NON-DESTRUCTI

VE TESTING

BY:- SWAPNIL NIGAM

INTRODUCTION Non-destructive Testing is an examination

or inspection performed on a component in any manner which will not impair its future use.

The terms Non-destructive Examination/Evaluation(NDE) and Non-destructive Inspection(NDI) are also used for this technology.

USES OF NDT METHODS Flaw detection and Evaluation. Leak Detection. Location Determination. Dimensional measurements. Structure and microstructure

characterization. Estimation of mech. & phy. Properties. Material sorting & chemical composition.

COMMON NDT METHODS Dye Penetrant Inspection Magnetic Particle Inspection. Ultrasonic Inspection Radiographic Inspection Eddy Current Inspection Acoustic Emission Inspection

DYE PENETRANT TEST INTRODUCTION :-

Oldest method of NDT. An extension of the visual inspection

method. Also called Liquid Penetrant test or

Penetrant Inspection. Used to detect casting, forging and

welding surface defects.

PRINCIPLE :- Based upon Capillary Action. A low surface tension fluid penetrates

into clean and drying surface breaking discontinuities.

After adequate penetration time has been allowed, excess penetrant is removed and developer is applied.

The developer A low surface tension fluid penetrates

into clean and drying surface breaking discontinuities.

After adequate penetration time has been allowed, excess penetrant is removed and developer is applied.

The law stated is thermodynamically rigorous ,i.e., it takes no account of the activities of the various species involved & thus, is expected to be applied in very dilute solutions.

Also, the law in its simple form is not applicable, when the distributing species undergo dissociation or association in either phase.

DISTRIBUTION RATIO:-In practical application, we are concerned with

the fraction of the total solute present in one or other phase, thus, its convenient to use “Distribution Ratio(D)”, i.e.,

D(CA)a

(CB)b

Where,CA denotes concentration of ‘A’ in all its form as determined analytically.

SEPARATION COEFFICIENT:-If the solution contains two solutes ‘A’ and ‘B’,

then it often happens that in conditions favouring complete extraction of ‘A’ , some ‘B’ is also extracted.

The effectiveness of separation then increases with the magnitude of the “Separation factor(or coefficient)” which is related to the individual distribution ratios as follows;

β DA

DB

β SEPARATION FACTOR

Where,

THEORY The greater the number of small extractions,

the greater the quantity of solute removed. This means,

For example, suppose we have

Amount of solute in aqueous phase(xo)=300g

Volume of aqueous phase = 100ml

Volume of organic phase to be added = 200ml

Distribution ratio of the particles = 0.5

NOW,

The total amount of solute (x n) left non-extracted in the aqueous phase (‘V’ ml) on adding the extractive organic phase (‘v’ ml) can be calculated using the formulae,

xn xoD

DV

V V

n

WHERE, xo = amount of solute present before adding extractive solvent D = Distribution ratio of the solute particles n = Number of times the solvent is added

CASE 1:

If n=1, i.e., the extractive solvent is added in one complete go, then, from the formulae,

we find that, x1 = 60g, that means 240g of the solute gets extracted.

CASE 2:

If n=2, i.e., if we add the extractive solvent in two parts each of 100 ml, then,

v=100ml, and using the formulae, we find x2 to be 33g, which implies that, 267g of the solute has been extracted.

Hence, from the above example it is clear that, it is more efficient to carry out small extraction with small equal portions of the extractive solvent, rather than using single large volume.

The inorganic solutes, with which we are concerned, tend to be more soluble in water rather than organic solvents. Also, there occurs a large loss of electrostatic solvation energy if, inorganic solutes are directly expected to be extracted by organic solvents.

Thus, for the extraction of inorganic solutes, we use appropriate reagents which can mask the water solubility of the inorganic ionic species by neutralizing their charge.

The masking of the water solubility of the inorganic ionic species present in water can be done in two ways:

By formation of a neutral metal chelate complex, or

By ion association.

Chelation complexes These complexes are often termed as

INNER COMPLEXES, when uncharged. In these complexes the central metal ion

coordinates with the poly-functional organic base to form a stable ring. For example, copper(II) acetylacetonate or iron(III) cupferrate.

