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TOPICS: METALLURGY, METAL PROPERTIES, & DISCONTINUITIES
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Documents Governing Welding Inspection
Discontinuities
Duties & Responsibilities
Welding Terms and Symbols for welding Brazing and NDE
Metallurgy
NDE
WPS/ PQR
Safety
Welding Brazing Cutting & Soldering
Metal Properties and Destructive Testing
Well, back to AWS B5.1 to see what else the CWI needs to know AWI WI
Knowledge & Skills • Understand the gundamentals of welding metallurgy • Witness procedure qualification • Certify documented results compliance • Verify Procedure qualification compliance
SWI
WELDING METTALURGY FOR THE WELDING INSPECTOR
The science dealing with the internal structure of metals and properties
WELDING METTALURGY
Concerned with the changes occuring in metals during
welding Such as:
Thermal Effects Dilution Effects
DISCUSSION TOPICS
Changes that happen during heating
Changes that happen during cooling
Structures metal that exist in
Heat treatments and what each will produce
Alloying, combining elements
Phrases
Matter made up of atoms
Have a home location in solids
Atoms are very small
ATOMIC STRUCTURE
Oscillate around home position
Electrons orbit atomic nuclei
LOWEST INTERNAL ENERGY & SHORTEST INTERATOMIC SPACING SOLIDS HAVE
• Minimum internal energy • Atoms fixed in place • Atoms vibrating • Orbiting electrons • Crystalline structure
HIGHER INTERNAL ENERGY & GREATER INTERATOMIC SPACING LIQUIDS HAVE
• Higher Internal energy • Atoms free to move • Atoms vibrating more
• Orbiting electrons • No fixed structure
SOLID TO LIQUID
• Higher internal energy • Atoms free to move • Atoms vibrating more
• Minimum internal energy • Atoms fixed in place • Atoms have “home” position
• Orbiting electrons • No fixed structure
• Atoms vibrating • Orbitin electrons • Crystalline structure
THERMAL EXPANSION ON HEATING & THERMAL CONTRACTION ON COOLING • Curvature down in B & C due to expansion
• As it liquifies expansion forces can’t be maintained by liquid so bar straightens • Cooling to solid shrinkage stresses curves up
WELDING STRESSES (TENSILE)
Residual stress is caused by heating, melting, cooling & solidifying metals
Remain after welding is completed (residual stress)
Residual stress can be as high as yield strength
Can cause distortion (welding stress exceeds yield of material)
Can cause cracking (wedlding stress exceeds tensile strength of material)
Relieved by three methods
STRESS RELIEVING
Can be accomplished in three ways
Most stress relief is done thermally but peen during welding can be effective, as is vibratory stress relief • Thermal - Controlled heating & cooling • Vibratory - High frequency probes • Peening - Use of heavy pneumatic hammer
CRYSTAL STRUCTURES
• BCC - Body Centered Cubic • FCC - Face Centered Cubic • BCT - Body Centered Tetragonal
Iron at room temperature Iron above 1333 F Iron quenched to martensite at room temperature
• HCP - Hexagonal Close Packed
Ti and Mg
Examples of BCC include Fe-iron, Cr-chromium, W-tungstend & Nb-niobium Examples of FCC include Pb-lead, AI-aluminium, Cu-Copper, Au-gold and Ag-silver Examples of HCP include Ti-titanium, Mg-magnesium and Ice
COMMON CRYSTAL STRUCTURES
Iron at room temperature
IRON ABOVE 1333 F
Iron quenched to martensite at room temperature
Ti and Mg
METAL SOLIDIFICATION
HEAT REMOVAL
DENDRITE FORMATION
SECOND LAYER OF DENDRITES
WHAT’ MISSING HERE?
MAYBE DISTORTION FROM SHINKAGE?
