Chapter 9: Study Guide Summary

Question 1

What are typical internal weld discontinuities?

Answer 1

• Incomplete fusion
• Slag inclusions

These can affect the integrity of the weld.

Question 2

Answer 2

Arc Strike

Question 3

True or false: Weld spatter usually has associated magnetic particle indications.

Answer 3

FALSE

Unless there are other discontinuities, weld spatter typically does not show magnetic particle indications.

Question 4

What must be done during reinspection after grinding out a discontinuity?

Answer 4

Use a more sensitive test technique to guarantee the discontinuity is removed completely.

Care must also be taken not to reduce the cross section below allowable tolerances.

Question 5

What are examples of surface discontinuities in welds?

Answer 5

• Cracks
• Inadequate penetration
• Porosity
• Slag lines
• Undercutting

These can result from improper welding practices.

Question 6

What are grinding marks in welding?

Answer 6

Variations in thickness above and below the base metal due to uneven grinding

Result in sharp contours around the edges of the grinding mark.

Question 7

What are common causes of nonrelevant indications?

Answer 7

• Geometric or section changes
• Improper surface preparation
• Excessive magnetization
• Magnetic writing
• Permeability variations
• Residual and external fields
• Metallurgical changes

These factors can mask relevant indications during inspections.

Question 8

Answer 8

Inadequate root penetration

Question 9

What contaminants can cause improper surface preparation?

Answer 9

• Oil
• Grease
• Dirt
• Scale
• Paint

These can trap particles and distract from relevant indications.

Question 10

What characterizes surface discontinuities?

Answer 10

Sharp, fineline definition with specific physical characteristics

These include depth, width, and length that affect indication formation.

Question 11

What is a common method to salvage an expensive part with a discontinuity?

Answer 11

Reworking the part through grinding

Proper engineering analysis is required to ensure safety.

Question 12

What are residual fields?

Answer 12

Fields left by prods or magnetic yokes used with high current levels

These can confuse inspectors and may require demagnetization for clarity.

Question 13

What occurs during welding that leads to undercutting?

Answer 13

Exposed upper edges of the weld bevel melt and run down into the deposited metal

This happens when insufficient filler metal is deposited to fill the resultant groove.

Question 14

What may cause gas to develop during welding?

Answer 14

• Quality of the base metal
• Electrodes used
• Poor regulation of the arc current
• Operator technique

Excessive gas evolution may prevent escape from the molten metal pool before solidification.

Question 15

What is the purpose of cutting a specimen containing a discontinuity?

Answer 15

To examine the fracture face and gather information about the discontinuity’s origin.

Breaking the specimen at a reduced cross section allows visibility of the discontinuity.

Question 16

What are slag inclusions?

Answer 16

Trapped slag in deposited weld metal during solidification

Often located at edges of underlying metal deposits, characterized by irregular shapes.

Question 17

What can cause cracks in welds?

Answer 17

• Inadequate welding system or materials
• Internal stresses from cooling

Cracks can be parallel or perpendicular to the weld seam.

Question 18

What types of changes are prevalent in geometric and section changes?

Answer 18

• Internal splines
• Subsurface holes
• Space between holes or keyways

These changes can cause leakage fields and may mask fatigue cracks.

Question 19

What is the high cost associated with in industrial contexts?

Answer 19

The high cost of an industrial breakdown or shutdown caused by a broken part is intolerable.

Machinery can be maintained by periodic in-service tests.

Question 20

What is a characteristic of slag inclusions in welding?

Answer 20

Slag line, intermittent or continuous lines at the edge of the weld groove

These discontinuities are caused by insufficient cleaning of slag between welding passes.

Question 21

What types of metallurgical changes can produce nonrelevant indications?

Answer 21

• Different metallurgical structures in welds
• Areas with drawn temper
• Decarburized areas
• Strain lines from cold forming

These changes can affect the permeability and indicate issues.

Question 22

What factors determine the effect of a discontinuity on strength?

Answer 22

• Safety factor used by the designer
• Location of the discontinuity

Discontinuities in low-stress areas may be acceptable.

Question 23

What causes weld spatter?

Answer 23

Improper electrodes or long arcs

Appears as rounded spots of excess metal on the surface near the weld seam.

Question 24

What factors affect the reliable interpretation and evaluation of test indications?

Answer 24

Human factors affect reliability; tests must be reproducible and indications must be recorded.

Refer to Chapter 10, ‘Probability of Detection’ for more details.

Question 25

What is the normal **destructive method** for determining crack depth?

Answer 25

Filing, chipping, or grinding a groove to measure the depth of the indication. ## Footnote There are also electronic instruments available for nondestructive measurement.

Question 26

What is the purpose of **grinding out a discontinuity**?

Answer 26

To equalize the loading of the area ## Footnote Often used to salvage a part after appropriate engineering analysis.

Question 27

What happens when the welding arc is started or displaced onto the **base metal surface**?

Answer 27

An irregular deposit of filler metal occurs near the weld seam ## Footnote This may be accompanied by an indentation due to melting of the base metal.

Question 28

What can examination of the **discontinuity surfaces** reveal?

Answer 28

It can reveal the cause or source of the discontinuity. ## Footnote Techniques like magnetic particle testing can show the extent of the discontinuity.

Question 29

Gas inclusions detected during magnetic particle testing are seen as what type of indications?

