Posted by TVP on April 11, 2008 at 11:27:57:
In Reply to: Flow Line Checking for ERW Tubes posted by Kaarthic.N on April 11, 2008 at 07:20:34:
Microetching with Picral (4g picric acid + 100 mL ethanol) is used to observe flowlines on welded tubes. The ferrite grain boundaries are not revealed, but instead it is the carbides present in the pearlite phase that are etched. Adding 0.5-1% zephiran chloride improves etch rate and uniformity. Alternatively you can macroetch a cross-section by immersing a sample for 15-30 minutes in a 1:1 ratio of HCl and water heated to 60-80 C. Remove the black smut by scrubbing with a soft brush under running water.