Radiograpic Film Interpretation

Art of extracting maximum information from radiography image. This requires subjective judgment of the interpreter

Interpret is to give the meaning of to explain. Evaluate is to determine the worth of something. Indication is a density change appearing on a radiograph. False indications are film artifacts, screen Problems, fog, scatter x-ray diffraction. Discontinuity is a break in the test specimen’s structural continuity. Defect is a condition that renders the specimen unsuitable for intended service.

Factors affecting the interpretation of test results:

  • Type of materials being welded.
  • Type of weld and joint preparation.
  • Welding processes.
  • Radiographic process.
  • Radiographic technique.
  • The applicable code or standard.

Function of a qualified interpreter :

  • Radiographic quality: Analysis of R.T technique and development regarding procedures.
  • Analysis the radiographic image to determination of the nature and extent of any abnormal deviation.
  • Evaluate by comparing the interpreted. Information with standard / specification.
  • Report results: accurately and clearly.
  • And he/she know the complete details about concerned manufacturing process like welding, forging, casting, extrusion, etc.

Radiograph Interpretation – Welds

In addition to producing high quality radiographs, the radiographer must also be skilled in radiographic interpretation. Interpretation of radiographs takes place in three basic steps:

  • Detection
  • Interpretation
  • Evaluation

All of these steps make use of the radiographer's visual acuity. Visual acuity is the ability to resolve a spatial pattern in an image.

The ability of an individual to detect discontinuities in radiography is also affected by the lighting condition in the place of viewing, and the experience level for recognizing various features in the image. The following material was developed to help students develop an understanding of the types of defects found in weld elements and how they appear in a radiograph.

Discontinuities are interruptions in the typical structure of a material. These interruptions may occur in the base metal, weld material or "heat affected" zones. Discontinuities, which do not meet the requirements of the codes or specifications used to invoke and control an inspection, are referred to as defects.

Radiographic Indications on General Welding

The following discontinuities are typical of all types of welding.

Cold Lap :

The arc does not melt the base metal sufficiently and causes slightly molten puddle to flow into the base material without bonding.

Radiographic Cold Lap

Porosity :

Porosity is the result of gas entrapment in the solidifying metal.

Radiographic Porosity

Cluster porosity :

Cluster porosity is caused when flux coated electrodes are contaminated with moisture.

The moisture turns into a gas when heated and becomes trapped in the weld during the welding process. Cluster porosity appear just like regular porosity in the radiograph but the indications will be grouped close together.

Radiographic Cluster Porosity

Slag Inclusions :

Slag inclusions are nonmetallic solid material entrapped in weld metal or between weld and base metal. In a radiograph, dark, jagged asymmetrical shapes within the weld or along the weld joint areas are indicative of slag inclusions.

Radiographic Slag Inclusions

Incomplete penetration (IP) or lack of penetration (LOP) :

Incomplete penetration (IP) or lack of penetration (LOP) occurs when the weld metal fails to penetrate the joint. It is one of the most objectionable weld discontinuities. Lack of penetration allows a natural stress riser from which a crack may propagate. The appearance on a radiograph is a dark area with well-defined, straight edges that follows the land or root face down the middle of the weldment.

Radiographic Incomplete penetration / lack of penetration

Incomplete fusion :

Incomplete fusion is a condition where the weld filler metal does not properly fuse with the base metal. Appearance on radiograph: usually appears as a dark line or lines oriented in the direction of the weld seam along the weld preparation or joining area.

Radiographic Incomplete fusion

Internal concavity or suck back :

Internal concavity or suck back is a condition where the weld metal has contracted as it cools and has been drawn up into the root of the weld. On a radiograph it looks similar to a lack of penetration but the line has irregular edges and it is often quite wide in the middle of the weld image.

Radiographic Internal concavity or suck back

Internal or Root Undercut :

Internal or root undercut is an erosion of the base metal next to the root of the weld. In the radiographic image it appears as a dark irregular line offset from the middleline of the weldment. Undercutting is not as straight edged as LOP because it does not follow a ground edge.

