Power Engineering 2A2 - Part 1
Spot/Projection welds?
- 2 relatively thin surfaces that are fused together on opposite sides of the surfaces, by spot welding a current through the materials - Projection welding is a variation of spot welding in which one of the surfaces has small raised projections.
Basing Proof Test results from Yield Strength?
- 3 specimens are cut from the tested part and an average yield strength is determined. P = 0.5 H X Ys/Ya
Phosphor Bronze composition/properties?
- 90% copper, 9.75% tin, 0.25% Phosphorus - Strong, hard, resilient. Used for bushings and high grade springs
Describe the Vickers Hardness test indentor.
- A 136 degree diamond, square based pyramid is used - Loads used range from 1 kg to 120 kg with standard loads of 5, 10, 20, 30, 50, 100 and 120 kg
What is Shear Load?
- A force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force.
Opposite of metal hardness is...?
- A hard metal is does not possess TOUGHNESS. - Hardness: resistance to deformation
What is the principle of Liquid Penetrant testing?
- A liquid with a low surface tension is applied to a surface. The penetrant will enter any discontinuities and by use of a developer solution the cracks become visible when drawn back out from the surface.
Define Malleability:
- A materials ability to deform under compressive stress; often characterized by a materials ability to form a thin sheet by hammering or rolling - without fracture.
Define Ductility:
- A measure of a metals ability to undergo significant plastic deformation before rupture, which may be expressed as elongation or percent area reduction from a tensile test. - Often characterized by a materials ability to be stretched into a wire
What is Hardness?
- A measure of the resistance of a material to surface indentation
What are Noble Metals?
- A metal that resists chemical action and does not corrode or oxidize, and is not easily attacked by acids
Describe the Carbonitriding process.
- A source of carbon and nitrogen is introduced into the furnace at a temperature above the transformation temperature for the given steel - A less severe quenching process follows the hardening process
What is Martensite?
- A structure of fine carbide needle-like grains that are extremely hard and are formed during the transformation from Austenite - Rapid cooling is desired so the carbon does not have a chance to precipitate as Pearlite but instead forms as Martensite
Definitions and Terms for welding are referenced in what material?
- ANSI/AWS Standard Welding Terms and Definitions
Who developed the standardized welding symbols we used today? Who approved them?
- AWS created them - ANSI approved them * CSA standard very closely follows the AWS standard, as well as the ASME and National Board of Boiler Inspectors *
What are the 3 possible inspection status's after a specimen has been NDT'd?
- Acceptable - Rejected - Re-work required
1 safety benefit when NDE is used for testing?
- Accidents can be prevented including damage to property, injuries and loss of life
What is a Material Test Report?
- Also known as a certificate of testing, these reports are made available by the vendor and give a comprehensive chemical and physical analysis of the metal before the part was manufactured. It is essentially a copy of the recipe for the metal produced. - Identifies heat number, chemical composition, ASME spec number, grade of steel, schedule #, tensile strength, yield point, and any results of any specialized testing
What advancement has been made from Steel reinforced Aluminum Conductors?
- Aluminum Conductor Composite Cores (ACCC) - 75% lighter than steel wit a comparable tensile strength for a given diameter - unaffected by corrosion
What is one remarkable property of Aluminum that is utilized in the construction of heat exchangers? (hint: Cryogenic plants)
- Aluminum is the only metal known the increases in tensile strength as its temperature decreases
2 modern Aluminum alloys that are growing in popularity?
- Aluminum lithium alloys - Aluminum Metal Matrix Composites (ceramic additive; silicon carbide, alumina oxide, boron)
Describe the "Hall-Heroult" process and what is its purpose.
- Aluminum oxide is dissolved in molten Cryolite in an electrolytic cell - An electrical current fuses these minerals together forming molten aluminum which settles and is tapped off the bottom of the bed - Purpose of this process is to produce pure Aluminum
What is a Proof Test (Hydrostatic Deformation test)?
- An experience based method used to establish a safe design pressure for components that don't already have set designated rules for construction/testing - A full size prototype is actually subjected to hydrostatic pressure testing until yielding, bursting, or acceptable performance has been achieved - MAWP is then calculated by an appropriate formula which includes the strength of the material and an acceptable safety factor
Define weld 'Melt Through'.
- An intentional thickness of weld that surpasses the root. This amount is measured from the root to the peak of melt through material. The purpose of melt through is reinforcement.
Annealing in High Carbon Steels?
- Annealing in high carbon steels can induce brittleness by allowing larger grain formation ; reducing toughness and ductilityTrue
What is annealing and what type of microstructures does it produce?
- Annealing processes are heat treatments that alter the physical and sometimes chemical properties of the material for the purpose of increasing its ductility, remove residual stresses, decrease hardness and increase machinability - Annealing produces pearlite microstructures (ferrite, pearlite, cementite)
What are Dimensional weld Discontinuities and give a few examples.
- Any inconsistencies or departures from specified dimensions in the weld, weld joint, or parents metal. Imperfect shapes or unacceptable contours also fit into this category - Undercut, undersell, overlap etc.
What is Spheroidizing?
- Any process of prolonged heating/cooling of steel that converts the carbide content of the matrix into a rounded or spheroid structure - Metals in this form are the softest and most workable
Describe Hypoeutectoid Steels.
- At room temperature, low and medium carbon steels (below 0.8% C) always have a Ferrite component that make them tough and ductile and an FE-C influence from the Pearlite that lets them remain moderately Hard.
Considerations to remember when using Fluorescent particles and UV light for mag particle testing?
- Black light must have sufficient intensity - Black light intensity must be measured every 8 hours or whenever work station is changed - Black light minimum warm-up time is 5 minutes - Inspector must be in darkened area 5 minutes before inspection begins - Photosensitive glasses are not permitted
4 most common hardness testing techniques?
- Brinell - Rockwell - Vickers - Knoop
Bronze/bronze alloy composition and properties?
- Bronze is an alloy of copper and Tin - May contain: Phosphorus, lead, zinc, silicon nickel and aluminum - Bronze alloys have a high resistance to corrosion, possess good machinability and have increased strength over the parent metals
5 basic weld joints?
- Butt - Tee - Lap - Edge - Corner
5 basic weld joint types?
- Butt joint - Lap joint - Tee joint - Corner joint - Edge joint
Dye penetrant application for a LP examination?
- Can be applied by dipping, spraying, immersing, or electrostatically applying the penetrant - Temperature of liquid should be between 15 and 50 deg.C - Penetrant dwell time depends the specific test medium, specimen material, ambient and material temperature and the desired defects detection sensitivity - Dwell times can range from 5 mins - 30 mins
Hypereutectoid Steels?
