Identifying and Preventing Typical Welding Defects

Welding defects are irregularities in a weld that deviate from the intended specification and can impair the mechanical properties, load-bearing capacity or operational safety of the welded joint. They generally arise from an interplay of material, welding process and process parameters. Which deviations count as defects and which as permissible irregularities is determined by the requirements for the component and the applicable standards. capilla supports companies in classifying typical defect patterns and selecting suitable filler materials for prevention.

The most common welding defects include porosity, cracking in various forms such as hydrogen, solidification and end crater cracks, lack of fusion, slag inclusions, undercuts and weld spatter. Technically they are classified into volumetric defects, separating defects and fusion and undercut defects at the weld. capilla advises on preventing these defect patterns through appropriately matched filler materials and correct process control.

In metal active gas welding, typical welding defects include primarily pores – both metallurgically caused by insufficient shielding gas coverage and mechanically by moisture, contamination or coatings in the joint area. Additionally, lack of fusion from insufficient welding power, slag inclusions when using slag-forming flux-cored wires and weld spatter from unsuitable parameters and polarity occur. capilla offers filler materials for MIG/MAG welding and supports with advice on parameter selection to reduce these defect patterns.

Lack of fusion describes incomplete fusion between the weld metal and the base material or between individual passes in a multi-pass weld. It reduces the load-bearing cross-section of the joint and is caused primarily by insufficient welding power, too high a welding speed, welding in the downhill position, off-centre arc guidance or too long an arc. capilla supports with expert advice on selecting the appropriate filler material and process control to ensure reliable fusion.

Shrinkage cavities are voids that form during solidification of a metal due to volume contraction. They are primarily a defect pattern from foundry technology. In welding, the phenomenon occurs in a limited form as end crater cavities, when welding power is reduced too rapidly at the weld end and the weld pool shrinks strongly during solidification. Classic welding defects such as pores, cracks, lack of fusion or slag inclusions are to be distinguished from these. capilla supports in selecting suitable filler materials and process-side design of the weld run-off to prevent end crater defects.

Cracks during welding arise when stresses, unfavourable microstructure states or introduced elements exceed the ductility of the weld metal or heat-affected zone. Hydrogen cracks arise from atomic hydrogen that penetrates the weld metal and heat-affected zone during cooling and triggers cracks in areas of high internal stress. Solidification cracks are promoted by sulphur and phosphorus that accumulate in the weld centreline during solidification and form low-melting films at grain boundaries. End crater cracks arise at the weld run-off when welding power is reduced too rapidly. capilla offers low-hydrogen filler materials and advises on material and process selection to specifically reduce susceptibility to cracking.

Hot cracks, technically solidification cracks, occur with increased risk in dissimilar metal joints – that is, welded joints between different base materials. The cause is the dilution of the weld metal with two different materials, which can lead to unfavourable concentrations of low-melting trace elements at grain boundaries, to microstructure transformations and to stresses from different thermal expansion coefficients. Critical factors are the selection of a suitable filler material with controlled dilution behaviour and adapted process control that limits dilution with the base materials. capilla advises on material and filler material selection for dissimilar metal joints and supports in preventing hot cracks in demanding welding applications.

Welding defects create weak points in the weld and increase the effort for rework. They cause additional costs, delays in fabrication and can impair the operational safety of a component. How critically a defect manifests itself depends on the application of the component and the design requirements. capilla supports companies in systematically analysing recurring defect patterns and preventing them through suitable filler materials and process coordination.

Assessment is based on the application of the component and the requirements for the design. Which irregularities are permissible is already defined during design. The relevant permissibility limits are defined in standards such as EN ISO 5817, which specifies assessment groups for welds in metallic materials. capilla advises on classifying weld defects in the respective application and selecting suitable filler materials for the required assessment group.

The filler material directly influences mechanical properties, solidification behaviour and susceptibility to typical welding defects. Low-hydrogen filler materials reduce the risk of hydrogen cracks; correct re-drying before use maintains the low hydrogen content. A material combination of base material and filler material suited to the application reduces the risk of solidification cracks and dilution problems. capilla develops filler materials for demanding applications and supports in selecting the appropriate filler material for the respective welding process.