Destructive Testing

Question 1

Definition of strain

Answer 1

Strain.- Term used to describe the amount of deformation of a part when stressed.

Question 2

Definition of stress

Answer 2

Stress :- Internal resistance that is offered by the metal when an external force is applied to it.

Question 3

Definition of hardness

Answer 3

Hardness:- The ability of a material to withstand indentation or abrasion.

Question 4

Definition of toughness

Answer 4

Toughness: - The ability of a material to withstand shock or impact loading.

Question 5

Definition of ductility?

Answer 5

Ductility:- The ability of a material to be drawn or stretch without fracture or crack.

Question 6

Definition of elastic

Answer 6

Elastic Force:- When a stress is applied to a material no permanent forming will occur in the elastic zone and after this stress is removed it will return to the original structure.

Question 7

Definition of impact test?

Answer 7

Impact Test:- Are employed to determine the behaviour of material when subjected to shock load.

Question 8

Definition of vessel

Answer 8

Closed container designed to hold gases or liquids at pressure different from the ambient(outside) pressure

Question 9

Definition of a heat exchanger

Answer 9

Heat Exchanger: two fluids with different temperatures flow thru, one thru tunes and other outside tunes but inside shell. Heat is transferred from one fluid to the other thru tube walls from tube side to shell side or visa versa.

Question 10

Explain why Hardness tests are carried out in welding in the Fabrication environment.

Answer 10

To determine if the weld metal matches that of the parent metal and if a cross section of a joint is subjected to hardness tests, the relative values in the weld, the HAZ and parent metal can be investigated.
b.) High values in the HAZ will indicate a fast quench condition and may suggest the necessity of changes in the welding technique in order to increase the heat input and reduce the quenching effect and hardness.
c.) The result my demand a change in either parent metal or electrode.

Question 11

Discuss 5 precautions to be observed when performing a Hardness Test.

Answer 11

Surfaces to be tested should be flat and free from ridges.
b.) Impressions should be taken from representative locations.
c.) Specimen should be firmly supported.
d.) Load should be applied normal to the surface.
e.) Take care when testing soft and thin materials.

Question 12

Name two main tests types of Impacts Tests found?

Answer 12

A.)Charpy V-Notch- Specimen struck in the middle.
b.) Izod- Specimen gripped at one end and loaded as a countless beam.

Question 13

Name two properties that are indicated by a notch impact test,

Answer 13

a.) Notch Sensitivity.
b.) Notch Toughness.

Question 14

Name 3 factors necessary for Brittle Fracture.

Answer 14

a.) Sufficiently low temp.
b.) Presence of a notch.
c.) Stress (triangle).

Question 15

explain why a Charpy V notch impact test are employed in a welding and fabrication environment

Answer 15

The test applied is one in which a notched specimen is broken by a swinging hammer and the amount of energy required to break the specimen is recoded. The notch in the specimen will be on the opposite of the swinging hammer.

Question 16

fully explain CTOD testing?

Answer 16

The test is performed by placing the specimen into a three point bending and measuring the amount of crack opening.
b.) This is done by means of a strain gauge attached to a clip placed between two accurately positioned knife edges at the mouth of the machined notch.
c.) As bending proceeds, the crack tip plastically deforms until a critical point is reached when the crack has opened sufficiently to initiate a cleavage crack

d.) As a rule of thumb, a COD value of 0.1mm and 0.2mm at the minimum service temperature is regarded as demonstrating adequate toughness.

Question 17

What does a Metallographic test (Macro) - examination reveal.

Answer 17

a.) Soundness of welds.
b.) Number of weld passes
c.) Heat affected zone (HAZ)
d.) Location and depth of penetration.

Question 18

Name two main types of Metallographic tests?

Answer 18

a.) Macro Specimens - Cross section (macroscopic) examination of plain C/S welds.
b.) Micro Specimens - Small defects at high magnification.(Microscopic examination-mirror like) etching.