- Carbon content exceeds 0.8% - Exhibits high tensile strength and used in tools such as axes and chisels - at 723 deg.C thee steels become a mixture of cementite and pearlite
What % carbon content is the threshold for when Normalizing is used in steels?
- Carbon steels with LESS than 0.8% Carbon
Electromagnetic Yoke technique?
- Coil is wound around a U shaped core of soft iron. Part being examined completes the path of electromagnetism. - AC yoke must be able to lift 4.5 kg and DC yokes must lift 20.4 kg - Magnetic flux lines run between the poles of the yolk making this procedure good for detecting transverse cracks but not longitudinal cracks
Describe Nitriding as a Heat Treatment hardening process.
- Completed at temperature BELOW the transformation (recrystallization) range of iron (500-600 deg.C) in a ammonia environment - Ammonia dissociates into nitrogen and hydrogen at these temperatures - Atomic nitrogen diffuses into the surface layer of the steel forming IRON NITRIDES which are extremely hard - Nitriding does not require subsequent quench hardening
Preparations before completing a Liquid Penetrant test?
- Consider all guidelines or specifications: code of construction, company specifications, special customer specifications - If no specifications for the test are available, follow the ASME Section V Article 6 procedure
Basic summary of the Rockwell Hardness Test?
- Constant load is applied for a period of time (10-30 seconds), using an indentor with a predetermined diameter - Mean diameter of the indentation is determined - Brinell hardness # is calculated or determined from an appropriate table; usually load ranges from 500kg - 3000 kg
Aluminum Bronze characteristics/uses:
- Contains up to 12% aluminum - Superior wear resistance - Anti-galling properties - Corrosion resistant and strong - Used for bearings, bushings and machine parts
6 common indicative defect results from a LP test?
- Continuous lines - Intermittent lines - Rounded areas - Small dots - Diffuse - Brilliance
Explain the Intermetallic phenomenon in relation to Aluminum-copper alloy, and why an extremely hard alloy results during the process.
- Copper Aluminum micro-particles are extremely hard and interfere with surrounding aluminum atoms by preventing easy slippage of their atomic-plane structures, resulting in hard strong alloy.
Most common metal that Aluminum is alloyed with? The process in making copper-aluminum alloy?
- Copper. - This is achieved by heating aluminum to 550 deg.C and saturating the crucible with copper of about 5% by weight. Because the copper is not positively soluble, it has to be precipitation hardened by use of rapid cooling with cool water - an inter metallic compound is formed.
Affect of Spherical type weld defects?
- Create voids, displace weld metal, reduce the intended volume of deposited weld metal. - Not as serious as notching
Pre-cleaning before conducting a Liquid Penetrant examination?
- Critical part to the examination; specimen is cleaned of all dirt, scales, oils, fingers prints and surface residues - Paint or galvanic corrosion may need to be removed mechanically - Grinding can roll over crack defects and oppose penetrant dye
When is DC current used for Mag. Particle Testing? Why?
- Dc current is used when inspecting for sub-surface cracks because the continuous DC current penetrates deeper into the test material. AC current diminishes with its alternating direction
Name a few methods of applying the force during a Rockwell Hardness test.
- Dead weight - Pneumatic - Spring - Hydraulic - Impact
Base Metal discontinuities?
- Deficiencies in the chemical, physical or mechanical properties of the base metal which may contribute to a defect in the weld - Typically happen during the production the metal or subsequent processing and manufacturing
Properties/uses of Lead?
- Dense, malleable, soft, lubricious, highly corrosion resistant, and has a low melting point - Extracted from lead sulphide ore (galena) - Used in batteries, ammunition, cable sheathing, bearings, construction and electrolytic refining and plating
Physical properties of aluminum?
- Density of 2699 kg/m3. Only magnesium is less dense @ 1738 kg/m3. - Very good heat and electrical conductivity - Low tensile strength - Very malleable and ductile
Final cleaning procedures for a LP test?
- Developer coating is removed with water, air/liquid mixture/ or in a liquid-solvent immersion tank.
Main disadvantages of the Knoop test?
- Difficulty of using a microscope to measure indentation within 0.5 micrometer accuracy - Time required to perform the test is lengthy - Load, temperature and environment can affect procedure results
Define Hydrometallurgy:
- Dissolving the metal from the ore and recovering it as a powder
Define Electrometallurgy:
- Dissolving the metal from the ore with the use of electricity, plate the metal out of solution
Define a welding 'Fault'.
- Do not use this word, it is not recognized by ANSI/AWS standards. It is often confused with discontinuity, defect and flaw.
Aluminum and its use in electrical equipment?
- Does not have to be surface protected since its highly resistant to corrosion; a thin surface oxide layer forms - Used in high-voltage transmission lines because its lighter than copper and does not need to insulated
3 types of particles used for Mag. Particle testing?
- Dry iron powder - Iron powder in wet suspension - Fluorescent particles
Drying stage of a LP test?
- Either done with very low pressure air or in a oven that doesn't exceed 50 deg.C
2 main types of Strain?
- Elastic Strain - Plastic Strain
Longitudinal technique for Mag Particle Testing?
- Electrical coils are wrapped around the examined surface. Current passing through the coils produces a longitudinal magnetic field PARALLEL to the axis of the coil
Most common copper refining processes?
- Electrolysis - Acid leaching - Smelting
5 Cost Savings benefits when using NDE for testing?
- Eliminate amount of faulty material; prevents waste - Customer satisfaction > repeat business - Manufacturing control upstream before construction stages proceed - Eliminates delivery of faulty product - Insurance costs reduced due to service reliability
2 ways Strain can be expressed?
- Engineering strain - Relative strain
Hardness testing and Manufacturing processes?
- Ensures uniformity of heat treated components for pressure parts manufacture - Completed on materials that have been cold worked, quenched and tempered, or precipitation hardened - Mill test reports are used to confirm suitability for service
3 defined groups/categories of Metallurgy?
- Extractive - Mechanical - Physical
5 criteria for conducting a Visual Examination?
- Eye to surface distance must be within 610 mm (2 feet) - Angle of view can't be less than 30 degrees to the surface being inspected - Minimum illumination of 162 lux (15 foot candles) - Small anomaly illumination required = 538 lux (50 foot candles) - Persons conducting visual inspection must be capable of reading standard J1 letters on a Jaeger eye chart
Working theory of Magnetic Particle Inspection?
