Saturday, August 15, 2015

Porosity in Welding - Causes and Preventions (Part 1)

What are most common causes of porosity in welding and how can they be prevented? You can refer below to find the answers you need.

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Porosity in Welding - Causes and Preventions (Part 2)
5 Tips to Avoid Porosity in Welding

Porosity is defined as cavities in a weld as a consequence of gas entrapment. The gas introduction in the weld is associated with certain mistakes that should be eliminated. The in-weld metal porosity is varied by location and shape of occurrence. For example, while some gas cavities are in spherical shape, some, like the worm holes, are in long shape. Then to predict mistakes possibly causing porosity and the related preventions is important before welding. Specified below are details about most common causes of weld porosity along with their solutions.


1. Moist electrodes

As recommended, employ the baked electrodes in the process of stick welding to avoid any moisture content involved in the weld metal. At worst, there may be small cavities created in the weld metal because the steam can be driven out during the welding heat. Porosity occurs when the low hydrogen electrodes or stainless steel electrodes aren’t appropriately kept in the dry condition. Certain moisture is needed within a limit in low hydrogen electrodes though, in some case, the weld metal will be subjected to porosity if moisture surpass the limit. Follow those steps for prevention:

Parent metal is required to be preheated for moisture removal.
The electrodes must be kept in the dry condition.
Before use, apply last backing.
It is a must that electrodes are not oven baked prior to use, as there requires a humble amount of moisture for enhanced performance and weldability of electrode.

2. Polluted surface

Parent electrodes or metals may be prone to contamination in the atmosphere. Any moisture, oil, grease content on the surface has something to do with the gas formation as being under exposure of welding temperature, and can induce porosity in your weld. To fix it, wipe off the material by particular procedure of surface preparation.

3. Inappropriate gas shield

Porosity can eventuate in case of inappropriate gas shield inducing air entrapment. The welding worker is required to check the attachment of the gas hose with the equipment, and get rid of any hose contamination. Right connection would avert any gas shield loss and no air entrapment as a result. Also, draughts and air flow in the shop can lead to the gas flow restricted. There requires screening to keep away from such restrictions in the gas flow.

4. Insufficient electrode de-oxidant

In time of solidification, lower solubility can make excess oxygen release from the weld metal that then can suffer carbon monoxide formation. The porosity occurs as a result. In this case, certain de-oxidants are often added in the filler metals, electrodes, and even in the parent metals for oxygen content removal (also, de-oxidation). Thus, insufficient de-oxidants can induce bad de-oxidation and are the culprit to weld defect. For prevention, employ electrodes with sufficient de-oxidants.

5. Too high flow rate of gas shield

The flow rate of gas shield is too high, and then air can be pulled into the weld metal, which may lead to turbulence. Optimize your gas flow, offer welds of quality without gas loss. Also, it would save cost.


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