CH3

CH3 C

C

O

O

CH2

CH3

CH3 C

C O

CH ½ Cu2+

CH3

CH3 C

C

O

OCH

Cu/2

CH3

CH3 C

C

O

OCH

Cu/2

Copper(II) acetylacetonate

H

OH

Factors which affect the stability of the chelate complexes:Basic strength of the chelating group

(more is the basic strength, more is the stability).

Nature of the donor atoms of chelating agent (soft-base type donor atoms form most stable complexes with the small group of class B metal ions, i.e., soft acid. Eg. Dithizone used for extraction of Pb2+.)

Size of the ring (five or six membered conjugated chelate rings are more stable, since they have minimum strain).

Resonance & steric effect (more are the resonance structures of the chelate ring, more will be its stability. Eg. Copper(II) acetylacetonate is more than copper chelate of salicylaldoxime. Also, the steric hindrance must be minimum).

CRITICAL INFLUENCE OF pH ON SOLVENT EXTRACTION OF METAL CHELATES:

The quantitative treatment of the solvent extraction of the neutral metal chelate can be done on the basis of the following assumptions;

Solvation plays no significant part in the extraction process.

The solutes are uncharged particle & their concentrations are so low that the solutions do not deviate much from ideality.

The reagent and the metal complex exist as undissociated molecules in both phases.

The formation of neutral metal(M) chelate complex, from a chelating reagent HR, takes place according to the following equation;

Also, the dissociation of the chelating reagent HR in the aqueous phase is given by the equation;

Mn+ n R- MRn

HR R-H+

Now, the above equilibria can be expressed in terms of the following thermodynamic constants;

Dissociation Constant (K), &Partition Coefficient (p).

in the following manner as described

in the equations

Dissociation constant of the

KMn+ R-

R

w w

w

n

c

complex

H+

MH n

r

reagent

Partition Coefficient of the

pMRn w

MRn oc

complex

HR

HRr

reagent

The Distribution Ratio(D) ,i.e., ratio of the amount of metal extracted into the organic phase as complex to that remaining in all forms in the aqueous phase is;

D MRn o

MRn w wMn+

The equation for Distribution Ratio can be further reduced to the form,

D oHR

wHR

n

K

Where,

K Kc

rK p

c

r*p*

( )n

And the % of solute extracted is given by;

D K*wHR

If the reagent concentration remains virtually constant, then

log( )E

log( )100-E - log( )K* npH

Thus, we observe that the distribution of the metal in the given system is a function of pH alone.

The equation of the % of solute extracted represents sigmoid curves, when E is plotted against pH. The slope of the curve depends upon ‘n’.

If pH1/2 is defined as the pH value at 50% extraction, i.e., E%=50, then,

pH1/2 n-1 log( )K*

The difference in pH1/2 values of two

metal ions in a system is a measure of the ease of separation of the two ions. If the values are far apart, excellent separation can be achieved by controlling pH.

The pH1/2 values may be altered using a competitive complexing agent.

Ion-association complex These complexes are formed when the

species to be extracted associates with oppositely charged ions to form neutral extractable species.

Such complexes can clusters with increasing concentration, particularly in an organic solvent of low dielectric constant.

Some types of ion-association complexes that have been recognized are:

Those formed from the reagents yielding large organic ions, eg. Tetraphenylarsonium[(C6H5)4As+], which tend to form large ionic clusters with oppositely charged ions, like ReO4

- . They do not have a hydration shell & thus, disrupt the water structure, due to which the tend to be pushed into the organic phase.

Those involving a cationic or anionic

chelate complex of the metal ion. Thus, the chelating reagent consists of two uncharged donor atoms. Eg. 1:10 phenanthroline forms cationic complexes.

Those in which solvent molecules are directly involved in the formation of ion- association complex. Eg. ethers, esters etc.

