Gas Pore, Worm Holes and Surface Porosity

There are 3 common types of weld cavities; They are gas pore, wormholes and surface porosity (including Crater pipe).

Let us explore them.

1. Gas Pore

A gas pore is a trapped cavity within the weld metal that has a basic round shape and comes in a form of isolated, elongated cavity and surface pore.

Meanwhile, a group of gas pore that is uniformly distributed, clustered (localized) or linear is called porosity which comes in a form of localized or finely dispersed.

Table 1: The cause and prevention of gas pore.

The gas pore is strong with this one!

Gas pores on a radiograph film.

2. Worm Holes

A wormhole does not contain worms in it. Just kidding.

During the solidification process, trapped gas may form elongated or tubular cavities in the weld metal. This can either be in a single form or in groups.

Eventually, the entrap gases build up progressively between the solidifying metal crystals (dendrites), forming characteristic elongated pores of circular cross-section.

In certain cases, some of the trapped gas can even break through to the weld surface thus looking like a wormhole.

Guess which one is the wormhole?

The cause and prevention of wormholes in the weldment.

Wormholes and porosity, they all look the same…

3. Surface Porosity

Surface porosity is simply a gas pore that breaks the surface of the weld. The origins of surface porosity are similar to those for uniform porosity.

The cause and prevention of surface porosity.

Shrinkage during weld solidification can cause a surface porosity called Crater pipe.

It is usually formed at the end of a weld run and often occur while welding with current too high or inoperative crater filler (slope out using TIG).

Crater filling is a particular problem due to the low heat input of TIG welding which needs to reduce the weld current (slope out) in a series of descending steps until the arc is extinguished.

A pipe in the crater.