Dec 13

Defects in Welding

1. Porosity: Gas porosity get to be visible as round or stretched insubstantial shady spots, occurring separately or in bunches or scattered all through the casting. This is caused by gas formation during solidification by evaporation of moisture or unstable material from the mold surface. Insufficient core baking, venting or capture of air in the cope surface of the casting before complete solidification could also be the reason. The term ‘gas porosity’ is used to refer to shady dark spots on the radiograph, whose diameters are normally inside 0 to 1 mm.

01-NDT Gas porosity in Welding - Welding defects

01-NDT Gas porosity in Welding - Welding defects-porous holes

2. Slag inclusion and slag lines show up on the radiograph as dark, uneven shapes. These may be isolated, clustered or randomly distributed. A slag line appears as a linear dark shade, continuous or intermittent along the edge of the weld. Slag inclusions happen because of entrapment of foreign materials in the cavities during welding.

01-NDT testing - slag inclusion

3. Incomplete penetration appears on the radiograph as constant or discontinuous dark lines, typically of uniform width, happening in the middle of the weld. This is caused by the failure of the weld metal to fill the root gap.

01-NDT testing - lack of fusion

4. Lack of fusion appears on the radiograph as a thick, dark line. It may also show as diffused and wavy, depending upon the defect introduction with respect to the radiation beam. This flaw is caused by the failure of the weld metal to ruse with the parent metal or previously deposited weld metal. In case of lack of sidewall fusion, the radiographic image illustrates the appearance of a narrow, dark band parallel to the weld bead.

01-NDT Testing - lack of fusion - Welding defects

5. Cracks appear on the radiograph as sharp, straight or jagged dark lines with tapered ends. Cracks may appear in longitudinal or transverse directions. Cracks may occur in the weld and heat affected zones. The effect is caused by the rupture of the weld metal during solidification due to shrinkage or by fracture when cold, because of uneven stresses and poor handling.

01-NDT Testing - cracks in weld - rupture in the weld

6. Undercuts appear on the radiograph as dark lines of uneven width along the edge of the weld. This defect is caused by the formation of a groove or a channel on the surface of the base metal at the toe of the weld bead due to high temperature.

01-NDT Testing - undercuts - weld bead

7. Burn through appears on the radiograph as a dark, round or elongated area surrounded by a lighter ring. This is caused by the melting of metal from the root of the weld or through the backing strip.

8. Icicles appear on the radiograph as secluded, white, rounded indications, irregularly with a small, dark spot in the center. This is caused by fused droplets of weld metal extending beyond the root of the weld.

01-NDT Testing - isicles- fused droplets

9. Tungsten inclusions appear on the radiograph as white areas of round or uneven shape, either segregated or in bunch. This is acquired by the entrapment of tungsten particles in the weld metal. These particles are broken pieces from the tungsten electrode.

You might also like

Welding Technology | Electro Gas Welding (EGW)
Electro Gas Welding: Electro Gas Welding is an arc welding process that uses an arc between a continuous...

Resistance Welding Process | Pipe Welding Equipment | Resistance Welding Dissimilar Metals
Resistance Welding: Resistance welding is a process in which two or more parts are welded by the coordinated...

NDT X Ray Testing | NDT Radiographic Testing | Radiography Test For Casting
Interpretation of Casting Radiographs Castings are made of different metals and by various methods....

Submerged Arc Welding SAW | Submerged Arc Welding Deposition Rates | Submerged Arc Welding Flux Composition
Submerged arc welding: (SAW) In submerged arc welding also known as hidden arc welding, submerged melt...

Tagged with:
Dec 13

Interpretation of Casting Radiographs

Castings are made of different metals and by various methods. Sand molded castings often have more surface irregularities than casting produced by metal mold and investment methods. Knowledge of various casting processes and casting defects helps effective radiographic evaluation. The major defects in castings and weldments are given below:

1. Gas porosity become visible as round or elongated soft shady spots, taking place individually or in clusters or distributed throughout the casting. This is caused by gas formation during solidification by evaporation of moisture or volatile material from the mold surface. Insufficient core baking, venting or entrapment of air in the cope surface of the casting before complete solidification could also be the cause. The term ‘gas porosity’ is used to refer to shady dark spots on the radiograph, whose diameters are usually within 0 to 1 mm.