- Faces of a crack will form north and south poles if a magnetic flux is established in the test piece - Particles of iron are attracted to the poles that form at the crack (90 degrees to current flow) when electrical current is applied
5 Service Reliability benefits when using NDE for testing?
- Flaws can be sized for critical engineering assessment - Remaining life span can be estimated - Online testing reduces service and production losses - Inspection intervals can be established for maximum benefit - Prevents unscheduled downtime
Structural Discontinuities?
- Flaws in the weld deposit or heat affected zone; potential for failure is directly related to its shape and location in the weld - Planar defects such as cracks and lack of fusion are sharp and pointed. These have high risk for failure - Pores and non-metallic inclusions are usually rounded and are less potential for failure
Metals that have FCC unit cell structures in the solid state?
- Gold, aluminum, silver, lead, nickel, gamma iron (iron between temperatures 910 - 1390 deg.C)
General characteristics of 'Metals'?
- Good conductors of heat and electricity - Generally malleable and ductile - Occur naturally in ores in the form of chemical compounds such as sulphides or oxides
What is Hardening for the purpose of heat treatment and whats its main difference from Annealing?
- Hardening involves heating mild steel to a temperature above the austenizing range and then cooling it RAPIDLY to increase HARDNESS by the formation of MARTENSITE - The main difference is rapid cooling instead of gradual cooling
Design requirements to approve Potable hot water heaters by means of Proof Testing?
- Heads are of the same geometry and thickness - Cylindrical shell and tubes only differ by length - Opening are the same size and type as those on the proof tested vessel
What is Case Hardening?
- Heat treatment process that produces martensite in the outer layer only, leaving the interior alloy to retain a tough ferrite-pearlite composition
Describe 'latent heat of fusion' in relation to metals.
- Het energy is added until temperature no longer increases and the cohesive bonds holding the individual atoms together break. This causes the metal to melt.
Advantages of Steel Core aluminum strand power line conductors?
- High Tensile strength
Multidirectional magnetization technique?
- High amperage power packs operate up to 3 circuits which energize one at a time. an over magnetization results in multiple directions. This requires only 1 processing step instead of 2
Properties of materials with large grain size?
- High creep/deformation resistance under constant loading - More prone to cracking
Characteristics of metals with the Body-centered cubic structure?
- High strength - Low ductility - Very resistant to shear deformities
Properties/uses for Iron-Tin Brass?
- High strength and hardness - Used in the manufacture of bearings, valves, fittings, and naval propeller castings
Properties of materials with small grain size?
- High tensile strength - Highly ductile
3 groups of Tin-Lead solders and their uses?
- High-lead (up to 80% lead), general purpose (25%-50% Tin:Lead ratio) and high-tin solders (up to 80% Tin) - High lead solders are used for joining tin-plated containers and automobile radiators
Which law of physics defines strain and what does it state?
- Hooke's Law can be used to define strain and states the stress in a solid is directly proportional to the resulting strain
How would indentation hardness testing be useful in the field?
- Identification of welding consumable misuse or ensuring proper heat treatment after fabrication/repair can be performed from the in field or in shop hardness test.
5 Material Verification benefits when using NDE for testing?
- Identify chemical property differences - Identify metallurgical property differences - Material can be identified for sorting through NDE analysis - Identify differences in zones of heat treatment - Differences in physical properties can be identified
Defects and surface conditions which can limit how effective a Liquid Penetrant test is?
- If the surface is porous - Subsurface defects - Very wide and shallow defects - Contaminated surfaces that have not been throughly cleaned - Insufficient penetrant dwell time - Surface temperature too high or low
Purpose of Tempering?
- Improve mechanical properties of the steel including: Increase ductility and toughness with slightly reduced hardness - Example: A sword that has been quench hardened and tempered will not shatter but will retain a hard sharp edge
What is the purpose of Welding Symbols?
- Included on construction drawings to clearly and completely provide the welder all the information necessary to successfully complete the required weld
Test Gauge requirements for performing a Proof Test?
- Indicating gauge is connected directly to water heater for indicating hydrostatic pressure - An additional gauge is installed when indicating gauge is not 100% visible - Dial range of these gauges is 1.5 times the intended maximum test pressure - Gauges must be calibrated
ASME Section V, Article 6 Liquid Penetrant test procedure specifications?
- Inspection conditions (ambient and UV light requirements) - Penetrant, remover, emulsifier and developer to be used - Pre cleaning and post cleaning requirements - Penetrant dwell times - Developer dwell time before interpretation
List 9 operating environment variables to consider when choosing a metal for a pressure piping application.
- Internal or External maximum pressures - Maximum and minimum temperatures - Tensile and compressive stress loads - Vibration and cyclic stress loads - Chemical corrosion exposure - Temperature gradients and thermal expansion stress factors - Stress loading on nozzle and flange connections - Impulse stresses (hammering, hydraulic shock, physical collisions, liquid slugging) - Heat conductivity
What is a Stud in reference to weld terms?
- Involves attaching a small stud, either perpendicular or at an angle, to a surface. Welding current flows directly through the stud into the surface, rather than using a welding rod.
Describe a 'Scarf' butt weld joint.
- Joining edges are machines flat and at an angle; the pieces then slide together. Scarf joints are common for Brazing.
Disadvantages of Steel Core aluminum strand power line conductors?
- Larger diameter is required to carry a given electrical load - Inner steel core is prone to corrosion - Cost more than pure aluminum lines
What is Pearlite in relation the Iron-Carbide Equilibrium diagram?
- Layered Structure (microscopically) of Ferrite and Cementite - Appears dark grained in colour and forms in iron-carbon alloys BELOW the lower critical change line (723 deg.C) - Occurs in steels and cast irons - Forms from slow cooling from 723 deg.C and occurs as a Eutectoid reaction
What is Babbitt?
- Lead-based or Tin-based alloys used to line the bearings for machinery - Vary from 80% lead: 5% tin to 80% Tin: 0% lead - Babbitt is a form of white metal - Antimony and copper are usually present as a small percentage
Characteristics of White Metals?
- Low melting point which allows for easy casting/manufacture - Strong and ductile; not vulnerable to cracking - Soft enough to contour to a shaft - Good thermal conductors to dissipate heat
What are the 4 mineral ore sources for Copper (Cu)?
- Malachite - Bornite - Cuprite - Chalocpyrite
Test records for water heaters subjected to Proof Testing?
- Manufacturer and authorized inspector must both witness the test - Form HLW-8 is completed by inspector and manufacturer designate
Define Pyrometallurgy:
- Melting the ore in a furnace to release the metal
Uses of the Knoop Hardness test?
