waynekoe
I disagree your contention that the welders are still qualified. If they had qualified on an open root test, perhaps they can be considered prequalified. Table 4.12, Essential Variable (6) says; The omission of backing (if used in trhe WPQR test) However, ceramic backing is not steel backing, and steel backing is an essential variable for prequalification. Therefore, the omission of steel backing by substituting ceramic backing would make it an open root joint. Thus, if the welders qualified with the typical steel backed joint found in Figure 4.21, 4.22, and 4.23, they would not be qualified. If they qualified using figure 4.24, 4.25, 4.27, 4.28, or 4.29, It would still be a stretch for me, but in that case the welder might be considered qualified.
Gerald
In addition to the paragraphs you quoted here, paragraph 3.1, third sentence, it says that in order to be prequalified, the WPS must comply with Section 3.