External Defects


A groove melted into the base metal adjacent to the WELD TOE OR WELD ROOT AND LEFT UNFILLED by weld metal

Typical Appearance of Undercut

Undercut Adjacent to Fillet Weld



The projection of weld metal beyond the weld toe or weld root

Overlap Examples

Undercut & Overlap

Lack Of Penetration

Excessive Penetration

Weld metal melting through Base Metal and hanging below weld


Definition: When an undesirable open hole has been completely melted through the base metal. The hole may or may not be left open.

Cause: Excessive heat input.

Prevention: Reduce heat input by increasing travel speed, use of a heat sink, or by reducing welding parameters.

Repair: Will be defined by standards. Filling may suffice. Otherwise, removal and re welding may be required.

Excessive Reinforcement

Definition:Specifically defined by the standard. Typically, Reinforcement should be flush to 1/16”(pipe) or flush to 1/8” (plate or structural shapes).

Cause:Travel speed too slow, amperage too low

Prevention:Set amperage and travel speed on scrap plate.

Repair:Remove excessive reinforcement and feather the weld toes to a smooth transition to the base plate

Insufficient Reinforcement

Definition: Specifically defined by the standard. Typically, Under fill may be up to 5% of metal thickness, not to exceed 1/32” as long as the thickness is made up in the opposite reinforcement. Not applied to fillet welds.

Cause: On root reinforcement -Too little filler metal will cause thinning of the filler metal. In OH position, too hot or too wide will cause drooping of the open root puddle.

Prevention: Use proper welding technique. Use backing or consumable inserts. Use back weld or backing.

Repair: Possibly simply increase the face reinforcement. If back welding is not possible, must remove and re weld.

Insufficient Fill on the Root Side (Suck back)

Definition: The weld surface is below the adjacent surfaces of the base metal at the weld root.

Cause: Typically improper joint preparation or excessive weld pool heat.

Repair: Back weld to fill. May require removal of weld section by grinding for access to the joint root

Suck back


Definition: Small particles of weld metal expelled from the welding operation which adhere to the base metal surface. Cause: Incorrect welding parameters, high amperages, long arc length, damp electrodes

Prevention: Correct the cause.

Repair: Remove by chipping, grinding or sanding.

Scattered Surface Porosity

Porosity are gas pores found in the solidified weld bead.
Single Pore
Uniformly Scattered

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