MIL-STD-1894B
and density. The average size of fine porosity is 0.031 in. (0.79 mm) in diameter
and that of coarse porosity is 0.063 in. (1.59 mm) in diameter.
b. Clustered porosity. Clustered porosity appears the same as scattered porosity
except that the pores are concentrated in one area, generally at the start of a bead
or an interrupted arc.
c. Linear porosity. The type most common in partial-penetration welds results from
expanding gasses generated in the normally unfused area. The cavities are linearly
distributed at the root of the weld deposit and generally range from 0.031 in.
(0.79 mm) in diameter to 0.063 in. (1.59 mm) in diameter.
d. Gas cavities. This discontinuity generally results from inadequate shielding gas or
severe contamination of the gas. It appears the same as scattered porosity except
that the average cavity size is approximately 0.125 in. (3.18 mm) in diameter.
e. Incomplete (inadequate) penetration. In partial penetration welds this
discontinuity consists of a linear root void in excess of the unfused area normally
present in this type of joint. It appears on the radiograph as a straight dark line at
either root or at both roots. When present at both roots the two images should be
separated if properly radiographed.
f. Lack of fusion. Lack of fusion is failure of the weld metal to fuse completely with
the base metal or with the preceding bead. Lack of fusion resulting from trapped
slag appears on the radiograph as a dark elongated line varying in width. Lack of
fusion not accompanied by slag generally occurs along the weld interface and
produces a hair-line unfused condition. This is difficult to reveal unless the plane
of the discontinuity is parallel with the X-ray beam.
4.4 Discontinuity grading. Discontinuity severity grading of the reference standards was
selected to extend from standard 1, which represents a high-quality weld, to that of standard 5,
which is indicative of poor workmanship and is usually rejected in commercial practice.
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