Objective 03: Welding Discontinuities

Question 1

What is the objective of good welding practice?

Answer 1

To produce weldments with the integrity to ensure they perform adequately for the service intended

Question 2

What does good welding practice try to avoid?

Answer 2

Weld discontinuities that may lead to defects

Question 3

What are 4 causes of Weld Discontinuities?

Answer 3

1. Departures from qualified procedures
2. Altering weld designs
3. Substituting or using defective materials
4. Substituting or using defective electrodes

Question 4

Why can weld discontinuities be problematic?

Answer 4

They can cause a structure to fail in service which can be costly and jeopardize safety

Question 5

What does the existence of Weld Discontinuities necessitate?

Answer 5

The identification, evaluation, and disposition of Weld Discontinuities

Question 6

What is the first step in welding inspection?

Answer 6

Visual identification of imperfections in welds

Question 7

How effective is visual indentification of weld imperfecions?

Answer 7

It can usually reveal 80% of weld imperfections

Question 8

How can weld imperfections not detectable visually be uncovered?

Answer 8

NDE can reveal their location and size

Question 9

How are weld imperfections evaluated?

Answer 9

The Inspector judges whether or not the discontinuity is likely to become a defect leading to failure based on the use of specifications, standards, and codes which provide acceptance and rejection criteria for types of weld discontinuities

Question 10

What does an Inspector require to know and have experince with to properly evaluate weld imperfections?

Answer 10

1. The flaws associated with a particular welding process and procedure
2. The metallurgy of the base metals and filler metals used
3. The design of the weld joint

Question 11

What possible decisions (disposition) can the evaluation of weld discontinuities lead to?

Answer 11

1. The weldment is acceptable
2. Requires rework
3. Unsuitable for the service intended and must be removed

Question 12

Can personnel involved in the inspection be involved in the final disposition decisions?

Answer 12

No, especially when the decisions are of a critical nature requiring an engineering assessment

Question 13

Is there a standard welding terminology?

Answer 13

Yes

Question 14

Weld Defect

Answer 14

A discontinuity or flaw whose size, shape, type, location, or orientation creates a substantial chance of material failure and is therefore detrimental to the integrety of the pressure equipment

Question 15

Weld Discontinuity

Answer 15

Any local variation in material continuity; including changes in geometry, properties of composition or structures, holes, cavities, or cracks

Question 16

Weld Fault

Answer 16

Defect, imperfection or flaw

Question 17

Why shouldn’t the term Fault be using for welding?

Answer 17

It is imprecise and there are other precise terms that can be used

Question 18

Weld Flaw

Answer 18

An imperfection in the material that may or may not be harmful

Question 19

What is another term for Flaw in Welding?

Answer 19

Imperfection

Question 20

What are 3 categories by Cause of Weld Discontinuities?

Answer 20

1. Weld Procedure
2. Weld Design
3. Metallurgical Causes

Question 21

What are classes by Description of Weld Discontinuities?

Answer 21

1. Dimensional
2. Structural
3. Base Metal Properties

Question 22

Dimensional Discontinuities

Answer 22

Any inconsistencies or departures from specified dimensions in the weld, weld joint, or parent metal and includes welds with imperfect shapes or unacceptable contours, incl. undercut, underfill, and overlap

Question 23

Structural Discontinuities

Answer 23

Flaws in the weld deposit or heat affected zone where the flaw’s potential for failure is directly related to its shape and location in the weld

Question 24

How severe are planar defects, e.g. cracks and lack of fusion?

Answer 24

They are sharp and pointed and create severe notching and high potential for failure

Question 25

How severe are pores and non-metallic inclusions in welds?

Answer 25

They are usually rounded and pose less potential for failure

Question 26

Base Metal Discontinuities

Answer 26

Deficiencies in the chemical, physical, or mechanical properties of the base metals which may contribute to a defect in rg weldment

Question 27

How do Base Metal Discontinuities mainly arise?

Answer 27

From the production of the metal and its subsequent processing and manufacturing

Question 28

What is the property most affected by weld defects?

Answer 28

Weld Strength

Question 29

What is particularly problematic about planar-type defects?

Answer 29

They can cause rapid propagation of cracking through a weldment

Question 30

Weld Discontinuity Notching

Answer 30

Abrupt changes in the contour of the weld where it fuses to the base metal

Question 31

What is problematic about Weld Discontinuity Notching?

Answer 31

They can reduce the fatigue resistance of welded joints and cause failure even though the yield strength of the original base metal was never exceeded

Question 32

What is Fatigue Failure in welded joints associated with?

Answer 32

Cyclical loading of the joint

Question 33

What is problematic about Spherical Type Weld Defects?

Answer 33

1. Create voids 2. Displace weld metal 3. Reduce intended volume of deposited weld metal

Question 34

What is the result of failure to fill a joint or melting away of the base metal?

Answer 34

Reduction of the through thickness of the base metal

Question 35

What is problematic about inappropriate chemical properties when welding?

Answer 35

It can cause a weldment to lose impact and tensile strength in a very hot or cold environment

Question 36

What is problematic about failing to match base metal to electrodes correctly?

Answer 36

It can cause a loss of resistance to corrosion at the surface of a metal

Question 37

What are the 5 basic weld joints?

Answer 37

1. Butt 2. Tee 3. Lap 4. Edge 5. Corner

Question 38

How can a weld failure occur if the weld deposit forming the joint is sound?

Answer 38

The joint has some undesireable features

Question 39

What are some undesireable weld joint features?

Answer 39

1. Highly restrained tee and corner joints, unless properly designed, are sites of weld failure 2. Misaligned butt joints can be areas of high stress 3. Steep transitions between thick and thin lapped material can create areas of high stress

Question 40

Is the degree of weld quality possible, the same as the degree of weld quality necessary?

Answer 40

No

Question 41

What determines the required degree of weld quality necessary?

Answer 41

The function imposed on the weldment