EXTRACTION REAGENTS NAME FORMULAE REMARKSACETYLACETO-PHENONE

CH3COCHCOCH3

DIMETHYL-GLYOXIME

CH3COCHCOCH3

Partition Chromatography II

Reverse Phase Chromatography– Nonpolar Stationary Phase– Polar Mobile Phase

Normal Phase Chromatography– Polar Stationary Phase– Nonpolar Mobile Phase

Column Selection Mobile-Phase Selection

Partition Chromatography III

Research Applications– Parathion in Insecticides: O – CH3CH2O P O NO2

CH3CH2O

– Cocaine in Fruit Flies: A Study of Neurotransmission by Prof. Jay Hirsh, UVa

Adsorption Chromatography

Classic Solvent Selection Non-polar Isomeric Mixtures Advantages/ Disadvantages Applications

What is Ion Chromatography?

Modern methods of separating and determining ions based on ion-exchange resins

Mid 1970s Anion or cation mixtures readily resolved on HPLC

column Applied to a variety of organic & biochemical systems

including drugs, their metabolites, serums, food preservatives, vitamin mixtures, sugars, pharmaceutical preparations

The Mobile Phases are...

Aqueous solutions – containing methanol, water-miscible organic solvents– also contain ionic species, in the form of a buffer – solvent strength & selectivity are determined by kind

and concentration of added ingredients– ions in this phase compete with analyte ions for the

active site in the packing

Properties of the Mobile Phase

Must– dissolve the sample– have a strong solvent strength leads to reasonable

retention times– interact with solutes in such a way as to lead to

selectivity

Ion-Exchange Packings

Types of packings– pellicular bead packing

• large (30-40 µm) nonporous, spherical, glass, polymer bead

• coated with synthetic ion-exchange resin• sample capacity of these particles is less

– coating porous microparticles of silica with a thin film of the exchanger• faster diffusion leads to enhanced efficiency

Ion-Exchange Equilibria

Exchange equilibria between ions in solution and ions on the surface of an insoluble, high molecular-weight solid

Cation exchange resins– sulfonic acid group, carboxylic acid group

Anion exchange resins– quaternary amine group, primary amine group

CM CelluloseCation Exchanger

DEAE CelluloseAnion Exchanger

Eluent Suppressor Technique

Made possible the conductometric detection of eluted ions.

Introduction of a eluent suppressor column immediately following the ion-exchange column.

Suppressor column– packed with a second ion-exchange resin

Cation analysis Anion analysis

Size Exclusion Chromatography(SEC) Gel permeation(GPC), gel filtration(GFC)

chromatography Technique applicable to separation of high-molecular

weight species Rapid determination of the molecular weight or

molecular-weight distribution of larger polymers or natural products

Solute and solvent molecules can diffuse into pores -- trapped and removed from the flow of the mobile phase

Specific pore sizes.average residence time in the pores depends on the effective size of the analyte molecules– larger molecules– smaller molecules– intermediate size molecules

SEC(continued)

SEC Column Packing

Small (~10 µm) silica or polymer particles containing a network of uniform pores

Two types (diameters of 5 ~ 10 µm)– Polymer beads– silica-based particles

Advantages of Size Exclusion Chromatography Short & well-defined separation times Narrow bands--> good sensitivity Freedom from sample loss, solutes do not interact

with the stationary phase Absence of column deactivation brought about by

interaction of solute with the packing

Disadvantages

Only limited number of bands can be accommodated because the time scale of the chromatogram is short

Inapplicability to samples of similar size, such as isomers. – At least 10% difference in molecular weight is required

for reasonable resolution

Instrumentation

Instruments required:– Mobile phase reservoir– Pump– Injector– Column– Detector – Data system

Schematic of liquid chromatograph

Mobile phase reservoir

Glass/stainless steel reservoir Removal of dissolved gases by degassers

– vacuum pumping system– heating/stirring of solvents– sparging– vacuum filtration

Elution methods

Isocratic elution– single solvent of constant composition

Gradient elution– 2 or more solvents of differing polarity used

Pumping System I

Provide a continuous constant flow of the solvent through the injector

Requirements– pressure outputs up to 6000 psi– pulse-free output– flow rates ranging from .1-10 mL/min– flow control and flow reproducibility

of .5% or better– corrosion-resistant components

Pumping System II

Two types:– constant-pressure– constant-flow

Reciprocating pumps– motor-driven piston– disadvantage: pulsed flow creates noise– advantages: small internal volume (35-400 L), high

output pressures (up to 10,000 psi), ready adaptability to gradient elution, constant flow rates

