Method of Simulating Spherical Voids for Use as a Radiographic Standard

This invention was made in the course of, or under, a contract with the Energy Research and Development Administration.

One of the problems that can occur when two pieces of material are welded together is the formation of small voids or pores in the weld joint. These voids can be detected through the use of radiographic techniques; however, to accurately determine their size, metallographic sectioning and measurement with a microscope is required, thus destroying the sample. As can be seen in FIG. 2 of the drawings, the size of the image of a void on X-ray sensitive film C is dependent on the proportional distances of the void between the film and the X-ray source. Sphere A and sphere B are identical in size; however, sphere A appears to be larger than sphere B on the radiographic images of the plate.

Thus, a need exists to provide a means of measuring voids in welds which (1) does not require destroying the weld, and (2) is sufficiently accurate to use as a standard in quality control operations. The present invention was conceived to meet this need in a manner to be described hereinbelow.

It is the object of the present invention to provide an improved method for simulating voids for use as a radiographic standard.

The above object has been accomplished in the present invention comprising a method of providing a radiographic standard for weld voids comprising the steps of drilling or etching identical hemispheres in each of two plates of welding material, placing a carbon bead of a desired size in one of the plate hemispheres and aligning the other plate hemisphere on the bead, bonding the plates to encase the bead, and radiographing the bead using various proportional distances between the bead and an X-ray film, whereby the resulting radiographs serve as standards for use in quality control comparisons of voids in actual welds.

FIG. 1 illustrates the method by which spherical voids are made for use as a radiographic standard, and

FIG. 2 illustrates the possible variation in radiographs of the same pore size at different depths in a weld.

The structure illustrated in FIG. 1 of the drawings is utilized in conjunction with radiographs thereof to provide standards for comparisons of voids in actual welds. In FIG. 1, a plate 11 of welding material has a hemisphere 9 etched or drilled therein, and a plate 12 of welding material has a corresponding hemisphere 10 etched or drilled therein. After a carbon bead 13, or other spherical material of low atomic number, is placed in one of the plate hemispheres, the other plate hemisphere is aligned on the carbon bead when the plates 11 and 12 are brought together, after which the plates are bonded together thus encasing the bead 13. It should be understood that various units, such as illustrated in FIG. 1, with different positions for the drilled or etched hemispheres, or with more than one simulated void such as illustrated in FIG. 2, are utilized in providing a variety of simulated radiographic standards for subsequent comparisons of voids in actual welds.

Thus, radiographs of the bead, or beads, can then be made using various proportional distances between the bead, or beads, and the X-ray film, and standards can then be developed to use for quality control comparisons of voids in actual welds.

The present invention can be used to develop standards for most types of weld joints, forgings, or castings by using similar techniques. In one example, the present invention can be utilized to evaluate transition (e.g., tube-to-header) weld joints; some typical materials that are used to form transition weld joints are Incoloy 800, 316 stainless steel, and 21/4 chromium-1 molybdenum.

Carbon beads have been found to be highly satisfactory for alignment purposes because they can be produced in a variety of spherical sizes and because they attenuate the X-ray beam a negligible amount in comparison to that of the thicker and denser metal.

The size of the void to be simulated could vary with the material thickness or particular application, but may be as small as 0.001-0.002 inches. Thus, as pointed out above, a series of radiographs can be made with a sphere of a particular size located at various depths in the welding material. Also, spherical voids of differing sizes can be placed in the material at various depths and radiographed. These radiographs can then be used to standarize the minimum detectable radiographic void size in various locations for future classification of voids in actual welds.

This invention has been described by way of illustration rather than by limitation and it should be apparent that it is equally applicable in fields other than those described.