Volume 4, Number 4
October 2005
Q. Can you provide background about the hole type penetrameter; what determines the shape, why two percent of part thickness was selected and can a penetrameter or the permanent designation or ID number be modified?
A. The shape of the penetrameter or pene, is determined by its thickness. Penetrameters less than or equivalent to 0.160 in. (4.1 mm) in thickness (a 160 pene) are rectangular. Penetrameters more than 0.160 in. thick are circular. These shapes are an industry convention and do not affect the penetrameter’s radiographic characteristics.
The two percent penetrameter thickness and required hole sizes possibly evolved from engineering decisions made in reference to questions such as; "What is the largest inclusion we can afford to have in the part but not be able to find?" and “What thickness of penetrameter can be reliably seen on the film image?” As thickness of the test material increases, the size of the indication you can afford to miss also increases. Thus, a thicker penetrameter and larger required hole is specified.
For film to be considered properly exposed, the outlines of both the penetrameter and the required hole must be visible. If both are visible, it is assumed that any discontinuity in the part that is thicker than two percent of the part thickness and bigger than the diameter of the required hole will also be visible. The part may also contain discontinuities smaller than two percent, but the individuals that determine code content have decided that anything that small would not affect use of the part.
Penetrameter selection is dictated by the governing code or standard. Most US standards refer back to ASTM E-1025 (Annual Book of ASTM Standards, Vol. 03.03) for the design and manufacture of hole-type penetrameters. According to ASTM E-1025, penetrameter dimensions, width and length, may be modified as long as the modifications are documented and attached to any report concerning the modified penetrameter. However, paragraph 4.1.2.2 states that the identification shall be lead numbers. If a modified penetrameter is used and the lead numbers won't fit on the modified penetrameter, the numbers may be placed beside the penetrameter on the part. ASTM E-1025 requires that the lead ID numbers for all circular penetrameters be placed beside the penetrameter on the part. TNT
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