01-gas porosity in castings

01-NDT Testing of Gas Porosity

2. Gas holes appear as dark circular images, isolated or in clusters. Gas holes are caused by gas trap in molten metal. Suppose the molten metal solidifies in the casting before all gases escape, it results in gas entrapment producing gas holes.

01-gas holes - flaws - NDT radiographs

3. Micro-porosity/Shrinkage porosity/Micro-shrinkage: These appear as an overall mottled appearance in aluminum alloy castings, and dark streaks or a spongy appearance in magnesium alloys. These are very fine cavities, usually around the grain boundaries. This defect occurs in casting when overall metal shrinkage is more than the normally expected shrinkage factor. The defect is due to improper feeding of the molten metal and occurs when the pouring temperature is higher than the ideal temperature.

4. Shrinkage appears as dendrite, filamentary or jagged darkened areas. These are caused due to contraction of metal while the casting solidifies. This defect usually occurs when there is change in section thickness of the casting and non-uniformity of temperature at different thicknesses.

01-NDT Testing of shrinkage

5. Cracks: These occur as hot tears or cold cracks (also called stress cracks). Hot tears appear as rugged dark lines of variable width and numerous branches with no definite line of continuity. Hot tears occur during or immediately after solidification. Cold state cracks shows generally as a continuous single narrow, sharp dark line all over the length. Such cracks take place whereas internal stresses are found out by a thermal gradient.

01-NDT Testing of cracks - hot tears - stress cracks

6. Dross appears as a dark, round or irregularly shaped images due to slag filling up the void entrapped in castings. These may look lighter if the density of inclusion is more than the density of the parent material. Inclusions may be due to slag, sand or oxides.

01-radiography test measurements - x ray tests of ndt

7. Cold shut appears as a dark line of variable length with a definite, smooth outline. Cold shuts are formed when two streams of molten metal flowing from different directions fail to unite. The creation of a cold shut is due to slow pouring, interrupted pouring or pouring the molten metal at too low temperature.

01-cold shuts - NDT radiographic test

8. Segregation appears as lighter or darker patches on the radiograph depending on the density of segregated constituents of the alloy. During the melting and casting processes, certain constituents of the alloy may separate from the alloy. This local concentration of the constituents results in a difference in densities on the radiograph, provided the density of the segregated portion is different from the density of the casting alloy. It is possible to have local segregation, in which shrinkage or a hot tear are filled with segregate. The terms used for such indications are shrinkage segregation and sealed hot-tear, respectively.

9. Misruns seem as a major darkened space of variable dimensions with a distinct, smooth outline. Misruns are produced by failure of the molten metal to completely fill a section of casting leaving the region void. This could occur as a result of lack of fluidity or pouring at too low a temperature.

10. Diffraction mottling appears as a spurious image on the radiograph and isn’t a casting defect. This mottling effect appears as star shaped representation in case of austenitic steel or in aluminum alloys. This effect of visualization are caused by the diffraction of radiation by the crystals of the metal. The mottling appearance vanishes if the radiograph is taken at a slightly changed angle of incidence.

11. Diffused chaplets are small bars with end plates used for maintaining the portion of mould core. These chaplets normally ruse with the casting. If not fused, these appear on the radiograph as darks, smooth lines conforming to the shape of the chaplet. This is caused by pouring the metal at too low a temperature to fuse the chaplet.

You might also like

Casting Inspection | Non Destructive Testing | Destructive Testing
Inspection of Castings: A large number of methods have been developed to inspect castings for defects...

Metal Casting | Steel Molding
Metal casting process: Definition: “Casting (or) Foundry is a process of forming objects by putting...

Special Casting Process | Special Casting Techniques | Special Casting Methods
Introduction to Special Casting Process Now a day’s special Casting process has been developed to...

Permanent Mould Casting | Gravity Die Casting
Permanent Mould Casting: Permanent mould casting, also sometimes called gravity die casting employs...

Tagged with:
Page 1 of 16812345Next »102030Next »Last »
preload preload preload