What's Porosity in Welding? How Porosity Causes and What's the Top Remedies to Minimise Them !!

Porosity

Porosity in welding is a defect that occurs when gas bubbles become trapped in the weld pool as it solidifies and freezes, creating cavities in the weld metal. These pores or holes can be internal or break through the surface and come in different shapes. The most common type is spherical porosity, which is rounded, but elongated holes can be called wormholes or piping. 

Gas bubbles trapped in the weld metal, which can weaken the weld and make it more likely to crack or corrode. 

Also known as wormhole welds, porosity defects occur when there is an entrapment of air or gas bubbles in the weld. The welding process often generates gases like hydrogen, carbon dioxide, and steam. A cross-section of porous weld beads often resembles a sponge with an accumulation of trapped air bubbles.

The entrapped gases may be localized in a specific location or uniformly distributed in the weld. These gas bubbles can weaken the joint of the weld metal, predisposing them to fatigue and damage. Depending on their formation, these orbital welding errors can occur as:

Porosity defect in welding

Gas Porosity. 

This is a small, spherical-shaped cavity generated from trapped gases. The various forms include surface pores, elongated cavities, linear porosity, etc.

Worm Holes. 

These are elongated or tubular cavities formed during the solidification of trapped gases. You can see them as single holes or a group of holes throughout the weld surface.

Surface Porosity. 

This is a kind of porosity that breaks the surface of the weld metal.

Causes of Porosity

Inadequate coating of electrode or use of corroded electrode.

Presence of grease, oil, water, rust, or hydrocarbon on the weld surface.

Using incorrect shielding gas.

Too high arc voltage or gas flow. The voltage should typically be between 15 to 30 volts.

Poor surface treatment of base metal.

Remedies for Porosity

Choose the suitable electrode and filler material.

Ensure proper cleaning of the base metal and prevent pollutants from entering the welding area.

To enhance the welding process and facilitate gas escape, adjusting the welding speed is crucial, as it varies across different welding techniques. 

For example, MIG welding is most effective at a travel speed of 14 to 19 inches per minute (IPM), while TIG welding achieves optimal results at a slower pace of 4 to 6 IPM.

Configure the gas flow meter to the correct flow settings. Depending on the welding technique, the gas flow should be between 22 to 30 cubic feet per hour (CFH).

References

https://www.twi-global.com/technical-knowledge/job-knowledge/defects-imperfections-in-welds-porosity-042#:~:text=Porosity%20is%20the%20presence%20of,wormhole

BOC

https://www.boconline.co.uk

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