Question 19

Weldability Test?

Answer 19

-Is the ability of the metal to be welded under the fabrication conditions imposed, into a specific, suitably designed structure and to perform satisfactory in the intended services.

Question 20

Name two (2) common Weldability tests for Metallographic Tests.

Answer 20

A. Controlled Thermal Severity Test. (CTS)
b.) Cruciform Test - Is a modification of a double “T” Joint originally for weld metal studies.

Question 21

Controlled Thermal Severity Test ? CTS

Answer 21

The Controlled Thermal Severity Test Carenon is a of to plates, one square and one rectangular.
b.) The Square plate is 3” on a side and is fastened by a “ bolt through its centre to the rectangular plate and anchored by welding.

c.) The test weld at the right side of the specimen is called the bithermal weld because the plates supply two paths for heat flow, one in each plate.
d.) The test on the left side is called the trithermal weld since heat can flow in one direction in the top plat and in two directions in the bottom plate, or a total of three plates.
e.) The contracting surfaces are ground before assembly to ensure efficient heat flow.
f.) After the specimen is assembled and has cooled to room temperature, the bithermal weld is deposited, the specimen is allowed to cool to room temperature and the bithermal weld is deposited, the specimen is allowed to re-cool and the trithermal weld is deposited.
g.) After a hold for 72 hours at room temperature the degree of cracking is determined by measuring the crack length of three metallographic specimen’s cur from cross sections of the weld.

Question 22

Name some properties of the metal that is usually determined from Tensile Test.

Answer 22

a.) Ultimate Tensile Strength
b.) Yield strength
c.) Percentage reduction in area
d.) Percentage elongation

Question 23

Name two Basic types of Bend Tests

Answer 23

á.) The Guided Bend Test
b.) The Free Bend Test

Question 24

What is a Guided Bend Test?

Answer 24

The test is carried out by preparing specimens and bending them in a special jig, the dimension of which vary with specimen thickness.
b.) Used in operator and Procedure Qualification
c.) Determine the ability of a welder to make sound welds.
d.) Determine the suitability of Welding Procedure for Construction.
e.) To prevent stress raisers and premature failures.

Question 25

List three types of basic Guided bend tests for welded but joints in a plate and what type of defects are revealed by each test

Answer 25

a.) Face Bend - The specimen is bent so that the face of the weld is in tension and it reveals the general quality of the weld and surface defects.
b.) Root Bend - The specimen is vent so that the root of the weld is in tension and the test reveals any lack of penetration or lack of fusion at the root off the weld.
c.) Side Bend - The specimen is bended sideways, and this test is preferred for double “V” butt welds for the revealing of internal root defects.

Question 26

What does the fracture surface of a Nick Break Test reveal?

Answer 26

a.) It reveals the internal stresses such as Porosity.
b.) Slag inclusions,
c.) Lack of Penetration.
d.) Lack of fusion.

Question 27

Name three types of Measuring Equipment.

Answer 27

a.) Thermo couples- High temp-temp of furnaces (stress relieving)
b.) Surface pyrometers - Used in a Welding shop.
c.) Indication crayons - Used by Inspectors

Question 28

Why is a Pneumatic Pressure Test dangerous?

Answer 28

a.) It is heavier than air and displaces all oxygen.
b.) Contain a great amount of stored energy when rapidly expanded (| 100 times).
c.) Invisible and deadly.
d.) Minimum brittle fracture temperature could be exceeded when not controlled.

Question 29

What can be done to increase the Fatigue Life of a welded structure?

Answer 29

a.) Reduce stress concentration at toes of welds.
b.) Contour weld joints by grinding smooth.

Question 30

What is Miner’s Ruler

Answer 30

-It is to estimate fatigue life left of a sample which has undergone cyclic stresses at varying amplitudes.

Question 31

What is Tensile Test?

Answer 31

it is the resistance of a material to a force that is acting to pull it apart.