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2024年4月4日发(作者：蒋虹雨)

General Welding Discontinuities

The following discontinuities are typical of all types of welding.

Cold lap is a condition where the weld filler metal does not properly fuse with the

base metal or the previous weld pass material (interpass cold lap). The arc does

not melt the base metal sufficiently and causes the slightly molten puddle to flow

into base material without bonding.

Porosity（气孔）

Porosity

（气孔）

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

can take many shapes on a radiograph but often appears as dark round or

irregular spots or specks appearing singularly, in clusters or rows. Sometimes

porosity is elongated and may have the appearance of having a tail This is the

result of gas attempting to escape while the metal is still in a liquid state and is

called wormhole porosity. All porosity is a void in the material it will have a

radiographic density more than the surrounding area.

（密集气孔）is caused when flux coated electrodes are

（夹渣） are nonmetallic solid material entrapped in weld metal or

Cluster porosity

contaminated with moisture. The moisture turns into gases 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.

Slag inclusions（夹渣）Slag inclusions

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.

Incomplete penetration (IP) or lack of penetration (LOP)（未焊透）

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 center of the weldment.

Incomplete fusion （未融合）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.

Internal concavity or suck back（内凹）Internal concavity or suck back（内凹） is 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 lack of penetration but the line has irregular edges

and it is often quite wide in the center of the weld image.

Internal or root undercut（根部咬边）

Internal or root undercut

（根部咬边） 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 centerline of the weldment. Undercutting is not as straight edged as LOP

because it does not follow a ground edge.

External or crown undercut（外咬边）

External or crown undercut

（外咬边） 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.

Offset or mismatch（错边）（错边） are terms associated with a condition where two pieces

being welded together are not properly aligned. The radiographic image is 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 failure of the weld metal to fuse with the land area.

Inadequate weld reinforcementInadequate weld reinforcement（未焊满）（未焊满） 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 more

(darker) than the image density of the surrounding base material.

Excess weld reinforcement（焊缝余高过高）

Excess weld reinforcement

（焊缝余高过高） 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.

Cracks（裂纹） 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.

Discontinuities in TIG welds

The following discontinuities are peculiar 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（夹钨）

Tungsten inclusions

（夹钨）.

（夹钨）

. 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 as a lighter

area with a distinct outline on the radiograph.

Oxide inclusions are usually visible on the surface of material being welded

(especially aluminum). Oxide inclusions are less dense than the surrounding

materials and, therefore, appear as dark irregularly shaped discontinuities in the

radiograph.

Discontinuities in Gas Metal Arc Welds (GMAW)

The following discontinuities are most commonly found in GMAW welds.

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-（烧穿） results when too much heat causes excessive weld metal to

Burn

-Through

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).

Radiograph Interpretation – Castings（铸件）

The major objective of radiographic testing of castings is the disclosure of defects

that adversely affect the strength of the product. Casting are a product form that

often receive radiographic inspection since many of the defects produced by the

casting process are volumetric in nature and, thus, relatively easy to detect with

this method. These discontinuities of course, are related to casting process

deficiencies, which, if properly understood, can lead to accurate accept-reject

decisions as well as to suitable corrective measures. Since different types and

sizes of defects have different effects of the performance of the casting, it is

important that the radiographer is able to identify the type and size of the defects.

ASTM E155, Standard for Radiographs of castings has been produced to help the

radiographer make a better assessment of the defects found components. The

castings used to produce the standard radiographs have been destructively

analyzed to confirm the size and type of discontinuities present. The following is a

brief description of the most common discontinuity types included in existing

reference radiograph documents (in graded types or as single illustrations).

RADIOGRAPHIC INDICATIONS FOR CASTINGS

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 can't 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.

Sand inclusions and dross are nonmetallic oxides, appearing 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 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 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 can be recognized in a number of

characteristic by varying appearances on radiographs. There are at least four types: (1) cavity; (2)

dendritic; (3) filamentary; and (4) sponge types. Some documents designate these types by numbers,

without actual names, to avoid possible misunderstanding.

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.

Dendritic shrinkage is a distribution of very fine lines or small elongated cavities

that may vary in density and are usually unconnected.

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 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 are thin (straight or jagged) linearly disposed discontinuities that occur

after the melt has solidified. They generally appear singly and originate at casting

surfaces.

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.

