Q. What is the difference between ASTM B136-84 and B-136-77 for the Modified Dye Stain Test? What effect would the concentration of the nitric acid solution have on the test results? What does ASTM B-136-84 list as the correct nitric acid concentration? D.B.
A. I’m not sure what the difference is. My copy is B136-84. You would have to buy both versions from ASTM and compare them, but there is probably no significant difference. The basic test has been the same for more than 40 years. My guess is that the old type dye could probably not be obtained anymore, so Version 84 was changed to reflect a readily available dye.
In the procedure, nitric acid is mixed equal parts with water. The nitric acid used to make this mixture is called 42° Baume—the strongest commercially available nitric acid other than “fuming nitric acid.” Nitric 42° Baume is 70% nitric acid and 30% water. When mixed 50/50 with water, this results in the testing solution of 35% (vol). If the nitric acid is too strong or weak, an inaccurate read on the quality of the seal could result. Apply a few drops of nitric acid to make a puddle on the test part. Allow to stand for 2 min. Rinse the acid off and dry. Apply a drop of the blue dye on the same area where the nitric acid puddle was and allow it to remain for 5 min. Rinse the dye off and rub the area with a dab of powdered (0000) pumice on a damp cloth. Rinse, dry and observe. If any blue dye remains, the parts are not completely sealed. If the test piece is a dark color, there shall be no detectable color change after the nitric acid has been rinsed off.