Radiographic Internal or Root Undercut

External or crown undercut :

External or crown undercut is an erosion of the base metal next to the crown of the weld. In the radiograph, it appears as a dark irregular line along the outside edge of the weld area.

Radiographic External or crown undercut

Offset or mismatch :

Offset or mismatch are terms associated with a condition where two pieces being welded together are not properly aligned. The radiographic image shows a noticeable difference in density between the two pieces. The difference in density is caused by the difference in material thickness. The dark, straight line is caused by the failure of the weld metal to fuse with the land area.

Radiographic Offset or mismatch

Inadequate weld reinforcement :

Inadequate weld reinforcement is an area of a weld where the thickness of weld metal deposited is less than the thickness of the base material. It is very easy to determine by radiograph if the weld has inadequate reinforcement, because the image density in the area of suspected inadequacy will be higher (darker) than the image density of the surrounding base material.

Radiographic Inadequate weld reinforcement

Excess Weld Reinforcement :

Excess weld reinforcement is an area of a weld that has weld metal added in excess of that specified by engineering drawings and codes. The appearance on a radiograph is a localized, lighter area in the weld. A visual inspection will easily determine if the weld reinforcement is in excess of that specified by the engineering requirements.

Radiographic Excess Weld Reinforcement

Cracks :

Cracks can be detected in a radiograph only when they are propagating in a direction that produces a change in thickness that is parallel to the x-ray beam. Cracks will appear as jagged and often very faint irregular lines. Cracks can sometimes appear as "tails" on inclusions or porosity.

Radiographic Cracks

Radiographic Indications In Tig Welds

The following discontinuities are unique to the TIG welding process. These discontinuities occur in most metals welded by the process, including aluminum and stainless steels. The TIG method of welding produces a clean homogeneous weld which when radiographed is easily interpreted.

Tungsten Inclusions :

Tungsten is a brittle and inherently dense material used in the electrode in tungsten inert gas welding. If improper welding procedures are used, tungsten may be entrapped in the weld. Radiographically, tungsten is more dense than aluminum or steel, therefore it shows up as a lighter area with a distinct outline on the radiograph.

Radiographic Tungsten Inclusions

Oxide Inclusions :

Oxide inclusions are usually visible on the surface of material being welded (especially aluminum). Oxide inclusions are less dense than the surrounding material and, therefore, appear as dark irregularly shaped discontinuities in the radiograph.

Radiographic Oxide Inclusions

Radiographic Indications in Gas Metal Arc Welds (GMAW)

The following discontinuities are most commonly found in GMAW welds.

Whiskers :

Whiskers are short lengths of weld electrode wire, visible on the top or bottom surface of the weld or contained within the weld. On a radiograph they appear as light, "wire like" indications.

Burn-Through :

Burn-Through results when too much heat causes excessive weld metal to penetrate the weld zone. Often lumps of metal sag through the weld, creating a thick globular condition on the back of the weld. These globs of metal are referred to as icicles. On a radiograph, burn-through appears as dark spots, which are often surrounded by light globular areas (icicles).

Radiographic Burn-Through

Radiographic Indications On Castings

Gas porosity or blow holes :

Gas porosity or blow holes are caused by accumulated gas or air which is trapped by the metal. These discontinuities are usually smooth-walled rounded cavities of a spherical, elongated or flattened shape. If the sprue is not high enough to provide the necessary heat transfer needed to force the gas or air out of the mold, the gas or air will be trapped as the molten metal begins to solidify.

Blows can also be caused by sand that is too fine, too wet, or by sand that has a low permeability so that gas cannot escape. Too high a moisture content in the sand makes it difficult to carry the excessive volumes of water vapor away from the casting. Another cause of blows can be attributed to using green ladles, rusty or damp chills and chaplets.