Inclusions are nonmetallic materials in a supposedly solid metallic matrix. They may be less or more

dense 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 shows itself as a variation in section thickness, usually on radiographic

views representing diametrically opposite portions of cylindrical casting portions.

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; how tears

are usually systematic flaws. If flaws are identified as hot tears in larger runs of a

casting type, they may call for explicit improvements in technique.

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 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.

Radiographic Indications for Casting Repair Welds

Most common alloy castings require welding either in upgrading from defective

conditions or in joining to other system parts. It is mainly for reasons of casting

repair that these descriptions of the more common weld defects are provided here.

The terms appear as indication types in ASTM E390. For additional information,

see the Nondestructive Testing Handbook, Volume 3, Section 9 on the

"Radiographic Control of Welds."

Slag is nonmetallic solid material entrapped in weld metal or between weld

material and base metal. Radiographically, slag may appear in various shapes,

from long narrow indications to short wide indications, and in various densities,

from gray to very dark.

Porosity is a series of rounded gas pockets or voids in the weld metal, and is

generally cylindrical or elliptical in shape.

Undercut is a groove melted in the base metal at the edge of a weld and left

unfilled by weld metal. It represents a stress concentration that often must be

corrected, and appears as a dark indication at the toe of a weld.

Incomplete penetration, as the name implies, is a lack of weld penetration through

the thickness of the joint (or penetration which is less than specified). It is located

at the center of a weld and is a wide, linear indication.

Incomplete fusion is lack of complete fusion of some portions of the metal in a

weld joint with adjacent metal; either base or previously deposited weld metal. On

a radiograph, this appears as a long, sharp linear indication, occurring at the

centerline of the weld joint or at the fusion line.

Melt-

Melt

-through is a convex or concave irregularity (on the surface of backing ring,

strip, fused root or adjacent base metal) resulting from complete melting of a

localized region but without development of a void or open hole. On a radiograph,

melt-through generally appears as a round or elliptical indication.

Burn-

Burn

-through is a void or open hole into a backing ring, strip, fused root or

adjacent base metal.

Arc strike is an indication from a localized heat-affected zone or a change in

surface contour of a finished weld or adjacent base metal. Arc strikes are caused

by the heat generated when electrical energy passes between surfaces of the

finished weld or base metal and the current source.

Weld spatter occurs in arc or gas welding as metal particles which are expelled

during welding and which do not form part of the actual weld: weld spatter appears

as many small, light cylindrical indications on a radiograph.

Tungsten inclusion is usually denser than base-metal particles. Tungsten

inclusions appear most linear, very light radiographic images; accept/reject

decisions for this defect are generally based on the slag criteria.

Oxidation is the condition of a surface which is heated during welding, resulting in

oxide formation on the surface, due to partial or complete lack of purge of the weld

atmosphere. Also called sugaring.

Root edge condition shows the penetration of weld metal into the backing ring or

into the clearance between backing ring or strip and the base metal. It appears in

radiographs as a sharply defined film density transition.

Root undercut appears as an intermittent or continuous

groove in the internal surface of the base metal, backing

ring or strip along the edge of the weld root.

Real-time Radiography

Real-time radiography (RTR), or real-time radioscopy, is a nondestructive test

(NDT) method whereby an image is produced electronically rather than on film so

that very little lag time occurs between the item being exposed to radiation and the

resulting image. In most instances, the electronic image that is viewed, results

from the radiation passing through the object being inspected and interacting with

a screen of material that fluoresces or gives off light when the interaction occurs.

The fluorescent elements of the screen form the image much as the grains of

silver form the image in film radiography. The image formed is a "positive image"

since brighter areas on the image indicate where higher levels of transmitted

radiation reached the screen. This image is the opposite of the negative image

produced in film radiography. In other words, with RTR, the lighter, brighter areas

represent thinner sections or less dense sections of the test object.

Real-time radiography is a well-established method of NDT having applications in

automotive, aerospace, pressure vessel, electronic, and munition industries,

among others. The use of RTR is increasing due to a reduction in the cost of the

equipment and resolution of issues such as the protecting and storing digital

images. Since RTR is being used increasingly more, these educational materials

were developed by the North Central Collaboration for NDT Education (NCCE) to

introduce RTR to NDT technician students.

Real-

Real

-time Radiography: An Introductory Course Module for NDT Students

time Radiograph

y: An Introductory Course Module for NDT Students

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