Pumping System III

Displacement pumps– syringe-like chambers activated by screw-driven

mechanism powered by a stepper motor– advantages: output is pulse free– disadvantage: limited solvent capacity (~20 mL) and

inconvenience when solvents need to be changed Flow control and programming system

– computer-controlled devices– measure flow rate– increase/decrease speed of pump motor

Sample Injection Systems

For injecting the solvent through the column Minimize possible flow disturbances Limiting factor in precision of liquid chromatographic

measurement Volumes must be small .1-500 L Sampling loops

– interchangeable loops (5-500 L at pressures up to 7000 psi)

LC column

LC injector

Liquid Chromatographic Column

Smooth-bore stainless steel or heavy-walled glass tubing

Hundreds of packed columns differing in size and packing are available from manufacturers ($200-$500)

Add columns together to increase length

Liquid Chromatographic Columns II Column thermostats

– maintaining column temperatures constant to a few tenths degree centigrade

– column heaters control column temperatures (from ambient to 150oC)

– columns fitted with water jackets fed from a constant temperature bath

Detector

Mostly optical Equipped with a flow cell Focus light beam at the center for

maximum energy transmission Cell ensures that the separated

bands do not widen

Some Properties of Detector

Adequate sensitivity Stability and reproducibility Wide linear dynamic range Short response time Minimum volume for reducing zone broadening

More Properties of Detector

High reliability and ease of use Similarity in response toward all analytes Selective response toward one or more classes of

analytes Non-destructive

Types of Detector

Refractive index UV/Visible Fluorescence Conductivity Evaporative light scattering Electrochemical

Refractive Index I

Measure displacement of beam with respect to photosensitive surface of dectector

Refractive Index II

Advantages– universal respond to nearly all solutes– reliable– unaffected by flow rate– low sensitive to dirt and air bubbles in the flow cell

Refractive Index III

Disadvantages– expensive– highly temperature sensitive– moderate sensitivity– cannot be used with gradient elution

UV/Visible I

Mercury lamp = 254nm = 250, 313, 334 and 365nm with filters Photocell measures absorbance Modern UV detector has filter wheels for rapidly

switching filters; used for repetitive and quantitative analysis

UV/Visible II

UV/Visible III

Advantages– high sensitivity– small sample volume required– linearity over wide concentration ranges– can be used with gradient elution

UV/Visible IV

Disadvantage– does not work with compounds that do not absorb light

at this wavelength region

Fluorescence I

For compounds having natural fluorescing capability

Fluorescence observed by photoelectric detector

Mercury or Xenon source with grating monochromator to isolate fluorescent radiation

Fluorescence II

Advantages– extremely high sensitivity– high selectivity

Disadvantage– may not yield linear response over wide range of

concentrations

Conductivity

Measure conductivity of column effluent

Sample indicated by change in conductivity

Best in ion-exchange chromatography

Cell instability

Evaporative Light Scattering I

Nebulizer converts eluent into mist Evaporation of mobile phase leads to formation of

fine analyte particles Particles passed through laser beam; scattered

radiation detected at right angles by silicon photodiode

Similar response for all nonvolatile solutes Good sensitivity

Evaporative Light Scattering II

Electrochemical I

Based on reduction or oxidation of the eluting compound at a suitable electrode and measurement of resulting current

Electrochemical II

Advantages– high sensitivity– ease of use

Disadvantages– mobile phase must be made conductive– mobile phase must be purified from oxygen, metal

contamination, halides

Data System

For better accuracy and precision Routine analysis

– pre-programmed computing integrator Data station/computer needed for higher control levels

– add automation options– complex data becomes more feasible– software safeguard prevents misuse of data system

Electrophoresis…charged species migrate in electric fieldSeparation based on charge or mobility

Capillary electrophoresishigher voltages can be used as the heat can be dissipated

Capillary electrophoresis