Radiographic Gas porosity or blow holes

Sand inclusions and dross :

Radiographic and inclusions and dross

Sand inclusions and dross are nonmetallic oxides, which appear on the radiograph as irregular, dark blotches. These come from disintegrated portions of mold or core walls and/or from oxides (formed in the melt) which have not been skimmed off prior to the introduction of the metal into the mold gates. Careful control of the melt, proper holding time in the ladle and skimming of the melt during pouring will minimize or obviate this source of trouble.

Shrinkage

Shrinkage is a form of discontinuity that appears as dark spots on the radiograph. Shrinkage assumes various forms, but in all cases it occurs because molten metal shrinks as it solidifies, in all portions of the final casting. Shrinkage is avoided by making sure that the volume of the casting is adequately fed by risers which sacrificially retain the shrinkage. Shrinkage in its various forms can be recognized by a number of characteristics on radiographs. There are at least four types of shrinkage: (1) cavity; (2) dendritic; (3) filamentary; and (4) sponge types. Some documents designate these types by numbers, without actual names, to avoid possible misunderstanding.

Radiographicand Shrinkage

Cavity shrinkage :

Cavity shrinkage appears as areas with distinct jagged boundaries. It may be produced when metal solidifies between two original streams of melt coming from opposite directions to join a common front. Cavity shrinkage usually occurs at a time when the melt has almost reached solidification temperature and there is no source of supplementary liquid to feed possible cavities.

Radiographicand Cavity shrinkage

Dendritic shrinkage :

Dendritic shrinkage is a distribution of very fine lines or small elongated cavities that may vary in density and are usually unconnected.

Radiographicand Dendritic shrinkage

Filamentary shrinkage :

Filamentary shrinkage usually occurs as a continuous structure of connected lines or branches of variable length, width and density, or occasionally as a network.

Sponge shrinkage :

Cold shutsSponge shrinkage shows itself as areas of lacy texture with diffuse outlines, generally toward the mid-thickness of heavier casting sections. Sponge shrinkage may be dendritic or filamentary shrinkage. Filamentary sponge shrinkage appears more blurred because it is projected through the relatively thick coating between the discontinuities and the film surface.

Cracks

Cracks are thin (straight or jagged) linearly disposed discontinuities that occur after the melt has solidified. They generally appear singly and originate at casting surfaces.

Radiographicand Cracks

Cold shuts

Cold shuts generally appear on or near a surface of cast metal as a result of two streams of liquid meeting and failing to unite. They may appear on a radiograph as cracks or seams with smooth or rounded edges.

Radiographic Cold shuts

Inclusions

Inclusions are nonmetallic materials in an otherwise solid metallic matrix. They may be less or denser than the matrix alloy and will appear on the radiograph, respectively, as darker or lighter indications. The latter type is more common in light metal castings.

Core shift

Core shift shows itself as a variation in section thickness, usually on radiographic views representing diametrically opposite portions of cylindrical casting portions.

Radiographicand Core shift

Hot tears

Hot tears are linearly disposed indications that represent fractures formed in a metal during solidification because of hindered contraction. The latter may occur due to overly hard (completely unyielding) mold or core walls. The effect of hot tears as a stress concentration is similar to that of an ordinary crack, and hot tears are usually systematic flaws. If flaws are identified as hot tears in larger runs of a casting type, explicit improvements in the casting technique will be required.

Misruns

Misruns appear on the radiograph as prominent dense areas of variable dimensions with a definite smooth outline. They are mostly random in occurrence and not readily eliminated by specific remedial actions in the process.

Mottling

Mottling is a radiographic indication that appears as an indistinct area of more or less dense images. The condition is a diffraction effect that occurs on relatively vague, thin-section radiographs, most often with austenitic stainless steel. Mottling is caused by interaction of the object's grain boundary material with low-energy X-rays (300 kV or lower). Inexperienced interpreters may incorrectly consider mottling as indications of unacceptable casting flaws. Even experienced interpreters often have to check the condition by re-radiography from slightly different source-film angles. Shifts in mottling are then very pronounced, while true casting discontinuities change only slightly in appearance.