Porosity in Welding: Causes, Types, and How to Detect It

What is porosity in welding?

Porosity in welding refers to small cavities or holes that form within the weld metal due to trapped gas as the metal solidifies. These gas pockets compromise the weld's structural integrity, potentially leading to weaker joints, increased susceptibility to corrosion, and even failure under stress. Understanding and addressing porosity is crucial across all welding applications to maintain high-quality and durable welds.

Types of Porosity in Welding

Welding porosity can manifest in several distinct forms, each with unique characteristics and causes. From scattered and uniform porosity to more complex issues like linear and wormhole porosity, understanding these types is essential for identifying defects and improving weld integrity.

Scattered Porosity:

Scattered porosity is characterized by small holes distributed randomly throughout the weld. Scattered porosity lacks a specific pattern and can appear as "spots" of gas pockets in the weld.

Common Causes: Often due to issues with shielding gas, contamination on the metal surface, or an improper gas mixture. Moisture and dirt on the base material can also contribute.
Impact: Reduces the overall strength of the weld and can be a starting point for corrosion or cracks.

Linear porosity:

Linear porosity appears as a line of holes or cavities following a specific path along the weld, either on the surface or deeper within the weld.

Common Causes: Typically caused by consistent process issues, such as a gas leak or contamination that follows a repetitive pattern during welding.
Impact: This type of porosity creates a critical weak point, making the weld more susceptible to structural failure.

Uniform porosity:

Uniform porosity involves cavities that are more consistently distributed. Although it resembles scattered porosity, the holes appear more regularly spaced or grouped.

Common Causes: Often results from recurring contamination or systematic issues in gas flow during the welding process.
Impact: Even a "controlled" distribution of porosity can negatively affect the durability and strength of the weld.

Wormhole porosity:

Identified by elongated holes resembling tunnels or "wormholes," this type of porosity extends deeper into the weld.

Common Causes: Usually a result of gas entrapment during welding, improper shielding, or unwanted gases in the base metal.
Impact: Wormhole porosity can significantly compromise the weld's structural integrity, making it prone to cracks or failure.

Crater porosity:

Crater porosity occurs at the end of a weld when the molten metal fails to solidify uniformly, leaving a depression or "crater."

Common Causes: Often happens when the welding process is not properly concluded, leaving a concave crater at the weld's endpoint.
Impact: This can create stress concentrations, leading to potential cracking or failure.

Traditional methods to detect porosity in welds

Visual Inspection Techniques:

Surface porosity is often visible as small pinholes or pits. This straightforward method allows welders to quickly identify potential defects. However, not all porosity is visible; subsurface porosity can remain hidden, requiring additional inspection.

Non-Destructive Testing (NDT) Methods:

To uncover hidden porosity, several NDT techniques are used, including:

Radiographic Testing (RT): Uses X-rays or gamma rays to reveal internal weld structures and detect hidden cavities.
Ultrasonic Testing (UT): Sound waves detect imperfections within the weld by analyzing reflections or wave pattern changes.
Dye Penetrant Testing (PT): Effective for surface-breaking porosity; a dye is applied to the weld and will seep into cracks or pores, becoming visible with a developer.

Common Indicators of Porosity Issues

Surface Pores or Pits on the Weld Bead: Small pinholes on the surface often indicate trapped gas, potentially signaling deeper issues within the weld.
Spattering During Welding: Excessive spatter may point to poor shielding, contamination, or parameter fluctuations, all of which can lead to porosity.
Weakness or Cracking Under Stress: Porous welds are weaker and more likely to crack under stress, reducing their overall durability and lifespan.
Inconsistent Weld Appearance or Color: Uneven coloration or texture may indicate trapped gases or insufficient shielding, hinting at hidden porosity.

Using High-Tech Weld Camera Systems to Detect Signals of Porosity in Welds

Xiris Weld Monitoring Cameras offer cutting-edge solutions for detecting behaviors in the melt pool and it’s temperature, these can indicate porosity and other defects in welds. With High Dynamic Range (HDR) capabilities and powerful machine vision tools, these cameras reveal many imperfections that might otherwise go unnoticed.

Xiris weld cameras are designed for easy integration to existing weld automation with robust IP65-rated housings that can withstand harsh industrial environments. This durability makes them suitable for a wide range of welding applications, from light manufacturing to heavy industry.

By providing clear, real-time visual feedback, Xiris cameras empower welders to maintain superior weld quality and achieve exceptional results in their operations.

The Xiris Audio AI Tool monitors weld audio in real-time, measuring signals to alert the system or operator if an anomaly, such as porosity issues, is detected. Alerts can be recorded with video or process data for further evaluation. This tool is available in WeldStudio™ 3 Pro.

Pro software at https://info.xiris.com/xiris-weldstudio-3-weldstudio-3-pro