FINAL CONDITION SEGREGATION
GRAIN SIZE EFFECTS
FINE GRAINED MATERIALS • Have good tensile • Have good ductility • Have good low temperature
COARSE GRAINED MATERIAL • Have slightly lower strength • Are slightly less ductile • Have good high temperature properties
EX. SA-333 Gr 6
EX. SA-105
Same chemistry but different grain size due to cooling rate
TWO METHODS OF ALLOYING
INTERSTITIAL
SUBSTITUTIONAL
Alloying is the adding elements to change mechanical or physical properties
INTERSTITIAL ALLOYING
Atoms go into space between other atoms in the structure
Results in lattice distortion
SUBSTITUTIONAL ALLOYING
SUBSTITUTIONAL Add atoms almost the same size which replace other atom in structure ie CR into Fe
Result in Lattice Distortion
MICROSTRUCTURE OF IRON
• Microstructure of commercially pure iron • White grains are ferrite • Grain boundaries are shown
• Darker globules are nonmetallic inclusions
IRON-CARBON PHASE DIAGRAM
For given carbon content a verbical line can be drawn through the horizontal axis Moving up that line will show what microstructure will exist at various temparature
Where Carbon changes from BCC to FCC Vertical axis = Temperature Changes Horizontal axis = Amount of carbon present
PHASE IN STEEL
A BCC solid solution of carbon in gamma iron also called alpha iron, Fe Iron carbide, Fe C Gamma iron, a stable phase of 300 series stainless, is formed when heated above the A3 transformation line, forming an FCC solid solution of carbon in iron. A layered or lamellar structure composed of ferrite and cementite A phase of iron, which forms on cooling, very fine particle size An unstable constituent of iron formed without diffusion by rapid quenching from austenite phase above the A3 transformation line
FERRITE
CEMENTITE
AUSTENITE
PERALITE
BAINITE
MARTENSITE
COOLING RATES
LAMELLAR APPEARANCE OF PEARLITE
WHITE AREAS -FERRITE DARK AREAS -CEMENTITE
1500 X Magnification
BAINITE
MARTENSITE
Note how etches are very dark This is due to the many fine carbides present
Structure referred to as needle-like Achieved by rapid cooling
Weld Area & Fe - Fe C Diagram 3
HEAT INPUT
How do we calculate heat input?
No need to memorized the formula, It will be given on the test. Joules/inch = Current x Voltage x 60 Travel Speed (IPM)
PRE-HEAT
Has significant effect on the resulting microstructure of the HAZ Be careful when using other alloys, Preheat can be harmful ie 304 stainless • Slow Cooling Rate • Reduces distortion • Reduces hydrogen • Produces less martensite • Reduce risk of cracking
Carbon Equivalent (CE) Determines the combined effects of various alloying elements on the hardenability of particular steel CE = % C + %Mn + %Ni + %Cr + %Cu + %Mo 6 15 5 13 4
• Not all CE formulas are the same • Watch for changes in “+” and “-”
• Why do we need carbon equivalents? • No need to memorize the formula it will be given on the test
Carbon Equivalent (CE) CE = % C + %Mn + %Ni + %Cr + %Cu + %Mo 6 15 5 13 4 Given a chemistry of : .12 carbon, .99 manganese, .0075 nickel, .20 chromium, .05 copper & .15 molybdenum Put the numbers in the formula:
CE = .12 + .99 + .0075 + .20 + .05 + .15
6 15 5 13 4
Then simplify the formula by dividing the top number by the bottom number for each of the elements:
CE = .12 + .99 + .0075 + .20 + .05 + .15 CE = .366846 or .37
Watch for changes in “+” and “-” and the decimal points
CE VS PREHEAT
Carbon Equivalent
Preheat temperature
< 0.45 0.45 - 0.60 > 0.60
Optional 200 - 400 F 400 - 700 F
• Is there any basis to use for determining whether preheat is advisable or not? • The above is suggested as a guide for selection of either the hardness control or hydrogen control method to prevent cracking
Annealing - Slow cooled in a furnace Normalizing - Slow cooled in still air Quenching (to harden) - Rapid cooling Sub-critical - below transformation temperature Tempering Stress Relieving Heat treatments for Steels Super-Critical - Above transformation temperature
