Common Weld-Related Discontinuities

Common Weld and Weld-Related Discontinuities

Weld Discontinuities

Common Weld-Related Discontinuities: A weld discontinuity is any interruption in the normal flow of the structure of a weldment.

The interruption can be found in the physical, mechanical, or metallurgical characteristics of the material or weldment.

If the discontinuity exceeds the acceptance criteria being used, it becomes a defect.

 

All metals, heat-affected zones, and welds have discontinuities. The
heat affected zone (HAZ) is the base metal next to the weld that did not melt but was hot enough
to change its mechanical properties or its microstructure properties.

 

As all metals are crystalline structures, the interruptions at each of the grain
boundaries reflect an interruption of the normal flow of the material. But size, location, extent, and other factors must be applied to see if the product is fit for a purpose.
When a defect is indicated, it means that the defect exceeds the acceptable limits of the code or specification being applied

 
Fillet Weld with Overlap 

Overlap is a protrusion of the weld metal beyond the weld
toe and base metal. It can be likened to applying a wad of chewing gum to a surface. When the load is applied to the gum, it will peel from the surface. The welded joint will act in the same way under load, and the result will be weld failure.

 

 It is obvious that overlap must be avoided if we are to prevent peeling off of the weld metal when a load is applied.

 

Failure of the joint is certain when the overlap is located in the weld.

 

This is a serious defect and should be avoided. It may be caused by low welding current, slow travel, or improper electrode manipulation.

Fillet Weld with Insufficient Leg

A reduction in leg length means a reduction in the size of the
fillet weld. If the demands of a joint require a fillet of a certain size, any reduction of that size results in a weld that does not possess the physical properties needed for safe operation.

 

Failure is sure to result. This defect is usually caused by improper electrode angle and faulty electrode manipulation. In addition, these faults in the welding technique may be accompanied by too fast travel.

 

Fillet Weld with Incomplete Fusion

This defect is usually found at the root of the weld and at the plate surfaces (fusion face), Fig. 4-40. Incomplete fusion is usually caused by welding with the current too low, an improper
speed of travel, and/or improper electrode manipulation.
When these conditions exist during welding, the deposited weld metal may have slag inclusions and porosity (gas entrapment).

Fillet Weld with Various Other Discontinuities

The possible defects that can be encountered in the base material or the
weld bead.