Welding Defects of the steel

 

Numerous application-specific products are manufactured by the joining of two or more similar or dissimilar materials. Welding is one of the most common joining methods used in the case of metallic materials. The most common welding methods are gas metal arc welding (GMAW) or Manual Inert Gas (MIG) welding, gas tungsten arc or tungsten inert gas (TIG) welding, plasma arc welding, laser welding, electron beam welding. Generally, process selection is based on the product specification, process capability and cost. The above mentioned welding processes are routinely used in industries for the fabrication of almost all types of metallic products.

However, as with any other welding process, weld defects can occur. Most defects encountered in welding are due to an improper welding procedure. Once the causes are determined, the operator can normally and relatively easily correct the problem.

Porosity is a collective name describing cavities or pores caused by gas and non-metallic material entrapment in molten metal during solidification. There are many causes which include contamination, inadequate shielding, unstable arc, arc gap too short and poor welding technique in general. Porosity can be minimized in many different ways – by the proper selection of electrodes and/or filler materials, improved welding techniques, more attention to the work area during weld preparation and a slower speed to allow gasses time to escape.

The effects of porosity on performance depend on quantity, size, alignment, and orientation to stresses. When clustered at the weld’s center, porosity is not considered a dangerous fatigue promoter, or detrimental to fatigue resistance, although it may reduce the static stress carrying capacity of the weld.

Undercutting is one of the more severe welding defects. It is essentially an unfilled groove along the edge of the weld. The causes are usually associated with incorrect electrode angles, incorrect weaving technique, excessive current and travel speed. Undercutting can be avoided with careful attention to detail during preparation of the weld and by improving the welding process. It can be repaired in most cases by welding up the resultant groove with a smaller electrode.
Incomplete fusion or penetration is an internal planar discontinuity that is difficult to detect and evaluate, and very dangerous. It occurs when the weld metal does not form a cohesive bond with the base metal or when the weld metal does not extend into the base metal to the required depth, resulting in insufficient throat thickness.

Welding Defects of the steel