- Microhardness test that measures hardness of micro-constituents of a matrix - Utilized in failure analysis of components and testing of extremely brittle materials
Tools for assistance with visual inspection?
- Mirrors, magnifying lenses, artificial illumination, etc.
What is a Heat Number in relation to a Material Test Report?
- Molten metal is sampled from every ladle during the smelting stage. Each one of these ladle test samples is given a Heat Number which identifies the batch - If a piece of pipe is cut, the heat number must be copied onto the undesignated piece of material.
When is Magnetic particle testing useful?
- Mostly used for detecting surface defects on ferromagnetic materials including iron, nickel and cobalt (not austenitic steels) - Sub surface discontinuities can be examined with the use of DC electrical current
Eutectic Reaction?
- No pasty state phase; liquid alloy of iron-carbon changes directly into solid state austenite and cementite - Occurs with 4% carbon content and temperature of 1130 deg.C
Define the word "Imperfection".
- Not recognized by ANSI/AWS standards but is used fairly often. Can be understood to have same definition as a "Flaw".
Describe a Flare-Bevel type butt joint.
- One edge has a curved profile while the other is flat at 90 degrees.
Interim cleaning for a LP test?
- Penetrant can be dissolved or re-emulsified so it can be washed with water - Surface is checked for residual penetrant. This is done under UV light if fluorescent dye is used. - Low pressure water is used to ensure penetrant isn't agitated out of the surface cracks
Both ductility and malleability are aspects of a materials...?
- Plasticity: the extent to which a solid material can be plastically deformed without fracture - The plasticity is dependant on temperature and pressure
Prod technique for Mag Particle Testing?
- Portable prod contacts are pressed against the test surface
Circular Magnetization (direct contact) technique?
- Produces circular magnetic fields perpendicular to the part being tested - Used for small parts with no interior openings - Circular magnetic field develops stray fields across defects lying in the same direction as the current contacts (longitudinal)
What are the 5 common stress points in a Tensile Strength test?
- Proportional Limit - Yield stress - Proof stress - Ultimate tensile strength - Final instability point
Describe the Normalizing Process.
- Raise steel temperature approx. 55 deg.C above the recrystallization temperature into the austenite region - Hold at that temperature to ensure even Normalizing throughout - Cool in still air at a rate not exceeding 100 deg.C/hour - Furnace should have an oxygen free atmosphere to prevent oxide scale formation
Properties of pure copper?
- Reddish brown in colour - Weighs 20% more than iron - Tough, malleable, ductile and can be forged into sheets/bars or drawn into wire - Excellent electrical and heat conductivity - Highly resistant to corrosion
Properties of pure Iron?
- Relatively soft - Ductile - Low strength - Possesses few of the noble properties commonly associated with steel
3 purposes of Normalizing?
- Relieve internal stresses from welding, forging or machining - Refine grain size and promote uniform composition to increase ductility and toughness - Improve machinability
Describe the Knoop Hardness test.
- Rhombic-based pyramidal diamond that produces a diamond shape is used - Long diagonal to short diagonal uses a 7:1 ratio in length - Depth point in indentation is 1/30th of the long diagonal length - Typical test loads are below 500 G; 100 G most common - Strictly confined to laboratory applications
Give 4 primary benefits to using NDE techniques.
- Safety - Cost Savings - Service Reliability - Material verification
ANSI established what 5 minimum requirements for manufacturers to identify pipes, fittings and flanges?
- Size - Wall Thickness - Schedule Designation - Material Designation - Manufacturers stamp/symbol
Properties of Tin?
- Soft, white metal with good corrosion resistance and lubricity
Purpose of Spheroidizing?
- Soften higher carbon alloy steels and allow more formability
Define the Proof Stress point in regards to a tensile strength test.
- Sometimes referred to as the Yield stress of the material because it is more definitive. Points A and B aren't always obvious - This is the point where the specimen has undergone a certain value of strain of 0.2% (0.2% proof stress)
Define the 'Root Opening' of a weld.
- Space intentionally left between the 2 joined surfaces (not completely butted together) - This gap is clearly visible when the weld does not fully penetrate the material
Charpy impact test?
- Specimen is held at each end and is struck in the middle (force is vertical)
Izod Impact test?
- Specimen is held on one side of the notch and is struck on the other side of the notch. - Force is horizontal
Describe the Quenching process.
- Steel with a carbon content over 0.8% is heated above the upper transformation temperature and held there to allow the formation of austenite - Part is then quickly immersed in a liquid such as brine, water or oil
Describe Ferrite.
- Structural name for iron in the BCC form and occurs at temperatures below 912 deg.C - Maximum amount of carbon atoms that ferrite can contain is .025% at 723 deg.C - Ferrite describes a structure - not a composition - Above 771 deg.C = Paramagnetic, Below 771 deg.C = Ferromagnetic
Describe Austenite.
- Structural name of Iron in the FCC form; also referred to as 'Gamma Iron' - Contains dissolved carbon up to 2% concentration - All quenching heat treatment procedures must begin from the gamma iron phase - Non-magnetic allotrope of Iron that exists of the critical Eutectoid temperature of 727 deg.C - This state exists at room temperature in some stainless steels
What are 4 methods of Destructive Testing?
- Tensile test (tests tensile strength) - Hardness Tests - Impact tests - Proof tests
9 fundamental steps to performing a Liquid Penetrant examination?
- Test Preparations - Pre Cleaning - Dye penetrant application - Interim cleaning - Drying - Developing procedure - Inspection - Final Cleaning - Quality control
Describe the "Bayer Process" and what does it achieve?
- The Bayer process produces Alumina from Bauxite - Bauxite ore is crushed/milled and then ran through a caustic leaching operation - the final product is Alumina
What is Polymorphism and what does it have to do with metals?
- The ability of a metal to change its unit cell structure through varying temperature ranges. - Most metals exhibit this property; most important for the study of iron.
What is Impact Testing and what are the 2 common test procedures?
- The ability of a metal to resist fracture when subjected to shock loading; energy required to break a piece of metal with standardized shape and a cross-sectional area of 1 cm squared. - The Charpy and Izod tests
What is the most important factor when using the indentation by load technique for Hardness Testing?
- The ability to provide indentations that are geometrically similar and well defined.
2 factors that are considered when choosing the type of steel for a particular job?
- The basis of safety - The metal survivability A factor of safety must always be retained.
What is the allotropy of Iron?
- The change in atomic cell structure dependant on temperature - Various physical forms of metals can affect their: melting point, hardness, metal solubility, and alloying chemistry.
Describe Cementite.
