Stress Relieving

Weld Defects and Inspection

Weld Defects

Weld defects are discontinuities in the weld metal, base metal, or heat affected zone (HAZ) of butt, tee, corner, and lap joints. The severity of the discontinuity is judged according to its type, size, and location. Not all discontinuities are rejected as defects.

This section describes the following weld defects:

• Cracks
• Porosity
• Inclusion
• Incomplete Fusion
• Inadequate Joint Penetration
• Undercut
• Underfill
• Laminations
• Delamination

Cracks

This section covers the Definition, Cause, and Types of cracks.

Definition

Cracks are brittle separations in the weld and base metal. They usually occur near existing discontinuities or mechanical notches associated with the design.

Hot cracks develop at elevated temperatures immediately upon solidification of the metal. Hot cracks develop along grain boundaries.

Cold cracks--also called delayed cracks or hydrogen cracks--develop hours or even months after solidification. Cold cracks are most often associated with hydrogen embrittlement.

Figure 21 shows different types of weld cracks.

Figure 21: Cracks in a Weld

Cause

One or more of the following factors contribute to crack formation:

• High residual stresses that exceed the ultimate strength of the material
• Hydrogen embrittlement

Types

Table 16 lists and describes the six basic types of cracks.

Table 16: Types of Cracks

Porosity

This section covers the Definition, Cause, and Types of porosity.

Definition

Gas entrapped in solidifying metal forms spherical or elongated pores in the weld, known as porosity. Porosity in the weld and heat affected zone may lead to cracking.

Figure 22 shows types of weld porosity.

Figure 22: Porosity in a Weld

Cause

One or more of the following factors contribute to porosity:

• Improperly controlled welding process
• Contaminated base metal
• Variable composition base metal
• Hydrogen in the weld and HAZ

When the weld cools slowly, entrapped gas may rise and escape from the surface before the weld solidifies.

Types

Table 17 lists and describes the four basic types of porosity.

Table 17: Types of Porosity

Inclusions

This section covers the Definition, Cause, and Types of inclusions.

Definition

An inclusion is a metallic or nonmetallic substance entrapped within weld metal, between weld passes, or between the weld and base metal.

Figure 23 shows types of weld inclusions.

Figure 23: Inclusions in a Weld

Cause

The cause of inclusions depends on the type.

Types

Table 18 lists and describes the two basic types of inclusions.

Table 18: Types of Inclusions

Incomplete Fusion

This section covers the Definition and Cause of incomplete fusion.

Definition

Incomplete fusion occurs when the base metal and weld metal fail to coalesce across all boundaries.

Figure 24 shows incomplete fusion between the weld bead and the base metal.

Figure 24: Incomplete Fusion Between Weld Bead and Base Metal

Figure 25 shows incomplete fusion between two weld passes.

Figure 25: Incomplete Fusion Between Two Weld Passes

Cause

One or more of the following factors contribute to incomplete fusion:

• Improper welding techniques
• Improper preparation of materials for welding
• Improper joint design
• Insufficient welding heat
• Improper electrode manipulation
• Lack of access to all weld joint boundaries to be fused during welding
• Tightly adhering oxides

Inadequate Joint Penetration

This section covers the Definition and Cause of inadequate joint penetration.

Definition

Inadequate joint penetration indicates that the weld has not penetrated the joint to the depth required.

Cause

One or more of the following factors contribute to inadequate joint penetration:

• Insufficient welding heat
• Improper electrode manipulation or guidance
• Improper joint design or alignment

Figure 26 shows inadequate joint penetration due to internal misalignment.

Figure 26: Inadequate Joint Penetration Due to Internal Misalignment

Undercut

This section covers the Definition and Cause of undercut.

Definition

Undercut is the mechanical notch at the fusion boundary of the weld. Undercut occurs at the junction of the weld and base metal at the toe of fillet welds, at the fusion line of groove welds, and at the root of groove welds made from one side only.

Some undercut is acceptable. When the degree of undercut exceeds acceptable limits, it is considered a defect.

Figure 27 shows internal and external undercut.

Figure 27: Undercut in a Weld

Cause

Either or both of the following factors contribute to defective levels of undercut:

• Improper welding technique
• Excessive welding heat

Underfill

This section covers the Definition and Cause of underfill.

Definition

Underfill is a depression on the weld that dips below the surface of the workpiece.

Figure 28 shows underfill at the root surface.

Figure 28: Underfill at the Root

Cause

Underfill occurs when the welder or welding operator fails to fill the weld joint to the level required by the welding procedure specification.

Laminations

This section covers the Definition and Cause of laminations.

Definition

Laminations are planar elongations either internal or extending to the surface of an end or edge. They most often occur in rolled or forged products. Laminations may be the source of gas voids or cracks in adjacent butt welds.

Cause

Laminations occur when gas voids, nonmetallics, or ingot shrinkage cavities are rolled flat.

Delamination

This section covers the Definition and Cause of delamination.

Definition

Delamination is a lamination that has been separated. Delaminations can be internal and discovered only through ultrasonic tests or external and visible at the edges or ends of pieces.

Cause

Residual stress from welding or applied stress causes a lamination to separate and form a delamination.

Comparing Weld Defects

Table 19 summarizes common weld defects and their locations.

Table 19: Comparing Weld Defects

Weld Inspection

This sections covers weld inspection's Function and Method.

Function

Weld inspection is a quality control procedure that examines and evaluates the following:

• The weld
• The welder performance
• The weld procedure

Method

Inspectors use nondestructive examination methods to find most weld defects. For more information on the types of weld inspections, see Inspection.