section 10 (nxpowerlite).ppt

Haward Technology Middle East 1Section 10

AWS Certified Welding Inspector (CWI)

Section 10

Visual Inspection and other NDE Methods and Symbols



Visual Inspection

Very cost effective

Limited to surface only

Requires• Training• Experience• Welding knowledge• Proper tools

Must be continuous, ongoing



Application of VT

Before welding

During welding

After welding



VT Before Welding Review documents

Check welding procedures

Qualify/Certify welders, or check certifications

Establish hold points

Develop inspection plan

Develop system for reject identification

Develop defect repair system



VT Immediately Before Welding

Check base and filler metals

Check welding equipment

Check weld preparations

Check joint fitup

Check weld joint cleanliness

Check preheat, if required



VT During Welding

Note welder skills

Check welding variables/procedure compliance

Examine tacks and roots

Check backgouged surfaces

Check preheat temperatures

Check interpass temperatures

Check interpass cleaning



VT After Welding

Examine weld appearance

Check weld size and length

Check part dimensions

Monitor other NDE methods

Monitor postweld heat treating

Prepare inspection reports



Visual Inspection Tools



Prebending and Presetting Pieces to Allow for Distortion



Temperature Measurements

Required for:

• Preheat

• Interpass temperature limits

• Post weld heat treatments

Typically achieved by:

• Temperature sensitive crayons

• Digital pyrometers



Temperature-sensitive Crayons



Digital Contact Pyrometer



Fillet Weld Size

Convex or concave

Use correct template gage

Estimate between gage sizes

Measure to nearest 1/32” or 1/16”

Measure smallest region



Measuring Fillet Size



Nondestructive Testing

“Method of testing to evaluate quality and not effect end-use serviceability”



Elements of all NDE Methods

Source of probing energy

Discontinuities alter probing energy

Detection of energy alteration

Indication of energy alteration

Recording and evaluating indications



Common NDE Methods

Penetrant - PT

Magnetic Particle - MT

Radiographic - RT

Ultrasonic - UT

Eddy Current - ET



Penetrant Testing

Surface discontinuities only

Relies on penetrant ‘bleedout’

Magnifies discontinuity size

Several methods



PT Types

Visible dye

Fluorescent dye

Three removal systems:

Solvent

Water

Emulsifiable



Clean the Surface



Apply Penetrant



Dwell Time

Varies with the nature of the job, typically in the range of 2 to 20 minutes, or longer in special cases



Remove Excess Penetrant



Apply Developer

In this example, spray can is too close to the weld surface, which can lead to excessive developer on surface. A distance of 10-12 inches is better.



Excessive Developer

Note ‘runs’ caused by excess developer; this can mask discontinuities



Evaluate PT

Note porosity and crack indications



Clean Part

Post inspection removal of developer residues may be required, particularly if work piece is to be weld repaired or painted.



PT Advantages

Relatively simple

All types of metals

Quite sensitive

Quite portable



PT Limitations

Somewhat slow

Limited to surface

Smooth surfaces required



PT Results

Sketches

Photographs

Lift off tapes



Magnetic Particle Testing

Parts are magnetized

Iron particle accumulation at flaw

Magnifies flaw size

Relatively quick process



Aspects of a Magnet

Magnetic flux (field)

North and south poles

Like sign poles repel

Opposite signs attract

Flux lines are parallel to each other; do not cross



Magnetic Fields

Produced by two methods:

Permanent magnets

Electro magnets

• Direct current

• Alternating current

• Half wave rectified AC



Permanent Magnet



Electromagnets

“A current-carrying conductor creates a magnetic flux around the conductor

and perpendicular to the current flow.”



Magnetic Field Around Conductor



MT Principles

“A flaw oriented transverse to magnetic flux creates poles of

opposite signs at edges of flaw. Very attractive to iron particles”



Magnetic Particles

Iron based

Dry or wet

Types

• Color dyed

• Fluorescent



Longitudinal Magnetism



Circular Magnetism



MT Steps

Magnetize part

Apply iron particles

Evaluate accumulation

Clean part

Demagnetize part



MT Equipment

AC / DC bench units

AC yokes

AC / DC yokes

AC / DC prods

AC / DC coils



Central Conductor Method



MT Method---Yoke



MT Method---Prods



MT Advantages

Rapid

Very sensitive

Low cost

Portable



MT Limitations

Magnetic materials only

Poor with thick coatings

Limited to surface, or near-surface

Demagnetization may be required



MT Results

Sketches

Photographs

Lift off tapes



Radiographic Testing

“Based on the principle of preferential radiation transmission or absorption.”