- The common name for Iron-Carbon in the form of molecular iron carbide (Fe3C) - High carbon content and very brittle - normally considered a ceramic in its pure form
The main concern with metallurgy and industry is...?
- The complexity of the solid-to liquid-to solid phase changes metals go through as they are refined - The chemical and physical properties exhibited by them during these transitions
At least 2 separate examination techniques are used when conducting a Mag. particle test. What is the most important part of the 2nd test that is completed?
- The flux lines should be perpendicular to the lines used for the first test. This is to ensure sufficient overlap and to inspect for any defects going in alternate directions.
4 varying factors that determine Iron-Carbon Equilibrium?
- The initial concentration of carbon in the ferrite mixture - Temperature - Cooling rate - Presence of other alloy metals
Define True Strain.
- The instantaneous change in length compared to the original length
How do you specify the size of a fillet weld?
- The lengths of the legs: the perpendicular distances from the parent metal to the toes of the weld.
Define Ultimate Tensile Strength:
- The maximum load a specimen sustains during a test - The UTS may or may not equate to the strength at fracture - Brittleness and ductility will affect this measurement, as well as temperature
What is the piping DN#?
- The metric conversion for NPS pipe (inches -> mm)
Describe Carburizing as a Heat Treatment hardening process.
- The part is heated to the transformation temperature in an atmosphere of carbon monoxide (CO). Carbon diffuses into the surface of the metal increasing martensite formation in this area. The part is then later quench hardened - Example would be Carburizing with an acetylene rich torch and then quenching in oil
Describe the Peritectic reaction in relation to the upper left of the Iron-Carbide Equilibrium diagram.
- The point where liquid delta iron, in the BCC form, changes directly into solid austenite without going through a pasty state phase - Occurs at 1492 deg.C
Define the Ultimate Tensile Strength in regards to a tensile strength test.
- The point where plastic deformation becomes unstable and a narrow region forms in the specimen - This is the peak maximum value of nominal stress during the test (X-axis)
What is Tempering in relation to hardening?
- The process of heating already quenched steels to a specific temperature below their transformation ranges, which forces saturated carbon in the martensite back into stable iron carbide (cementite) and ferrite mixture, and then cooling to room temperature at a rate that won't reintroduce martensite
Define Engineering Strain.
- The ratio of change in length : the original length of the specimen
The letter scheme used to describe the results of a Rockwell Hardness test define what?
- The scale symbol (type of material tested) - Type of indentor used - Major load #
Sub-critical Annealing (Process annealing)?
- The steel is heated to just below its austenite transformation temperature and cooled slowly to reduce internal stresses
What is Shear Strength?
- The strength of a material or component against the type of yield or structural failure when the component fails in shear.
Define the Yield Stress in regards to a tensile strength test.
- The stress at which yielding occurs across the whole specimen - Deformation is purely plastic and non-reversible
Define the Proportional Limit in regards to a tensile strength test.
- The stress point which slip (glide) due to dislocation movement occurs - Graph is linear up to this point - Above this point is where elastic to plastic transformation occurs
Define Elastic Strain.
- The stretching of a material within its elastic limit; the limit of where it will return to its original dimensions when the stress is removed
Define 'Extractive' Metallurgy.
- The study of extraction and purification of metals from their ores. This includes a stepped process which can utilize Pyrometallurgy, Hydrometallurgy or Electrometallurgy
What is Physical Metallurgy?
- The study of the structure of metals - property of metals are intimately related to their structures - The physical metallurgy - or structure of a metal - can be changed by modifying chemical composition, alloys and heat treatments
What is Mechanical Metallurgy?
- The study of the techniques and mechanical forces that shape and make finished forms of metal - The study of the effects of stress, time and temperature
Purpose of the Lower Critical Change Line on the Iron-Carbide Equilibrium diagram?
- The temperature at which an iron alloy of ANY carbon composition returns to a BCC unit cell structure. The diagram indicates this temperature at 723 deg.C
During the Inspection stage of a LP test, how is the operator responsible for the results?
- They are responsible for ambient light or UV light intensity, ensuring light levels are constant.
Basing Proof Test results on Tensile Strength?
- This method is used when no yielding occurs during the proof test.
Working principle of the developer in a LP test?
- Through lateral expansion of the penetrant medium within the crack, the crack width is enlarged and the visibility of even the smallest cracks is visible
What alloy is added to Naval Brass? Why?
- Tin is added to brass to make "naval brass" - Superior resistance to saltwater corrosion results
Purpose of heat treating a metal?
- To force a physical and/or chemical transformation in the alloy and then cool it at a rate that the material retains the desired properties - Heat treatment for the purpose of stress relieving is the main concern for power engineers
What are 4 major factors to a successful Magnetic Particle Test?
- Type of Magnetic particles - Surface conditioning before testing - Proper Examination techniques - Acceptance criteria for testing
Points typically listed in a Metal Specification Chart?
- Type of metal according to ASTM # - Title including composition and how its welded - Commonly used type/grade within specification - Description of material - Its end use
5 pieces of information included in a Welding Symbol used for a construction drawing?
- Type of weld - Size of weld - Spacing requirements for the weld - Exact location of the weld - Special procedures for the weld
When molten metal cools and solidifies, what action do unit cells take?
- Unit cells become packed together to form 3 dimensional crystals that occupy a space lattice. Further growth of these crystals form dendrites (evergreen tree looking crystals)
2 forms of Visual Inspection?
- Use of the naked eye - Remote visual inspection with electronic video systems (must be as good or better as the naked eye; high resolution)
Circular magnetization (central conductor) technique?
- Used for tubing or ring shaped parts - Magnetization is achieved by surrounding the the test piece by a circular magnetic field so longitudinal cracks and star shaped cracks can be detected
What is Seam Welding?
- Used on thin materials - A continuous weld is is made where the 2 surfaces butt or overlap each other - Electrodes usually in the form of wheels press the pieces together from opposite sides. The electrodes travel along the seam applying current to fuse them together
Plug or Slot welds?
- Used to join 2 relatively flat pieces with a series of small welds that are deposited into drilled plugs or machined slots
Describe what a Staggered Intermittent Fillet weld is.
- Used where strength of a joint is not critical or where complete sealing of a joint is not necessary - Length of individual welds as well as pitch (centre to centre) must be considered
Why is it hard to compare Impact tests according to the different standards regulating them?
- Varying parameters of the striker, machine and test pieces can offset test results slightly and are therefore hard to compare
Main advantage of Knoop testing?
- Very small sample required for a number of possible tests
Types of NDE examination?
- Visual - Magnetic particle - Ultrasonic - Liquid Penetrant - Acoustic Emissions detection - Leak testing - Radiographic
Define 'Unit Cells' in relation to the atomic structure of metals.
