Objective 03: Welding Discontinuities Flashcards
What is the objective of good welding practice?
To produce weldments with the integrity to ensure they perform adequately for the service intended
What does good welding practice try to avoid?
Weld discontinuities that may lead to defects
What are 4 causes of Weld Discontinuities?
- Departures from qualified procedures
- Altering weld designs
- Substituting or using defective materials
- Substituting or using defective electrodes
Why can weld discontinuities be problematic?
They can cause a structure to fail in service which can be costly and jeopardize safety
What does the existence of Weld Discontinuities necessitate?
The identification, evaluation, and disposition of Weld Discontinuities
What is the first step in welding inspection?
Visual identification of imperfections in welds
How effective is visual indentification of weld imperfecions?
It can usually reveal 80% of weld imperfections
How can weld imperfections not detectable visually be uncovered?
NDE can reveal their location and size
How are weld imperfections evaluated?
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
What does an Inspector require to know and have experince with to properly evaluate weld imperfections?
- The flaws associated with a particular welding process and procedure
- The metallurgy of the base metals and filler metals used
- The design of the weld joint
What possible decisions (disposition) can the evaluation of weld discontinuities lead to?
- The weldment is acceptable
- Requires rework
- Unsuitable for the service intended and must be removed
Can personnel involved in the inspection be involved in the final disposition decisions?
No, especially when the decisions are of a critical nature requiring an engineering assessment
Is there a standard welding terminology?
Yes
Weld Defect
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
Weld Discontinuity
Any local variation in material continuity; including changes in geometry, properties of composition or structures, holes, cavities, or cracks
Weld Fault
Defect, imperfection or flaw
Why shouldn’t the term Fault be using for welding?
It is imprecise and there are other precise terms that can be used
Weld Flaw
An imperfection in the material that may or may not be harmful
What is another term for Flaw in Welding?
Imperfection
What are 3 categories by Cause of Weld Discontinuities?
- Weld Procedure
- Weld Design
- Metallurgical Causes
What are classes by Description of Weld Discontinuities?
- Dimensional
- Structural
- Base Metal Properties
Dimensional Discontinuities
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
Structural Discontinuities
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
How severe are planar defects, e.g. cracks and lack of fusion?
They are sharp and pointed and create severe notching and high potential for failure
How severe are pores and non-metallic inclusions in welds?
They are usually rounded and pose less potential for failure
Base Metal Discontinuities
Deficiencies in the chemical, physical, or mechanical properties of the base metals which may contribute to a defect in rg weldment
How do Base Metal Discontinuities mainly arise?
From the production of the metal and its subsequent processing and manufacturing
What is the property most affected by weld defects?
Weld Strength
What is particularly problematic about planar-type defects?
They can cause rapid propagation of cracking through a weldment
Weld Discontinuity Notching
Abrupt changes in the contour of the weld where it fuses to the base metal
What is problematic about Weld Discontinuity Notching?
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
What is Fatigue Failure in welded joints associated with?
Cyclical loading of the joint
What is problematic about Spherical Type Weld Defects?
- Create voids
- Displace weld metal
- Reduce intended volume of deposited weld metal
What is the result of failure to fill a joint or melting away of the base metal?
Reduction of the through thickness of the base metal
What is problematic about inappropriate chemical properties when welding?
It can cause a weldment to lose impact and tensile strength in a very hot or cold environment
What is problematic about failing to match base metal to electrodes correctly?
It can cause a loss of resistance to corrosion at the surface of a metal
What are the 5 basic weld joints?
- Butt
- Tee
- Lap
- Edge
- Corner
How can a weld failure occur if the weld deposit forming the joint is sound?
The joint has some undesireable features
What are some undesireable weld joint features?
- Highly restrained tee and corner joints, unless properly designed, are sites of weld failure
- Misaligned butt joints can be areas of high stress
- Steep transitions between thick and thin lapped material can create areas of high stress
Is the degree of weld quality possible, the same as the degree of weld quality necessary?
No
What determines the required degree of weld quality necessary?
The function imposed on the weldment