Diffusion Movement of atoms within a solution, be it a solid liquid or gas. When a block of pure gold and a block of pure lead are clamped together, a week bond will fom
SOLUBILITY
Dissolving Salt into water
Solid into liquid
Movement of atoms within a solution, be it a solid liquid or gas
Diffusion mechanism
Dissolving Sugar in Cold and Hot Tea
Temperature effects
Some sugar remains in the bottom of the glass no matter how much you stir
Solubility limit
SOLID SOLUBILITY
At temps of 1600-1700 F carbon can be added to the surface of steelt he material which can be useful for resisting wear and abrasion “Pack Carburizing”
• Unique to metals • Solid into Solid • Solubility Limit • Temperature effects
By exposing steel to ammonia at similar temps, nitrogen atoms enter the surface of steel “Nitriding”
STAINLESS STEELS Contain at least 12% Cr
• Austenitic • Martensitic • Ferritic • Precipitation hardening • Duplex • Super Duplex
304, 316 410, 420 430 17-4, 15-5
2205 2507
Sentization of Austenitic (FCC) Alloys
Sensitization reduces the corrosion resisstance in many environments HAZ corrosion IGA (Intergranular corrosion attack) due to sensitization
Formation of Chromium carbides between 800 - 1600 F
1250 F is the most severe temperature for this formation
Avoiding Sensitization
Solution annealing, water quenching C & Cr separate at 2000F Using titanium or niobium combines with C instead of CR
Heat treatment (SAWQ)
Stabilized Grades
Low Carbon Grades (ELC)
Documents Governing Welding Inspection
Discontinuities
Duties & Responsibilities
Welding Terms and Symbols for welding Brazing and NDE
Metallurgy
NDE
WPS/ PQR
Safety
Welding Brazing Cutting & Soldering
Metal Properties and Destructive Testing
What determines a Metal’s Properties
• Physical Properties (density) • Alloy Chemistry • Alloy Heat treatment • Cold Work
What determines a Metal’s Properties Mechanical properties are often very dependent upon heat treat condition.
To determine the heat treat condition prior to welding or mechanical testing can be very important. The effect of welding on the heat treat condition and mechanical properties should be considered Welding procedures are aqualified according to the base material heat treatment and help ensure return of the material’ s mechanical properties after welding
What determines a Metal’s Properties
Numerous tests are used to determine mechanical properties & mechanical properties & chemical makeup of metals • Toughness
Welding Inspectors Should Know..
1) When test is applicable 2) What results are provided 3) How to determine results in compliance with specifications
• Hardness • Strength • Ductility • Soundness • Impact Strength
The ability of a material to bear an applied load • Load maty be applied in different ways including . . . tensile, torsional , fatigue , shear , impact & compression • The reaction of a material to a load is stress • A load of 30 tons on a cross sectional area of 1 sq. inch will induce in the material a stress of 1qc. inch will induce in the material a stress of 30 tons per sq. inch
Strength is commonly expressed in two ways . . .
• Ultimate tensile strength (UTS) The maximum load carrying capacity of material
• Yield Strength
The strength level at which permanent deformation begins
Tensile Testing can provide . . . Yield strength Percent Elongation Pervent Reduction of Area Elastic Limit Toughness
Tensile Testing Area of a rectangle = width x thickness If the width & thickness of the tensile specimen’s reduced section is as shown below, what is the cross sectional area
Used to compute Yield Strength
Used to compute Tensile Strength
Typical Stress/Strain Curve - Steel
Stress is proportional to strength which is applied load divided by cross sectional are Strain is the amount of stretch in given length Elastic means stress & strain are proportional Slope of curve = Modules of elasticity
Stress - Strain Diagram High and medium Strength Steels
Two steels . . . One very strong but brittle One weaker but ductile
Which one is which?