- When a metal changes state from molten to solid, the rigid atomic structure of the atoms settles in 1 of 3 possible configurations: 1) Face-centered cubic (FCC) unit cells 2) Body-centered cubic (BCC) unit cells 3) Close Packed Hexagonal (CPH) unit cells
Considerations a boiler inspector would make when evaluating weld imperfections?
- Whether or not the defect is likely to lead to equipment failure. This requires experience and knowledge of the welding process and procedure used, the metallurgy of the base/filler metals used, and design of the weld joint - Evaluation also involves checking specifications, standards and codes were followed which provide good criteria for acceptance or rejection
How do you determine what the shape of the specimen should be for a Tensile Strength test?
- Whether the test is using the ASTM E8 or ASTM D638 procedure
Errors in determining mean diameter from a Brinell test are usually cause of incorrect instrument readings or a poorly defined indentation boundary. Error in reading a Brinell microscope should not exceed _____ mm over a 7mm scale.
.01 mm over a 7mm scale
American Society for Testing and Materials (ASTM) piping specifications "A" and "B" are defined as what 2 categories?
1) "A": represents all carbon steels and alloys 2) "B": represents all non-ferrous materials
2 types of Indentors for the Rockwell test?
1) 120 degree diamond cone (Rockwell C test) 2) 1.6 mm ball (Rockwell B test)
2 main categories of materials testing?
1) Destructive: purposely causes damage 2) Non-Destructive: Retains its integrity and usefulness
4 Vickers Hardness Test Guidelines?
1) Full test load must be applied for the required time - usually 15 seconds 2) Spacing of indentations is important: Indentations should be 2.5 times indentation-measurement away from the edge of the specimen 3) Diagonals must be measured perfectly centred with the microscope; any offset will skew accuracy 4) Micrometer microscope should be calibrated against a stage microscope
Steel properties as carbon content increases? Decreases?
1) Hardness and brittleness increase as carbon content increases 2) Ductility, softness and weldability increase as carbon content decreases
Describe the Full Annealing Process.
1) Heat the steel to just above the transition temperature required to produce Austenite (temperature depends on %Carbon) 2) Temperature required for steels 0.8% C and greater is 723 deg.C 3) Hold temperature to allow for uniform crystal restructuring 4) Cool very slowly to room temperature; maximum rate of 38 deg.C/hour. Typical procedure is to leave in the annealing furnace or pack in sand or some other type of insulator
3 types of defects that NDE is used for discovering?
1) Inherent defects: created during initial production 2) Processing defects: created during processing/construction stages 3) Service defects: created during the service life
All piping, tubing, fittings and structural materials used in Plants can be categorized into 6 groups of metals:
1) Low carbon steel (mild): < .30% carbon 2) Medium carbon steel: >.30% - <.60% 3) High carbon steel: >.60% - <1.5% 4) Cast Irons: Carbon content = 2% and 6% 5) Alloy steels: Low carbon steels with alloys including manganese, chromium, vanadium, nick, moly, tungsten, and other elements 6) Non Ferrous metals: Copper, aluminum, brass, nickel, tungsten, zirconium
3 Hardness testing categories?
1) Microhardness: < than 200 g load 2) Low-load hardness testing: 200 g to 3 kg load 3) Macrohardess testing: > 3 kg load
Weld Discontinuities which may lead defects are usually caused by what 4 factors?
1) Not following qualified weld procedures 2) Altering weld designs 3) Substituting or using defective materials 4) Substituting or using defective electrodes
Hydrostatic Deformation Test Procedure steps:
1) Outer surface of test piece thoroughly cleaned and brittle coating is applied (indicates displacement) 2) One half of anticipated MAWP is applied gradually. 3) The remaining half of pressure is increased in steps of 1/10th anticipated MAWP, with short breaks in between these stages 4) Test stopped when MAWP pressure has been reached or at the first sign of yielding 5) Pressure reduced to zero to inspect for strain displacement.
1? B31.1 lists codes for what? 2) B31.3 lists codes for what? 3) B16.5 lists codes for what?
1) Power piping 2) Hydrocarbon process piping 3) Pipe flanges and fittings
What are the 5 specific Examination Techniques for Magnetic Particle Testing?
1) Prod Technique 2) Longitudinal Magnetization Technique 3a) Circular Magnetization Direct Contact Method 3b) Circular Magnetization Central Conductor Method 4) Electromagnetic Yoke Technique 5) Multidirectional Magnetization Technique
Main differences between the Brinell test and the Rockwell test?
1) Rockwell test is a measure of penetration rather than diameter 2) Rockwell test applies 2 loads; the first one designated for zeroing before the 2nd test is completed. First load is 10 kg and second load is 60, 100 or 150 kg. 3) The Brinell uses a 10 mm diameter ball where as the Rockwell test has multiple indentor types; 120 diamond cone and 1.6 mm ball, etc.
Describe the basic procedure to perform an Impact test.
1) Specimen formed into rectangular bar with 45 degree V notch removed 2) Specimen placed in tester anvil 3) Bar is struck with striker mounted on a pendulum, causing the piece to break. The height the pendulum rises compared to height from original position is measured. 4) The difference in potential energy before and after the strike is a measure of the energy absorbed in the fracture.
Give 3 examples where weld defects could occur in the actual weld joint.
1) Tee and Corner joints that are highly restrained 2) Misaligned butt joints 3) Steep transitioned thick and thin lap joints
2 ways to measure indentation in regards to Hardness Testing?
1) Use a specific force and measure the penetration depth of indentation OR area of indentation 2) Measure the load that is applied to the inventor mechanism
7 advantages of the Vickers Hardness test over other hardness tests?
1) Vickers method accepted worldwide 2) Diamond indentor is accurate and shape isn't distorted under load 3) Impressions are smaller, thus damage is limited to finished products 4) Light loads allow testing of thin/vulnerable materials 5) Only one scale for the hardness of all materials 6) Damage to the indentors is more readily visible as viewed under microscope 7) Diagonal square impression is more accurately measured than the diameter ball impression
2 types of developers for LP testing? Means of application of developer?
1) Wet and Dry developers 2) Spraying by use of aerosol cans, LP air, spraying pistols, electrostatic pistols * Brushing or painting on developer is NOT acceptable *
Most common Brinell test ball diameter?
10 mm
How many atoms make up a Close-packed hexagonal structure?
17 atoms total
Describe a Flare-V butt joint.
2 surfaces with curved profiles (90 degrees usually) are brought together to form a weld groove with curved sides
How deep can defects be examined with DC current Mag. Particle testing?
