The Problem With Sectioned RPT Samples
The results of three cuts made through the same Reduced Pressure sample, illustrating the potential variations that might be found because of minor segregation in the bubble formation. The alloy is 356, and the samples were taken at the Kingsville Plant of ThyssenKrupp-Stahl Co.
A similar result on a second sample with a much lower hydrogen level than Sample 1, above, and on a 319 alloy melt. If the target hydrogen production level is for a high sample density (low gas), the potential for error is obviously rather high, and scrap castings could result.
Note: In addition to the variations in bubble density that may exist between sections on the same sample, the subjective estimates of individual readers have been noted to vary by as much as two or three levels.