Answer 29

Spherical or rounded indications ## Footnote These inclusions are a result of gas trapped in the molten metal.

Question 30

Why is **recording indications** important?

Answer 30

It is important for project books or reports and maintaining a history of the part to show crack growth. ## Footnote Techniques for recording indications have evolved from tape transfers to digital cameras.

Question 31

Answer 31

Slag inclusion

Question 32

What are **subsurface discontinuities**?

Answer 32

Discontinuities detectable if not too deep ## Footnote Detection depends on size and orientation; characterized by broader and fuzzier indications.

Question 33

What is the first step in evaluating an **indication** during inspections?

Answer 33

Determine if the indication is caused by a **discontinuity** or another condition ## Footnote This initial assessment is crucial for proper interpretation of the indication.

Question 34

What technique can be used to estimate crack depth nondestructively?

Answer 34

Ultrasonic shear waves and surface waves can be used in some cases. ## Footnote The part configuration often limits the application of such techniques.

Question 35

Answer 35

Slag lines

Question 36

What is the purpose of **nondestructive testing programs** used by airlines and the U.S. Air Force?

Answer 36

To check critical areas for fatigue and monitor crack growth until it reaches a specific subcritical size. ## Footnote These programs are indispensable maintenance tools.

Question 37

True or false: Arc strikes usually have magnetic particle indications detected.

Answer 37

FALSE ## Footnote Unless there are other discontinuities associated with the arc strike, usually there will be no indications detected.

Question 38

What effects do **discontinuities** have on serviceability?

Answer 38

* Directly affect strength * Act as stress risers * Allow corrosion to propagate ## Footnote Can lead to fatigue cracks and unexpected failures.

Question 39

Answer 39

Undercut

Question 40

What does **inadequate penetration** of the weld root indicate?

Answer 40

A straight line indication void of a root bead ## Footnote This may result from excessive spacing between plates or improper beveling.

Question 41

What can a **deep etch** reveal when examining a forging?

Answer 41

It can show the flow lines of the metal and often reveal the cause of the discontinuity. ## Footnote This is important for determining if a discontinuity is caused by improper forging practices.

Question 42

What can cause **permeability variations**?

Answer 42

* Heat-affected zones on welds * Differences in chemistry between joined metals ## Footnote These variations can produce nonrelevant indications.

Question 43

What is **fracture toughness**?

Answer 43

A parameter in the strength of materials that indicates how resistant a material is to crack growth. ## Footnote It is important during the design stage of critical items like pressure vessels.

Question 44

What does **excessive magnetization** cause?

Answer 44

Leakage fields on the edges, corners, and ends of parts ## Footnote This is most prevalent with longitudinal magnetization.

Question 45

What can inadequate penetration appear as along the edge of a **weld bead**?

Answer 45

A very narrow straight line ## Footnote This may occur due to two different thicknesses of material being welded together or misalignment of the weld bevels.

Question 46

What should an inspector remember about the **grouping of magnetic particles**?

Answer 46

It indicates that something is **different** in that area ## Footnote This serves as a warning to evaluate and determine the cause and severity.

Question 47

What are **periodic testing** and **continued operation** used for in aircraft structures?

Answer 47

They are standard procedures to check critical areas for fatigue and monitor crack growth. ## Footnote Many times, a small crack will not grow during in-service usage.

Question 48

What type of joint weld preparations may not correspond with the center of the weld seam regarding lack of penetration?

Answer 48

Asymmetrical joint weld preparations, such as K-shaped bevel preparations ## Footnote These are sometimes used in T joints.

Question 49

What is generally not acceptable for **repair welding** a forged part?

Answer 49

Repair welding is not acceptable because it essentially becomes cast metal, adversely affecting the strength of the parent forged metal. ## Footnote Documentation of such repairs is normally required.

Question 50

Inadequate penetration might be serious in the thickest dimension of the welded plate or pipe due to what phenomenon?

Answer 50

Shrinkage drawing unfused surfaces close together ## Footnote This situation can occur with square butt weld preparations on thinner materials.

Question 51

What is **magnetic writing**?

Answer 51

Indications formed when two magnetized parts are rubbed together ## Footnote These indications differ in location and shape from normal indications.

Question 52

What is the consequence of misunderstanding the effects of **discontinuities**?

Answer 52

Parts may be scrapped unnecessarily ## Footnote Scrapping may be economical if the part's cost is low and failure could cause larger issues.

Question 53

Answer 53

Slag Inclusion

Question 54

What is the **critical crack size**?

Answer 54

The minimum length of a crack that would cause catastrophic failure. ## Footnote Crack size tolerances are becoming part of contractual requirements for new aircraft.

Question 55

How does **incomplete sidewall fusion** appear?

Answer 55

Narrow, straight lines parallel to the weld ## Footnote Can be open to the surface in the toe of the weld.

Question 56

What does **fracture mechanics** study?

Answer 56

Fracture mechanics studies how cracks grow and determines the size of a crack that would cause part failure. ## Footnote It is a valuable technique for engineers, especially for critical items.

Question 57

What is **incomplete fusion**?

Answer 57

Thin layer of oxide separating filler metal from base metal ## Footnote Occurs due to insufficient heat or scale on the fusion face.

Question 58

How do magnetic particle indications of undercutting appear?

Answer 58

Straight or jagged lines parallel or perpendicular to the axis of the weld seam ## Footnote The indication may appear on one side of the weld or on both sides.