Roundule Tensile Specimens Simple geometry Uniform cross section Reduced section Smooth surface finish Gage marks
Tensile Strength = Load/area “ Standard “ Round Specimen .500" Diameter
Area of a Circle Calculation ( using diameter directly )
D 4
2
Area =
Using same diameter of .500"... Area = 3.1416 x (0.500) 4 2 Steps are: .500" x .500" = .25 in .25 x 3.1416 = .7854 in .7854 in / 4 = 0.19635 in Area = 0.2 in (rounded off) 2 2 2 2
Calculation of Tensile Strength Same as “ load at fracture “
Load to break = Area of sample =
2 12,500 lbs 0.20 in
Tensile strength = Tensile strength = Steps are: 12, 500 divided by .2 =
load / area 12,500 lbs / 0.20 in
2
Tensile strength = 62,500 psi
Compare results to required minimum tensile strength of the base metal
The there is Yield Strength - Yield strength is determined by: Yield point / area Yield point? How do we get that value? Tensile test (already covered), the extensometer and the offset method
Transverse extensometers are designed for the accurate determination of the transverse strain in a specimen. The transverse strain sensors are designed to be clamped directly to the specimen Or ...Identifies Yield Point Extensometer
Used to determine Yield Point Usually offset at .2% (.002 in / in ) Line drawn parallel to curve (same slope) Intersection with curve is Yield Point Offset Method
“Fatigue” Cyclic Application of load
The strength of a mental when exposed to repeated reversals of cyclic stresses. Fatigue Strength
Fatigue Testing
1. Prepare samples 2. Test series of various loads 3. Test to failure, record cycles 4. Test at maximum load vs no failure 5. Plot data 6. Determine endurance limit *This type of testing is normally performed by a laboratory, not the CWI
Notch Effects on Fatigue
Endurance limit of - 49,000
Endurance limit of - 18,000
Surface Finish Effects on Fatigue
Endurance Limit The maximum stress at which no failure will occur, regardless of cycles
1047 results show no failure will occur at 43ksi & below
AI 2014-T6 has no endurance limit due to the effects of work hardening
Directional Properties
Both strength and ductility are affected by the rolling direction of the metal The three axes of rolling direction are referred to as the X, Y and Z directions
Rolling Directions
X Direction (Rolling Direction) - Y Direction (Rolling Direction) -
Best Strength & Ductility 10 - 30% Less Strength 20 - 50% Less Ductility
Z Direction (Through Thickness) - Still Lower Strength and Ductility
Elastic - No permanent deformation (like a rubber band) Plastic - Permanent Deformation (like silly putty) Metal Behavior Under Load
Elastic Behavior of Steel
Ductility Terms
Ductility may be defined as... Percent elongation %El Percent reduction of area %RA *Need to learn to calculate using formulas that will be provided
Percent Elongation a way to express Ductility
Original gage length = 2.0 in. After testing, “Final” gage length = 2.6 in. % Elongation = final length = original length x 100 Original length % Elongation = 2.6 - 2.0 x 100 = 30% Steps are : 2.6-2.0=.6 0.6 /2.0=.3 0.3 x 100 = 30% Elongation 2.0
Percent Reduction of Area Ductile Brittle
Using same area fomula as for tensile strength Original area = 0.2 in. Final area = 0.1 in. % Reduction of area (%RA) = ? %RA = original area - final area x 100 original area %RA = 0.2 - 0.1 x 100 = 50% 0.2 2 2 Percent Reduction of Area
Hardness Ability to resist indetation • Hardness testing Steps • Prepare surface • Make indetation • Measure indentation • Determine hardness
Hardness Test
Test Measure resistance to indentation BHN X 500 = Approximate Tensile strength
Used as an adjunct to Visual Inspection Non Destructive - Brinell test on 4x8 plate 1" thick Destructive - Brinell test on face of die plate for printing $20 bills Hardness Test
Indenter Types
Vickers Hardness Test
Temperature Effects
As metal temperatures increase: Strength decreases Hardness decreases Ductility increases
Strength increases Hardness increases Ductility decreases As metal temperatures decrease:
Toughness The ability to absorb energy
Given by the area under the stress-strain curve or determined by impact testing such as Charpy V Notch or CTOD testing
Toughness Comparison
Remember the area under the curve represents the toughness of the material Then we can see that monel is a tougher material than mild steel
Notch Toughness Toughness in the presence of surface notches and rapid loading (also referred to as “Impact Strength”)
