inches

Knoo

Hardness

Drilled Hole

Laser Cut Hole


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NDE

Wetmagnetic

particle

Inspectionof

cracked bolt


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Types of Damage Mechanisms

Fatigue Fractures

Wear Welding Defects Corrosion

Casting Flaws Liquid Metal

Embrittlement

Selective Dissolution

Manufacturing/MetalWorking Defects Quality Assurance/

Quality Control (QA/QC)


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Fatigue Fractures

Mechanical FailuresBeach marks (macroscopic

features)

Fatigue Striations

(microscopic features)


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WearGear reductionbox

Evidence of asurfacetreatment

Absence of a

surfacetreatment


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Corrosion

Compressor Bi-metallic oil seal

Pitting and subsequent cracking caused by water inzinc-type antiwear additives operating above 140

deg F


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Liquid Metal Embrittlement

SEM/EDS of Crack onWorn Shaft

PbSn, Sb

Ni alloy


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Selective Dissolution

Dealuminification inNiAl Bronze selective

attack of a phase


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Manufacturing/Metal Working

Defects QA/QC Inspections Inspection at

suppliers facility

Incoming materialinspection

In-processinspection

Finished materialinspection


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Pipe Mill Defect -

QA/QC

Extrusion Laps


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Case Studies

Case Study #1 Failure of Compressor Cylinder Flange/Bolts (Fatigue)

Case Study #2 Failure of Riser Fasteners (Hydrogen

Embrittlement/Intergranular Cracking)

Case Study #3 A fun one; Failed Spinal Screws (Fatigue)

C St d #1 C St ti


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Case Study #1 - Compressor Station

Hick-up PN 113175


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Case Study #1

Fractured bolts and flange atcompressor cylinder


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Case Study #1 The Line Up


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SEM AnalysisFatigue Striations

Cut Threads


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Case Study #1

276283283

Knoop micro hardnessimpressions at thread

root.

Cut threads are evident.


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Case Study #1 - Conclusions

Fasteners failed by High Cycle Fatigue Material and strength levels were adequate Increase frequency of inspections Bolts with cut threads should be considered as

replacements.


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Case Study #2

Fasteners in bolted flange connection operatingin a seawater environment

Case Study #2 - Fractography


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Case Study #2 FractographyIntergranular Fracture


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Case Study #2 - Metallography

Intergranular cracking


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Case Study #2 Hardness Testing

Micro hardness tests onbanded structure


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Case Study #2

Failure due to Hydrogen Embrittlement Intergranular fracture mode Improper heat treatment revealed by hardness

variations in a banded structure, which mayhave contributed to the failure.


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Case Study #3

Fractured Spinal Screw

Stage I Crack Initiation Stage II Crack

Propagation

Stage III - Overload

Stage IStage II

Stage III

( )


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What to do (or not do)!


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SUMMARY A variety of characterization

techniques are used in ametallurgical evaluation to

characterize various damagemechanisms.

Some projects require limitedscope based on budget

constraints.

Some require multi-disciplinedengineering support and extensiveevaluations

Each technique provides specificinformation that allows theinvestigator to assess the results

and their contribution to the cause.

Metallurgical Failure Analysisserves numerous clients in areassuch as:

Failure Analysis and Prevention Third party review, audits, and

oversight of inspections

On site metallurgical evaluations.

Forensic Investigations


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Metallurgical Failure Analysis

Leo Vega

Contact Info:281-897-1045 direct

832-868-7449 cell

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11 - Leo Vega Bolt Failure Analysis