10 causes of Weld Porosity and their practicable prevention
Weld Porosity is referred to as cavities produced due to the entrapment of gas in weld metal. The introduction of gas in a weld is supported by some mistakes that ought to be eliminated.
Porosity is categorized according to the shape and location of occurrence. Some gas cavities occur in the spherical shape, some in elongated (like in case of wormholes) while on the other hand, some cavities occur throughout weld metal and some on the weld surface.
These gas cavities appear either singly called voids or uniformly distributed throughout the weld and sometimes developed in clustered form. These voids and cavities are produced primarily by gas entrapment during the solidification procedure of weld. So making the prediction about mistakes that may cause porosity and their removal is an essential part of welding.
Given below are the 10 reasons for Weld porosity and their solution
1.Moist Electrodes
It is recommended to use baked electrodes in Stick welding process in order to avoid involvement of moisture content in the weld metal. In worst, steam can be driven out, during the heat of welding which creates small cavities in the weld metal. Porosity eventuates when stainless steel electrodes or low hydrogen electrodes are not properly kept in dry condition. Although in low hydrogen electrodes some moisture is required within a limit, for better performance but is some case if moisture exceeds from the limit, the weld metal will prone to porosity. For prevention following are the steps to follow;
Parent metal must be preheated in order to remove any moisture.
The electrodes must be stored in dry conditions.
Apply final backing before use.
Electrodes must not be oven baked before use because a little amount of moisture is required for better performance and weld-ability of the electrode.
2.Contaminated Surface
Parent metal or electrodes may be subjected to atmospheric contamination. Any grease, oil or moisture content on surface contribute to gas formation when exposed to welding temperature and may cause porosity problems in your weld. In order to fix it, clean the material by specified surface preparation procedures.
3.Improper Gas Shield
The possibility of air entrapment due to inconsistent gas shield may also cause porosity problems. For this, the welder must check gas hose attachment with the equipment and remove hose contamination if any. Correct connection prevents any loss of gas shield and consequently no air entrapment. Moreover, airflow and draughts in the shop can cause the restriction in gas flow. Some sort of screening is required to avoid such kinds of restrictions in the gas flow.
4.Too High Gas Flow
The High flow rate of the gas shield may cause turbulence due to which air can be drawn into the weld metal. Optimize gas flow, provides quality welds with no gas loss. Moreover, it saves cost on the other side.
5.Inadequate Electrode deoxidant
During solidification, the excess oxygen comes out from weld metal due to reduced solubility and may undergo carbon monoxide formation that may cause porosity too. For this, some deoxidants are added in electrodes, filler metals and even in parent metals to remove the oxygen content (which is so-called deoxidation). Therefore inadequate deoxidants may result in poor deoxidation and are responsible for weld defects. In order to prevent this, use electrodes with adequate deoxidants.
6.Too High Arc Length
Too much longer arc length (in other words high voltage) is also a cause of weld porosity. If the welding gun is held away from the joint keeping arc length longer, the magnitude of shielding is reduced which may lead to air entrapment from atmosphere. Correct arc length is recommended primarily to avoid draughts/breezes.
7.Incorrect Surface Treatments
The release of gases, during painting/surface treatments, can impair weld characteristics. Treatments like zinc coating or galvanizing produce gas and other unwanted particles. In an endeavor to fix this problem, make predictions about the outcome of chemical reactions before specific surface treatments.
8.Openwork Surface
Any surface which is open to atmospheric air can be contaminated. Air introduction from the back side through root opening gets entrapped in the weld puddle. Make sure that weld joint is protected from such kinds of air crevices.
9.Laminated Surface
Laminated surface also creates a disturbance in welding. In case of welding a laminated workpiece, prepare un-laminated parent metal to conduct quality weld procedure.
10. In-Appropriate Flux
Welding flux must be treated with great care as they have the capability to absorb moisture (granular SAW flux). They must be supplied in dry condition. On the other hand, use of low activity flux results in surface porosity. That is why it is recommended to use high activity flux which offers quality welds with no porosity.