A noth is typically a surface indentation which has the ability to concentrate stress • IE • Scratches • Weld ripples • Undercut Many more
Stress Risers A surface condition, or geometric feature, that increases the applied stress at the condition or geometry
Stress risers cause Premature Failures
Stress Risers A surface condition, or geometric feature, that increases the applied stress at the condition or geometry
Stress risers cause prematurea failures
Charpy Impact Test Specimens 55 mm long
10 mm x 10mm square
Notch at specific depth & radius
“Charpy” is one type of notch toughness test , what is another? Hint: specimen is notched toward one end and stood up in the fixture for the pendulum to strike on the notched side
Toughness Testing
Impact testing notch toughness Transition temperature Charpy impact specimen in testing fixture
Charpy Test
Prepar notched specimens (sets of 3 or 5) Test each specimen set at a specific temperature Impact sample anvil will strike specimen on side opposite the V notch
Ductility
The ability of a metal to deform without breaking
Ductile material shows deformation Brittle material exhibits little or no deformation before fracture
Ductile - to- Brittle Transition Temperature The temperature at which a metal fracture mode changes from ductile to brittle Determined by Charpy testing at different temperatures and plotting data Welding can increase the ductile to brittle transition temperature - - It is vital to observe welding procedure conditions.
Charpy Impact Test Results
• Energy absoption in Ftlbs. • Percent shear • Lateral expansion in Mils
FREEDOM FROM DISCONTINUITIES Types of soundness Tests
Bend Testing • Nick - Break • Fillet - Break
BEND TEST SAMPLES Transverse Weld Bend Specimens
SIDE BEND
SIDE BEND
FACE BEND
FACE BEND
BEND TEST SAMPLES Transverse Weld Bend Specimens
Notice the curvature of pipe
Face bend
Root Bend
BEND TEST SAMPLES Longitudinal Weld Bend Specimens
Notice the curvature of pipe
Face bend
Root Bend
Guided Bend Test Jig • Prepare Sample • Orient in Jig • Bend sample (Weld & HAZ in bend) • Evaluate bend to code
What is proper orientation?
Guided Bend Test Jig
Wrap - around Bend Test Jig Better for aluminum bends than guided bend test jig
Nick Break Test
Evaluation of Nick-Break Test
Break in weld • Evaluate soundness of weld by inspecting ends of pieces • Accept or reject based on written criteriia of code or specification
Filler Break Test
Prepare Sample Break Sample Evaluate Fracture Since this is a “soundness test” the fracture must reveal the weld contents, not how fusion took place.
Metallographic Testing
Shows structure of metal Macroscopic • Less than 10x Microscopic • Typically more than 100x
Photomicrograph
Corrosion Testing Evaluates metals in corrosive environments
The CWI may or may not be involved in corrosion testing
Determines Chemistry of Metals Chemical Testing
Spectrographic - determines material's chemistry Combustion (CO, CO2 determination) Wet chemistry (titration) X-Ray fluorescence (XRF) - can be performed in the field to sort materials using magnetic properties and color changes from reagents
Chemical Composition • Metals are...mixtures of elements, referred to as alloys Minor changes in alloy composition can have major effects on alloy properties such as mechanical strength, corrosion resistance For example : • Iron has a tensile strength in the range of 30 ksi but by adding 0.1% of carbon this strength can be almost doubled
Chemical Elements in Steels C - S - P - Si - Mn - Cr - Mo - Ni - Al - V - Nb - Most Important Undesirable Undesirable Deoxidizer Combines with S Hardenability, Corrosion Resistance
Hardenability Toughness, Ductility Deoxider Hardenability Stabilizer
Low Alloy Steels High Alloy Steels • High Strength, low alloy • Automotive & Machinery • Low Temperature • Elevated Temperature • Corrosion resistant • High Temperature • High Strength
Addition of Cr, Ni, V Ex. Hastelloy C & 304SSt
Car parts made of low alloy steels = energy absorption by metal parts in cars, not body parts = saving lives
Documents Governing Welding Inspection
Discontinuities
Duties & Responsibilities
Welding Terms and Symbols for welding Brazing and NDE
Metallurgy
NDE
WPS/ PQR
Safety
Welding Brazing Cutting & Soldering
Metal Properties and Destructive Testing
Weld and Base Metal DISCONTINUITIES This section will cover the importance of evaluation of weld to determine their suitability for an intended service.