4 mm
Rules for Hydrostatic testing of water heaters does not allow test pressure to increase ___ spa above MAWP.
69 kPa
Ductility is maximized in what ratio Copper:Zinc?
70% copper to 30% zinc. This composition is used in cartridge brass
# of atoms contained in a BCC structure?
9 atoms total
Define welding Defect:
A discontinuity or flaw, whose size, shape, location, or orientation creates a substantial chance of material failure; the discontinuity is detrimental to the integrity of the pressure equipment
Define 'Evaluation' in relation to NDE.
A judgment made based on codes, standards or engineering assessment on the significance of an indication. Evaluation determines if the indication is detrimental to the service life of the component.
Define 'Indication' in relation to NDE.
A noticeable response to a NDE test that requires interpretation to determine its significance
Define 'Interpretation' in relation to NDE.
A study to determine the cause of an indication (labelling or naming the discontinuity, i.e. cold lap, fatigue, crack)
What is a Box Weld?
A weld that travels around corners.
Referring to the Eutectoid Reaction Region, Define the following points: - A1 - Ar1 - Ac1
A1: Critical temp. between pearlite phase field and austenite phase field (eutectic transformation line @ 723 deg.C) Ar1: Critical temp. between Pearlite and Austenite during cooling Ac1: Critical temp. between Pearlite and Austenite during heating
Referring to the Eutectoid Reaction Region, Define the following points: - A3 - Ar3 - Ac3
A3: Critical temp between Ferrite-Austenite phase field and austenite phase field Ar3: " but during cooling stage Ac3: " but during heating stage
Referring to the Eutectoid Reaction Region, Define the following points: - Acm - ARcm - ACcm
Acm: Critical temperature between Cementite-Austenite phase field and Austenite phase field ARcm: " but during the cooling stage ACcm: " but during the heating stage
Aluminum alloys used for transmission lines?
Aluminum-magnesium-silicon alloy that has a high conductivity (no steel core)
Define the word "Flaw".
An imperfection in the material that may or may not be harmful.
Define Discontinuity:
Any local variation in material continuity; including changes in geometry, properties of composition or structure, holes, cavities, or cracks.
Name of the ore that Aluminum mostly originates from?
Bauxite - a reddish brown ore mostly sourced from Jamaica and Australia
Examples of real world products that are typically Case Hardened?
Bearings, machine tools, crankshafts, cams, valves, gears, rollers, hand tools
2 most common Copper Alloy groups?
Brasses and Bronzes
How are Aluminum MMC's made?
By solidifying molten alloys that have been reinforced with boron or ceramic fibres
Percentage carbon content in Carbon Steels and Cast Iron?
Carbon Steels: Alloys containing 2% or less carbon Cast Iron: 2% - 6% carbon
What are 2 common Thermochemical case hardening processes for low alloy steels?
Carburizing and Nitriding
90 % of the worlds Primary copper occurs in which types of Ore?
Chalcopyrite and Bornite
Examples of BCC metals?
Chromium, tungsten, molybdenum, vanadium, alpha iron (solid state iron below 910 deg.C) and delta iron (iron above 1390 deg.C)
Basic composition of Brass?
Copper and Zinc
ASME section 3 and 8 use design methods according to what?
Design-by-analysis
ASME section 1 uses experience based design methods, known as...
Design-by-rule
Define 'Weld Depth'.
Distance from the surface of the material to the root of the weld.
Groove welds are almost always used for Lap joints. True or False?
FALSE. They are mostly used for BUTT joints
Liquid Penetrant testing can discover sub surface cracks. True or False?
False.
What is one common way to group discontinuities in welds?
Group them according to their causes. ie) - Weld Procedure used (wrong procedure) - Weld Design (wrong design) - Metallurgical causes (poor quality)
Proper reporting of a Vickers hardness result?
Hardness measurement > HV (hardness vickers) > Load measurement
Characteristics of CPH structured unit cells?
Intermediate strength and Intermediate ductility
What are the defining temperature ranges for 'Low Temp' and 'High Temp' carbon steels?
Low = -45 deg.C to less than 425 deg.C High = -29 deg.C to less than 425 deg.C - These limits are the lowest temperatures expected from either the process fluid or the external operating environment. - This design specification is based off the Charpy impact test for Brittleness
Three grades of Carbon Steel?
Low carbon steel: .04% to .30% carbon (mild steel) Medium carbon steel: .31% to .60% carbon steel High carbon steel: .61% to 1-1.50% carbon steel (tool steel)
Most common steels in a Power Plant?
Low carbon steels and Alloy steels
Design, Construction and Installation of boilers/pressure vessels require in part the submission of...?
Material specifications, size, schedule, and primary service rating of all primary piping and fittings used in that construction.
2 types of magnets that can be used for Mag. Particle inspection?
Permanent magnets or Electromagnets
Transformation properties of Quenching?
Strength and Hardness INCREASE as Toughness and Ductility DECREASE
Metals can exist in 3 common physical states depending on what?
Temperature and pressure
Who is responsible for the regulatory domain of metal specifications in North America?
The ASME is responsible for specifications, tolerances and construction and writing these codes. ANSI then approves these codes and signs off on them.
Define 'Root' of a weld.
The bottom edge of a weld OR the deepest point of a weld
What is weld 'Reinforcement'?
The distance between the peak of the weld and the surface material.
What is the Critical Cooling Rate in regards to Hardening?
The slowest that a material can be cooled before undesirable Pearlite is formed instead of Martensite
Define the Final Instability Point in regards to a tensile strength test.
This is the failure point at which fracture occurs
Unidentified metals should never be used for construction anywhere in a plant. True or False?
This is true. There are surprisingly tons of inferior counterfeit products out there. Ensure that all steel products designated for pressure service are marked and stamped
A "J" groove is essentially a half "U" groove. True or False?
True
As piping schedule increases, wall thickness increases. True or False?
True
Hardness tests can confirm required strength of weld and base metal repairs, or any abnormalities in the HAZ (Heat Affected Zone). True or False?
True
Heat Soaking for too long a period encourages grain enlargement in any annealing procedure (no matter what %C content) and increases brittleness in the metal. True or False?
True
Notch defects can reduce fatigue resistance of welded joints and cause failure even though the yield strength of the original base metal was never exceeded. True or False?
True
Planar-type defects can cause rapid propagation of cracking through a weld. True or False?
True
Plastic strain refers to irreversible defloration of a material - which it has exceeded its elastic limit. There is no mathematical equation to relate the stress to plastic strain. True or False?
