Radiography Says Slag, Ultrasonics Says Nothing
A 2-1/4 in. thick SA-516 Gr. 70 shell course was radiographed per UW-51 using a single-wall technique and a 2-2T hole-type IQI on the source side, with film density 2.3-2.6. In one 12 in. length of longitudinal seam the film shows a rounded indication about 3/16 in. across and a straight, slightly darker indication 1-1/4 in. long that the Level II calls elongated slag. A manual ultrasonic scan of the same seam, made by another technician the week before, recorded no indications. The shop wants to accept both indications and move to PWHT and hydrotest, noting that 1-1/4 in. is less than two-thirds of the thickness.
1. Apply the acceptance logic. Is the shop's arithmetic argument sufficient to accept the linear indication?
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No, because the arithmetic only applies after the indication has been classified, and classification is the real question.
If it is genuinely elongated slag, the single-indication length limit is two-thirds of the thickness, here 1.5 in.; 1.25 in. passes that test. But acceptance also requires that the total length of such indications in any 12 in. of weld not exceed the thickness (2.25 in.), so the sum in that 12 in. must be counted, not just the largest one. The rounded indication must be evaluated against the rounded-indication chart for the applicable thickness and the length of weld examined, not against the elongated rule.
More important, cracks, lack of fusion, and incomplete penetration are unacceptable at any length. A straight, darker, sharply defined indication in a 2-1/4 in. weld is not automatically slag; a tight lack of sidewall fusion or a toe crack can look like this, and RT is weak at detecting planar flaws oriented normal to the beam. The shop is treating a classification assumption as a finding.
2. How would you resolve the conflict between the radiograph and the ultrasonic result, and why is the sequencing urgent?
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The conflict is expected rather than surprising: radiography and angle-beam ultrasonics respond to different flaw orientations and volumes, and a manual UT scan reported as clean is only as good as its technique, couplant, coverage, and operator. Neither result invalidates the other; they answer different questions.
Resolve it with a written, qualified examination: PAUT or TOFD over the suspect 12 in. plus margin, from both sides where geometry allows, with the indication plotted and sized, and PT or MT on the accessible cap and root and on any ground window. If the reflector is planar and oriented across the fusion line, it is unacceptable regardless of length and must be excavated.
The sequencing is urgent because the vessel is about to be heat treated and hydrotested. A repair after final PWHT requires another heat treatment cycle, additional test specimens under UCS-85 if the aggregate time changes, and another hydrotest. Finding and fixing the flaw now, before PWHT, is the cheapest and most defensible path; accepting it because the length passes one paragraph is the most expensive.
3. What would you check about the radiograph itself and about the earlier ultrasonic examination before giving weight to either?
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For the radiograph: technique qualification and whether the single-wall exposure was actually achievable at that thickness and geometry, geometric unsharpness against the Section V limit, source-to-object distance, IQI essential-hole visibility for the density range, film and processing condition, density limits, and whether the darker linear indication sits in a region shadowed by reinforcement or backing. Also check that the film was interpreted by qualified personnel and that the indication was measured on the film, not estimated.
For the ultrasonic examination: was there a written procedure, what technique and angles were used, was the weld cap ground or was scanning done over a rough cap, was coverage actually complete through the thickness, what reference blocks and calibration, and is the technician qualified for the technique applied. A manual scan over an unprepared cap that reports nothing is weak evidence.
Given both records are questionable, neither one should be the basis for acceptance. The decision should rest on a re-examination with a controlled technique and a documented result, and the inspector should record why the earlier data were discounted.