A 9 mm Fusion-Line Indication with a Negative MT
A 12 mm thick carbon steel butt weld is radiographed using a single-wall technique. The film shows a 9 mm long, slightly curved dark indication near the fusion line. It has a sharp upper end and a rounded lower end. The density at the indication is about 3.9, while the base metal density is 2.1. The acceptance standard states: any crack or lack of fusion is unacceptable; individual slag inclusions up to 3 mm are acceptable; aligned slag inclusions totaling more than 12 mm in any 150 mm are unacceptable; porosity is evaluated by comparison with a reference chart. A second exposure at 20° shows the same indication in the same weld location, but shorter. The Level II must classify the indication and decide acceptance. The weld is also magnetic-particle tested, and MT shows no indication.
1. Classify the indication as far as the radiograph allows and apply the acceptance standard. Does the density affect your interpretation?
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The indication is 9 mm long and sits at the fusion line. Its sharp upper end, straight-to-slightly-curved body and persistence at the same weld location on the 20° view favor a planar defect, most likely lack of fusion or a crack, rather than a rounded slag inclusion. A planar indication is unacceptable at any length under the stated standard. Even if the classifier decided it was slag, an individual 9 mm inclusion exceeds the 3 mm individual limit, so the weld is still unacceptable. The density of 3.9 is within the 2.0–4.0 range but near the dark end, where fine detail can be lost; view it on a strong illuminator and, if the shape is still ambiguous, re-radiograph at a lower density rather than guessing. Do not average the length or treat the shorter second view as a smaller defect; the first view shows the maximum projected length.
2. MT is negative. What is the value of that result, and what disposition, additional testing and reporting actions do you recommend?
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MT is a surface method. A negative MT result does not clear a subsurface lack of fusion or an internal crack, and it does not override a radiographic indication at the fusion line. Its value is limited to showing that no surface-breaking defect connects to the indication; it supports, but does not prove, that the defect is subsurface. Disposition: reject or hold the weld pending repair or further evaluation. UT is the preferred supplementary method for planar fusion-line defects because it can size and locate them through the thickness; if UT is also negative, the RT indication still requires resolution by re-shoot or cross-sectional repair, not automatic acceptance. Report the film number, weld number, technique and angle, density, indication location and length, classification, the acceptance-standard revision, the MT result, and the disposition. Retain the original film and the second view for traceability and client review.