X-Ray Machine (Aimed Down)



Radiation Absorption

“Thicker, or higher density materials absorb more radiation, resulting in less

transmission to the film.”



Absorption vs Thickness



Metal DensitiesGrams/cubic centimeter

Aluminum 2.70

Steel 7.87

Copper 8.96

Lead 11.34

Tungsten 19.30



Absorption vs Density



Radiation Types

Gamma radiation sources

• Iridium 192

• Cobalt 60

• Cesium 137

X-Ray

• Machine



RT Steps

Position radiation source

Position film behind object

Expose radiation

Develop film

Evaluate



Film Density Vs Flaws

Darker film zones:

Cracks, slag, porosity

Incomplete joint penetration

Lighter film zones:

Tungsten inclusions

Melt through, reinforcement



2 T hole

1 T hole

4 T hole

Hole Type Image Quality Indicators



Wire Type Image Quality Indicators



RT Equipment

Radiation source• X-ray machine • Gamma radiation

source Radiation monitor Film holders IQI’s

Densitometer/film density strips

Film processor Film viewers



Orientation of Source, Plate, & Film



RT Advantages

Detects subsurface flaws

Used for all materials

Film is permanent record

• If stored properly



RT Limitations

Radiation hazard

Requires access to both sides

Flaw orientation

Flaw types

Film interpretation



RT Results

Film

Video tape

Sketches



Ultrasonic Testing

“Based on the propagation of sound waves through materials,

and the reflected echo from density changes.”



Piezoelectric Effect

“Refers to materials which can convert electrical energy to mechanical energy and vice

versa.”



Principles of Sound

Sound travels within a given material at a constant velocity, based in part, on material density. Sound will not travel in a vacuum. There are several types of sound waves:

Longitudinal (straight beam)

Shear (angle beam)

Others not pertinent to weld inspection



UT Equipment & Operation

Electronic base unit

Piezoelectric transducer

Calibration blocks

Couple probe to part with couplant

Carry out testing

Evaluate signals



UT Process



Longitudinal Calibration



UT Process - 1 of 2



UT Process - 2 of 2



Angle Beam Testing of Weld



Weld Testing - 1 of 2



Weld Testing - 2 of 2



UT Advantages

A true volumetric test

One side access

Very accurate

Deep penetration - 200

Critical flaws found

Equipment fully portable



UT Limitations

Highly skilled operator

Smooth surfaces

Groove welds > 1/4” thick



Eddy Current Testing

“Based on the principle of eddy currents being formed in

conductive materials in the presence of an AC coil and changes in those eddy currents by material

changes.”



Induced Eddy Currents

Test Coil

Conductive Material



ET Uses

Flaw detection

Metal thickness

Coating thickness

Metal hardness

Heat treatment



ET CRT Displays



ET Equipment

Base unit, CRT or meter

AC probe (coil)

Calibration standards



ET Advantages

No contact required with part

No couplant required

Readily Automated

Applicable to all metals



ET Limitations

Highly skilled operator

“Too sensitive”

Shallow penetration - 3/16”

Calibration standards required

Requires surface cleanliness

Magnetic materials more difficult



NDE Symbols

Similar to weld symbols

Shorthand notation

Very useful

Combine with weld symbols



Standard Location of Elements for NDE Symbols



NDE Test Methods - Abbreviations1 of 2

Acoustic Emission AET

Eddy Current ET

Leak LT

Magnetic Particle MT

Neutron Radiography

NRT



NDE Test Methods - Abbreviations2 of 2

Penetrant PT

Proof PRT

Radiography RT

Ultrasonic UT

Visual VT



WIT Summary

Have covered much material in 3 days

Workbook and Sample Fundamentals Exam are good guides to your grasp of each Module, and may point towards areas needing more study in Manual

Urge all to study these subjects in greater depth as part of continuing education

section 10 (nxpowerlite).ppt

Documents