True
Results from a Proof test establishing MAWP must be analyzed, witnessed and approved by an authorized inspector. True or False?
True
Stress = E (mod. of elasticity) X Strain. True or False?
True
Stress = Load/cross-sectional area. True or False?
True
Stress is calculated from the load inflicted on the specimen and strain and is a measure of the elongation. True or False?
True
The behaviour of ferritic steels under notch conditions cannot be predicted. ie) some materials that are ductile under tension will behave brittle when they are notched. True or False?
True
The welding symbol for a groove weld indicates the specific groove configuration to be used. True or False?
True
Ultimate Tensile Strength measurement will fluctuate with temperature for different materials. True or False?
True
Vickers hardness # is determined using a table for the appropriate load, identifying the average diagonal value and reading the appropriate hardness value. True or False?
True
Water Heater parts should withstand (without major deformation) a Hydro pressure that is minimum 3 times greater than the desired MAWP. True or False?
True
Welding Procedure Specifications should be supported by a Procedure Qualification Report that has either Rockwell Superficial Hardness or Vickers Diamond Pyramid tests completed. True or False?
True
The Rockwell hardness test is not considered a bulk hardness test. True or False?
True, but it is a Macrohardness test.
Butt welds should have traverse hardness testing completed throughout the HAZ, weld metal and base metal. True or False?
True.
Commercial piping sizes 6" in diameter and larger are only manufactured in EVEN inch number. True or False?
True.
Developer may take up to 60 mins to activate when testing Austenitic steels using the LP test procedure. True or False?
True.
Nitriding produces the hardest surface out of all Hardening processes possible. True or False?
True.
Quality Control: "ASME Section V, Article 6 deals with maintaining the highest quality for liquid dye penetrant processes to provide consistent inspection results in accordance with article 24 SE standards: 1, 2, 3, 4". True or False?
True.
Visual Inspection is the most widely used technique for surface inspection, alignment of mating surfaces, and evidence of leaking. True or False?
True.
Shear strength of metals is primarily determined by the type of Unit Cell Structure exhibited. True or False?
True. 1) HIGH ATOM PACKED DENSITY FCC structures are very ductile (easy to elongate) with a low shear strength - Ex.) Lead. 2) LOW ATOM PACKED DENSITY BCC structures have high hardness and a high shear strength. Ex.) Iron
It is important to identify discontinuities before examining defects. True or False?
True. Discontinuities should be grouped according their identification. ie) - Dimensional - Structural - Base metal
Ductility and malleability are not always coextensive. True or False?
True. Gold is both ductile and malleable while Lead has a very low ductility but high malleability.
Tin-based babbitt is used primarily for High Speed-Heavy load applications and Lead-based babbitt is used for lower speeds and lighter loads. True or False?
True. Lead based babbitts are tougher but less ductile than the tin based babbitts.
FCC metals will have notch behaviour similar to their regular tensile properties. If they are brittle in Tension, they will be brittle when notched. If they are ductile in Tension, they will be ductile when notched. True or False?
True. Low temperatures will not alter these characteristics either.
All high alloy steels have less than 0.8% carbon in their alloy. True or False?
True. No transformation products other than Pearlite and Ferrite are produced during Normalizing
Stress is Inversely Proportional to the cross sectional area of an object under load. True or False?
True. Stress becomes greater as cross sectional area decreases.
The Vickers Hardness test can be considered a low-load microhardness test or a macro hardness test. True or False?
True. Test loads range from 1 g to 120 kg. The diamond test point is used to measure hard materials at high loads, of small areas.
Normalizing produces the toughest possible steels. True or False?
True. The ASME codes require normalized and tempered materials in any of their specifications for steel forgings and castings. These products are just hard enough to machine freely leaving the surface free of tears.
Weldability is more difficult for higher content carbon steels and even more difficult for cast-iron metals. True or False?
True. The higher carbon content, the harder to weld.
In all piping, the outside diameter is mostly constant and varying wall thickness determines inside diameter of the pipe. True or False?
True. The thicker the wall thickness, the higher the pipe schedule rating.
Manufacturers are at times responsible to provide a procedure for visual examination. True or False?
True. These procedures must include: - How examination is performed - Type of surface condition and cleaning procedures - Methods/tools for surface preparation for cleaning - Whether direct or remote viewing is used - Special illumination instruments that should be used - Sequence in which the operation is performed - Critical data points that should be recorded - Report forms or statement of examination results
All designations for pressure piping and fittings in North American plants use an ASME or CSA specification. True or False?
True. This a a requirement stated within the regulations to do with boiler and pressure vessel construction
Metals manufactured for pressure equipment MUST be tested before service. True or False?
True. This testing involves not only the parent metal but the weld metal as well.
Important factors to consider when conducting a Tensile Test?
True. To ensure valid results, consideration is given to the specimens shape and dimensions, plus the choice of grips and faces.
ASME Sections 1 and 8 allow a Burst Test to be stopped before actual bursting occurs. True or False?
True. When the test pressure justifies the design pressure, it can be stopped. However, the test specimen should not be designated for service.
What is the first step in identifying imperfections in welds?
Visual Inspection - which can reveal up to 80% of weld imperfections. The remaining 20% can be detected by non-destructive techniques.
Cooling mediums for Hardening Processes?
Water, brine, oil, air and is usually promoted by agitation
Property most affected by weld defects?
Weld strength
When can Proof testing not be used to pass a pressure part for construction?
When Section 1 of the ASME Codes (Rules for the Construction of Power Boilers) already has published design rules for that specific component. It is for this reason Proof Testing is seldom employed and is only used for very unique designs.
When are Fillet welds used?
When the 2 adjoining weld surfaces are 90 degrees to each other. The fillet weld is deposited into the 90 degree joint and assumes a somewhat triangular cross-section.
Surface conditioning before mag particle testing is normally not necessary but should be used when?
Whenever surface irregularities can mask indications
When conducting a tensile strength test, it is important the break occurs where?
Within the gauge length.
Materials that possess CPH unit cell structures?
Zinc, magnesium, cadmium, titanium
Describe Eutectoid Steel.
- 0.8% Carbon exactly - Made of 100% Pearlite (layered Ferrite and Cementite) - Used for railway rails
What is the lowest melting point of any iron-carbon mixture according to the Iron-Carbide Equilibrium diagram?
- 1130 deg.C and at 4% carbon concentration; austenite and cementite are formed simultaneously
Face-centered Cubic (FCC) unit cells?
- 14 atoms make up the FCC cell - Properties include: high ductility, low shear, low tensile strength, but good thermal and electrical conductivity