DEFECT
• A non-conforming discontinuity • All discontinuities are not defects
Defect = Rejectable Discontinuity
Acceptance or Rejection must be per a Code or Specification
• All defects are Discontinuities
DISCONTINUITY CRITICALITY Location of maximum stress is usually on the surface of the part
• Linear vs Non-Linear • End condition - Sharpness • Surface vs Sub-surface
• Fatigue • Impact • Loading - Uniform vs Non- Uniform
CRACK A fracture type discontinuity characterized by a sharp tip and high ration of length & width ( depth) to opening displacement
Most Critical because Linear and Sharp end Condition
Which code permits cracks to remain as acceptable? API 1104 (crater cracks)
Types of Cracks
Underbead Cracks • Often delayed cracking • Caused by hydrogen • Difficult to detect • Avoid with low H process 2
Incomplete Fusion A weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads.
Incomplete Fusion Only for Groove Welds
Melt Thru (Internal Protrusion)
Inclusions are Any entrapped foreign solid material such as slag, flux, tungsten or oxide
Porosity Cavity type discontinuities formed by gas entrapped during weld metal solidification
Scattered Surface Porosity
Elongated Surface Porosity
Also called “Pockmark”
Wormhole Porosity
Undercut A groove melted into the base metal adjacent to the weld to or weld root & left unfilled by weld metal Located on surface Potentially sharp end condition
Underfill A condition in which the weld face or the root surface is below the adjacent surface of the base metal Usually means the weld is not finished. Occurs in weld groove
Overlap Usually linear - Creates sharp notch (stress riser)
Fillet Weld Convexity
The maximum distance from the face of a convex fillet weld perpendicular to a line joining the weld toes • Applies only to fillet welds • Can create a sharp angle
Weld Reinforcement Well, if “Convexity” is only for fillet welds, what term is used to describe groove welds?
Improper & Acceptable Treatment of Weld Reinforcement
Can form martensite Good crack starter
Arc Strike A discontinuity resulting from an arc, Consisting of any localized remelted metal, Heat-affected metal, or change in the surface profile of any metal object
Photomicrograph of arc strike
SPATTER Metal particles expelled during fusion welding that do not form Remove for NDE Remove for painting
LAMINATION A discontinuity with separation or weakness generally aligned parallel to the worked surface of a metal Base metal discontinuity only is planar in orientation usually oxide filled not the same as “Delamination”
DELAMINATION
Lamellar Tear A subsurface terrace and step like separation in the base metal, parallel to the surface, caused by tensile stresses in the through- thickness direction Base metal only usually outside the HAZ result of Z direction stress Clean steels are the solution
Dimensional • Shape imperfections • Distortion • Size Irregularities
Defeat is not the worst of failures not to have tried is the tru failure
HOMEWORK FOR TONIGHT
1) QUESTIONS ON PAGES 501 - 530 2) DEFINITIONS ON PAGES 530 - 541
3) THEN IN • PART C BOOK (API 1104) • STUDYGUIDE QUESTIONS • SEC 10-APPB OR PART D BOOK (AWS D1.1) CE 3
THANK YOU
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